Interferometer design based on mixed optical fiber for realizing complex conjugate elimination by using dispersion and related aspects

Abstract

A high-dispersion single-mode hybrid optical fiber (1900) located in one of a reference arm or a probe arm of an optical interferometer imaging system, the hybrid optical fiber (1900) comprising: at least two optical fibers (1902, 1902), at least one of the at least two optical fibers having a different core diameter and a different dispersion characteristic than at least one other of the at least two optical fibers, wherein the at least two optical fibers are welded end to end to form a hybrid optical fiber, and wherein a length of each of the at least two optical fibers is based on a relative relationship of a core diameter of the optical fiber and a center wavelength of a light beam passing through the hybrid optical fiber, and a target GDD per unit length based on a target length of the hybrid optical fiber, the hybrid fiber adds an additional GDD value relative to the fiber in the other of the reference arm or the probe arm of the optical interferometer.

Description

TECHNICAL FIELD

[0001] The present invention relates to a hybrid fiber-based differential dispersion interferometer design, for example, to a design suitable for use with high dispersion techniques to remove residual complex conjugate image artifacts from 2D image scans such as Optical coherence tomography (OCT), B-scan images. BACKGROUND

[0002] Optical coherence tomography (OCT) is an imaging modality that uses low-coherence interferometry to generate three-dimensional images of a sample. An OCT system typically consists of a broadband light source, reference and sample optical arms, and a detection arm consisting of a spectrometer or photodiode detector. The interference pattern of light reflected from the reference and sample arms is measured at the detector and electronically processed to generate a tomographic image showing the relative positions of reflectors in the sample. By scanning the beam in the sample arm, different spatial locations can be probed, and a 3D image of the sample can be constructed.

[0003] Signal processing of the OCT signal requires multiple steps, one of which is a Fourier transform of the detected interference signal. Since the measured signal is real-valued, a Fourier transform of it produces a complex signal with identical positive and negative frequency components. This data mirroring is known as a complex conjugate artifact, which limits the available imaging range to potentially half of the theoretical value. Techniques to remove or suppress the conjugate artifact, known as complex conjugate resolution (CCR) methods, can double the imaging range in OCT immediately. However, known CCR systems and methods are difficult to implement in practice in many cases due to the need to add expensive and complex optical components in the OCT scanning system. Furthermore, multiple image acquisitions are required to generate the required phase information to remove the conjugate image. This slows down the imaging time, results in reduced system performance, and is also very susceptible to sample motion, especially when imaging a live subject.

[0004] Optical coherence tomography (OCT) is a technique that uses optical instrumentation to generate cross-sectional images of biological tissue. Using monochromatic light with a constant phase difference, axial (depth) resolutions far below 8 microns can be achieved. It is therefore desirable if such an OCT system can be used to generate scans in real time while probing (in vivo) living tissue and in other applications. Since OCT scans cannot penetrate to very deep depths, they are particularly useful for probing skin tissue and in ophthalmology. Different OCT scan images are constructed from multiple one-dimensional scans (A-scans) at different depths to create two-dimensional images (B-scans). By acquiring B-scans closely enough and quickly enough, a volumetric image (C-scan) of the sample tissue probed by the OCT can be obtained.

[0005] However, various technical problems present challenges that affect the development of OCT scan images in applications, potentially resulting in the inability to achieve real-time streaming of OCT scan images.

[0006] One of such technical challenges is how to quickly remove complex conjugate image artifacts present in OCT scan images. It is known that in frequency domain OCT systems, a mismatch in dispersion between the sample arm and the reference arm can be used to iteratively suppress complex conjugate artifacts and increase the imaging range. Hofer et al. in their paper “Fast dispersion encoded full range optical coherence tomography for 800 nm and 1060 nm retinal imaging”, Optics Express, Vol. 18, No. 5, March 2010, page 4898, discloses a fast dispersion encoded full range (DEFR) algorithm that detects multiple signal components per iteration. However, despite being faster than the earlier known techniques, this technique is still relatively slow, taking about 5 to 10 seconds to process a single image, which means that it is not suitable for real-time image processing applications, such as removing complex conjugate images from OCT scan images generated in real time from retinal ophthalmic surgical procedures, despite its speed being significantly faster than the technique proposed by Hofer et al. in their paper “Fast dispersion encoded full range optical coherence tomography”, Optics Express, Vol. 17(1), 2009, which describes an example OCT dispersion system. Both algorithms described by Hofer in these papers are very slow in processing full range images, hindering their use in real-time applications. Furthermore, the algorithms described by Hofer et al. also use static selection of key processing parameters, which requires manual optimization of the processing parameters for a particular image dataset. This limits the use of this method for imaging different types of samples under different imaging conditions due to differences in signal strength and image clarity. SUMMARY

[0007] The disclosed technology aims to mitigate or eliminate at least some of the limitations in the prior art by using a hybrid fiber based interferometer design, and aims to improve complex conjugate cancellation in OCT scanner applications. In particular, but not exclusively, some embodiments of the disclosed technology can improve the performance of the disclosed method when performing CCR in real time.

[0008] The following abstract sets forth features of the disclosed technology that, in some embodiments, can be preferred features. The present invention is defined by the appended claims.

[0009] A first aspect of the disclosed technology includes a highly dispersive single mode hybrid fiber located in one of a reference arm or a probe arm of an optical interferometer imaging system, the hybrid fiber comprising: at least two optical fibers, at least one of the at least two optical fibers having a different core diameter and different dispersion properties than at least one other of the at least two optical fibers, wherein the at least two optical fibers are fusion spliced end to end to form the hybrid fiber, and wherein a length of each of the at least two optical fibers is based on a relative relationship of the core diameter of that optical fiber to a center wavelength of a light beam passing through the hybrid fiber, and based on a target GDD per unit length of a target length of the hybrid fiber, wherein the hybrid fiber adds an additional GDD value relative to an optical fiber in the other of the reference arm or the probe arm of the optical interferometer.

[0010] In some embodiments, the additional GDD value is between 31000 (fs 2 ) and 46000 (fs 2 ).

[0011] In some embodiments, the length of at least one of the optical fibers in the hybrid fiber is different than the length of at least one other of the optical fibers.

[0012] In some embodiments, the length of each optical fiber is determined by: calculating a target group velocity delay (GVD) for a predetermined length of the hybrid fiber; converting the target GVD to a target optical fiber dispersion parameter (OFDP) for a center wavelength of light passing through the hybrid fiber; determining at least two optical fiber types, each optical fiber type having an OFDP that bounds the target OFDP; converting the OFDP of each determined optical fiber type to a GVD at the center wavelength; for each of the determined optical fiber types, determining a length of the optical fiber based on the GVD of the respective optical fiber at the center wavelength such that the optical fibers collectively provide an optical path that matches a predetermined optical path length of the hybrid fiber when fusion spliced end to end.

[0013] In some embodiments, the hybrid optical fiber includes a length of coherent 630-HP optical fiber and a length of Corning HI780 optical fiber.

[0014] In some embodiments, the hybrid optical fiber is located in a reference arm of an optical interferometer imaging system that includes the OCT device.

[0015] In some embodiments, the hybrid optical fiber is configured to introduce a predetermined level of dispersion in the reference arm of the optical interferometer to remove complex conjugate image data in an OCT image output by the OCT device.

[0016] In some embodiments, the hybrid optical fiber is located in a reference arm of an optical interferometer configured to output OCT imaging data from the OCT device. The ratio of the two component optical fibers that form the hybrid optical fiber can have a ratio such that for a 6 meter hybrid optical fiber optical path length, 5 meters includes coherent 630-HP optical fiber and 1 meter includes Corning HI780 optical fiber. In some embodiments, these optical fibers can be replaced with optical fibers having the same or similar optical properties, such as those listed in Table 1 of the DETAILED DESCRIPTION, for example, other glasses having a set of optical properties including at least the same refractive index, group refractive index, and light transmission.

[0017] Another aspect of the disclosed technology includes an OCT assembly including an OCT interferometer assembly including: an OCT detector assembly; a sample arm configured to direct an OCT probe beam from an OCT light source of the OCT assembly to a subject and to direct a returned OCT probe beam from the scanned subject to the OCT detector assembly; and an OCT system reference assembly of adjustable optical path length including a hybrid optical fiber according to the first aspect disclosed herein or any one of the embodiments thereof, wherein the reference assembly is configured in a reference arm of the OCT detector assembly, wherein OCT light from the OCT light source is split to travel as a reference beam along the reference arm and as an OCT probe beam along the sample arm, and wherein the returned reference beam and the returned probe beam are combined and the OCT detector assembly is configured to detect an interference in the combined returned OCT light from the reference arm and the sample arm.

[0018] In some embodiments, the OCT assembly further includes an image processor, wherein the OCT detector of the OCT interferometer assembly is configured to output a signal to the image processor including a detected interference pattern of the returned combined OCT light, wherein the interference pattern of the returned OCT reference light and the OCT probe light is Fourier transformed by the image processor.

[0019] In some embodiments, the image processor is configured to perform a computer-implemented complex conjugate cancellation (CCR) method to remove complex conjugate artifacts in the Fourier transformed signal, wherein the reference beam optical path in the reference arm of the hybrid glass fiber OCT system provides sufficient dispersion to enable the CCR method to remove CC artifacts in real time.

[0020] In some embodiments, the dispersion along the hybrid glass fiber is sufficient to allow a computer-implemented CCR method to remove complex conjugate artifacts in real time in an OCT B-scan or volume scan.

[0021] In some embodiments of the disclosed technology, the highly dispersive retroreflector comprises a light-filtering glass that is transparent at least in the near infra-red (IR) wavelength range, and is configured to cause incident broadband low-coherence light to experience differential dispersion at least in the near infra-red (NIR) wavelength range.

[0022] In some embodiments, the retroreflector is transparent in the same wavelength range in which the differential dispersion occurs, but in other embodiments its transparent wavelength range can be different from the wavelength range in which the differential dispersion occurs.

[0023] In some embodiments, the light-filtering glass has a median group delay dispersion in the range of 38000 (fs 2 ) to 40000 (fs 2 ).

[0024] In some embodiments, the light-filtering glass has a median group velocity dispersion in the range of 1100 fs 2 / mm to 1280 fs 2 / mm.

[0025] In some embodiments, the retroreflector comprises a glass having one of the following properties (for incident light with a spectral center at 850 nm): an index of refraction of 2.5129 for light at a wavelength of 850 nm; a group index of refraction of 2.7268 (ng) for light at a wavelength of 850 nm; a group velocity delay of 1120.75 fs2 / mm; a transparency of 95.7% for light at a wavelength of 850 nm.

[0026] In some embodiments, the retroreflector has a conical exterior, and the conical interior comprises at least three mirror facets that are collectively configured to perform retroreflection of incident light.

[0027] In some embodiments, the disclosed technology includes a bulk glass differential dispersion interferometer assembly for extended depth imaging in optical coherence tomography (OCT), the interferometer assembly including an automated optical path length optical mechanical assembly including a fixed first retroreflector at one end of an optical path, a tunable second retroreflector co-located with the fixed highly dispersive retroreflector on a mount that is movable to form a tunable optical path in the interferometer assembly, wherein the highly dispersive retroreflector includes a filter glass that is transparent at infrared (IR) wavelengths and is configured to cause differential dispersion between broadband low coherence incident light in a near infrared (NIR) wavelength range.

[0028] In some embodiments, the interferometer assembly is located on a probe arm of an OCT scanning system, and the highly dispersive retroreflector is configured to cause differential dispersion between broadband low coherence incident light returned from a reference arm and the probe arm of the OCT system in a near infrared (NIR) wavelength range.

[0029] In some embodiments, the interferometer is configured to output light for complex conjugate cancellation of the incident OCT light.

[0030] In some embodiments, the filter glass material has a median group delay dispersion ranging from 38000 (fs 2 ) to 40000 (fs 2 ).

[0031] In some embodiments, wherein the median group dispersion velocity of the filter glass material is a value in a range from 1100 fs 2 / mm to 1280 fs 2 / mm.

[0032] In some embodiments, the highly dispersive retroreflector (1500) includes a glass having one of the following properties (for incident light with a spectral center at 850 nm): an index of refraction of 2.5129 for light at 850 nm wavelength; a group index of refraction of 2.7268 (ng) for light at 850 nm wavelength; a group velocity delay of 1120.75 fs 2 / mm for light at 850 nm wavelength; and a transparency of 95.7% for light at 850 nm wavelength.

[0033] In some embodiments, the highly dispersive retroreflector can include an IRG27 glass, for example manufactured by Schott.

[0034] In some embodiments, the first retroreflector (1604) and the second retroreflector (1602) comprise glass having the following properties (for incident light with a spectral center at 850 mm): an index of refraction of 1.5098 for light of 850 nm wavelength; a group index of refraction of 1.5249 (ng) for light of 50 nm wavelength; a group velocity delay of 40.13 fs / mm; and a transparency of 99.8% for light of 850 nm wavelength. 2

[0035] In some embodiments, the first retroreflector and the second retroreflector can comprise BK7 glass, for example manufactured by Schott.

[0036] In some embodiments, the highly dispersive retroreflector has a cone interior comprising at least three mirror facets collectively configured to perform retroreflection of incident light.

[0037] In some embodiments, the disclosed technology comprises an optical coherence tomography (OCT) apparatus configured to perform real-time OCT, the apparatus comprising: an illumination arm comprising at least one light source for OCT; a reference arm; an OCT probe arm via which an OCT probe beam is emitted; and a data or output arm via which returned OCT light is passed for processing by an image processor; and at least one dispersive retroreflector in the reference arm or the OCT probe arm according to the first aspect disclosed herein or any of its embodiments.

[0038] In some embodiments, the dispersion between the reference arm and the probe arm is variable and set above a minimum threshold in order to separate a complex conjugate image from the OCT image for output for display.

[0039] In some embodiments, the OCT apparatus further comprises at least one additional dispersive component provided in one of the reference arm or the OCT probe arm.

[0040] In some embodiments, the at least one additional dispersive component is located in the reference arm and comprises a dispersive glass window.

[0041] In some embodiments, the at least one additional dispersive component is located in the reference arm and comprises a dispersive glass window, wherein the physical path length of the reference arm is configured to compensate for the dispersive window, or vice versa the physical path length of the OCT probe arm is lengthened to compensate for the dispersive window.

[0042] In some embodiments, the OCT apparatus comprises a bulk glass differential dispersion interferometer component for extended depth imaging in optical coherence tomography (OCT), the interferometer component comprising an automated optical path length optomechanical component.

[0043] ​In some embodiments, the OCT device of the third aspect comprises an OCT scanner adapter according to any of the embodiments disclosed herein.

[0044] In some embodiments, the at least one dispersive optical component disposed in the OCT probe arm comprises one or more of a dispersive optical fiber, a dispersive dichroic mirror, a dispersive OCT objective lens, and a dispersive OCT field lens.

[0045] In some embodiments, the image processor can perform a computer-implemented image processing complex conjugate removal (CCR) method, for example for removing complex conjugate image data from image data in real-time using dispersion, the method comprising: receiving an image signal comprising image data including complex conjugate image data (902), performing a baseline signal subtraction (906); re-sampling the resulting wavelength data to generate linear wavenumber image data (908, 910), processing the linear wavenumber image data to generate a result of complex conjugate removal (CCR) using an iteration of at least one CCR image processing algorithm, computing a CCR image from the CCR result, and separating the CCR image from the received OCT image data to remove the complex conjugate image data.

[0046] In some embodiments, the CCR image processing algorithm uses an adjustable threshold value in each iteration step.

[0047] Advantageously, by adjusting the threshold value of each iteration step, the CCR image can be generated faster.

[0048] Advantageously, an initial threshold value can be determined for each individual scan image, for example by applying a frequency-amplitude histogram resulting from an image Fourier transform. The initial threshold value can be set to a percentile above a certain value in the histogram.

[0049] Another benefit of the disclosed image processing method is that the processing parameters are selected based on properties of the original image, so the processing parameters can be optimally selected to adapt the threshold level before any iteration of the complex conjugate removal processing according to the image processing method of one of the disclosed embodiments. In other words, in some embodiments, each image is provided with a prediction of what the optimal threshold should be.

[0050] Unlike selecting a series of different static threshold values and repeating the processing of the OCT scan image to select each static threshold value according to the final image result, the embodiments of the image processing method employing the CCR algorithm according to the disclosed technology dynamically adjust the threshold value in each threshold value.

[0051] Secondly, by combining the processing method, using a dedicated GPU and selecting the system dispersion parameters, it is possible to do all this in real-time (<30ms), thus enabling real-time video processing.

[0052] In some embodiments, the algorithm according to the disclosed technology is implemented using a dedicated processor or processing circuitry. For example, in some embodiments, the algorithm can be implemented using a graphics processing unit (GPU). In some embodiments, the method is performed in real time.

[0053] For example, using some embodiments of the disclosed technology, an image can be generated in 30 milliseconds. This allows CCR images to be used in OCT systems for applications such as surgical procedures (e.g. eye surgery), which in some embodiments of the disclosed technology is particularly important due to the need to generate images in real time during a procedure without excessive delay.

[0054] In some embodiments, the CCR image data computed from the CCR result includes amplitude and / or phase data of the resulting CCR image.

[0055] In some embodiments, the method further includes logarithmic scaling of the resulting CCR image. This can be helpful for visualizing the data, especially when the data range spans several orders of magnitude.

[0056] In some embodiments, processing the linear wavenumber image data to generate a complex conjugate cancellation result includes performing multiple iterations of a CCR image processing algorithm that includes applying dispersion correction to the linear wavenumber image signal data, performing a signal transform, such as a Fourier transform (e.g. a fast Fourier transform (FFT)).

[0057] computing the amplitude of the result of the signal transform performed on the linear wavenumber image signal data; computing a variable threshold for each iteration of the algorithm, setting the signal transform result to zero for each signal transform result value for which the amplitude does not satisfy a storage condition based on the threshold for the current iteration, storing the signal transform result for each signal transform result for which the amplitude satisfies the storage condition based on the threshold for the current iteration, computing an inverse signal transform (e.g. an inverse FFT) for all stored signal transform results, applying an inverse dispersion correction, and extracting and subtracting a real image component from the original image spectral data.

[0058] While in some embodiments the signal transform can include a Fourier transform that decomposes the input signal into sinusoidal components having discrete frequencies, in some embodiments of the image processing method disclosed herein, an alternative signal transform can be used instead, such as a suitable wavelet transform.

[0059] In some embodiments, satisfying the condition for storing the signal-transformed result (i.e., the frequency component of the input signal having an amplitude within a given frequency bandwidth) comprises satisfying or exceeding a calculated, variable, condition threshold amplitude value for storing the OCT scan image data for that frequency component.

[0060] In some embodiments, satisfying the condition for storing the signal-transformed result comprises exceeding a calculated (variable) storage condition threshold.

[0061] Advantageously, since the storage condition threshold is not static, some embodiments of the disclosed technology can provide better, automatic optimization of processing parameters for a given image data set.

[0062] Advantageously, since the signal strength and image clarity can vary, the variable storage condition threshold in some embodiments allows for imaging different types of samples under different imaging conditions.

[0063] In some embodiments, after the final iteration is performed, the method optionally further comprises adding any remaining iteration residual signal to the final output signal.

[0064] In some embodiments, the algorithm processes each A-scan, and then the A-scans are superimposed to generate a B-scan of the tissue sample or other object of interest being scanned.

[0065] In some embodiments, the CCR algorithm performs multiple iterations to extract the true image component and subtracts the result from the initial image spectral data of that iteration until the stored signal-transformed result value comprises a complex-valued image without any significant conjugate image artifacts.

[0066] In some embodiments, the method further comprises performing signal apodization. This is an optional processing parameter set by the user that helps condition the input signal to have zero values at the ends of the signal, thereby helping to reduce edge artifacts when performing the signal transformation in the image processing algorithm according to the disclosed technology.

[0067] In some embodiments, the calculated variable threshold is based on an empirical formula.

[0068] In some embodiments, the variable threshold is calculated using a derived formula.

[0069] In some embodiments, the variable threshold is calculated using a threshold based on image properties, such as a histogram-based intensity distribution.

[0070] Advantageously, this enables the variable threshold to be dynamically adjusted based on one or more image properties of the current image. Such properties can vary with optical alignment of the sample or other dynamic imaging conditions.

[0071] In some embodiments, the method is implemented by a graphics processing unit capable of processing images within 30 milliseconds.

[0072] In some embodiments, the image data is OCT image data, and the method further comprises outputting an OCT image based on the received image data, wherein the complex conjugate image data has been removed.

[0073] In some embodiments, the output OCT image does not contain perceptible complex conjugate images when displayed.

[0074] According to another aspect (second aspect) of the disclosed technology, an Optical Coherence Tomography (OCT) apparatus configured to perform real-time OCT comprises: an illumination arm comprising at least one optical light source; a reference arm; an OCT probe arm via which an OCT probe light beam is emitted; and a data arm via which returned OCT light is transferred to an image processor (148) for processing, the image processor being configured to perform the method according to the first aspect and / or at least one of its embodiments disclosed herein.

[0075] In some embodiments of the OCT apparatus, the reference arm and the probe arm are above a minimum design threshold for ensuring separation of complex conjugate images from the OCT image for output for display.

[0076] In some embodiments of the OCT apparatus, the OCT apparatus further comprises at least one dispersive component provided in one of the reference arm or the probe arm.

