Processing techniques for optical retinal imaging

Abstract

The invention relates to processing techniques for optical retinal imaging. A computer-implemented method for processing each set of a plurality of sets of OCT images of a series of OCT images of a portion of the retina by performing, for each set of the plurality of sets of OCT images of the series of OCT images, a respective indication of tissue velocity at a location in an axial direction in the OCT images; calculating a corresponding comparison value based on the image quality or similarity of the first OCT image and the second OCT image in the set; if the comparison value is equal to or greater than a threshold, using phase information in the first OCT image and the second OCT image in calculating a respective indication of tissue velocity at the location; and omitting the phase information from the calculation if the comparison value is less than a threshold value.

Description

field

[0001] Example aspects of the present invention generally relate to the field of optical coherence tomography (OCT), and specifically to techniques for processing OCT data generated by a Fourier domain OCT imaging system to generate optical retinal imaging (ORG) data that is indicative of the physiological response of the retina of a subject's eye to optical stimulation. background

[0002] Optical coherence tomography (OCT) is an imaging technique based on low-coherence interferometry that is widely used to acquire high-resolution two-dimensional and three-dimensional images of optically scattering media such as biological tissue.

[0003] Depending on how depth ranging is achieved, OCT imaging systems can be classified as time-domain OCT (TD-OCT) or Fourier domain OCT (FD-OCT) (also known as frequency domain OCT). In TD-OCT, the optical path length of the reference arm of the interferometer of the imaging system varies with time during the acquisition of the reflectivity profile of the scattering medium (referred to herein as the "imaging target") imaged by the OCT imaging system, and the reflectivity profile is often referred to as a "depth scan" or "axial scan" ("A scan"). In FD-OCT, the spectral interferogram produced by the interference between the light in the reference arm of the interferometer and the light in the sample arm at each A scan position is Fourier transformed to simultaneously acquire all points along the depth of the A scan without any change in the optical path length of the reference arm. FD-OCT can allow much faster imaging than scanning of the sample arm mirror in the interferometer because all back reflections from the sample are measured simultaneously. Two common types of FD-OCT are spectral domain OCT (SD-OCT) and swept source OCT (SS-OCT). In SD-OCT, a broadband light source delivers many wavelengths to the imaging target, and a spectrometer is used as a detector to measure all wavelengths simultaneously. In SS-OCT (also known as time-coded frequency-domain OCT), the light source is swept across a range of wavelengths, and the temporal output of the detector is converted into spectral interferometry.

[0004] OCT imaging systems can also be classified as point scanning (also called "point detection" or "scanning point"), line scanning, or full-field, depending on how the imaging system is configured to acquire OCT data at various locations on an imaging target. A point scanning OCT imaging system acquires OCT data by scanning a focused sample beam across the surface of an imaging target, typically along a single line (which may be straight, or alternatively curved to define a circle or spiral) or a set of (usually substantially parallel) lines on the imaging target surface, and acquiring an axial depth profile (A-scan) for each of a plurality of points along the line, one point at a time, to create OCT data comprising a one-dimensional or two-dimensional array of A-scans representing a two-dimensional (i.e., B-scan) or three-dimensional (i.e., C-scan or volume scan) reflectance profile of the sample.

[0005] Line scan OCT imaging systems acquire OCT data by scanning with focused light across the surface of an imaging target. The measured reflectance from the imaging target is used to generate OCT data comprising a two-dimensional reflectance distribution (i.e., a B-scan) of the sample. By scanning with focused light across multiple locations on the imaging target, OCT data comprising a three-dimensional reflectance distribution (i.e., a C-scan or volume scan) of the sample can be obtained. Typically, the focused light is straight and is scanned in a direction perpendicular to it, although in some cases it can be curved and the scanning direction adjusted accordingly. Full-field OCT imaging systems acquire OCT data by projecting a light beam onto the imaging target to acquire OCT data comprising a three-dimensional reflectance distribution (i.e., a C-scan or volume scan) of the sample.

[0006] OCT imaging systems can also be classified as phase-resolving, where both the intensity and phase of light reflected from the imaging target are measured as a function of axial depth. Modern FD-OCT imaging systems typically possess a degree of phase stability, which allows them to be used as phase-resolving OCT imaging systems.