[0077] In some embodiments of the OCT apparatus, the at least one dispersive component in the reference arm comprises: one of a dispersive optical fiber or a dispersive glass window in the reference arm, wherein a physical path length of the reference arm is configured to compensate for the dispersive window, or vice versa a physical path length of the OCT probe arm is lengthened to compensate for the dispersive window; and one or more dispersive back reflectors in the reference arm, wherein a dispersive amount is determined by an optical path length through the dispersive back reflectors.

[0078] In some embodiments of the OCT apparatus, the at least one dispersive optical component provided in the OCT probe arm comprises one or more of: a dispersive optical fiber, a dispersive dichroic mirror, a dispersive OCT objective, and a dispersive OCT field lens.

[0079] According to another aspect of the disclosed technology, a computer program product comprising computer code which, when loaded from a memory and executed on one or more processors or processing circuitry of an apparatus, is configured to cause the apparatus to implement the method disclosed herein.

[0080] According to another aspect of the disclosed technology, an image processor comprises one or more processors or processing circuitry, including a graphics processing unit, wherein the image processor is configured to execute computer code that, when executed, causes the image processor to implement a complex conjugate cancellation method according to any of the embodiments disclosed herein.

[0081] Advantageously, the OCT scanner system can include exemplary embodiments of the MEMS scanning mirror assembly as disclosed herein for use within an OCT adapter for a microscope. The OCT adapter 206 system design has a compact structure, in the sense that the optical design of the MEMS scanning mirror enables an optimal short housing stack height to be achieved by the optical pass formed by the microscope optics and the attached OCT scanner objective, and is also compact in the lateral direction since the optical path traveled by the probe light within the scanning mirror assembly block is less than 40 mm, thereby supporting high scan rates and having a resolution of 6 microns or less in the resulting OCT images.

[0082] This is useful in ophthalmic surgery since the surgeon needs to use a microscope or similar device to generate a magnified image of the surgical area by using the microscope optics in order to more clearly view the surgical site while keeping the patient within reach of the surgeon's arms. In other words, some embodiments of the OCT scanner system design disclosed herein enable a combined stack height of the microscope and attached OCT adapter to be much lower than was previously possible. This design better balances the design constraints to enable the surgeon to view the area being scanned by the OCT scanner through one or more eyepieces of the microscope while keeping the area being scanned within the focal plane of the microscope optics and still allowing the surgeon to physically touch the scanned area for surgical purposes.

[0083] Other aspects of the compact design provide additional benefits. For example, the design of the scanning mirror assembly reflects the feedback beam used to feedback the scanning mirror position to a different optical plane than the optical plane used by the OCT probe beam, and the optical path of the reference beam used to determine the scanning mirror position is advantageously configured to reduce the likelihood of light returning from the feedback arm contaminating the mirror position reference beam or its light source, or the OCT probe beam.

[0084] The various aspects described above, the appended claims, and the examples disclosed herein and below can be suitably combined, as will be apparent to those of ordinary skill in the art.

[0085] Other features and advantages will be readily appreciated as the same become understood from the following specification, claims, and drawings when considered in connection with the example disclosed in one aspect or embodiment. BRIEF DESCRIPTION OF DRAWINGS

[0086] Some embodiments of the disclosed technology will now be described, by way of example only, with reference to the attached drawings in which:

[0087] Figure 1 The basic principles of a spectral domain OCT system are schematically illustrated;

[0088] Figure 2A and 2B Anterior and posterior perspective views of an OCT scanner adapter 206 for a microscope according to some embodiments of the disclosed technology are schematically illustrated;

[0089] Figure 3A and 3B Various views of components of an example of an OCT scanner adapter 206 according to some embodiments of the disclosed technology are schematically illustrated;

[0090] Figure 4 An enlarged view of the OCT scanner adapter 206 shown in Figure 3A and 3B An enlarged view of the OCT scanner adapter 206 shown in

[0091] Figure 5A An example of a MEMS scanning mirror assembly optical design according to some embodiments of the disclosed technology is schematically illustrated;

[0092] Figure 5B More details of the input arm in Figure 5A are schematically illustrated;

[0093] Figure 6 An example of a collimating lens assembly of the input arm in Figure 5A is schematically illustrated;

[0094] Figure 7 An example of an objective lens assembly of a MEMS scanning mirror assembly according to some embodiments of the disclosed technology is schematically illustrated;

[0095] Figure 8A An example of an OCT image of a contact lens and layered phantom with CCR image data is shown;

[0096] Figure 8B An OCT image of Figure 8A without CCR image data is shown;

[0097] Figure 9 An example of an image processing method for removing complex conjugate image data from image data according to some embodiments of the disclosed technology is shown;

[0098] Figure 10An example of an algorithm for generating signal transformations that are not affected by conjugate images is shown in accordance with some embodiments of the disclosed technology;

[0099] Figure 11A and 11B More details of two examples of the algorithm are shown schematically; Figure 10

[0100] Figure 12 An image processing device configured to implement a method for removing CCR image data from OCT images is shown schematically in accordance with some embodiments of the disclosed technology;

[0101] Figure 13 An example of a system in accordance with embodiments of the disclosed technology is shown schematically;

[0102] Figure 14 An example of a method in accordance with some embodiments of the disclosed technology is shown schematically;

[0103] Figure 15A and 15B Different views of a retroreflector in accordance with some embodiments of the disclosed technology are shown schematically;

[0104] Figure 16 An example of a reference arm assembly in accordance with some embodiments of the disclosed technology is shown;

[0105] Figure 17 An example of another method in accordance with some embodiments of the disclosed technology is shown schematically;

[0106] Figure 18 An example of another method in accordance with some embodiments of the disclosed technology is shown schematically; and

[0107] Figure 19 shows a hybrid optical fiber in accordance with some embodiments of the disclosed technology. DETAILED DESCRIPTION

[0108] The following detailed description provides examples of embodiments of the disclosed technology that are sufficiently detailed to enable one skilled in the art to practice the disclosed technology.

[0109] OCT scans come in two forms, time-domain OCT (TD-OCT) and spectral-domain OCT (SD-OCT). SD-OCT employs a spectral detection technique on the spectrum of the OCT interferometer output.

[0110] Figure 1 The operation of an example spectral domain optical coherence tomography (SD-OCT) interferometer scanning system 100, which includes some embodiments of the disclosed technology, is shown schematically.​

[0111] In Figure 1 In the example SD-OCT system 100 shown, the SD-OCT system 100 can be used to generate optical coherence tomographic images of an in-vivo tissue sample 116, such as a human eye, by using the OCT light scanning beam to probe within the tissue sample 116.

[0112] Obviously, Figure 1 The system 100 is shown schematically in FIG. 1 and is not drawn to scale. Figure 1 The positions of the components of the SD-OCT system 100 shown in FIG. 1 and their relative sizes do not necessarily reflect their true or relative positions or sizes in example embodiments of the disclosed technology.

[0113] In the following, when referring to an OCT scan image or image data, this can refer to a one-dimensional A-scan, a two-dimensional B-scan comprising a plurality of A-scans, or a volumetric scan image comprising a plurality of B-scans, as will be apparent to the person of ordinary skill in the art where appropriate.

[0114] As Figure 1 As shown, the SD-OCT system 100 comprises a low coherence broadband optical scanning light source 102. The scanning light source 102 is suitably connected to a coupler 104, which is configured to split the light from the light source 102 into an OCT light reference beam following an optical path 103a along a reference arm 103, and an OCT light probe or scanning beam following an optical path 105a along an OCT probe arm 105. The OCT light returning along the reference arm 103 and the probe arm 105 will have different phase shifts, which when the returning light is recombined at the coupler 104, will produce an interference. The combined light signal is output from the coupler along a detection or output arm 107, and the light interference pattern is detected using a spectrometer 136. The light signal 146 output by the spectrometer 136 is then processed by an image processor 148, for example by applying a Fourier transform to the output light signal 146, thereby generating OCT scan data, which can then be displayed on a suitable display 152.

[0115] The different phase shifts between the OCT light returning from the reference arm and the OCT returning from the probe arm, which result in the detected interference pattern, arise because the OCT light is returning from one or more different structures at different depths on or within the scanned tissue sample 116. In some embodiments, the scanned tissue sample can comprise a different type of object of interest 112 than an in-vivo tissue sample located in a human body region.

[0116] The phase shift that generates the interference is influenced by the different depths of the structures within the scanned sample that return the OCT light. The interference caused by the phase shift makes the signal output 146 of the spectrometer 136 available to generate images called tomograms that can visually display the depth of one or more such structures in the scanned or probed region and their location in the scanned or probed region.

[0117] In Figure 1 In some embodiments of the SD-OCT system 100 shown, the center wavelength of the broadband OCT light source 102 is 860 nm (nanometers) and the bandwidth is 100 nm. In some embodiments, more than one light source 102 is used to provide broadband low coherence OCT scanning light over the desired bandwidth.

[0118] The probed OCT light beams are received after being backscattered or reflected or otherwise returned by any structures at particular depths of the region 116, including the scanned tissue sample. In some embodiments, one or more or all of the optical paths 101a, 103a, 105a, 107a can be implemented by suitable single mode optical fibers and can include one or more sections in which the light beams propagating along the optical fibers travel in free space.

[0119] Figure 1 In the embodiment of the SD-OCT system 100 shown schematically in

[0120] In some embodiments, the interference between the returned reference light beams and the returned OCT probe light beams that occurs along the output arm 107 is measured using a suitable spectrometer 136, such as the one shown in Figure 1 to determine the depths of the scanned cross-sectional images. Other embodiments of the OCT system 100 can use other techniques to measure the interference and generate the output signal 146.

[0121] In some embodiments of the OCT system 100, one or more or all of the optical paths 101a, 103a, 105a, 107a include suitable single mode optical fiber and / or include one or more sections in which the OCT beam propagating along the fiber propagates in free space as it propagates out of or into the coupler.

[0122] In some embodiments of the disclosed technology, while the optical path lengths followed by the reference and probe beams are matched, the dispersion properties of the optical fiber along which each beam propagates are configured to be different to improve removal of complex conjugate images from the OCT image output, thereby improving the image quality of the OCT scan images and obtaining the speed of complex conjugate-eliminated OCT scan images.

[0123] In some embodiments, the term OCT scan is used herein to refer to B-scan and volume scan images of a tissue region (also referred to herein as a tissue sample) 116 generated using a spectral domain SD-OCT scanner system 100.

[0124] In Figure 1 In the spectral domain OCT example shown schematically in

[0125] Figure 1 The shown spectrometer 136 includes a collimating lens 138 through which the returned light passes through a grating 140 to generate a spectrum-dependent interference pattern. The interference pattern is focused via an objective lens 142 onto a line array camera 144, and an image signal representing the interference pattern is transmitted from an output 146 to a suitable image processing system 148. However, in alternative embodiments, another suitable type of interference detector can be used in the output arm 107.

[0126] Figure 1 In the shown embodiment of the SD-OCT system 100, the spectrometer 136 measures the spectral interference in the returned OCT beam by measuring the intensity modulation as a function of frequency in the returned OCT beam. The rate of change of intensity at different frequencies is indicative of the location of different reflecting layers in the sample.

[0127] The OCT probe beam propagates from the OCT probe branch 105 of the coupler 104 along the optical path 105a of the coupler 104, before entering the OCT scanner 164. Figure 1 The shown example OCT scanner 164 includes a collimating lens 110, a scanning mirror assembly 310 (as Figure 3A As shown in Figs. 4 and 5, for example as described later below, the scanning mirror assembly 310 includes a reflective surface 334 (see, for example, Fig. 5) that is configured to be scanned by a scanning mirror 332 (see, for example, Fig. 4) to scan the OCT probe beam 106 along a scan plane 312. Figure 3Aor the scanning mirror 112 of FIG. 5, the reflective surface 334 deflects the OCT scan beam out of the scanner 164 via the objective lens 114 and toward the focal plane 154 in the scan region 116. The scanning mirror assembly 310 includes a mirror positioning system that includes a secondary light source 158 that is also reflected by the scanning mirror 112 of the scanning mirror assembly toward the sample region 116 being scanned. The scanning mirror assembly includes a mirror positioning system 156 that includes a light source 158 for detecting mirror position and a mirror position detector PSD 160. The OCT scanner 164 also includes an objective lens 114 that focuses the OCT scan beam on the focal plane 154 within the tissue or sample region 116 being scanned.

[0128] The scanning mirror 112 can include a microelectromechanical system (MEMS) scanning mirror that is angularly moved by a mirror mover (not shown) in the scanning mirror assembly 310. Movement of the scanning mirror 112 causes the OCT probe beam to be scanned over the sample or other object of interest being scanned and the resulting interference pattern is used to generate an OCT B-scan image from the system output 156. Figure 1

[0129] Movement of the mirror mover is performed under the control of a controller 162. The controller 162 can be located in the scanning mirror assembly that includes the scanning mirror 112 or can be remote from the scanning mirror 112.

[0130] Figure 1 The mirror positioning system 156 shown includes an optical angular displacement mirror position measurement system 156. This system provides feedback to the controller regarding mirror position and, in some embodiments, this enables closed loop control of the MEMS-based scanning mirror position in some embodiments.

[0131] In use of the OCT scanner 164, the scanning mirror 112 directs the OCT beam along a scan path under the control of the controller 162 by the mirror mover mechanism. After reflection by the mirror 112, the OCT probe beam passes through a telecentric objective lens 114 that focuses the OCT probe beam at different locations in the focal plane 154 of the sample tissue 116 being scanned. As Figure 1 Illustratively, the focal plane 154 is shown as lying in an imaginary x-y plane with depth information being provided normal to the z-axis.

[0132] Figure 1 A telecentric objective lens 114 is shown through which the probe beam passes to the sample 116 and also through which the returning probe beam is reflected, where three exemplary exiting telecentric beams are shown that are focused at different locations within the focal plane 154, which lies as Figure 1 ​The x-y plane is shown. The exit, telecentric beams in each example come from different locations of the scanning mirror assembly 112, in other words, Figure 1 Three sequentially arranged telecentric beam locations are shown schematically by way of example. This is to schematically show how the telecentric OCT scanning or probing beams are moved to illuminate different regions as a B-scan or volume scan progresses.

[0133] The region being scanned includes a sample of tissue 116. In Figure 1 this includes tissue of an eye 116, which can be an in-vivo or ex-vivo tissue sample. In other uses of the OCT scanning system, other types of human or animal tissue can be scanned in-vivo or ex-vivo, where the OCT scanning images can be used to visualize internal structures at different depths in the tissue.

[0134] For example, as Figure 1 shown, an eye 116 is shown schematically, including a pupil 118 surrounded by an iris 120, behind which is a posterior chamber 122 and zonular fibers 124, and in front of which is a lens 126 and cornea 128 of the eye. Figure 1 Also shown are an anterior chamber 130 of the eye, as well as ciliary muscles 132 and suspensory ligaments 134, all of which can be scanned using an OCT system such as the OCT system 100 and shown as internal structures in the tomographic imaging presented on the display 152.

[0135] In surgical procedures on human eyes or other biological eyes or other tissue, the use of OCT can improve the likelihood of success of the procedure due to the extremely low accessibility of the surgical site. In some embodiments, the OCT system 100 can be used to perform two- or three-dimensional scans of regions of the eye 116 during a surgical procedure and create images that can be presented in real-time to the person performing the procedure. This can allow for a better understanding of the depth of any procedure being performed as the surgical procedure is being performed. Providing depth information of the surgical region in real-time during the procedure can help the surgeon avoid making incisions that are too deep (which can unnecessarily damage deeper tissue) or too shallow (in which case the procedure can not be successful and / or the surgical site can take longer to heal).

[0136] As Figure 1Illustratively, the interferometric signal output 146 of the spectrometer 136 of the OCT system 100 is post-processed by an image processor 148. For example, the signal output 136 can image process the OCT scan by a Fourier transform or other suitable signal transformation. This can initially generate a distorted OCT scan image, which can then be subjected to additional image processing to remove the distortion, and then the OCT scan image 150 is output to a suitable display 152. Some embodiments of the OCT scanner system 100 can also use image processing to remove complex conjugate artifacts to enhance the depth range of the acquired images.

[0137] The display 152 can be part of the device that contains the SD-OCT system 100 and performs the image processing, or it can be a different device. Some example embodiments of the disclosed technology use the OCT probe beam to generate a series of OCT scan images 148 fast enough to provide a real-time video stream on the display 152 that includes the OCT scan images 150. In some embodiments, the display 152 can be a near-eye display. In some embodiments, the display 152 can be a large display system that includes multiple displays to present information to the surgeon and / or others in the operating room. The display 152 can be integrated into the SD-OCT system 100 or located externally to it.

[0138] Figure 1 Of the components shown in FIG. 1 forming the OCT scanning system 100, one or more components can be separated from the optics forming the OCT scanner 164. By separating the OCT scanner optics, the OCT scanner 164 can have a more compact form factor. The more compact OCT scanner 164 can be better placed in the vicinity of the sample region being scanned.

[0139] In some embodiments, the OCT scanner system 100 includes the OCT scanner 164 provided as a microscope adapter, for example, for use with a surgical microscope. Figure 5A and 2B An OCT scanner adapter 206 of a microscope 200 is shown illustratively in FIGS. 3, 4, and 5. In some embodiments, the microscope 200 includes a surgical microscope suitable for use in a surgical procedure. The housing 202 of the microscope 200 has a base that, in some embodiments, is configured to accommodate one or more microscope accessories, allowing the OCT scanner adapter 206 to be attached to the base of the microscope housing. The OCT scanner adapter optics objective 114 can also be used as a microscope objective 210 (see also FIGS. 3, 4, and 5). Figure 1 、 3B and 4).

[0140] Examples of microscope systems with OCT scanner adapters

[0141] Figure 1and 2B A front and back perspective view of an OCT scanner adapter 206 for a microscope is shown schematically, i.e. an OCT scanner microscope attachment 206 according to some embodiments of the disclosed technology. The term OCT scanner adapter refers herein to an OCT scanner adapter microscope attachment. In some embodiments of the disclosed technology, a reference to an OCT scanner adapter can also refer to a device comprising an integrated OCT scanner adapter.

[0142] Figure 3A and 2B An OCT scanner adapter 206 of Figs. 1-4 is shown mounted to the base of a microscope 200. The OCT scanner adapter 206 microscope attachment can retrofit a microscope 200 by, for example, removing all existing microscope attachments from the microscope base and attaching the OCT adapter 206 to the base of the microscope 200, for example with its original microscope attachment points. Once properly fixed in place, the structural form of the OCT scanner adapter aligns the objective lens 210 with at least one optical channel of the microscope optics, for example the back channel or the channel for the microscope camera. In some embodiments, the base of the OCT adapter can also provide attachment points for adding attachments. Figure 1 3B and 4. The OCT scanner adapter 206 microscope attachment can retrofit a microscope 200 by, for example, removing all existing microscope attachments from the microscope base and attaching the OCT adapter 206 to the base of the microscope 200, for example with its original microscope attachment points. Once properly fixed in place, the structural form of the OCT scanner adapter aligns the objective lens 210 with at least one optical channel of the microscope optics, for example the back channel or the channel for the microscope camera. In some embodiments, the base of the OCT adapter can also provide attachment points for adding attachments.

[0143] In some embodiments, the OCT scanner adapter 206 has a vertically compact structural form such that it does not add too much height h2 to the height hi of the microscope to which it is attached in use. By reducing the additional vertical height hi of the OCT scanner adapter 206, the ease of access to the scanned region can be improved when using the scanner to generate cross-sectional images of the scanned region 116 while using the microscope. The OCT scanner adapter 206 is also laterally compact. This means that when it is attached to the microscope 200, it does not overly hinder the surgical manipulation of the scanned tissue region, thus allowing the simultaneous performance of surgical manipulations.

[0144] In the following description, when referring to height, it is referred to scanning a tissue sample 116 from a position above the tissue sample, for example as can occur when the OCT scanner adapter 106 is mounted to the base of a surgical microscope 200.

[0145] ​Some embodiments of the OCT scanner 206 described herein can maintain a similar compact form factor and can be used in other contexts. Further, in some embodiments, the OCT scanner 206 can be provided integrated into other devices, such as the microscope 200. In some embodiments, the OCT scanner 206 can be distributed as an optional accessory to such devices, enabling it to be distributed and sold independently of the later-attached microscope. Thus, unless the context clearly dictates otherwise, references to height apply equally to other dimensional directions of the OCT scanner, which are substantially or approximately orthogonal to the OCT objective lens plane and to any device to which the OCT scanner is attached. Further, the direction of the OCT scanner and microscope stack can also vary depending on one or more of the patient orientation, the configuration of the microscope optics, and the eyepiece position.

[0146] In other words, references to height in the context of overall "height" are based merely on the assumed orientation of the OCT scanner and microscope relative to a supine patient, i.e., the orientation when the patient is being operated on by a surgeon. When the patient is supine, the surgeon can access the area being operated on according to the following embodiments of the OCT scanner adapter 206 enabled by the disclosed technology, while still being able to physically contact the eyepiece of the microscope 200 to which the OCT scanner 206 is attached. In some embodiments, this geometry configuration can vary depending on the configuration of the microscope optics and / or the patient orientation and / or the location of the surgical area. Thus, in the following description, references to the height of the microscope and the OCT scanner adapter 206 and / or the combined stack height can also refer to other dimensions of the microscope and the OCT scanner adapter 206 that act as constraints on the dimensional specifications of the OCT scanner, as will be apparent to one of ordinary skill in the art.