[0007] Optical retinal imaging (ORG) generally refers to detecting the physiological response of the retina of the eye to optical stimulation (i.e., the functional activity of the retina induced by light). ORG technology includes non-invasive optical imaging of this physiological response of the retina. For example, an OCT imaging system can be used to image retinal neurons that exhibit size (size) changes in response to excitation of an optical stimulus. These size changes (usually changes in the length of the outer segment (OS) of the photoreceptors in the retina, which is the depth difference between the junction of the inner and outer segments (IS / OS) of the cone photoreceptors and the outer segment tip (COST) of the cone) cause phase changes in the light waves returned from the eye that are large enough to be detected by an OCT imaging system with phase resolution capability. Phase is very sensitive to movement in tissue, and many OCT imaging systems with phase resolution capability are able to resolve displacements of less than 10 nm, which may be much smaller than the axial resolution of the system or the wavelength of light used in imaging. Overview

[0008] According to a first example aspect of the present invention, a computer-implemented method is provided for processing each set of OCT images, including a first OCT image and a second OCT image, in a series of OCT images of a common portion of the retina of an eye acquired by a Fourier domain OCT imaging system to generate a corresponding indication of tissue velocity at a location along an axial direction in the OCT image. The method includes performing the following process for each of a plurality of sets of OCT images: calculating a corresponding comparison value, the corresponding comparison value being one of: (i) a value of an image quality metric calculated based on at least one of a first OCT image in the set and a second OCT image in the set, and (ii) a value of an image similarity metric that provides a measure of the degree of similarity between the images, the value of the image similarity metric being calculated based on the first OCT image in the set and the second OCT image in the set; calculating a corresponding indication of tissue velocity at a position along the axial direction using a phase value at a position along the axial direction in an A-scan of the first OCT image in the set and a phase value at a position along the axial direction in a corresponding A-scan of the second OCT image in the set; comparing the comparison value with a threshold to determine whether the comparison value is equal to or greater than the threshold; retaining the corresponding indication of tissue velocity at the position along the axial direction if it is determined that the comparison value is equal to or greater than the threshold; and discarding the corresponding indication of tissue velocity at the position along the axial direction if it is determined that the comparison value is not equal to or greater than the threshold.

[0009] According to a second exemplary aspect of the present invention, a computer-implemented method is provided for processing each set of OCT images, including a first OCT image and a second OCT image, from a series of OCT images of a common portion of a retina of an eye acquired by a Fourier domain OCT imaging system to generate a corresponding indication of tissue velocity (v) at a position along an axial direction in the OCT image. The method includes performing the following process for each of the multiple sets of OCT images: calculating a corresponding comparison value, the corresponding comparison value being one of: (i) a value of an image quality metric calculated based on at least one of the first OCT image in the set and the second OCT image in the set, and (ii) a value of an image similarity metric that provides a measure of the degree of similarity between the images, the value of the image similarity metric being calculated based on the first OCT image in the set and the second OCT image in the set; comparing the comparison value with a threshold value to determine whether the comparison value is equal to or greater than the threshold value; and upon the comparison value being determined to be equal to or greater than the threshold value, in calculating the corresponding indication of the tissue velocity at the position along the axial direction, the phase value at the position along the axial direction in the A scan of the first OCT image in the set and the phase value at the position along the axial direction in the corresponding A scan of the second OCT image in the set are used; and in a case where it is determined that the comparison value is not equal to or greater than the threshold value, the phase value at the position along the axial direction in the A scan of the first OCT image in the set and the phase value at the position along the axial direction in the corresponding A scan of the second OCT image in the set are omitted in calculating the corresponding indication of the tissue velocity at the position along the axial direction.

[0010] In the above method, the comparison value may be the maximum value of the calculated cross-correlation between the first OCT image and the second OCT image. For example, other similarity metrics that may be used instead are sum of squared differences, mutual information, normalized mutual information, and Kullback Leibler distance.

[0011] The computer-implemented method of the first example aspect or the second example aspect may further include generating a concatenation of the generated indications of tissue velocity such that the concatenation indicates how the tissue velocity at a location along the axial direction changes over time, and integrating the concatenation to generate data indicating how the optical path length at the location along the axial direction changes over time. In the event that the comparison value is determined not to be equal to or greater than the threshold, the corresponding indication of tissue velocity at the location along the axial direction is set to indicate zero velocity, such that the generated data includes one or more sets of equal consecutive values, and the method may further include smoothing the generated data by replacing one or more values ​​in one of the one or more sets of equal consecutive values ​​in the generated data with one or more estimated values, the one or more estimated values ​​being calculated based on adjacent values ​​adjacent to the set of equal consecutive values.