[0147] Now returning to Figure 5A and 2B The microscope optics are mounted within the microscope housing 202 to form an optical channel through which the area below the objective lens 210 of the OCT scanner adapter 206 can be viewed. In some embodiments, the objective lens 210 provided by the OCT scanner adapter 206 for the microscope 200 includes an objective lens 114 of the OCT scanner system 100 schematically illustrated in Figure 1 Thus, references to the objective lens 210 in the description can refer to the objective lens 114 of the OCT system 100, which includes different types of OCT scanners 164, unless the context clearly limits the reference to refer only to the use of the OCT scanner as an adapter or accessory to a microscope.

[0148] In Figure 1In the illustrated example embodiment of the OCT scanner adapter 206 , the OCT scanning optics are designed to have a compact form factor, minimizing the additional height h2 added to the height h1 of the microscope optics housing 202 .

[0149] Figure 3A and 2B Also shown are microscope handles 204a, 204b for positioning the microscope 200 over the area to be scanned (and observed). The OCT scanner adapter 206 includes a housing 208, which is secured to the base of the microscope 200 as shown. However, as described above, in some embodiments, the OCT scanner adapter 206 can have different configurations and / or orientations during use. Such different configurations and / or orientations of the OCT scanner adapter 206 during use can also achieve the compact design principles of the OCT scanner disclosed herein.

[0150] Figure 1 Shown Figure 1 Different rear views of the OCT scanner adapter 206 are shown. The rear view shows a data and / or power port 212, such as an RSJ45 Ethernet port or a USB port, and an optical port 214. Port 212 provides power to the OCT scanner adapter 206 and, in some embodiments, may include a Power over Ethernet port.

[0151] In some embodiments, the OCT scanning light is returned from the OCT scanner adapter 206 to the OCT scanning system 100 (eg, Figure 3A Interferometry components shown).

[0152] For example, in Figure 3A In the embodiment of the present invention, the return OCT light from the sample 116 is returned through the objective lenses 210 and 114 and output through the optical port 214 along the optical fiber 308a. The optical fiber 308a, along with the mirror lens assembly and other optical components of the OCT scanner adapter 306 along the optical path of the OCT scanning beam toward the scanned sample, together form part of the detection arm 105 of the FD-OCT system 100.

[0153] After emitting and illuminating the scanned sample tissue 116, the OCT light is reflected, backscattered, or otherwise returned. The returned OCT light then passes back through the coupler 104, where it interferes with the light returning from the reference arm 103. The returned OCT beam and the reference beam then propagate along the output arm 107 to the spectrometer 136, which outputs an optical interference signal 136 of the OCT and reference beams for image processing to generate OCT imaging data 146, which is presented on a display 152.

[0154] In some embodiments of the disclosed technology, for example Figure 3A , 2A and 2B, the returned OCT light is output from the OCT scanner adapter 206 through optical port 214 to the coupler 104, which passes the light to the spectrometer 136 of the spectral OCT system 100 via the coupler 104.

[0155] In the embodiments shown in Figure 3B and 2B , the OCT scanner housing 208, which includes the objective lens 210, adds a height h2 to the height hi of the microscope 200. By using the optical design of the OCT scanner optical assembly within the OCT scanner adapter 206 according to embodiments of the disclosed technology, the additional stack height introduced by attaching the OCT scanner adapter 206 to the microscope housing 202 H2 is minimized.

[0156] For example, some embodiments of the optical assembly design of the OCT scanner adapter 206 can have the optical design schematically shown in Figure 3A , 3B , 4, and 5A and 5B. This optical design lifts the OCT beam exiting from the scanning mirror assembly 310 up from the plane of the objective lens 114, 210 by a minimum amount before the OCT exits via the objective lens 114, 120. This allows the additional stack height h2 of the OCT scanner adapter to be less than 40 mm, and in some embodiments, the additional stack height h2 is 36 mm or less.

[0157] It should be understood that Figure 3B and 2B are not drawn to scale, and the x-y-z axes shown in the figures are schematic and are used only to illustrate the general front and back perspectives. As shown in Figure 4 and 2B , the microscope housing body stack height is hi, and is aligned with the Z axis, while the microscope housing base and the OCT scanner adapter 206 are primarily aligned with the X-Y horizontal plane. The base-mounted OCT scanner system stack height h2 is also aligned with the Z axis. This makes the full stack height h3 of the microscope including the microscope optics and the base-mounted OCT scanner of the microscope's body determined by hi and h2. Preferably, the combined height h3 of hi + h2 is short enough so that the microscope can be positioned to allow the user to operate the microscope while performing surgery on or through the area of the focal plane including the microscope objective lens 210 through which the OCT beam exiting the microscope is observable. The OCT optical design allows h2 to be minimized to 36 mm while still maintaining a suitable exit beam diameter, for example 10.6 mm, and still having a stack height of 36 mm or less in some embodiments.

[0158] Thus, by using the optical design of the scanning mirror assembly optics according to embodiments of the disclosed technology, the combined stack height h3 = hi + h2 can be made much shorter than possible with previous optical design configurations.

[0159] By minimizing the stack height as much as possible, the microscope can be better positioned for surgical procedures. For example, it can be placed far enough away from the tissue sample in focus to allow the user to access the tissue sample being operated on, but close enough to comply with typical human physical form factors. In other words, the OCT adapter height h2 is preferably minimized as much as possible to ensure that the user is able to routinely operate the microscope while the microscope is optically focused on the focal plane on the tissue sample by the OCT probe beam being emitted onto the tissue sample via the microscope objective 210 of the OCT scanner adapter 206.

[0160] Figure 3B and 2B Some embodiments of the OCT scanner adapter 206 microscope attachment shown include a scanning mirror assembly 310 (described in greater detail below) having a compact optical design that allows h2 to be minimized to 36 mm or less.

[0161] For example, in some embodiments, as described below with reference to Figure 4 、 3B and 4, the OCT scanner adapter 206 includes a microelectromechanical system (MEMS)-based two-dimensional (2D) scanning mirror assembly 310 of ultra-compact large numerical aperture that uses a point source 158 to determine the position of the mirror surface 334 in its optical design by a position sensitive detector 160.

[0162] Some embodiments of the OCT scanner assembly using the PSD 160 are capable of supporting very high scan rates, such as 36,000 A-scans per second or higher, where an A-scan is a depth scan of a point in the tissue. Each B-scan is formed from a plurality of adjacent A-scans, which can be used to generate an image with depth information of the area being scanned in the form of a slice through the sample being scanned to show the structure at different depths along the slice. In other words, a B-scan provides a cross-sectional view of the tissue sample along a single linear path, such as along a line as shown in FIG. 4. Figure 4A line scan) traverses the z-direction or depth direction with respect to the structure, defining a line in the x-y coordinates shown schematically. Some embodiments of the OCT assembly allow for real-time generation of high resolution images, for example 400 B-scans per second, across the entire field of view (FoV) being scanned, which can be, for example, a 20 mm x 20 mm or larger area. By performing a series of B-scans on the sample fast enough and close enough to each other, a three-dimensional volume or composite scan of the area being scanned can be formed and presented on the display 152.

[0163] Figure 4 , 4 and Figure 4 and 5B Embodiments of the scanning mirror assembly as the optical block 310 include various optical elements arranged in an optical design aimed at reducing the height h2 and lateral footprint of the OCT scanner adapter 206.

[0164] Some embodiments of the optical design of the scanning mirror assembly specify one or both of a minimum and maximum exit beam diameter of one or more optical components. For example, the OCT beam input via the optical fiber 308A, as it exits the collimating lens assembly 516 (e.g., collimating lens 602 as shown in Figure 3A In some embodiments, the beam diameter from the collimating lens can have an exit pupil diameter of 3.3 mm. Other design constraints can depend on the exit pupil diameter of the OCT beam from the collimating lens. For example, in some embodiments, the collimated OCT beam exits the collimating lens assembly with an exit pupil diameter of at least 3.1 mm (possibly up to 3.3 mm) and has a wavefront error of less than (about) 1 / 2 wave (rms (root mean square)).

[0165] Another exit beam diameter of interest is the beam diameter of the OCT beam 312 as it exits the focusing lens assembly 314 of the OCT scanner adapter 206 and then impinges on the fold mirror 316. The focusing lens 314 expands the OCT scan or probe beam diameter to 10.6 mm to set the OCT system numerical aperture and ultimately the resolution of the OCT scanner system based on the focal length of the OCT microscope objective 210. For an objective 210 with a working distance of 175 mm (non-focal length), the lateral resolution is 30 pm, in other words, the resolution is better than 33 line pairs per mm. This can be contrasted with a resolution of 6 microns (166 line pairs per mm) at the intermediate imaging plane located at the exit of the OCT objective assembly 510, 512.

[0166] In some embodiments, the user can be able to select the desired resolution of the OCT system via a suitable user interface (e.g., as shown in Figure 4The user interface of the device of the illustrated image processing system 148, which system includes or is connected to a display 152, sets the maximum FoV of the scan to be a 20 mm x 20 mm area, and in some embodiments the user interface is configured so that the user can adjust the position of the OCT scan FoV within a 25 mm box, although the full FoV of the OCT scan image is still a 20 mm x 20 mm area.

[0167] Embodiments of the disclosed technology for surgical procedures and other use environments that require real-time image processing can use a high dispersion configuration of the OCT system 100 with the OCT scan adapter 206.

[0168] The term real-time as used herein means that the processing delay is imperceptible, e.g., 60 ms or less, and in some embodiments a delay of about 30 ms or less can also be achieved. This design employs a high incidence angle at the scan mirror, which reduces compound angle coupling when performing 2D scans of the sample with high lateral optical resolution and a telecentric image plane.

[0169] The optical design of the scan mirror assembly 310 illustrated in Figures Figure 5A , 3B , 4 and 5A employs a high incidence angle at the scan mirror reflective surface 334 to reduce compound angle coupling when performing 2D scans of the sample, enabling the OCT scan to simultaneously achieve high lateral optical resolution and a telecentric image plane. Each OCT scan includes a large number of one-dimensional scans (A-scans) that provide depth information for a point in the area being scanned, e.g., a sample. Multiple A-scans are stacked together to create a two-dimensional image, referred to herein as a B-scan. A B-scan provides a slice through the area being scanned that shows the depth information along the path of the A-scans. Multiple B-scans through the area being scanned can provide a three-dimensional volume scan of the area being scanned.

[0170] The scanning mirror assembly 310 includes a movable reflective surface 334 that includes a microelectromechanical system having a suitably large numerical aperture. The term "large numerical aperture" herein refers to the clear aperture of the reflective surface 334, which preferably is greater than about 4 mm in diameter. The term "clear aperture" refers to the range of angles that can be imaged through the aperture, and within which range there are no support members, clips, or other immobilizing elements blocking. The greater the diameter of the clear aperture of the scanning mirror reflective surface 334, the slower the scanning rate because the probe beam covers a greater diameter. While MEMS mirrors with a clear aperture of about 7 mm are known in the art, such known MEMS mirrors with a large clear aperture are unable to achieve acceptable scanning rates for real-time imaging applications required by OCT, for example, in optical surgical procedures, even with optical feedback. In some embodiments, the scanning mirror has a clear aperture of 5 mm. In some embodiments, a 4.2 mm clear aperture scanning mirror assembly is used that is capable of performing scans at a sufficiently high rate to enable real-time imaging for Figure 4 The SD-OCT system shown uses a swept source for real-time surgical applications.

[0171] In OCT, axial and lateral properties are decoupled. The lateral resolution is defined by the objective lens in front of the sample and the focusing medium. The axial properties of the interferometric measurement are determined by the coherence properties of the OCT scanning light source, while also depending on how the returned OCT signal is sampled on the detector after returning from the sample. The axial resolution of OCT depends on the spectral bandwidth and the center wavelength of the OCT scanning light source. The axial imaging depth defines the axial range covered by a B-scan. It is also defined by the maximum fringe frequency that can be detected, as the maximum frequency of the interference spectrum can decode the maximum scanning depth.

[0172] An A-scan is an amplitude depth scan of a sample along one dimension, often referred to as the z-axis. A B-scan is a two-dimensional lateral scan of a sample formed by a series of A-scans. In other words, for each sample point, the spectral dependent interference fringe pattern produced by the counter reflection of the reference mirror of the OCT interferometer and the counter reflection of the sample is recorded as an A-scan. Multiple A-scans are performed to generate other scans, such as B-scans, which allow for the generation of a complete depth profile of the sample reflectivity at the position of the beam.

[0173] In some embodiments, the opening diameter is 4.2 mm or more.

[0174] In some embodiments, the OCT scanner adapter 206 includes a MEMS-based high-speed OCT mirror scanning assembly 310 that uses the position-sensitive detector system 160 to provide control loop feedback for controlling the positioning of the OCT beam during scanning. This control loop feedback offers technical advantages because it allows the OCT scanner to generate more B-scans per second of the scanned object of interest. In other words, the control feedback loop provided in some embodiments of the disclosed technology can suppress ringing and resonant behavior caused by sudden changes in the drive voltage at the end of the scan line.

[0175] Example of OCT microscope adapter design

[0176] Figure 4 An example embodiment of a MEMS microscope OCT scanner adapter 206 according to the disclosed technology is schematically shown, which is suitable for mounting to a Figure 3A to Figure 4 and 2B The base of the microscope 200 is shown as it is configured with optical components to minimize lateral and vertical footprint while maintaining suitable optical quality characteristics for OCT applications.

[0177] exist Figure 5A , the exemplary embodiment of the OCT scanner adapter 206 is shown to include a plurality of components contained within or mounted on an adapter housing 208. The adapter housing 208 includes a data / power port 212, such as a Power over Ethernet port or a high-speed USB port.

[0178] An optical port 214 is also provided for inputting and outputting OCT scanning light to the OCT scanner adapter 206. The optical fiber 308a is connected to the optical port 214 to transmit the OCT light from the Figure 3A The OCT scanning system 100 is shown with the coupler 104 being fed via the fiber optic connector 308 to Figure 1 The returned OCT light propagates back along the original path via the optical fiber 308a to the optical block 310 of the scanning mirror assembly shown in FIG. Figure 5A The coupler 104 is shown in FIG. Thus, the optical fiber 308a is Figure 5A The optical path 105a shown in the OCT scanning system 100 is a part of the optical path 105a, through which the OCT detection light illuminates the sample to be scanned, and the OCT light returned from the sample travels through the optical path to the sample. Figure 1-4 The coupler 104 output of the OCT scanning system 100 is shown in FIG. The optical fiber 308a has a suitable numerical aperture, preferably 0.14, to allow the OCT light in the near infrared region to propagate along its single mode.

[0179] The OCT light from the OCT light source 102 passes through the illumination arm 101 along the optical path 101a to the coupler 104, and then passes through the optical path 101a to the coupler 104. Figure 5Aof the probe arm 105 in FIG. 1, where the optical fiber 308a forms part of the optical path 105a. The OCT light along the optical fiber 308a is injected into the scanning mirror assembly optics block 310 through the OCT data connection fiber optic connector 308, and then propagates along the OCT arm 518 (see FIG. 5) of the MEMS scanning mirror assembly 310. Figure 5B

[0180] In some embodiments, the optical fiber connector 308 used to input the OCT light into the MEMS mirror block 310 is an optical fiber connector to an angle-polished connector.

[0181] The optics block that houses the MEMS scanning mirror assembly 310 also houses the optical components of the optical angular displacement mirror position measurement system 156 for the scanning mirror assembly, as shown in FIG. 6. Figure 5A The mirror position measurement system 156 is shown in FIG. 6. A controller 162 (see FIG. 1) is used to adjust the reflective surface 334 of the scanning mirror 112 shown in FIG. 1 using the mirror moving mechanism (not shown) of the MEMS scanning mirror assembly 310. The controller 164 can be implemented within the OCT scanner adapter 206 or provided remotely, in which case the control signals can be delivered to the mirror mover in the MEMS scanning mirror assembly 310 via the data port 212 of the OCT scanner adapter 206. Figure 5A Figure 1 The mirror position measurement system 156 is shown in FIG. 6. A controller 162 (see FIG. 1) is used to adjust the reflective surface 334 of the scanning mirror 112 shown in FIG. 1 using the mirror moving mechanism (not shown) of the MEMS scanning mirror assembly 310. The controller 164 can be implemented within the OCT scanner adapter 206 or provided remotely, in which case the control signals can be delivered to the mirror mover in the MEMS scanning mirror assembly 310 via the data port 212 of the OCT scanner adapter 206. Figure 5A

[0182] In some embodiments, the same mirror reflective surface 334 in the scanning mirror assembly housed in the optics block 310 reflects both the input OCT light beam and a mirror positioning reference light beam from a different source (see detailed description below). However, it is apparent to one of ordinary skill in the art that a separate mirror mounted on the same tilt axis can be used in other embodiments, as long as such a design does not adversely affect the stack height h2 of the OCT scanner adapter 206. Figure 3A

[0183] The OCT light received via the OCT data connection optical fiber 308 propagates along the optical path 105a, reflected at the reflective surface 334 in an optical plane that is different from the optical plane in which the light from the light source of the angular displacement mirror measurement system 156 is reflected.

[0184] The reflected OCT light beam then propagates along the optical path through the OCT scanner adapter 206, exits the adapter 206 via the microscope objective 210 to probe a subject of interest, such as a tissue sample, e.g., an intraocular eye tissue, as shown schematically in FIG. 1. Figure 5A ​​​​​

[0185] The OCT light reflected, backscattered or otherwise returned from structures within the tissue sample then propagates back along return path 105a through the scanning mirror assembly of optical block 310 and back along optical fiber 308a. The returned OCT light then exits from OCT scanner adapter 206 via optical port 214 and is fed into OCT system 100 where it is combined with light returned from reference arm 103 at coupler 104 and interferes. In Figure 5A In the OCT system 100, the resulting interference pattern is detected by spectrometer 136 which generates image data from which a tomographic image can be subsequently obtained by image processing, indicative of the scanned structures in the tissue located within the scanned FoV.

[0186] In Figure 3A to 3B In the example embodiment of OCT adapter 206 shown, the OCT probe beam 312 is output from the optical block housing the MEMS OCT scanning mirror assembly 310 and propagates towards fold mirror 316 which lifts the OCT beam from its optical plane by a minimum amount towards beam splitter 318. Beam splitter 318 reflects the incoming OCT beam to objective lens assembly 210 of OCT scanner adapter 206 which also serves as the objective lens of the microscope optics housed in microscope 200 when the OCT scanner adapter 216 is attached to microscope 200. The OCT probe beam is focused from objective lens 210 in a telecentric beam form to focal plane 154 in the scanned tissue as Figure 3A The focal plane is schematically shown to lie in the x-y plane. The resulting returned OCT light can be used to generate an OCTA scan which provides depth information orthogonal to focal plane 154, i.e. in the z direction as Figure 1 Movement of mirror surface 334 causes the telecentric beam to move over focal plane 154 in scanned region 116, thereby generating an OCTB scan image.

[0187] In Figure 5A The OCT scanner adapter 206 is configured such that objective lens 210 can serve as the objective lens of both the microscope optics and the OCT scanner system 100. A light blocking gasket 320 is provided around the aperture formed in the OCT scanner adapter 206 through which the OCT objective lens 210 aligns and extends with the optical passageway formed by the microscope optics of microscope 200.

[0188] The configuration of the deflecting mirror 316, beam splitter 318, and objective lens assembly 210 of the OCT scanner adapter 206 is cooperatively designed so that the OCT beam deviates from the plane along which it passes through the scanning mirror assembly by only a slight amount of lift so that it can be emitted through the objective lens 210. The required lift is affected by the tilt angles of the beam splitter and deflecting mirror, as well as the beam incidence geometry. By using this optical design, the additional height h2 that the OCT scanner adapter 206 adds to the height of the microscope is also minimized. For example, in some embodiments, the OCT scanner adapter housing 302 adds 40 mm or less to the overall height h1 of the microscope housing 202. In some embodiments, the additional height h2 is 36 mm or less. In some embodiments, by adopting appropriate beam splitter and deflecting mirror tilt angles, a lift of 27 mm or approximately 27 mm can be achieved.

[0189] In some embodiments, as Figure 1 As shown in the example embodiment of the adapter, the OCT probe beam 312 emerges from the optical block housing the scanning mirror assembly and first traverses free space to a focusing lens assembly 314, which allows adjustment of the focal plane of the scanned image. This allows adjustment of the focus at different depths. The focusing lens assembly 314 is driven by a motor 326 and also includes a travel limiter or stop 324. In some embodiments, the focusing mechanism provided by the adapter's focusing lens assembly 314 can be adjusted to control the OCT focal plane within a ±30 mm range, allowing focus to be applied to a range of depths within the sample for scanning. The OCT focal plane can be adjusted within a ±30 mm range and can be optimized during initial image acquisition for optimal signal-to-noise ratio (SNR). This is distinct from, and should not be confused with, the technique of moving the focus at the A-scan rate to extend the depth of focus within the sample. Movement of the focusing lens assembly 314 is slower than that required for A-scan acquisition and is not adjusted without user intervention unless the system detects significant movement in the sample.

[0190] In some embodiments, as Figure 5AAs shown, the OCT scanner adapter 206 is attached to the microscope 200 using fixtures (e.g., screws) that are provided in the grooves of the mounts 328a and 328b and can extend from the mounts 328a, 328b into the base of the microscope 200 into corresponding receiving holes or holes, preferably threaded holes in the base of the microscope 200, in order to fixedly engage the OCT scanning adapter 206 with the microscope. In some embodiments in which the OCT scanner adapter 206 is used as a microscope accessory, receiving holes or holes can also be provided on the base of the OCT scanner adapter 106 at locations corresponding to the locations of the receiving holes or holes in the base of the microscope 200. By having the same or similar fixed locations in the base of the OCT scanner adapter microscope accessory 206 as in the base of the microscope, different types of microscope accessories that would otherwise be attached to the base of the microscope 200 can be attached to the base of the OCT adapter. In other words, in some embodiments, the OCT scanner adapter 206 is configured to be attached to the base of the microscope as a microscope optical accessory. Some embodiments of the OCT scanner adapter microscope accessory 206 allow the OCT scanner adapter accessory 206 to have another microscope accessory attached to the base of the OCT scanner adapter.

[0191] Figure 3A Another view of the OCT scanner adapter 206 is shown. Figure 1 However, in Figure 5A , Figure 1 The locations of the light source or emitter 158 for the mirror positioning light beam 400 and the position sensitive detector (PSD) 160 of the optical angular displacement measurement system 156 in the optical block 310 are more clearly visible in the view shown.

[0192] Figure 5A The example of the angle of incidence θ of the mirror positioning illumination light beam 400 shown in Figure 5A at the reflecting surface 334 of the MEMS scanning mirror, which upon reflection forms the mirror positioning reference light beam that travels to the PSD 160.

[0193] It should be understood that the locations of the angles of incidence and the beam paths shown in the figures are for illustration purposes only and are not drawn to scale.

[0194] The design of the MEMS scanning mirror assembly is configured such that Figure 5AThe illumination mirror positioning beam 400 shown in FIG is reflected at a different optical plane by the reflective surface 334 of the scanning mirror to form a reference beam 402, which is transmitted along the optical plane of the positioning reference arm of the OCT scanning mirror assembly 310 to reflect the incident OCT scanning or detection beam 312 from the reflective surface 334, as shown in FIG. Figure 3A and 5A The scanning mirror assembly is further configured so that the returned positioning light is reflected by the mirror to another optical plane that is different from the reflection optical plane of the outgoing and returned OCT beams and the optical plane on which the incident mirror positioning beam is reflected, thereby minimizing interference of the positioning light on the light source of the OCT beam or the incident mirror positioning beam or the mirror positioning beam.

[0195] In the attached figure Figure 3B Schematically shows Figure 3B and 3B An enlarged view of the OCT scanner adapter 206. Figure 5A , the mirror position illumination beam 400 (shown as a dashed line) from the point light source 158 is incident on the reflective surface 334 of the OCT scanning mirror 500 at an angle of incidence (AOI) shown as θ, as shown in FIG. Figure 5A As shown. The mirror position reflects the light beam 402 (as Figure 3A For clarity, the return light of the incident light beam at PSD 160 is not shown in FIG. Figure 3A Shown in.

[0196] Figure 3A The illustrated OCT scanner optical assembly is arranged so that the OCT light emerging from the optical plane of the scanning mirror assembly is only slightly lifted from the optical plane by the deflecting mirror 316 toward the beam splitter 318. The beam splitter 318 allows the light to be transmitted through and back to the microscope optics while also reflecting the OCT probe beam to the same focal plane 154 as the microscope light. By optimally positioning the beam splitter and deflecting mirror relative to the objective 210, the height to which the OCT probe beam must be lifted by the deflecting mirror before being reflected by the beam splitter 318 and passing through the objective 210 can be reduced.

[0197] In some embodiments, the deflecting mirror elevates the OCT beam by 27 mm from the optical plane of the scanning mirror assembly.

[0198] Example of optical design of a scanning mirror assembly

[0199] In the attached figure Figure 1 An example of an optical design of a two-dimensional (2D) scanning mirror assembly is schematically shown, for example, as Figure 5B 、 3Band shown in FIGS. 4 housed in the optical block 310.

[0200] The optical design of the 2D scanning mirror assembly is applicable to other types of OCT scanners, such as Figure 5A the OCT scanner 164 in FIG. 1 and the OCT scanner adapter 206. Figure 5A The scanning mirror assembly 310 shown has an optical design that can be used for other applications than OCT that use scanning light that requires mirror positioning.

[0201] In other words, Figure 5B The 2D scanning mirror assembly optical design of FIG. 1 is not limited to OCT applications or devices, such as those shown in the drawings in all of its embodiments. Figure 5A It can be advantageously implemented in any other type of light scanning device where a compact transverse optical plane is beneficial.

[0202] Figure 1 Some example embodiments of the microelectromechanical system (MEMS) 2D scanning mirror assembly 310 shown have an optical design that includes a movable MEMS scanning mirror having a reflective surface 334, and a connector 308 for connecting to a point light source to produce a scanning light beam, for example as shown, an optical fiber 308a is connected via the optical fiber connector 308, the end of which (see FIG. 5b) then acts as a point light source for the light beam.

[0203] The scanning mirror assembly optics also include a collimating lens assembly 516 for introducing light via the connector 308. The collimating lens assembly 516 is configured to direct the exiting light beam from the point light source at a diameter greater than a threshold exiting light beam diameter, to the reflective surface appropriate for the desired scanning application. After reflection at the reflective surface 334 of the scanning mirror 112, the scanning light beam exits the scanning mirror assembly via the objective lens assembly 510, 512.

[0204] The reflective surface 334 is configured to reflect the incoming collimated light beam to form a scanning light beam, for example, if the point light source provides OCT light, an OCT probe light beam, in the form of a telecentric light beam 312, via the objective lens 510 and field lens 512 (collectively, the objective lens assembly 510, 512) from the mirror assembly and towards the telecentric image plane 154. The optical design of the components in the scanning mirror assembly is configured to ensure that the scanning light beam is capable of performing a scan with a resolution superior to a resolution threshold.

[0205] The optics of the scanning mirror assembly are configured to provide a scanning light beam from a point light source (such as an optical fiber or an optical fiber stub end face (see also Figure 5Atotal length L of the path to the telecentric image plane (700), which length is less than about 40 mm, to help keep the scan mirror assembly lateral dimension X small enough to allow the OCT scanner housing 308 to be lower in its design than required for lateral footprint. For example, as shown in FIG. 5, the width X of the scan mirror assembly is preferably less than 41 mm, for example, in some embodiments it can be 40.6 mm or less. The optical design is also configured to keep the depth Y as small as possible as shown in FIG. 5, for example, Y can be 35 mm or less, in some optical designs it can be as short as 34.5 mm or less. Figure 5A

[0206] Thus, in some embodiments, the total length L is kept as short as the optical design layout will allow to reduce the lateral and depth footprints X and Y to be as small as possible, so that the housing of the scanner including the scan mirror assembly 310 can also similarly have a small footprint.

[0207] By keeping the lateral footprint X as small as possible, side access to the area being scanned is improved, which is particularly beneficial when the scan mirror assembly 310 is a scan mirror assembly for an OCT scanner adapter 206 which is a surgical microscope attachment, as this can improve access to the surgical operating area when using the microscope to which it is attached.

[0208] In some embodiments of the scan mirror assembly, a threshold of the exit beam diameter from the collimating lens 516 is at least 3 mm, preferably at least 3.1 mm. By having an exit beam diameter of at least 3.1 mm, the scanner benefits from a better lateral resolution than is allowed with a small exit beam diameter.

[0209] In some embodiments of the scan mirror assembly, a threshold of the telecentric beam resolution at the telecentric imaging plane 700 is better than 6 microns. In other words, the scan image can resolve features in the sample being scanned that are less than 6 microns.

[0210] In some embodiments, the scan mirror 112 can be moved, for example, by the controller 162. In some implementations, the scan mirror assembly can be configured to move about its optical axis, and in some implementations the scan range is + / - 5 degrees.

[0211] In some embodiments of the scan mirror assembly, the numerical aperture of the optical fiber and the focal length of the collimating lens together determine a suitable threshold of the exit beam diameter after the collimated beam exits the collimating lens to be at least 3.1 mm to achieve the designed resolution at the focal plane. The combination of the focal lengths of the scan mirror objective and the scan mirror field lens determines the total length L of the path that the probe beam takes to exit the mirror assembly, which length L is preferably less than 40 mm or around 40 mm. ​

[0212] In some embodiments, such as when the scanning mirror assembly is used for OCT purposes, the optical fiber has a numerical aperture of 0.14. In other embodiments of the scanning mirror assembly, the optical fiber that feeds light to the scanning mirror assembly as a point source of light can have another suitable numerical aperture value, so long as the numerical aperture allows sufficient light to be fed along the single mode optical fiber 308a to the scanning mirror assembly for another use environment.

[0213] In some embodiments of the scanning mirror assembly, the objective lens 510 comprises a F2.7 bi-convex bi-concave lens and the field lens 512 comprises a F19 positive / negative meniscus bi-concave field lens.

[0214] In some embodiments of the scanning mirror assembly, the optical path difference (OPD) of the telecentric probe beam output by the scanning mirror assembly has a radius of curvature greater than 100 mm.

[0215] In some embodiments of the scanning mirror assembly, the telecentricity of the telecentric beam is better than 0.03 degrees of incidence angle with respect to the telecentric imaging plane.

[0216] In some embodiments of the MEMS scanning mirror assembly, the reflective surface 334 of the MEMS scanning mirror comprises a large aperture gold-coated silicon mirror bonded to an underlying mechanical structure.

[0217] Figure 6 Embodiments of the scanning mirror assembly 310 design shown schematically in FIGS. 1-5 can be implemented as an optical block in an OCT scanning system, such as the OCT scanning system 100 shown in FIG. 6. Figure 6 For example, in some embodiments, the scanning mirror assembly is implemented as an optical block having the X, Y footprint shown in FIG. 7 for use in a compact OCT scanner adapter 206 for a microscope, such as the OCT scanner adapter 206 shown in FIG. 8. Figure 6 For example, in some embodiments, the scanning mirror assembly is implemented as an optical block having the X, Y footprint shown in FIG. 7 for use in a compact OCT scanner adapter 206 for a microscope, such as the OCT scanner adapter 206 shown in FIG. 8. Figure 1 For example, in some embodiments, the scanning mirror assembly is implemented as an optical block having the X, Y footprint shown in FIG. 7 for use in a compact OCT scanner adapter 206 for a microscope, such as the OCT scanner adapter 206 shown in FIG. 8.

[0218] However, as noted above, Figure 7 and 5B The scanning mirror assembly 310 shown in FIGS. 1-5 has an optical design that can be used in a variety of different use environments in other types of scanner systems. In some embodiments, Figure 7 and 5B The mirror assembly shown in FIGS. 1-5 is provided as a scanning mirror assembly for an OCT device as shown in FIG. 6 and receives light injected by the optical fiber 308a. In other embodiments, a different point source of light can be used in place of the optical fiber 308a that acts as a point source of light for an OCT beam, such as shown in FIGS. 3, 4, 5A and 5B. Figure 7 The mirror assembly shown in FIGS. 1-5 is provided as a scanning mirror assembly for an OCT device as shown in FIG. 6 and receives light injected by the optical fiber 308a. In other embodiments, a different point source of light can be used in place of the optical fiber 308a that acts as a point source of light for an OCT beam, such as shown in FIGS. 3, 4, 5A and 5B. Figure 7 The mirror assembly shown in FIGS. 1-5 is provided as a scanning mirror assembly for an OCT device as shown in FIG. 6 and receives light injected by the optical fiber 308a. In other embodiments, a different point source of light can be used in place of the optical fiber 308a that acts as a point source of light for an OCT beam, such as shown in FIGS. 3, 4, 5A and 5B. 3B The mirror assembly shown in FIGS. 1-5 is provided as a scanning mirror assembly for an OCT device as shown in FIG. 6 and receives light injected by the optical fiber 308a. In other embodiments, a different point source of light can be used in place of the optical fiber 308a that acts as a point source of light for an OCT beam, such as shown in FIGS. 3, 4, 5A and 5B. The mirror assembly shown in FIGS. 1-5 is provided as a scanning mirror assembly for an OCT device as shown in FIG. 6 and receives light injected by the optical fiber 308a. In other embodiments, a different point source of light can be used in place of the optical fiber 308a that acts as a point source of light for an OCT beam, such as shown in FIGS. 3, 4, 5A and 5B.

[0219] In some embodiments, the mirror assembly 310 can be provided in an OCT scanner adapter 206 that functions as an OCT scanning attachment for the microscope 200. In some embodiments, the microscope can include a surgical microscope, and the mirror assembly 310 can be used to generate OCT scans of a sample tissue region undergoing a surgical procedure at a sufficiently high rate to allow real-time OCT tomographic imaging of the sample tissue region to be generated while the surgical procedure is being performed.

[0220] In some embodiments, Figure 3A The SD-OCT scanning system shown in FIG includes an OCT scanner adapter 206 including scanning mirror assemblies 112 and 310, the optical design of which is as follows: Figure 3A and 5B As shown in and described herein.

[0221] In some embodiments, the scanning mirror assembly 310 is configured such that the OCT light returning from the sample along the OCT detection arm 105 has a lateral optical resolution equal to or better than 6 microns, ie, a resolution better than 166 line pairs per millimeter.

[0222] In some embodiments, the scanning mirror assembly 310 comprises a MEMS 2D scanning mirror assembly comprising at least: a movable MEMS scanning mirror having a reflective surface 334; an optical fiber 308a connected via an optical fiber connector 308 and configured as a point light source for illuminating an OCT beam toward the reflective surface 334; and a collimating lens assembly 516 configured to output OCT light having an output beam diameter of at least 3.1 mm from the point light source toward the reflective surface 334. The reflective surface 334 is configured to reflect the incident collimated OCT beam to form an OCT probe beam and a reflector positioning reference beam. The OCT probe beam is emitted from the mirror assembly as a telecentric beam toward a telecentric image plane with a resolution of up to 6 microns. The optical components of the scanning mirror assembly 310 are configured to provide a total path length L from a) the end face of an optical fiber plug inserted into the optical fiber connector providing the point light source to b) the telecentric imaging plane, wherein the total path length L is less than 40 mm, and in some embodiments, preferably less than 36 mm. In some embodiments, objective lens assemblies 510 , 512 are provided in the detection arm of the scanning mirror assembly to focus the telecentric OCT beam via the OCT scanner (microscope) lens 114 , 210 .

[0223] The scanning mirror assembly 310 has an optical design that includes a reflective surface 334 of the MEMS mirror that is configured so that the incident mirror positioning beam is reflected to an optical plane that is different from the optical plane from which the incident OCT scanning beam is reflected. In this way, the scanning mirror assembly can also be used with Figure 3Amirror positioning systems such as the angular tilt mirror positioning system shown in

[0224] As mentioned above, Figure 2A and 5B Some embodiments of the MEMS-based scanning mirror assembly shown in Figure 7 , 3B and 4 are implemented as part of an OCT scanner 206, as shown in Figure 7 the SD-OCT scanning system shown in

[0225] In some embodiments of the MEMS scanning mirror assembly 310, the scanning mirror 112 is mounted on an underlying mechanical structure or support 500, as shown in Figure 5A which provides a mirror movement mechanism to allow the mirror surface 334 to pivot about its optical axis under the control of the controller 162.

[0226] In some embodiments, the reflective surface 334 of the MEMS scanning mirror assembly comprises a large-aperture gold-coated silicon mirror bonded to the underlying mechanical structure 500.

[0227] Figure 5A The angular displacement measurement system 156 shown in Figure 1 is implemented in embodiments of the MEMS mirror assembly of Figure 5A by a light source 158 comprising a suitable optical point source, such as a laser diode 502. The optical point source generates a light beam, referred to herein as the mirror positioning light beam 400 (shown as a dashed line in

[0228] The angular displacement measurement system 156 is used to determine the angular position of the MEMS scanning mirror assembly 310 relative to the incident mirror positioning light beam 400, as this allows the mirror position of the incident light beam to be determined as scanning is performed, and adjusted as scanning proceeds. OCT scans such as B-scans or volume scans are performed by using the controller 164 to move the mirror according to arbitrary scan parameters for a particular scan configuration (in some embodiments, these parameters can be input by a user and / or automatically determined for a particular type of scan).

[0229] In some embodiments, the position of the movable MEMS mirror surface 334 can be controlled using a suitable angular position controller (not shown) based on feedback from the position sensitive detector 160, in a closed loop control. Figure 5AA position sensitive detector 160 (not shown) is provided to perform the control. The position sensitive detector 160 detects the mirror positioning beam 402.

[0230] In some embodiments, the scanning mirror assembly 310 described above with reference to Figure 5A 、 3B , 4, 5A and 5B includes a position sensitive detector 160 configured to send feedback mirror position data to a controller 162 configured to control the position of the MEMS scanning mirror surface while performing a scan. However, in some embodiments of the compact OCT scanning mirror assembly 310 shown in the figures, the controller is deployed remotely. For example, in some embodiments it can be housed elsewhere within the OCT scanner adapter 206. Alternatively, in some embodiments it can be housed with other system components of the OCT scanner system 100 or deployed on a different platform with a user interface to allow input of scan parameters. In some embodiments, control signals can be sent from the remote controller 162 via a suitable data connection such as the data port 212.

[0231] In some embodiments, the mirror positioning light source illuminates the reflective surface of the mirror assembly at an incident angle θ of 62 degrees or more, preferably 67.5 degrees, to the normal to the plane of the mirror surface 334 to provide an optical mirror position feedback channel.

[0232] In some embodiments, the OCT light source illuminates the reflective surface of the mirror assembly at an incident angle θ of 28 degrees or less, preferably 22.5 degrees, to the normal to the plane of the mirror surface 334 to provide an OCT light channel.

[0233] In some embodiments, the minimum available aperture at the mirror surface is at least 4mm, which is particularly useful when the mirror assembly is incorporated into an OCT scanner device such as a compact OCT scanner 206 microscope attachment for surgical applications.

[0234] In some embodiments of the disclosed technology, the OCT device can use closed loop feedback to control the position of the scanning mirror. The use of closed loop feedback can be useful in embodiments requiring high scan rates, for example real time video or other forms of image sequences requiring OCT scans. The use of closed loop feedback supports the generation of OCT scans at high rates and low latency for time sensitive applications, for example when providing OCT scans to guide a surgical procedure, as it allows the mirror to move fast enough and accurately enough to achieve high scan rates and / or high scan resolution (i.e. high OCT image B-scan or volume scan resolution). However, in some embodiments, open loop control can be provided.

[0235] The disclosed technology aims to address at least some of the design constraints that exist when designing an OCT system for a surgical microscope. For example, one design constraint is that a smaller diameter scan mirror surface is more suitable to achieve higher scan rates. Numerical aperture is related to resolution. The clear aperture (i.e. mirror diameter) is related to scan size, as the underlying mechanical structure of the MEMS is the same, so a small diameter (e.g. 2mm diameter) mirror can achieve a greater tilt (up to + / - 7 degrees) before touching the MEMS base, whereas a large diameter mirror (e.g. 7.5mm diameter) can only tilt + / - 1.5 degrees before touching the base. This means that while a smaller diameter mirror can be used to scan a larger area, this will come at the expense of resolution.

[0236] In some embodiments, the threshold for the exit beam diameter of the OCT beam is based on the numerical aperture of the optical fiber and the focal length of the collimating lens assembly.

[0237] In some embodiments, the two-dimensional scan mirror assembly is configured to reflect the mirror positioning beam (400) incident in a first optical plane at a reflective surface (334) of the mirror to a position sensitive detector (160) configured to generate information about the tilt angle of the scan mirror reflective surface (344).

[0238] In some embodiments of the optical angular displacement measurement system 156 of the scan mirror assembly 310 shown in FIG. 5, the mirror positioning light from the light source 158 is first collimated by a suitable collimating lens assembly 503 to form a collimated illumination beam 400 incident on the reflective mirror surface 334. The collimated illumination beam 400 (schematically represented by the short dashed line in Figure 5A 、 4 and 5A) is then incident on the reflective MEMS mirror surface 334 at AOI = Q and is reflected to form a mirror position reference beam 402 (shown by the longer dashed line in Figure 2A 、 4 and 5A) that passes through the PSD lens assembly 504 and, in some embodiments, through an optional neutral density filter 506, and finally reaches the PSD 160 along the mirror positioning reference arm 501 of the scan mirror assembly.

[0239] However, the mirror positioning beam 400 can be reflected back or otherwise returned to the reflective surface 334 of the MEMS mirror by the PSD 160 (the reflected beam is not shown in Figure 5A). This is undesirable because this returned light can contaminate the illumination positioning beam and / or the input OCT beam. Other issues associated with stray light reflections in mirror position detector systems include: if any stray light hits the PSD 160, the detected spot position will be in error, and if reflected light enters the diode cavity, the diode's behavior may change, which can cause intensity fluctuations in the position detector beam, which the PSD detects as position changes.

[0240] Some embodiments of the disclosed technology include additional components such as light traps to prevent the returning reflective element of the positioning beam from being reflected by the MEMS mirror assembly 310. The light traps are appropriately configured and positioned to reduce the chance that any reflected mirror positioning reference beam will re-enter the emitter of the mirror positioning beam and / or contaminate the probe beam 312 before it reaches the interferometer.

[0241] As mentioned above, Figure 1 and 5B In some embodiments of the MEMS-based scanning mirror assembly shown in , the reflective surface is designed so that the OCT light input via the OCT optical coupler 308 is reflected from another area of ​​the MEMS mirror surface 334, and so that the mirror positioning reference beam 402 and the OCT scanning or probe beam are reflected in different optical planes.

[0242] The OCT scanning or detection beam reflected by the MEMS mirror surface 334 of the scanning mirror assembly 310 passes through the OCT objective lens 510 and the OCT field lens assembly 512 along the optical path after reflection, is output to the free space in the form of a telecentric beam, and propagates toward the deflecting mirror 316. Figure 1 、 3B As shown in the embodiment of FIG4 , the beam passes through the focusing lens assembly 314 before being incident on the deflecting mirror 318, which elevates the beam out of the optical plane of the scanning mirror assembly. In some embodiments, this allows the OCT focal plane to be focused within a range of + / - 30 mm, i.e., a range of different depths within the scanning area can be focused. However, in some embodiments of the OCT scanner, the focusing lens optics can be omitted.

[0243] The deflecting mirror 316 elevates the incident OCT scanning (or probe) beam from its optical path plane, which passes through the scanning mirror assembly, by reflecting the incident OCT scanning (or probe) beam toward the beam splitter 318. The beam splitter reflects the OCT scanning or probe beam from the microscope objective 210 of the OCT scanner adapter 206 toward the focal plane 154 for scanning tissue or a similar object of interest, which can be an in vivo tissue sample or an in vitro sample. The beam splitter 318 also allows the scanned area illuminated by the OCT to be observed via the microscope optics housed in the microscope 200.

[0244] In some embodiments, as Figure 12 and 3B As shown, the OCT probe beam 312 is input to the optics block by traveling along the optical path 105a within the optical fiber 308a and enters the scanning mirror optics block 310 via the OCT data connection optical fiber input 308. The OCT scanning or probe beam 520 is then passed through the collimating lens 516 toward the scanning mirror reflective surface 334. The mirror surface 334 reflects the OCT beam out of the optics block containing the scanning mirror assembly 310 via the probe arm 508, at which point the OCT beam travels in free space toward the deflecting mirror 316.

[0245] like Figure 1 、 3B As shown in the embodiment of the OCT adapter shown in Figures 4 and 5, the OCT scanning or probe beam 312 is focused by a focusing lens assembly 314 before reaching a deflecting mirror 316. The focusing lens assembly is driven by a motor 336, which adjusts the position of the focusing optics to allow a range of depths of focus to be achieved when performing a scan. In some embodiments, the focus range can be varied by + / - 30 mm.

[0246] The returned OCT light is reflected back along the OCT arm 518 of the scanning mirror assembly 310 via the MEMS scanning mirror surface 334. Figure 8A The coupler of the OCT system 100 is shown.

[0247] In the scanning mirror assembly 310, the input OCT beam is input from the end face 532 of the optical fiber 308a via the optical fiber connector 308, passes through the optical fiber connector 530 (see also Figure 1 ), through the OCT collimating lens 516 toward the scanning mirror assembly. The track length, i.e., the measurable physical distance of the path from the end face 532 to the surface of the scanning mirror, is Figure 2A and 5B L1 shown.

[0248] Figure 3A Also shown is the track length L2 from the scanning mirror surface to the telecentric imaging plane 700. The total track length L = L1 and L2, preferably less than or equal to the track length design threshold of 40 mm.

[0249] Figure 8A yes Figure 8B The enlarged view of FIG3 more clearly shows the position of the fiber connector 532 and the fiber end face 530, at which the optical fiber 308a, acting as a point light source, injects OCT light into the mirror scanning system 310. The OCT light enters the collimating lens 516 from the fiber end face 532, and the collimated illumination OCT beam is then incident on the reflective surface 334 of the MEMS scanning mirror and reflected to the OCT detection arm 105 (as shown in FIG3).Figure 1 as shown in FIG. 5B or 508 (as shown in FIG. 5A). Figure 8B

[0250] In the return direction (not shown for clarity, Figure 8B or 5B), the returning OCT light travels along OCT arm 518 (see also Figure 2A described below) and through collimating lens 516 to travel in another direction, then along optical fiber 308a via OCT data connection fiber 308, and finally exit OCT scanner adapter 206 via optical port 214.

[0251] In some embodiments, the OCT scanner is implemented using off the shelf (OTS) MEMS (microelectromechanical system) where the MEMS scanning mirror reflective surface 334 is provided by a large aperture gold plated silicon mirror bonded to the bottom mechanical structure 500 of the optical block 310. The OCT scanner 206 formed by this design provides a simplified and miniaturized optical system that has comparable optical performance to the larger galvanometer scanning mirror type systems known in the art for intraoperative OCT systems.

[0252] In some embodiments, the optical block design of the OCT MEMS mirror assembly 310 includes a 2D scanning mirror assembly and a complementary optical angular displacement measurement system 156 for measuring the position of the MEMS mirror system.

[0253] The mirror positioning system for measuring the angular displacement of the scanning mirror reflective surface 334 includes a mirror positioning light source 158 and a position sensitive detector (PSD) 160. The PSD can include a PSD lens assembly 504 and a neutral density filter 506 as well as the PSD 160. An example of a suitable PSD detector is a Hamamastu S599 14mm x 4mm active area position sensitive detector.

[0254] In some embodiments, the angular optical displacement measurement system 156 is provided in the same optical block as the MEMS scanning mirror assembly 310. In some embodiments, the optical angular displacement measurement system 156 is used to provide closed loop control of the MEMS scanning mirror position. The closed loop control can be achieved by measuring the incident angle Θ using the PSD 160 and providing the information of the mirror position derived therefrom to the controller, thereby enabling the controller to more precisely control the tilt angle of the scanning mirror reflective surface 334 during scanning.

[0255] ​This closed loop feedback can enable very high B-scan rates. For example, for a 4.2 mm diameter clear aperture mirror 112, using closed loop control, at least 400 B-scans per second can be achieved as a maximum scan rate, with full angular deflection of the maximum field of view (FoV).

[0256] In embodiments without closed loop control (i.e., open loop scanning), a low pass filter can be used to prevent the MEMS scanning mirror moving device from reaching its natural frequency excitation state, in which the MEMS scanning mirror moving device can resonate due to uncontrolled oscillations (which in turn can damage the MEMS scanning mirror moving device). In embodiments implementing open loop scanning, the maximum scan rate can be approximately 50 B-scans per second, which can be contrasted with the rates achievable with closed loop control. In some embodiments, using example embodiments of the MEMS scanning mirror assembly 310 according to the disclosed technology, scan rates of approximately 400 Hz or higher can be achieved with closed loop control.

[0257] In some embodiments, the optical assembly of the MEMS scanning mirror assembly 310 is cooperatively configured to provide a predetermined system numerical aperture through the microscope objective 210 to achieve a desired system optical resolution. That is, in some embodiments, the MEMS scanning mirror system assembly is appropriately configured such that the diameter of the collimated OCT beam 312 output along the OCT data connection fiber 308, after passing through the microscope objective 210, matches a desired minimum system optical resolution.

[0258] In some embodiments, all air-glass interfaces within the OCT scanner adapter 206 are designed to be convex to minimize any back reflections of the OCT beam as it propagates through the optical system.

[0259] Figure 8B An example embodiment of an OCT collimating lens is shown, also referred to herein as an OCT collimating lens assembly 516, such as the collimating lens 516 shown in the OCT arm 518 of the optical block (including the scanning mirror assembly 310) shown in FIG. 5. The OCT collimating lens 516 is provided along the OCT arm 518 of the scanning mirror assembly optical block 310. In the example embodiment shown in FIG. 5, the OCT collimating lens 516 is provided along the OCT arm 518 of the scanning mirror assembly optical block 310. Figure 8A In the example embodiment shown in FIG. 6, the OCT light fed through the fiber stub end 532 exits the OCT collimating lens assembly 602 as a collimated OCT output beam 604 having a collimated beam diameter of at least 3.1 mm. The collimated OCT beam then travels toward and reflects off of the scanning mirror reflective surface 334. The returning OCT light travels along the opposite path through the scanning mirror assembly and is focused by the collimating lens to the end of the fiber 308a, which collects the returning light, which can then propagate back to the coupler 104 of the interferometer system (such as the OCT system 100 shown in FIG. 1). Figure 1 In the example embodiment shown in FIG. 6, the OCT light fed through the fiber stub end 532 exits the OCT collimating lens assembly 602 as a collimated OCT output beam 604 having a collimated beam diameter of at least 3.1 mm. The collimated OCT beam then travels toward and reflects off of the scanning mirror reflective surface 334. The returning OCT light travels along the opposite path through the scanning mirror assembly and is focused by the collimating lens to the end of the fiber 308a, which collects the returning light, which can then propagate back to the coupler 104 of the interferometer system (such as the OCT system 100 shown in FIG. 1).

[0260] A suitable example of an OCT collimating lens 516 suitable for use in some embodiments of the disclosed technology is an F3.2 biconvex doublet lens. This lens has a thick crown glass portion, which reduces the radius of curvature of the lens surface, thereby improving color performance. In some example embodiments, the collimating lens has a focal length of 10 mm and a depth of focus of 100 microns, which ensures good mechanical focus stability. In some embodiments, the OCT collimating lens provides an exit beam having a collimated beam diameter of 3.1 mm (exit pupil diameter) with a wavefront error of less than 1 / 4 wave (root mean square, rms).

[0261] Figure 1 Examples of OCT objective lens assemblies 510, 512 are shown where the OCT beam 312 includes light 312a within a wavelength range, such as a wavelength range in the near infrared portion of the spectrum.

[0262] After being reflected from the reflective surface 334 of the scanning mirror assembly, the OCT light is first focused by the OCT objective lens 510 and then by the field lens 512 , and finally emerges as a telecentric beam 312 b . Figure 1 FIG. 3 shows multiple angularly related telecentric beams 312b focused on a telecentric imaging plane 700. 1,2,3 , where each beam 312b 1,2,3 It indicates the position where the OCT beam 312b is emitted at a specific scanning angle. In other words, the telecentric emitted beams 312b1, 312b2, and 312b3 are continuous beams generated as the B scan proceeds.

[0263] After being deflected from the mirror surface (in other words), the OCT beam 312 passes through the OCT objective lens assembly 510 (which in some embodiments also includes a field lens 512), which is designed so that all scanning angles (in the range of Figure 1 The OCT output light beams 312b1, 312b2, 312b3) schematically shown in the figure are all emitted perpendicular to the intermediate imaging plane and are therefore telecentric.

[0264] In some embodiments, all air-to-glass interface surfaces (e.g., 514) are convex to eliminate back reflection artifacts in OCT images. Figure 9 The OCT objective lens assembly shown converts the reflected angular input OCT scanning or probe beam 312a from the MEMS scanning mirror surface 334 into a telecentric OCT scanning or probe beam 312b (or more precisely, beam 312b). 1,2,3one of the OCT scan beams 312b is output to free space in some embodiments. In some embodiments, the telecentric OCT scan or probe beam 312b is first focused by a focusing lens assembly 314 before being elevated by the fold mirror 316 towards the beam splitter 318, as shown in FIGS. 3 and 4. Alternatively, for example, the telecentric OCT scan or probe beam 312b can be passed directly in free space to the fold mirror 316, which is then reflected to the beam splitter 318. Figure 1 and 3B Alternatively, for example, the telecentric OCT scan or probe beam 312b can be passed directly in free space to the fold mirror 316, which is then reflected to the beam splitter 318.

[0265] The focusing lens assembly 314 serves as an optical interface for the telecentric OCT beam 312b to the microscope objective 210. In some embodiments, the scanning mirror assembly can be used without the focusing lens assembly 314, but this would require the sample to be placed on the intermediate imaging plane 700, on which the telecentric OCT beam 312b would be focused when exiting the scanning mirror assembly. Thus, to use an OCT scanner 206 without a focusing lens assembly, the sample would need to be placed on the intermediate imaging plane 700 in some manner. For example, as shown in the OCT scanner example embodiments of FIGS. 3, Figure 10 , 3B and 4, a lens is required to achieve optical coupling with the microscope objective 210. Alternatively, the objective 210 would need to be shorter in focal length. Such a short focal length is not conducive to surgical applications. However, in some embodiments of the disclosed technology, the focusing lens assembly 314 can be omitted if the OCT scanner is used for another type of application. For example, an OCT scanner 206 used for eye imaging, particularly animal eye imaging, can not require a focusing lens 314.

[0266] In some example embodiments of the OCT scanner adapter 206 for a surgical microscope, the focusing lens assembly 314 is fixed and positioned at the appropriate back focal length to collimate and expand the incoming telecentric OCT beam 312b so that it has a 10.6 mm collimated beam diameter at exit. When the OCT beam 312 is collimated at exit from the focusing assembly, it will be focused on the focal plane of the microscope objective 310, the same as the microscope optics.

[0267] Alternatively, by adjusting the position of the focusing lens assembly 314 relative to the intermediate imaging plane, the object distance is effectively adjusted. This causes the focal position of the microscope objective 310 to change accordingly to accommodate the OCT scan, while the focal position of the microscope optics remains unchanged.

[0268] In some embodiments of the OCT scanner, as shown in FIGS. 3, Figure 1 , 3BAs with the example embodiments shown in FIGS. 4, the benefit of having a focusing lens assembly 314 is that if the surgeon moves the eye during the procedure, the OCT scanning system can use appropriate auto-focusing techniques in known techniques to focus the OCT at the specified anatomical feature.

[0269] Another benefit of embodiments of the OCT scanner 206 that includes a focusing lens assembly 314 is that the scanner can be used in certain situations even if the microscope 200 user (e.g., a surgeon or assistant) has incorrectly set the microscope optics. For example, if the microscope is non- parfocal, in other words, if the eyepiece of the microscope is set to infinity for a user with corrected vision through contact lenses or glasses, the microscope optics will be focused on the focal plane of the microscope objective. If the microscope eyepiece has not been set to accommodate the refractive error in the microscope user’s vision, some users can move the entire microscope (e.g., using the handles 204a, b shown in FIG. 6) to adjust or accommodate the refractive error in their vision. However, this movement of the microscope optics can cause the tissue sample being scanned or other scanned object of interest (e.g., an eye under surgery) to no longer be located on the actual focal plane of the microscope objective 210 provided by the OCT scanning system 206. In other words, if the microscope is misused, the focal point of the OCT beam 312 can need to be adjusted accordingly through a focusing lens assembly (such as the focusing lens assembly 314) to compensate. Figure 10 、 2B

[0270] In some embodiments, the OCT objective lens 510 is an F2.7 double convex doublet lens. The objective lens 510 is coupled with an F19 positive / negative meniscus doublet field lens 512 to convert the scanned collimated OCT beam 312 reflected from the surface 334 of the MEMS scanning mirror into an intermediate telecentric imaging plane as shown in FIG. 5. The OCT return beam passes through the OCT field lens and then through the OCT objective lens, followed by a reflection off the reflective surface 334 of the MEMS mirror again along the OCT output arm 518 through the OCT collimating lens 516 (see also FIG. 6) into the interferometer assembly (not shown in FIG. 5, see SD-OCT system 100 of FIG. 1). Figure 11A Figure 10 In some embodiments, as shown in the example embodiments of FIGS. 6 and 7, all air-to-glass interface surfaces (such as the surface 514 of the objective lens assembly 510 and the collimating lens 516 for the outgoing and return OCT beams (not shown)) are convex to eliminate back-reflection artifacts in the OCT images. Figure 10 Figure 11A Figure 11B

[0271] In some embodiments, as shown in the example embodiments of FIGS. 6 and 7, all air-to-glass interface surfaces (such as the surface 514 of the objective lens assembly 510 and the collimating lens 516 for the outgoing and return OCT beams (not shown)) are convex to eliminate back-reflection artifacts in the OCT images. Figure 11A 7

[0272] ​​​​​​​In some embodiments, the total track length L within the scan mirror assembly optical block is the sum of the length LI from the end face 530 of the optical fiber 308a at the fiber joint 532 to the reflective surface 334 of the scan mirror and the track length L2 from the surface 334 to the telecentric imaging plane 700, as shown in Figure 10 . The total track length L = LI + L2 is preferably less than 40 mm.

[0273] In some embodiments, the optical path difference OPD at the scanned sample has an OPD curvature greater than 100 mm.

[0274] In some embodiments, the OCT scan or probe beam is telecentric to better than 0.03 degrees of incidence angle.

[0275] In some embodiments, the focusing system 314 provides a mechanism for adjusting the OCT beam 312 so that the OCT focal plane can be controlled within a range of ±30 mm to align with the microscope optical channel focal plane.

[0276] In some embodiments, the MEMS OCT scanner has a lateral X-Y footprint where X is less than 42 mm and Y is less than 35 mm, as shown schematically in Figure 10 This enables the OCT scanner system housing to laterally fit the lateral dimensions of the microscope optics carrier housing footprint. This is advantageous to reduce the sterile field barrier in surgical applications. In some embodiments implementing the optical block of the scan mirror assembly 310, the dimensions of the optical block are: lateral width X is about or equal to 40.6 mm, depth Y is about or equal to 34.5 mm, and track length L is about 40 mm or less.

[0277] In some embodiments, the scan mirror assembly further comprises an optical angular displacement measurement system 156 for determining the tilt angle of the reflective surface relative to the incident light, the system comprising at least: a point light source, a collimating lens assembly for collimating light from the point light source to form a collimated mirror position measurement beam incident at the reflective surface; and a position sensitive detector, wherein the reflective surface is configured to reflect the incident collimated beam in a first optical plane to form a reflected position measurement beam travelling towards the position sensitive detector.

[0278] In some embodiments of the scan mirror assembly 310 described above, referring to the Figure 10 and 5B closed loop control of the position of the reflective surface of the MEMS mirror is provided by a position sensitive detector configured to provide angular displacement measurement information to a controller configured to control the tilt angle of the mirror surface relative to the illumination beam. In some embodiments, the closed loop control uses a PID feedback loop to adjust the drive voltage of the MEMS based on the position and also suppresses ringing artifacts caused by rapid direction changes.

[0279] Advantageously, in some embodiments, wherein the scanning mirror assembly comprises the scanning mirror assembly 310 in the OCT scanning device 206, the input beam comprises the OCT probe beam 312 which is reflected by the optical assembly along the OCT probe beam arm of the scanning mirror assembly to the sample or similar object of interest 116. The scanning mirror assembly 310 is configured to output the OCT probe beam 312 as a telecentric OCT probe beam to the focal plane 154 at the sample and the optical path length of the OCT probe beam from the light source 102 to the sample focal image plane 154 is configured to be equal to the optical path length travelled by the reference OCT beam from the same OCT light source 112 along the reference arm 103 of the connected interferometer OCT system 100 for 2D scanning of the sample region 116.

[0280] In some embodiments, the MEMS scanning mirror assembly 310 disclosed herein is provided as an optical block 310 in an OCT scanner adapter 206 for a surgical microscope 200 which forms part of the connected OCT system 100. The lateral footprint X of such an OCT scanner adapter 206 is preferably within or equal to the footprint of the surgical microscope housing and preferably also its length or depth footprint is within the footprint of the microscope. The OCT system 100 outputs the interference signal comprising the OCT scan data 146 to the image processor 148 of the OCT system 100. The image processor 148 then processes the interference signal 146, for example it can perform a signal transformation like a Fourier transform, so that an OCT image showing the internal scan structure within the scanned region is displayed in an image on the display 152. In some embodiments, this image can be generated in real time so as to guide the surgeon and / or other personnel on one or more suitable displays 152 in some embodiments.

[0281] In some embodiments of the OCT scanner adapter 206, the OCT scanner adapter 106 is configured to be fixed to the base of the housing of the microscope optics of the surgical microscope, wherein the OCT scanner adapter 216 increases the stack height of the surgical microscope by less than 40 mm, preferably by less than 36 mm.

[0282] In some embodiments of the OCT scanner adapter 206, the OCT scanner adapter 106 is configured to be fixed to the base of the microscope optics housing and to align the objective 114, 210 of the OCT scanner adapter 206 with the light passage of the microscope optics when the lateral footprint of the housing 208 of the OCT scanner adapter 206 is within the lateral footprint of the housing 202 of the surgical microscope 200.

[0283] In this way, a surgical microscope according to the disclosed technology can be provided, for example as Figure 2A and 2B illustrated. The surgical microscope 200 comprises microscope optics, a housing 202 containing the microscope optics and an OCT scanner adapter 206, wherein the OCT scanner adapter 206 comprises a scanning mirror assembly according to the disclosed technology, for example as Figure 2A and 3B illustrated by way of example. The OCT scanner adapter 206 can be configured to output image data which is later input into an image processor of an OCT system, such as the OCT system as Figure 11A illustrated.

[0284] Figure 10 The image processor 148 in the SD-OCT system 100 as illustrated is configured to receive the OCT scan image data output via the spectrometer 136. Any suitable device can be used as a platform for the image processor 148. In some embodiments, the device can comprise a general purpose computer system running an image processing algorithm, using one or more processors or processing circuitry to execute the image processing algorithm, see the example Figure 11A illustrated later in the description. The image data output by the spectrometer 136 is at least Fourier transformed by the image processing system 148, and the output of the image processing system 148 can be further processed, for example de- distortion processing of the Fourier transformed OCT scan image, as Figure 11A illustrated schematically.

[0285] Figure 11B and 8B illustrate OCT images that can be generated, for example by embodiments of the SD-OCT system 100 of Figure 11A , for example by using embodiments of the OCT scanner as an attachment to the surgical microscope 200 as Figure 11A and 2B illustrated schematically. In some embodiments, the OCT scanner adapter 206 of Figure 2 can comprise an OCT scanner adapter comprising optical assemblies as described in more detail in Figure 11A , 3B , 4, 5A, 5B, 6 and 7.

[0286] Figure 11B illustrate examples of OCT images of a typical contact lens and a layered tape phantom. Due to dispersion effects, a complex conjugate (CC) image artefact is shown as a highly blurred stripe in the OCT scan image. Figure 11A illustrate the use of an image processor, such as the image processor 148 of the SD-OCT system 100 ofFigure 10 The result of processing the image by the image processor 148 shown in FIG. 1 is configured to implement an example embodiment of a computer-implemented image processing method 900 for removing complex conjugate image data from image data in real time using dispersion according to the disclosed technology.

[0287] Figure 11B The OCT images in the figure have had complex conjugate image artifacts removed. Figure 11B The OCT images shown in are obtained by Figure 1 The OCT image data output by the OCT scanner adapter 206 is obtained by removing complex conjugate artifacts using an embodiment of an iterative image processing algorithm according to the disclosed technology, and Figure 12 The resulting image is Figure 1 The images shown in have similar image quality, but the complex conjugate image artifacts have been removed.

[0288] Embodiments of the disclosed image processing algorithms are intended to improve upon known techniques to prevent the occurrence of image distortion in SC-OCT systems such as Figure 12 Complex conjugate artifacts remain in the OCT scan image generated by the spectral data output (as shown). Figure 12 In the SD-OCT system 100 shown, the spectrometer 136 detects only the real part of the spectrum. Therefore, in order to avoid overlap of the sample structure and the complex conjugate mirror terms in the OCT image, only half of the available depth range can be used to generate the OCT scan image of the sample unless some CC mirror artifacts are removed from the OCT image before display.

[0289] To increase the removal of CC image artifacts from OCT scan images at a speed that allows real-time OCT scan images to be generated, example embodiments of the disclosed technology also include a computer-implemented method of removing CC image artifacts in OCT scan images using dispersion.

[0290] It is known that in the OCT interferometer system 100, the dispersion mismatch between the detection arm 105 and the reference arm 103 will cause a wavelength-dependent phase shift in the spectral interference fringes between the combined light returning from the reference arms 103 and 105. In the prior art, various techniques are also known to use the dispersion mismatch between the detection arm and the reference arm in a spectral domain (SD) OCT system to compensate for this phase shift.

[0291] Some embodiments of the disclosed technology aim to improve upon this known technique by providing an algorithm that iteratively suppresses complex conjugate artifacts, thereby reducing the size of the complex conjugate artifacts in OCT scans (e.g., those obtained by Figure 12The disclosed algorithm embodiment increases the imaging range in an OCT scan generated by the SD OCT system 100. By adjusting the threshold (frequency components above which the threshold is removed) in each iteration, the disclosed algorithm suppresses more CCR artifacts in each iteration, thereby generating cleaner OCT scans faster.

[0292] According to some embodiments of the disclosed technology, algorithms allow real-time OCT image data (e.g., from Figure 8A The algorithm numerically processes the data output by the spectrometer 136 in the real-time OCT scan image to suppress CCR artifacts in the real-time OCT scan image generated. Each iteration of the algorithm, when applied to the OCT scan, detects multiple signal frequency components above the frequency detection threshold adjusted in that iteration of the algorithm. In other words, for each OCTA scan, multiple iterations of the algorithm are performed to remove CCR artifacts from the OCT scan data, and the frequency detection threshold of the OCTA scan is adjusted in each iteration. This enables cleaner, more stable OCT scan images to be obtained more quickly to generate OCT B and C scans, and compared to algorithms that fix the detection threshold for each scan, more tomographic imaging data can be retained and the time required to generate each cleaner OCT scan image can be shortened. In some embodiments, the computer-implemented image processing method for removing complex conjugate image data from OCT image data can be performed in real time because the algorithm is relatively fast, allowing B-scan images to be generated in 30 milliseconds or less.

[0293] In some embodiments, image processing operates on a real-time stream of OCT scan images and is fast enough to reduce the latency in real-time streaming images after CCR cleanup to less than 60ms, but in some embodiments this can be as low as 30ms.

[0294] Figure 1An example embodiment of a computer-implemented image processing method 900 for removing complex conjugate image data from image data comprising an OCT scan is shown, the method 900 comprising at least the following steps at an image processing device 148: 902, receiving an image signal comprising image data, the image data comprising complex conjugate image data; 906, performing a baseline signal subtraction; resampling the wavelength data to generate linear wavenumber image data (908, 910), processing the linear wavenumber image data using an algorithm according to the disclosed techniques to generate a complex conjugate canceled (CCR) image result, i.e., removing complex conjugate artifacts from the OCT scan image to below a threshold level. At 912, at least one iteration (and preferably two or more iterations) of the image processing algorithm is performed for each OCT scan to generate image data comprising a complex conjugate canceled image at 914. The CCR image data may comprise phase and / or amplitude data, and in some embodiments, logarithmic scaling 916 of the OCT scan image data may be performed to facilitate outputting the CCR scan image data to a suitable display (e.g., a display). Figure 1 When using a display 150 in FIG, OCT scans are presented in a more visually meaningful / impactful manner over a wider frequency range.

[0295] In some embodiments, method 900 can be performed in real time. For example, an OCT scan image can be generated within 30 milliseconds using some embodiments of the disclosed technology. In some embodiments, the displayed image data calculated from the CCR results can include amplitude and / or phase data of the CCR result image. In other words, while amplitude data is typically used for OCT, in some embodiments, phase data also present in the CCR processing results can be used, or a combination of the two (amplitude and phase) can be used when generating image data from the CCR results.

[0296] In some embodiments, the linear wavenumber image data used to generate the complex conjugate cancellation result can be generated by performing a complex conjugate cancellation (CCR) image processing algorithm according to the disclosed technology multiple times, for example, Figure 2A Or the CCR algorithm shown in FIG11. For simplicity, FIG11 shows more details of two iterations of the algorithm, wherein the real OCT scan signal R0, 1102 (including the current signal amplitude varying with time) is input to the image processing device 148.

[0297] To generate a CCR OCT image, for example, Figure 14OCT scan images that remove CCR artifacts from the real OCT scan signals output by the SD scan system 100, some embodiments of the disclosed technology perform an OCT processing procedure that includes embodiments of the method 900, which includes acquiring OCT signals, performing signal apodization (optional), performing adaptive direct current (DC) subtraction to remove baseline current signals from the acquired OCT scan current signals output by the SD OCT system 100, re-sampling the wavelength data to be linear in wave number, and performing the CCR image processing algorithm 1000 according to the disclosed technology, such as the algorithm 1000 schematically shown in Figure 14 , 11A and 11B.

[0298] Turning briefly to Figure 12 , the image processing device 148 processes the input signal 1102 to correct for dispersion and applies an appropriate transform (such as a Fourier transform or a fast Fourier transform or similar technique) to generate frequency-amplitude information. Subsequently, by applying a suitable detection threshold to the OCT frequency scan data, it is possible to selectively store only signal frequencies with amplitudes above the threshold, which is schematically shown in FIG. 11 by “apply threshold a0max(|r0)”. This cleans up the frequency signal (see Figure 1 and 1008 in FIG. 11) and enables extraction of complex frequency signal data to generate an OCT scan image stored in 1014. An inverse transform and inverse dispersion are then performed (see 1016, 1018 in Figure 16 ), generating a cleaner signal than the original input 1102 in 1104.

[0299] In 1020, the real part of the cleaner signal is subtracted from the starting spectrum, and then a second iteration of the algorithm 1000 is performed, as shown in Figure 15A .

[0300] Figure 15A It is shown how the initial threshold is determined by a frequency distribution histogram of the Fourier transform, and then dynamically adjusted in each subsequent iteration of the algorithm in the manner shown in Figure 15B .

[0301] Returning to Figure 15A , it is shown in a flowchart that schematically illustrates a method of implementing an example embodiment of the algorithm 1000. As shown in Figure 16 , the computer-implemented method can be described in pseudo code as including:

[0302] applying dispersion correction to the re-sampled wavelength data of the acquired OCT signals, 1002;

[0303] performing a signal transform, such as a fast Fourier transform (FFT), 1004, on the dispersion-corrected signal;

[0304] computing the magnitude of the FFT result, 1006;

[0305] computing an adaptive storage threshold 1008 for the current iteration of the algorithm 1000 (e.g., based on an empirical formula) to determine whether to store the FFT result;

[0306] if the result of 1008 is determined to have a magnitude that exceeds the adaptive storage threshold, 1010, then the value of the FFT result is stored in 1014;

[0307] if the magnitude does not exceed the threshold, then the FFT result is set to zero, 1012; and an inverse FFT of the stored value is computed, 1016;

[0308] applying an inverse dispersion correction, 1018; and

[0309] extracting the real component and subtracting the result from the original spectrum, 1020.

[0310] Some embodiments of the algorithm 1000 can use an empirically derived or other type of formula to compute the variable threshold for storing the FFT result. However, some other embodiments can derive the variable storage threshold in different ways. For example, in some embodiments, the variable storage threshold can be derived from dynamic image properties such as image intensity distribution or other image properties.

[0311] Although the embodiments shown in the drawings and described herein involve a fast Fourier transform of an input signal from a spectrometer, it will be apparent to those of ordinary skill in the art that another suitable signal transform can be used in other embodiments of the disclosed technology.

[0312] By repeating the above steps of the algorithm a number of times, such as at least two more times, so that the algorithm is iterated at least a total of three times, an OCT image can be produced in which, in some embodiments, no appreciable CC image data can be contained in the OCT image, such as shown in FIG. 11, where a very clean signal is shown in 1110 after applying the inverse FT and inverse dispersion.

[0313] The algorithm also includes, in 1022, evaluating whether the real component of the signal-transform complex-valued image has any complex conjugate image artifacts. If so, another iteration is performed. If the signal-transformed image does not have a conjugate image effect, then the algorithm ends in 1024.

[0314] However, optionally, if there is any remaining iterative residual signal in the last iteration, ie if there is any residual CC image data, this may in some embodiments be added to the final output signal in 1026 .

[0315] In some embodiments, the calculated CCR image may be used to provide amplitude and / or phase data for the CCR-derived image.

[0316] In some embodiments, method 900 may further include performing logarithmic scaling on the resulting CCR image to aid in visualizing the data, which may range across several orders of magnitude.

[0317] Figure 16 Some embodiments of the algorithm shown include: applying dispersion correction, 1002; performing a fast Fourier transform (FFT) or similar complex signal transform on the linear wavenumber image signal data, 1004; calculating the amplitude of the linear wavenumber signal data after performing the FFT, 1006; calculating a variable threshold for each iteration of the algorithm, 1008, for each FFT result value whose amplitude does not meet the storage condition of the current iteration threshold, setting the FFT result to zero, 1012, for each FFT result whose amplitude meets the storage condition of the current iteration threshold, storing the FFT result, 1014, calculating an inverse FFT for all stored FFT results, 1016; applying an inverse dispersion correction, 1018; and extracting the real image component and subtracting the result from the initial image spectral data, 1020.

[0318] In some embodiments, the conditions for storing the FFT results include meeting or exceeding a calculated adaptive storage threshold, ie, meeting the threshold for storing FFT results for the current iteration or exceeding a calculated storage threshold set for that algorithm iteration.

[0319] By using the OCT scanner system 100 Figure 1 and 2B The OCT scanner adapter 206 and other scanning mirror systems execute the same algorithm on each A-scan image data generated, and then stack the A-scans to generate B-scan image data with or without any noticeable CC image data in some embodiments. This, in turn, allows for the acquisition of volumetric C-scan images with or without CC image artifacts.

[0320] At 1022 , some embodiments of method 900 iterate the CCR algorithm multiple times to extract the true image components and subtract the CCR results of each iteration from the initial image spectral data of that iteration until the stored FFT result values ​​comprise a complex-valued image without any significant conjugate image artifacts.

[0321] In some embodiments of the method 900 using the CCR algorithm 1000, the algorithm includes performing signal clipping 904. Signal clipping can use user-set processing parameters to adjust the input OCT signal to have zero values at each end. This helps reduce possible edge artifacts when performing the FFT in subsequent steps.

[0322] In some embodiments, the computed variable storage threshold for the OCT FFT results is based on an empirical formula.

[0323] Alternatively or additionally, in some embodiments, the computed variable storage threshold for storing the OCT FFT results can include an adaptive storage threshold in the first iteration that is adjusted based on dynamic image properties (such as intensity distribution or other properties) of the image currently being processed. For example, in some example embodiments, a histogram can be used to set the initial threshold. This can reduce the need for recalibration of the scanning system.

[0324] In some embodiments of the method 900, the method is implemented in hardware, such as by using a graphics processing unit capable of processing an image in 30 milliseconds.

[0325] In some embodiments, the image data is OCT image data, such as obtained using an OCT scanning mirror adapter for a microscope as shown in Figure 16 and 2B The OCT image data obtained by the OCT scanning mirror adapter for a microscope as shown in

[0326] Figure 16 and 11B An example of the iterative CCR algorithm is shown schematically in Figure 1 where the dashed line indicates the zero frequency position on the post-FFT graph.

[0327] Figure 9 to 13 An example is shown of a real image signal r0 going through dispersion correction, then Fourier transformation using, for example, a fast Fourier transform in the first iteration of the algorithm. Figure 11A The variable storage threshold a0max(|r0|) in the first iteration in Figure 1This is applied when storing the results as described later in

[15] . One embodiment of the threshold calculation is shown here, where the threshold varies in each iteration and is based on a ratio of the maximum image value in each iteration. However, other embodiments may use a predetermined threshold, or may use other image properties of the current image (e.g., intensity distribution or other signal properties) to dynamically determine an appropriate threshold. If the result is above the storage threshold, the data (e.g., the image is complex conjugate removed) is removed. Figure 1 and 11B The accumulated complex data in the data is accumulated in a suitable storage medium or memory.

[0328] Otherwise, the CC image data is discarded.

[0329] Next, an inverse Fourier transform (e.g., a fast Fourier transform) is performed, and inverse dispersion is applied to the data, and the real component is subtracted from the starting spectrum. The result is the new input signal R1 of the algorithm, to which dispersion correction is performed and a Fourier transform is applied. The result is then compared to a storage threshold, which in some embodiments varies with each iteration of the algorithm. If the result is above the threshold, the complex conjugate-cancelled data is added to the stored conjugate-cancelled data found in the first iteration. Otherwise, the data is not stored. After the comparison, the inverse Fourier transform and inverse dispersion correction are applied, and the real component can be subtracted from the starting spectrum of that iteration. The next iteration (at Figure 8A and 11B The second iteration shown in ) starts with a new threshold for storing spectra, which is Figure 1 In is a1max(|r1|), in Figure 1 It is expressed as r1>a1.

[0330] Figure 2A Schematically shown in Figure 1 An embodiment of the algorithm with Figure 1 Different. According to Figure 1 In the first iteration of the algorithm of the illustrated embodiment, a first threshold for storing complex data is set based on the frequency histogram obtained in 1006 from the Fourier transform of the input signal. n and a0 can be obtained, for example, based on a histogram of light intensity versus frequency of the scanned image being processed by:

[0331] a n =a0-n*(a0-a N ) / N

[0332]

[0333] a min =Minimum starting threshold

[0334] a max= maximum starting threshold

[0335] a N = final iteration threshold

[0336] Q tmin = minimum Q4 threshold

[0337] Q tmax = maximum Q4 threshold

[0338] Q 4x = upper quartile count

[0339] This allows the processing parameters to be based on the properties of the original image in the first iteration. This allows the best selected threshold level to be applied before the iterative CCR processing begins. In other words, the best threshold for the first iteration can be selected in advance based on the optical properties of that image. This dynamic adjustment is advantageous as it is able to automatically account for different scanning illumination settings.

[0340] In some embodiments, the method 900 and algorithm are performed by an image processing unit 148 of an optical coherence tomography (OCT) device configured to perform real-time OCT, such as the Heidelberg Spectralis® OCT device. Figure 1 A spectral domain OCT system 100 as shown. In some implementations, the system 100 can include an illumination arm 101 including at least one optical light source 103, a reference arm 103, an OCT probe arm 105 via which an OCT probe beam is emitted, and a data arm 107 through which returned OCT light is passed to an image processor 148 configured to perform embodiments of the method 900 according to the disclosed technology for example.

[0341] In some embodiments of the OCT device 100, the dispersion between the reference arm 103 and the probe arm 105 is configured to be higher than a minimum design threshold that separates the complex conjugate image from the OCT image output for display. The dispersion component can be provided in one of the reference arm or the probe arm, or even both, but this can cancel out the dispersion difference between the reference arm and the probe arm, and is therefore less desirable.

[0342] In some embodiments, at least one dispersion component in the reference arm includes a dispersion optical fiber.

[0343] In some embodiments, at least one dispersion component in the reference arm includes a dispersion glass window. The physical path length of the reference arm is shortened to compensate for the dispersion window, or conversely the physical path length of the OCT probe arm is lengthened to compensate for the dispersion window.

[0344] In some embodiments, at least one dispersive component in the reference arm comprises one or more dispersive retro-reflectors, and the amount of dispersion is determined by the optical path length through the dispersive retro-reflectors.

[0345] If the OCT system provides at least one dispersive optical component in the OCT probe arm (105), this can also include a dispersive optical fiber. Alternatively, in some embodiments, a dispersive dichroic mirror and / or a dispersive OCT objective 510 and / or a dispersive OCT field lens 512 can be used to introduce dispersion in the probe arm.

[0346] Figure 1 An image processor 148 according to the disclosed technology is schematically illustrated, comprising an input port for receiving or acquiring OCT image data (such as Figure 17 the image data 146 shown) output via the interferometer coupler 104 of the OCT system 100. Figure 18 The image processor 148 shown in Fig. 12 comprises an input port 1200, one or more processors or processing circuitry (1202) comprising a graphics processing unit 1204 for processing the input OCT signal data by performing the method 900 and / or executing the algorithm 1000. The resulting complex conjugate-free image data is then output via an output port 1208, and the output data 150 can be displayed on a suitable display device. Figure 18 The image processing unit 148 shown in Fig. 12 further comprises a suitable memory 1006 for storing image data.

[0347] In some embodiments, the method 900 can be implemented using a computer program product comprising computer code which, when loaded into a memory 1006 and executed on one or more processors or processing circuitry 1202, 1205 of an image processing device (such as Figure 19A the image processing device 148 shown in Fig. 12) is configured to cause the device to implement the method 900.

[0348] Example of using bulk glass differential dispersion in an interferometer

[0349] Some embodiments of the disclosed technology use a bulk glass differential dispersion interferometer design to support extended depth imaging in optical coherence tomography. These embodiments can be used in conjunction with the computational methods described above with reference to Figs. Figure 19A , 8B 9, 10, 11A, 11B, 13 and 14. The interferometer designs disclosed herein can be used in some embodiments in an OCT scanning system 100 as described above with reference to Figs. Figure 19B In some embodiments, the OCT scanning system 100 is used in conjunction with the computational methods described above with reference to Figs. Figure 1OCT scanning systems can include an OCT scanner adapter 206 for surgical microscopes that incorporates features described according to embodiments disclosed herein and / or as shown in Figure 19A 、 2B , 3A, 3B, 4, 5A, 5B, 6, or 7.

[0350] In optical coherence tomography, complex conjugate cancellation requires that there be a minimum amount of differential dispersion between the sample and reference paths of the system interferometer.

[0351] In an OCT system, when the light source consists of a broadband, short coherence length but spatially coherent superluminescent diode, the dispersion in the system is caused by the dispersion or wavelength dependent propagation velocity difference as the light propagates through the system optical path, referred to as group velocity dispersion or GVD, which is quantitatively defined by RP Photonics as the derivative of the inverse group velocity with respect to the angular frequency, as shown in the following equation:

[0352]

[0353] where:

[0354] c = speed of light in vacuum

[0355] λ = wavelength

[0356] n = refractive index

[0357] Group velocity dispersion (GVD) can also be defined as the group delay dispersion (GDD) per unit length.

[0358] Dispersion can be calculated according to the solid state material properties of the optical glass that makes up the OCT system by one of the following three industry standard dispersion formulas:

[0359] Sellmeier dispersion formula:

[0360]

[0361] Schott dispersion formula:

[0362] n 2 = a0+ a1λ 2 + a2λ -2 + a3λ -4 + a4λ -6 + a5λ -8

[0363] Conrady dispersion formula:

[0364] nλ = n0+ A / λ + B / (λ ^ 3.5)

[0365] The specific coefficients for each equation are provided by the glass manufacturer based on measured glass melt property data.

[0366] The high dispersion required for complex conjugate cancellation is at odds with typical optical design in the visible spectral range, as most transparent materials strive to achieve low second order dispersion, resulting in a flat dispersion curve in the NIR spectral range. For a CCR candidate material, the derivative of its dispersion curve in the near infrared spectral range should be similar to that of optical glasses in the short or ultraviolet wavelength range. Such a material is transparent at IR wavelengths and has high dispersion at NIR wavelengths, which means that the material will be used outside the conventional design range, and since this dispersion data is not compiled by the glass manufacturer, it must be calculated independently.

[0367] The disclosed technology uses filter glasses in the infrared (IR) wavelength range (e.g., lenses used in embodiments of the OCT scanner adapter 206 and / or the OCT system 100 disclosed herein) rather than optical design glasses to enhance the capabilities of the image processing system 148 of the SD-OCT system 100 to better remove complex conjugate artifacts and generate complex conjugate-canceled images with better resolution and extended depth range.

[0368] The drawings of the Figure 8A An example of a method for determining the group velocity delay GVD required for a filter glass material using Sellmeier coefficients is shown, in accordance with the disclosed embodiments. In other embodiments, a similar method can be employed to determine the required GVD if a different dispersion formula is used.

[0369] In Figure 1 , the Sellmeier dispersion equation for the target glass refractive index as a function of wavelength is first solved in S1402, then the coefficient of GVD, i.e., (λ 3 / 2πc 2 ), is calculated in S1404, where c = the speed of light in vacuum, then the second derivative of the refractive index with respect to wavelength, i.e., δ 2 n / δλ 2 , is calculated in S406, and subsequently the GVD coefficient obtained in S1404 is multiplied by the second derivative value in S1406 to determine the GVD of the glass in S1408. Subsequently, the GVD calculation of S1404-S1408 is repeated for each 20 nm wavelength increment within the OCT light bandwidth in S1410, which in some embodiments is centered at 850 nm with a bandwidth range of 100 nm about the center wavelength. The average GVD is then determined over the bandwidth range covered by S1410 in S1412, and then the group dispersion delay (GDD) is determined based on the average GVD value and the glass optical path length of the glass in the interferometer system in S1444.

[0370] The method 1400 can be performed using any suitable apparatus, such as the apparatus shown in FIGS. Figure 1 .

[0371] Through experimentation, the optimal GDD value range for CCR was determined to be 31,000 (fs 2 ) to 46,000 (fs 2 ).

[0372] Some embodiments of the disclosed technology replace one existing optical component in the path length adjustable OCT reference assembly shown as reference arm 103 in the OCT system 100 shown in FIGS. Figure 2A . Figure 14 to provide a retroreflector system as shown in FIGS.

[0373] In some embodiments of the disclosed technology, the reference assembly in the reference arm 103 includes a retroreflector with a longest retroreflected optical path length of 32.4 mm. Based on a GDD median value of about 38,500 (fs 2 ) and divided by the optical path length of 32.4 mm, this implies that a target GVD value of 1,190 (fs 2 / mm) is required to be achieved by the optical filtering glass material in the retroreflector design according to the disclosed technology.

[0374] The method 1400 described above is used to determine a set of desirable parameters for glass materials for OCT light with a center wavelength of 850 nm, such as a set of parameters including at least: glass refractive index n at 850 nm, group refractive index ng of light at 850 nm, GVD, and transparency (expressed as a percentage of transparency at 850 nm wavelength). These parameters are considered suitable for OCT light with a center of 850 nm and a bandwidth of 100 nm or about 100 nm, which is not the wavelength of light used in some embodiments of the disclosed technology, which uses light in the near infrared spectrum.

[0375] Example values for the parameters of glass and fiber characteristics are shown in Table 1 below:

[0376]

[0377]

[0378] Table 1: Example parameters for a highly dispersive glass

[0379] The values in Table 1 are provided as examples. They exemplarily illustrate optical characteristics suitable for use in hybrid or highly dispersive fibers that can be used in various example embodiments of interferometer systems, where the reference arm fiber length is 6 meters for a nominal center wavelength of 850 nm.

[0380] The OCT beam spectrum is preferably located in the infrared spectrum range (about 700 nm to 1000 pm) and in some embodiments can be limited to the near infrared spectrum (750 nm to 3 pm).

[0381] Here, the group refractive index (ng) is defined by the following equation, where l is the wavelength of the OCT light:

[0382]

[0383] Under these performance requirements, the only glass material with sufficient GVD and acceptable optical absorption characteristics within the OCT bandwidth is Schott glass IRG27 (see middle row of the table above). According to the calculations, the GVD of the IRG27 glass is equal to 1120.75 (fs 2 / mm), which, combined with an optical path length of 32.4 mm, results in a total GDD value of 36312 (fs 2 ), which is below the target median value, but above the minimum acceptable GDD value.

[0384] Figure 1 and 15B An example physical or mechanical design of a retroreflector is schematically shown, for example a retroreflector made of IRG27 glass, or a retroreflector having equivalent optical characteristics (e.g. same or similar refractive index, group refractive index (GVD) and optical transparency).

[0385] Figure 1 A side view of a retroreflector is shown, which employs a conical design, comprising three different reflecting surfaces S2, as shown in the plan view of Figure 14 to 18 . Figure 1 An example of the dimensions of the retroreflector reflecting surfaces S2 relative to a hypothetical surface SI (i.e. the "base" of the cone) is shown (see element 1500 marked in Figure 1 to Figure 12 ). The angles and dimensions (in mm) are only by way of example and are understandable to one of ordinary skill in the art.

[0386] Figure 1 to 12 An example embodiment of an automated path length optical mechanical assembly 1600 comprising an embodiment of a highly dispersive retroreflector 1500 is shown, implemented in accordance with the disclosed technology. Some embodiments of the automated path length optical mechanical assembly 1600 are configured for use in a reference arm 103 of an OCT system (such as the OCT system 100 shown in Figure 13 ).

[0387] In Figure 2BIn the embodiment, the assembly 1600 includes an adjustable glass retroreflector 1602, for example made of BK7 glass material manufactured by SCHOTT, or any suitable preferably optically equivalent glass material (see the preferred matching conditions of glass parameters in Table 1 above). ​ A fixed glass retroreflector 1604 is provided along a portion of the adjustable portion of the path length 1606 shown, the fixed glass retroreflector 1604 comprising the same glass material as the adjustable glass retroreflector 1602. The high dispersion retroreflector 1500 shown in FIG2 is fixed. By moving the position of the mount 1608 along the track 1606, the optical path length in the reference arm 103 can be adjusted to remove a desired level of complex conjugate artifacts from the interferometer output signal at a greater scanning depth than would otherwise be the case. When the OCT interferogram signal is processed by the image processor 148, the CCR removal operation can be applied, for example, to ​ The signal 146 output by the spectrometer 136 is shown. The processing may include the complex conjugate elimination method according to any embodiment disclosed herein, for example, as described above in conjunction with ​ The method 1000 described and / or the accompanying drawings ​ and 11B The iterative algorithm shown is used to implement method 1000.

[0388] In some embodiments, the high-dispersion retroreflector 1500 may include a filter glass that is transparent in at least the near-infrared (IR) wavelength range and is configured to cause incident broadband low-coherence light to undergo differential dispersion in at least the near-infrared (NIR) wavelength range.

[0389] In some embodiments, the retroreflector is transparent in the same wavelength range where differential dispersion occurs, but in other embodiments, its transparent wavelength range may be different from the wavelength range where differential dispersion occurs.

[0390] In some embodiments, the median group delay dispersion of the filter glass can be 38000 (fs 2 ) to 40000(fs 2 ), the median group dispersion velocity of the filter glass can be within 1100 fs 2 / mm to 40000fs 2 / mm value.

[0391] In some embodiments, the high dispersion retroreflector (1500) comprises glass having one of the following properties (for incident light having a spectrum centered at 850 nm): wherein for light having a wavelength of 850 nm, the glass has a refractive index of 2.5129; for light having a wavelength of 850 nm, the group refractive index is 2.7268 (ng); and the group velocity delay is 1120.75 fs.2 mm; for 850 nm wavelength light, the transparency is 95.7%.

[0392] The retroreflector 1500 can have a cone exterior, where the cone interior includes at least three mirrors collectively configured to perform retroreflection of incident light.

[0393] In some embodiments of the disclosed technology, a bulk glass differential dispersion interferometer assembly 1600 is provided for extended depth imaging in optical coherence tomography (OCT). The interferometer assembly 1600 can include an automated path length optical mechanical assembly including a fixed first retroreflector 1604 at one end of an optical path, an adjustable second retroreflector 1602 collectively with a fixed highly dispersive retroreflector 1500 on a mount 1608 configured to run along a track or rail 1608. By moving the mount 1608, the retroreflector 1500 is movable, and then an adjustable optical path is formed in the interferometer assembly 1600. In some embodiments, the highly dispersive retroreflector 1500 includes a filter glass. The filter glass can be transparent at infrared (IR) wavelengths, and configured to cause differential dispersion between broadband low coherence incident light (e.g., the returning OCT light and the returning OCT reference light described above in ​ OCT systems) at at least near infrared (NIR) wavelength ranges.

[0394] In some embodiments, the interferometer assembly is in a probe arm 105 of an OCT scanning system 100, and the highly dispersive retroreflector 1500 is configured to cause differential dispersion between broadband low coherence incident light returning from a reference arm 103 and the probe arm 105 of the OCT scanning system 100 at near infrared (NIR) wavelengths. In some embodiments, the OCT scanning system is a spectral domain OCT system having an interferometer configured to output OCT scanning interference signals, which are then processed for complex conjugate cancellation of incident OCT light on a tissue sample (e.g., the tissue sample 116 shown in ​ ).

[0395] In some embodiments, the median group delay dispersion of the filter glass material can have a value ranging from 38000 (fs 2 ) to 40000 (fs 2 ). The median group velocity dispersion of the filter glass material can have a value ranging from 1100 fs 2 / mm to 1280 fs 2 / mm.

[0396] In some embodiments of the assembly 1600, in which the highly dispersive back reflector (1500) comprises a glass having one of the following properties (for incident light with a spectral center at 850 nm): an index of refraction of 2.5129 for light of 850 nm wavelength; a group index of refraction of 2.7268 (ng) for light of 850 nm wavelength; a group velocity delay of 1120.75 fs / mm; a transparency of 95.7% for light of 850 nm wavelength, for example, the highly dispersive back reflector can comprise IRG27 glass manufactured by Schott_IRG. The fixed back reflector 1604 and the movable back reflector 1602 can respectively be a glass having the following properties (for incident light with a spectral center at 850 nm): an index of refraction of 1.5098 for light of 850 nm wavelength; a group index of refraction of 1.5249 (ng) for light of 850 nm wavelength; a group velocity delay of 40.13 fs / mm; a transparency of 99.8% for light of 850 nm wavelength. In some embodiments, the first back reflector and the second back reflector can comprise BK7 glass, for example, manufactured by Schott. In some embodiments of the assembly, the highly dispersive back reflector 1500 has a conical exterior, in which the conical interior comprises at least three mirror facets collectively configured to perform back reflection of the incident light. 2 2 In some embodiments of the assembly 1600, in which the highly dispersive back reflector (1500) comprises a glass having one of the following properties (for incident light with a spectral center at 850 nm): an index of refraction of 2.5129 for light of 850 nm wavelength; a group index of refraction of 2.7268 (ng) for light of 850 nm wavelength; a group velocity delay of 1120.75 fs / mm; a transparency of 95.7% for light of 850 nm wavelength, for example, the highly dispersive back reflector can comprise IRG27 glass manufactured by Schott_IRG. The fixed back reflector 1604 and the movable back reflector 1602 can respectively be a glass having the following properties (for incident light with a spectral center at 850 nm): an index of refraction of 1.5098 for light of 850 nm wavelength; a group index of refraction of 1.5249 (ng) for light of 850 nm wavelength; a group velocity delay of 40.13 fs / mm; a transparency of 99.8% for light of 850 nm wavelength. In some embodiments, the first back reflector and the second back reflector can comprise BK7 glass, for example, manufactured by Schott. In some embodiments of the assembly, the highly dispersive back reflector 1500 has a conical exterior, in which the conical interior comprises at least three mirror facets collectively configured to perform back reflection of the incident light.

[0397] Some embodiments of the assembly 1600 can be used by an optical coherence tomography (OCT) device 100 configured to perform real-time OCT, the device comprising: an illumination arm 101 comprising at least one light source 102 for OCT; a reference arm 103; an OCT probe arm 105 via which an OCT probe light beam is emitted; and a data arm 107 via which returned OCT light is transferred for processing by an image processor 148; and at least one dispersive back reflector in the reference arm 103 or the OCT probe arm 105.

[0398] In some embodiments, the dispersion between the reference arm and the probe arm is variable and is set above a minimum threshold in order to separate a complex conjugate image from the OCT image in order to output for display.

[0399] In some embodiments, the OCT device further comprises at least one additional dispersive component provided in one of the reference arm or the OCT probe arm.

[0400] In some embodiments, the at least one additional dispersive component is located in the reference arm and comprises a dispersive fiber.

[0401] ​In some embodiments, at least one additional dispersive component is located in the reference arm and includes a dispersive glass window, wherein the physical path length of the reference arm is configured to compensate for the dispersive window, or conversely the physical path length of the OCT detection arm is lengthened to compensate for the dispersive window.

[0402] In some embodiments, an OCT device includes a bulk glass differential dispersion interferometer assembly 1600 for extended depth imaging in optical coherence tomography (OCT), the system including an automated optical path length optomechanical assembly 1600 .

[0403] In some embodiments, the OCT device 100 includes an OCT scanner adapter 206 according to any of the embodiments disclosed herein.

[0404] In some embodiments, at least one dispersive optical component provided in the OCT detection arm (105) includes one or more of a dispersive optical fiber, a dispersive dichroic mirror, a dispersive OCT objective lens (510), and a dispersive OCT field lens (512).

[0405] Example of using hybrid fiber-based differential dispersion in an interferometer

[0406] Some embodiments of the disclosed technology use hybrid fiber-based differential dispersion in interferometers instead of bulk glass differential dispersion in interferometer designs to support extended depth imaging in optical coherence tomography. These embodiments can be combined with reference to the accompanying drawings. ​ 、 8B , 9, 10, 11A, 11B, 13 and 14. The interferometer design disclosed herein can be used in ​ Some embodiments of the OCT scanning system 100 are used. ​ The OCT scanning system may include an OCT scanner adapter 206 for a surgical operating microscope, which, in some embodiments, incorporates the OCT scanner described and / or described in accordance with the embodiments disclosed herein. ​ 、 2B , 3A, 3B, 4, 5A, 5B, 6 or 7.

[0407] As mentioned above, in optical coherence tomography, complex conjugate cancellation requires that there be a minimum amount of differential dispersion between the sample path and the reference path of the system interferometer. Optical coherence tomography (OCT) is an imaging modality that uses the principle of low-coherence interferometry to generate a three-dimensional image of a sample. OCT systems (such as ​ The system 100 shown includes a broadband light source 102 for OCT scanning light, a reference arm 103 and a sample optical arm 105 (also referred to herein as a detection arm or scanning arm, for example), and a detection arm 107 (including ​Spectrometer 136 is shown in the embodiment shown. Alternatively, in disclosed embodiments of the OCT system 100 that do not require a spectrometer, a photodiode detector may be used instead.

[0408] The interference pattern of light reflected from the reference and sample arms 103, 105 is measured at the detector 136 and detected using a suitable device (e.g. ​ The image processor 148 shown in FIG. 1 is electronically processed to generate a tomogram showing the relative locations of reflectors or structures in the sample that cause backscattering of the incident OCT light (see FIG. ​ 116 of, when the reflector or structure is an eye, examples of which are also ​ By scanning the OCT beam in the detection or sample arm using a scanning mirror assembly (such as the scanning mirror assembly 310 disclosed herein), different spatial locations can be detected to construct a 3D image of the sample. In other words, a volume scan can be generated from multiple B-scans.

[0409] Signal processing of OCT signals requires multiple steps, one of which is the Fourier transform of the detected interferometric signal. However, because the measured signal is real-valued, Fourier transforming it produces a complex signal with equal positive and negative frequency components. This data mirroring is known as complex conjugate artifact, and it limits the usable imaging range to half of what is theoretically possible. Techniques to remove or suppress conjugate artifacts are known as complex conjugate cancellation (CCR) methods and can instantly double the imaging range in OCT.

[0410] Some embodiments of the disclosed technology can be used as a block filter glass retroreflector in the reference arm to improve the efficiency of the CCR method disclosed herein. Additionally or alternatively, in some embodiments, hybrid fibers can be designed to improve the efficiency of CC artifact removal.

[0411] However, known CCR systems and methods are difficult to implement in many situations due to the necessity of adding expensive and complex optical components to OCT scanning systems. Furthermore, multiple image acquisitions are required to generate the necessary phase information for deconjugated images. This slows imaging time, resulting in reduced system performance, and is also highly susceptible to sample motion, particularly when imaging living subjects.

[0412] Since some embodiments of the OCT system 100 disclosed herein are intended to provide B-scans and preferably volume scans in real time while performing a surgical procedure, it would be advantageous if faster techniques could be used to render OCT images without CCR image artifacts. Removing CCR artifacts can also allow for increased depth resolution (in other words, resolution along the Z-axis) of any acquired OCT B-scan or volume image.

[0413] The disclosed embodiments include a method for determining a plurality of single mode fiber types, where one or more of the fibers have different core diameters, the plurality of single mode fibers collectively modify the dispersion along the core fiber by a predetermined amount to support CCR as part of an OCT interferometer reference assembly.

[0414] In optical coherence tomography, complex conjugate cancellation requires a minimum amount of differential dispersion between the sample and reference paths of the system interferometer.

[0415] In an OCT system, when the light source consists of a broadband, short coherence length but spatially coherent superluminescent diode, the dispersion in the system is caused by the dispersion or wavelength dependent propagation velocity difference of the light as it propagates through the system optical path, referred to as group velocity dispersion or GVD, which is quantitatively defined by RP Photonics as the derivative of the inverse group velocity with respect to the angular frequency, as shown in the following equation:

[0416]

[0417] where c = the speed of light in vacuum, l = wavelength, n = refractive index

[0418] Group velocity dispersion (GVD) can also be defined as the group delay dispersion (GDD) per unit length. For waveguides such as single mode fibers, the dispersion parameter is related to the GVD as shown in the following equation:

[0419]

[0420] with units of ps / (nm-km). Unit conversion calculators are well known in the art, such as the tool provided by RP photonics available from their website www.RP-photonics.com, which can be used to convert bulk glass GVD values to fiber-appropriate units.

[0421] The high dispersion required for complex conjugate cancellation is contrary to typical fiber design, which strives to minimize the dispersion of the fiber at a given wavelength.

[0422] However, the dispersion in a single mode fiber can be increased by reducing the fiber core diameter relative to the center wavelength sufficiently to increase the dispersion by the required amount. Given the prevalence in the industry, the core diameters of the fibers come in discrete increments that do not independently provide the required dispersion for a given length of fiber.

[0423] Therefore, the combination of fiber types with the appropriate core diameters must be quantitatively determined to present the required GDD values. ​ It is shown ​A version of the method of claim 1, wherein given a target GVD value and a required fiber length S 1702, the method 1400 can be used and adjusted to obtain the GDD from the average GVD value and the fiber length in S 1704, or to convert the average GVD value obtained in 1402 to the fiber dispersion parameter in S 1706.

[0424] ​ A computer-implemented method that can be used to calculate the required number of various fiber types in some embodiments of the disclosed technology is shown in more detail. The method 1800 includes calculating a target GVD for a fiber of a required optical path length in S 1802, converting the target GVD value to a target fiber dispersion parameter for an OCT illumination light with a center wavelength of 850 nm in S 1804, determining a fiber type that bounds the target fiber dispersion parameter in S 1806, obtaining the fiber dispersion parameter from the GVD for a center wavelength of 850 nm in S 1808, and using the parameter to calculate the length of each fiber type required to meet the target GDD while maintaining the required optical path length in S 1810.

[0425] It was determined empirically through experiments that, in order to obtain the best results for CCR in the system described above, an additional GDD value between 31000 (fs 2 ) and 46000 (fs 2 ) is required.

[0426] In some embodiments of the disclosed technology, the fiber components of the OCT reference assembly 1600 with adjustable optical path length include hybrid fibers, such as hybrid fibers with the GDD values described above over their length. The use of hybrid fibers with the GDD values described above can maintain the alignment stability of the reference assembly. In particular, given the operation of the OCT interferometer, the optical path length of the fiber is a fixed parameter, and therefore the fiber dispersion parameter must be sufficient to provide the required GDD based on the fixed fiber length.

[0427] ​ and 19B An alternative way of hybrid fiber 1900 based on two independent single-mode fibers 1902a, 1902b is shown exemplarily, covering a target fiber length TL. In ​ In this case, one fiber component of the hybrid fiber has a diameter D1A and a length TL1, while the other fiber component has a diameter or numerical aperture D2A and a length TL2, both together constituting a total length TL = TL1 + TL2, and a common GDD matching the target GDD for more effective removal of CC image artifacts in the resulting OCT scan. ​ It is shown that in some embodiments, arrangements of fibers with different orders can also be used.

[0428] Through the above process, two fiber types were identified whose combination exhibited the desired dispersion while maintaining the overall fiber path length. The successful combination consisted of TL1 (5 meters of Coheren 630-HP fiber) and TL2 (1 meter of Corning HI780 fiber). Then, in some embodiments of the reference arm optical assembly 103, the two fiber sections were fused together to create a single 6-meter-long fiber with the desired dispersion, in other words, TL=6.

[0429] In some embodiments of the disclosed technology, a high dispersion single mode hybrid fiber is located in an optical interferometer (e.g., including ​ The hybrid optical fiber comprises at least two optical fibers, wherein at least one optical fiber has a different core diameter and a different dispersion characteristic than at least one other optical fiber.

[0430] At least two optical fibers are fused end-to-end to form a hybrid optical fiber. Each of the at least two optical fibers is fused to at least one other of the at least two optical fibers. Each of the at least two optical fibers has, for example, ​ The length of TL1 or TL2, shown in FIG19B , is based on the core diameter of the fiber relative to the central wavelength of the light beam passing through the hybrid fiber and the target GDD per unit length of the hybrid fiber. The hybrid fiber adds an additional GDD value compared to the fiber in the other of the reference arm or the detection arm of the optical interferometer.

[0431] In some embodiments, using a dispersive component fiber in the reference arm can also make it easier to achieve power balancing between the reference and probe beams when they are subsequently combined. Conversely, if the dispersive component is located in the probe arm, additional compensation in the reference arm may be required in some embodiments to improve the balance between the returned reference beam power and the OCT beam power.

[0432] In some embodiments of the hybrid optical fiber 1900, the additional GDD value is 31000 (fs 2 ) and 46000(fs 2 )between.

[0433] In some embodiments of the hybrid optical fiber 1900 , the length TL1 of at least one optical fiber 1902 a is different from the length TL2 of at least another optical fiber 1902 b in the hybrid optical fiber 900 .

[0434] In some embodiments, the lengths TL1, TL2 of each respective component optical fiber 1902a, 1902b are determined by calculating a target group velocity delay GVD for a predetermined length of hybrid optical fiber, converting the target GVD to a target optical fiber dispersion parameter OFDP for a center wavelength of light passing through the hybrid optical fiber, determining at least two optical fiber types, each having an OFDP value that bounds the target OFDP value, converting the OFDP of each determined optical fiber type to a GVD at the center wavelength, and for each of the determined optical fiber types, calculating a length of the optical fiber based on the GVD of the respective optical fiber at the center wavelength such that the optical fibers collectively provide an optical path that matches the predetermined optical path length of the hybrid optical fiber when end-to-end spliced.

[0435] In some embodiments, the hybrid optical fiber 1900 includes at least one segment of coherent 630-HP optical fiber and at least one segment of Corning HI780 optical fiber, wherein at least one end of the segment of coherent 630-HP optical fiber is spliced to one end of the segment of Corning HI780 optical fiber.

[0436] In some embodiments of an optical interferometer, such as the OCT system 100 disclosed herein, the hybrid optical fiber is located in a reference arm 103 of the optical interferometer and introduces differential dispersion in the reference arm 103 compared to the return OCT imaging light obtained from scanning a sample with an OCT device according to any of the disclosed embodiments.

[0437] In some embodiments, the hybrid optical fiber 1900 is configured to introduce a predetermined level of dispersion in a reference arm 103 of an optical interferometer, such as the OCT system 100, to remove complex conjugate image data from OCT images output by an OCT device.

[0438] In some embodiments, the hybrid optical fiber 1900 is located in a reference arm of an optical interferometer configured to output OCT imaging data from an OCT device and has a length of 6 meters, wherein 5 meters includes coherent 630-HP optical fiber or optical fiber having similar optical properties, and wherein 1 meter includes Corning HI780 optical fiber or optical fiber having similar optical properties. Other glasses having equivalent properties can be used in some embodiments as will be apparent to those of ordinary skill in the art, for example, see the properties and parameters of these optical fibers in Table 1.

[0439] Example of using a high dispersion custom drawn single mode optical fiber

[0440] Some embodiments of the disclosed technology use an interferometer design in which, instead of end-to-end fusing two or more single mode optical fibers to form a hybrid optical fiber, a high dispersion custom drawn single mode optical fiber is used as part of an OCT interferometer reference arm.

[0441] Some embodiments of the disclosed technology use a highly dispersive optical fiber to provide differential dispersion in an interferometer to support extended depth imaging in optical coherence tomography. These embodiments can be used in conjunction with the calculation methods described above with reference to Figures ​ 、 8B , 9, 10, 11A, 11B, 13, and 14, and can also be used in some embodiments with bulk glass back reflectors to further increase the amount of differential dispersion provided. The interferometer designs disclosed herein can be used in some embodiments of the OCT scanning system 100 of ​ . In some embodiments, the OCT scanning system can include an OCT scanner adapter 206 for a surgical microscope that incorporates features described according to embodiments disclosed herein and / or as shown in ​ , ​ 、 2B , 3A, 3B, 4, 5A, 5B, 6, or 7.

[0442] To maintain single mode propagation in the optical fiber and meet the required dispersion parameters, a suitable bulk glass material with the appropriate GDD value must be quantitatively determined, which can be done using the methods described above with reference to Figures ​ 、 17 , and 18.

[0443] Through the above methods, a number of glass materials with sufficient group velocity dispersion (GVD) were determined to find an optical fiber dispersion parameter that can achieve the required GDD based on the fixed optical fiber length of an OCT reference assembly with adjustable optical path (as described with reference to the reference assembly 1600 and described above).

[0444] However, due to the manufacturing process of drawing bulk glass into an optical fiber, only one candidate material was found to provide the required dispersion over the optical path length TL of the reference assembly 1600. Based on the calculations above, this includes a highly dispersive optical fiber with a dispersion constant GVD that matches the GVD of Schott N-ZK7 glass, although other glass types with the same refractive index, group refractive index (GVD), and transparency as indicated in Table 1 can also be used as an alternative. Example values of these properties include a GVD of 41816 (fs 2 / m) at 850 nm, which corresponds to a dispersion parameter of -109 ps / (nm km) at 850 nm. If the optical path length in the highly dispersive fiber reference assembly is 6 meters of fiber, the total GDD value along the length of the reference arm fiber path is 250 (ps 2 ). While this is below the target median value, it is still acceptably above the minimum acceptable GDD value.

[0445] Some embodiments of the disclosed technology accordingly include a high-dispersion single-mode optical fiber comprising drawn bulk optical glass.

[0446] In some embodiments, the high-dispersion single-mode optical fiber includes a bulk optical glass having a fiber dispersion parameter associated with a group delay dispersion (GDD) value of 31,000 fs at a given wavelength of 860 nm and a bandwidth of 100 nm based on the glass dispersion coefficient measured using the Sellmeier method. 2 and 46000fs 2 between.

[0447] In some embodiments, the high-dispersion single-mode optical fiber is located in a reference arm of an optical interferometer configured to output OCT imaging data from the OCT device.

[0448] In some embodiments, the optical fiber comprises drawn bulk Schott N-ZK7 optical glass or drawn bulk optical glass having similar refractive index, group refractive index (GVD), and transparency properties as listed in Table 1.

[0449] In some embodiments, a high dispersion optical fiber may be selected by determining the GDD for a given length of optical fiber or, for example, by determining the group velocity delay (GVD) of a high dispersion single mode optical fiber comprising bulk drawn optical glass using a computer implemented method, wherein the method comprises determining a target GVD value based on inputs including at least a target group dispersion delay (GDD) value and an optical path length along the optical fiber, solving a Sellmeier dispersion equation for the refractive index of the optical glass as a function of wavelength within the wavelength interval, and iteratively determining over a plurality of incremental wavelength intervals within a predetermined bandwidth: determining an average GVD within the wavelength interval by determining a GVD coefficient as a function of wavelength (804), calculating a second derivative of the refractive index with respect to wavelength, multiplying the GVD coefficient as a function of wavelength by the second derivative of the refractive index with respect to wavelength, and averaging all determined GVD values ​​within the bandwidth to determine an average GVD within the bandwidth.

[0450] In some embodiments, the method further comprises calculating the GDD based on the average GVD value and the optical fiber length.

[0451] In some embodiments, the method further comprises converting the determined average GVD over the bandwidth into a fiber dispersion parameter.

[0452] In some embodiments, high dispersion optical fibers are used in OCT components (e.g. ​ In the optical OCT interferometer assembly in the detector arm of the OCT system 100).

[0453] In some embodiments, the OCT interferometer assembly may include an OCT detector assembly, such as​ a spectrometer such as the spectrometer 136 shown in the example OCT system 100; a sample arm configured to direct an OCT probe beam from the OCT assembly to a subject and to direct an OCT probe beam returned from the scanned subject to the detector assembly; and an OCT system reference assembly of adjustable optical path length, the assembly comprising a fixed optical path length highly dispersive single mode optical fiber comprising bulk drawn optical glass, wherein the reference assembly is configured in the reference arm of the OCT detector assembly.

[0454] In some embodiments, the interference pattern of the reference beam and the OCT beam returned by the detector assembly is Fourier transformed, wherein the dispersion along the reference beam optical path in the highly dispersive single mode optical fiber OCT system reference arm is sufficient to remove complex conjugate artifacts from the Fourier transform of the interference signal output by the OCT interferometer using a CCR based method.

[0455] In some embodiments, the dispersion along the optical glass fiber is sufficient to allow the CCR method to remove complex conjugate artifacts in real time from an OCT B-scan or volumetric scan.

[0456] In some embodiments, based on the fixed fiber length of the single mode fiber (comprising optical glass), the fiber dispersion parameter is configured to provide a group delay dispersion GDD value between 31000 fs 2 and 46000 fs 2 , wherein the GDD can be determined using appropriate methods such as one of the methods disclosed herein with reference to the figures. ​

[0457] In some embodiments, the optical glass comprises Schott N-ZK7 optical glass or an optical glass having the same refractive index, group refractive index (GVD) and transparency properties (e.g. properties having the parameter values listed in Table 1 above).

[0458] In some embodiments, the determined dispersion parameter of the optical fiber comprising the optical glass is about -109 ps / (nm-km) at a wavelength of 850 nm.

[0459] In some embodiments, the optical path length of the optical fiber is about 6 meters and the GDD is about 250 ps 2 .

[0460] The above embodiments can be combined with other disclosed embodiments of the same or another aspect of the disclosed technology in any suitable manner apparent to those of ordinary skill in the art.

[0461] In some embodiments (e.g. in the case of a single mode fiber comprising optical glass), the fiber dispersion parameter is configured to provide a group delay dispersion GDD value between 31000 fs ​ ​In some embodiments, the high dispersion single mode optical fiber that draws the bulk optical glass can be configured as the optical fiber in the reference arm of the interferometer. This can help improve the depth of resolution of the B-scans and volume scans when the OCT scanning system is performing real-time OCT scan streaming, for example, by allowing faster techniques to be used for the complex conjugate removal of the scanned images. However, other glasses with equivalent properties can be used in some embodiments, for example, glasses with the same optical properties as listed in Table 1.

[0462] The terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting of the present disclosure. As used herein, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0463] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items and can be abbreviated as " / ".

[0464] It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0465] It will be understood that, although the terms first, second, etc. can be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present disclosure.

[0466] Relative terms such as "below" or "above" or "upper" or "lower" or "horizontal" or "vertical" can be used herein for the purposes of describing one element's relationship to another element as illustrated in the figures. It will be understood that these terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures. It will be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to other elements or intervening elements can be present. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements present.

[0467] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0468] Although some aspects are described in the context of an apparatus, it is clear that these aspects also represent a description of the corresponding method, where blocks or devices correspond to method steps or features of method steps. Likewise, aspects described in the context of a method step also represent a description of the corresponding block or item or feature of a corresponding apparatus.

[0469] Some embodiments relate to a microscope 200 comprising an SD-OCT scanner system 100 that uses an OCT scanner adapter 206 to generate OCTA scans and B-scans using image processing techniques disclosed herein (e.g. in connection with one or more of ​ Alternatively, the microscope 200 can be part of or connected to the OCT system 100. As described in connection with one or more of ​ Alternatively, the microscope 200 can be part of or connected to the OCT system 100. As described in connection with one or more of

[0470] ​ A schematic illustration of a system 1300 configured to perform embodiments of the computer-implemented image processing method 900 as described herein is schematically illustrated. The system 1300 comprises a microscope 1302, 200 and a computer system 1306 comprising a display 1308. The microscope 1302, 200 is configured to acquire images and is connected to the computer system 1306. In some embodiments, the connection can comprise a suitable data connection, e.g. via a port 212 schematically illustrated in ​ 、 3A 3B and 4. In some embodiments, the computer system 1306 can comprise the image processing device 148. The computer system 1306 is configured to perform at least part of the methods described herein, e.g. embodiments of the method 900 comprising using embodiments of the algorithm 1000. In some embodiments, the computer system 1306, 148 can be configured to perform a machine learning algorithm.

[0471] In some embodiments, the computer system 1306, 148 and the microscope 200 can be separate entities, but in some embodiments can also be integrated in a common housing, such as the housing 202. The computer system 1306, 148 can be part of a central processing system of the microscope 200, and / or the computer system 1306, 148 can be part of a subcomponent of the microscope 200 (such as a sensor, actuator, camera or illumination unit of the microscope 200, etc.), or part of an OCT scanner adapter microscope accessory as shown in some of the figures as 206.

[0472] The computer system 1306, 148 can be a local computer device (e.g., a personal computer, a laptop, a tablet or a mobile phone) having one or more processors and one or more storage devices, or can be a distributed computer system (e.g., a cloud computing system having one or more processors and one or more storage devices distributed in different locations, such as a local client and / or one or more remote server farms and / or data centers).

[0473] The computer system 1306, 148 can include any circuit or combination of circuits. In one embodiment, the computer system 1306, 148 can include one or more processors, which can be of any type. As used herein, the processor can mean any type of computational circuit, such as, but not limited to, a microprocessor, a microcontroller, a complex instruction set computing (CISC) microprocessor, a reduced instruction set computing (RISC) microprocessor, a very long instruction word (VLIW) microprocessor, a graphics processor, a digital signal processor (DSP), a multi-core processor, a microscope or a field programmable gate array (FPGA) of a microscope component (such as a camera), or any other type of processor or processing circuit. Other types of circuit that can be included in the computer system 1306, 148 can be custom circuit, an application specific integrated circuit (ASIC), etc., such as one or more circuits (e.g., a communication circuit) in a wireless device, such as a mobile phone, a tablet, a laptop, a two-way radio and similar electronic systems. The computer system 1306, 148 can include one or more storage devices, which can include one or more memory elements suitable for the

[0474] Some or all of the method steps disclosed herein can be performed by (or using) a hardware apparatus, like for example, a processor, a microprocessor, a programmable computer or an electronic circuit. In some embodiments, some, each or all of the method steps can be performed by such an apparatus.

[0475] Depending on certain implementation requirements, embodiments of the disclosed technology can be implemented in hardware or in software. The implementation can be performed using a non-transitory storage medium (like a digital storage medium), a disc, like a DVD or a Blu-Ray Disc, a CD-ROM, a PROM, an EPROM, a EEPROM or a FLASH memory, containing electronically readable control signals which are capable of cooperating with a programmable computer system, such that the respective method is performed. Thus, the digital storage medium can be computer readable.

[0476] Some embodiments of the disclosed technology comprise a data carrier having electronically readable control signals, which are capable of cooperating with a programmable computer system, such that one of the methods described herein is performed.

[0477] Generally, embodiments of the present application can be implemented as a computer program product with a program code, the program code being operative for performing one of the methods when the computer program product runs on a computer. The program code can for example be stored on a machine readable carrier.

[0478] Other embodiments comprise the computer program for performing one of the methods described herein, stored on a machine readable carrier.

[0479] A further embodiment of the inventive methods is, therefore, a computer program having a program code for performing one of the methods, when the computer program runs on a computer.

[0480] A further embodiment of the present application is, therefore, a data carrier (or a digital storage medium, or a computer-readable medium) comprising, recorded thereon, the computer program for performing one of the methods described herein when the data carrier (or the digital storage medium, or the computer-readable medium) is accessed by a computer. The data carrier, the digital storage medium or the recorded medium are typically tangible and / or non-transitionary. A further embodiment of the present application is a device including a processor and a storage medium, the storage medium comprising the computer program for performing one of the methods described herein when the computer program is run by the processor.

[0481] The computer program can thus be downloaded to the processor and / or the storage medium from a data carrier (or a digital storage medium, or a computer-readable medium), via a computer program product (or a data carrier, or a digital storage medium, or a computer-readable medium), for example via an Internet or an Intranet or a network based on the LAN or WAN or the Internet or a combination thereof.

[0482] Another embodiment comprises a processing means, such as a computer, or a programmable logic device, configured to or adapted for performing one of the methods described herein.

[0483] Another embodiment includes a computer having fixed thereon the computer program for performing one of the methods described herein.

[0484] Another embodiment according to the disclosed technology includes a device or system configured to transfer (e.g., electronically or optically) a computer program for performing one of the methods described herein to a receiver. The receiver could, for example, be a computer, a mobile device, a memory device or the like. The device or system could, for example, comprise a file server for transferring the computer program to the receiver.

[0485] In some embodiments, a programmable logic device (e.g., a field programmable gate array) can be used to perform some or all of the functionalities of the methods described herein. In some embodiments, a field programmable gate array can cooperate with a microprocessor in order to perform one of the methods described herein. Generally, the methods are preferably performed by any hardware apparatus.

[0486] It should be understood that the application is not limited to the aspects described above, which can be varied in many ways. Such variations are not to be regarded as a departure from the scope of the application, and all such modifications as would be recognized by one skilled in the art in light of the remaining teachings and claims are intended to be included within the range of the application. In the drawings and specification, there have been disclosed aspects for purposes of illustration only and as an aid to understanding the application concepts. Its scope is set forth in the claims.

Claims

1. A highly dispersive single-mode hybrid optical fiber (1900) for placement in one of a reference arm or a probe arm of an optical interferometer imaging system, the hybrid optical fiber (1900) comprising: at least two optical fibers (1902, 1902), at least one of the at least two optical fibers having a different core diameter and different dispersion characteristics than at least one other of the at least two optical fibers, wherein the at least two optical fibers are end-to-end fusion spliced to form the hybrid optical fiber, and wherein a length of each of the at least two optical fibers is based on a relative relationship of the core diameter of the optical fiber to a center wavelength of an optical beam passing through the hybrid optical fiber, and a target GDD per unit length based on a target length of the hybrid optical fiber, wherein the hybrid optical fiber adds an additional GDD value relative to an optical fiber in the other of the reference arm or the probe arm of the optical interferometer.

2. The hybrid fiber according to claim 1, wherein the additional GDD value is between 31000 (fs 2 ) and 46000 (fs 2 ).

3. The hybrid optical fiber of claim 1 or 2, wherein the length of at least one of the optical fibers in the hybrid optical fiber is different than the length of at least one other of the optical fibers.

4. The hybrid optical fiber of any one of claims 1 to 3, wherein the length of each optical fiber is determined by: calculating a target group velocity delay (GVD) for a predetermined length of the hybrid optical fiber; converting the target GVD to a target optical fiber dispersion parameter (OFDP) for a center wavelength of light passing through the hybrid optical fiber; determining at least two optical fiber types, each optical fiber type having an OFDP that bounds the target OFDP; converting the OFDP of each determined optical fiber type to a GVD at the center wavelength; for each of the determined optical fiber types, determining a length of the optical fiber based on the GVD of the respective optical fiber at the center wavelength such that the optical fibers collectively provide, when end-to-end fusion spliced, an optical path that matches a predetermined optical path length of the hybrid optical fiber.

5. The hybrid optical fiber of any one of claims 1 to 4, wherein the hybrid optical fiber comprises a length of a Corning 630-HP optical fiber and a length of a Corning HI780 optical fiber.

6. The hybrid optical fiber of any one of claims 1 to 5, for placement in a reference arm of an optical interferometer imaging system comprising an OCT device.

7. The hybrid optical fiber of claim 6, wherein the hybrid optical fiber is configured to introduce a predetermined level of dispersion in the reference arm of the optical interferometer to remove complex conjugate image data in an OCT image output by the OCT device.

8. The hybrid optical fiber of any one of claims 1 to 7, for placement in a reference arm of an optical interferometer configured to output OCT imaging data from an OCT device, wherein for a hybrid optical path length of 6 meters, 5 meters comprises a Corning 630-HP optical fiber and 1 meter comprises a Corning HI780 optical fiber.

9. An OCT assembly comprising an OCT interferometer assembly, the OCT interferometer assembly comprising: an OCT detector assembly (136); a sample arm (105) configured to direct an OCT probe beam from an OCT light source of the OCT assembly to a subject (116) and to direct an OCT probe beam returned from the scanned subject to the OCT detector assembly; and and An OCT system reference assembly with tunable optical path length comprising a hybrid fiber according to any of claims 1 to 8, wherein the reference assembly is configured in a reference arm (103) of an OCT detector assembly, wherein OCT light from an OCT light source is split to propagate as a reference beam along the reference arm (103) and as an OCT probe beam along a sample arm (105), wherein the returned reference beam and the returned probe beam are combined and an OCT detector assembly (136) is configured to detect interference in the combined OCT light returned from the reference arm (103) and the sample arm (105).

10. The OCT assembly of claim 9, further comprising an image processor (148), wherein the OCT detector of the OCT interferometer assembly is configured to output a signal (146) comprising the detected interference pattern of the combined OCT light of the returned to the image processor (148), wherein, The interference pattern of the returned OCT reference light and OCT probe light is Fourier transformed by an image processor (148).

11. The OCT assembly of claim 9 or 10, wherein the image processor (148) is configured to perform a computer-implemented complex conjugate removal (CCR) method to remove complex conjugate artifacts in the Fourier transformed signal, and wherein the reference beam optical path in the hybrid fiber OCT system reference arm (103) produces sufficient dispersion in the reference beam to enable the CCR method to remove CC artifacts in real time.

12. The OCT interferometer of claim 11, wherein the dispersion along the hybrid glass fiber is sufficient to allow the computer-implemented CCR method to remove complex conjugate artifacts in real time in an OCT B-scan or volume scan.

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