[0012] In addition, in any of the foregoing items, the computer-implemented method may further include processing, prior to calculating the corresponding indication of tissue velocity at the position along the axial direction, phase values ​​at the position along the axial direction in the A-scan of the first OCT image in the set and the phase values ​​at the position along the axial direction in the corresponding A-scan of the second OCT image in the set to compensate for overall motion of a common portion of the retina during acquisition of a series of OCT images by the Fourier domain OCT imaging system.

[0013] According to a third exemplary aspect of the present invention, there is provided a computer program comprising computer-readable instructions that, when executed by a processor, cause the processor to perform the method of the first exemplary aspect or the second exemplary aspect, or any of the variations thereof set forth above. The computer program may be stored on a non-transitory computer-readable storage medium (e.g., such as a computer hard disk or CD), or may be carried by a computer-readable signal.

[0014] According to a fourth example aspect of the present invention, a data processing device is provided, which includes a processor and a memory storing computer-readable instructions, which, when executed by the processor, causes the processor to perform the method of the first example aspect or the second example aspect, or any variation thereof set forth above.

[0015] According to a fifth example aspect of the present invention, there is provided a data processing apparatus arranged to process each set of OCT images, including a first OCT image and a second OCT image, in a series of optical coherence tomography (OCT) images of a common portion of the retina of an eye (20) acquired by a Fourier domain OCT imaging system to generate a corresponding indication of tissue velocity at a position along an axial direction in the OCT images. The data processing device is arranged to perform the following process for each of multiple sets of OCT images: calculating a corresponding comparison value, which is one of the following: (i) a value of an image quality metric calculated based on at least one of a first OCT image in the set and a second OCT image in the set, and (ii) a value of an image similarity metric that provides a measure of the degree of similarity between the images, the value of the image similarity metric being calculated based on the first OCT image in the set and the second OCT image in the set; using a phase value at a position along the axial direction in an A-scan of the first OCT image in the set and a phase value at a position along the axial direction in a corresponding A-scan of the second OCT image in the set, calculating a corresponding indication of tissue velocity at a position along the axial direction; comparing the comparison value with a threshold to determine whether the comparison value is equal to or greater than the threshold; if it is determined that the comparison value is equal to or greater than the threshold, retaining the corresponding indication of tissue velocity at the position along the axial direction; and if it is determined that the comparison value is not equal to or greater than the threshold, discarding the corresponding indication of tissue velocity at the position along the axial direction.

[0016] According to a sixth exemplary aspect of the present invention, there is provided a data processing apparatus arranged to process each set of OCT images, including a first OCT image and a second OCT image, in a series of OCT images of a common portion of the retina of an eye acquired by a Fourier domain optical coherence tomography (OCT) imaging system to generate a corresponding indication of tissue velocity at a position along an axial direction in the OCT image. The data processing apparatus is arranged to perform the following process for each of the multiple sets of OCT images: calculating a corresponding comparison value, the corresponding comparison value being one of: (i) a value of an image quality metric calculated based on at least one of the first OCT image in the set and the second OCT image in the set, and (ii) a value of an image similarity metric that provides a measure of the degree of similarity between the images, the value of the image similarity metric being calculated based on the first OCT image in the set and the second OCT image in the set; comparing the comparison value with a threshold value to determine whether the comparison value is equal to or greater than the threshold value; and after the comparison value is determined When the comparison value is equal to or greater than the threshold value, the phase value at the position along the axial direction in the A scan of the first OCT image in the set and the phase value at the position along the axial direction in the corresponding A scan of the second OCT image in the set are used in the calculation of the corresponding indication of the tissue velocity at the position along the axial direction; and when it is determined that the comparison value is not equal to or greater than the threshold value, the phase value at the position along the axial direction in the A scan of the first OCT image in the set and the phase value at the position along the axial direction in the corresponding A scan of the second OCT image in the set are omitted in the calculation of the corresponding indication of the tissue velocity at the position along the axial direction.

[0017] The comparison value may be a maximum of the calculated cross-correlations between the first and second OCT images. Additionally or alternatively, the data processing device may be further arranged to: generate a concatenation of the generated indications of tissue velocity, such that the concatenation indicates how the tissue velocity at a location along the axial direction changes over time; and integrate the concatenation to generate data indicating how the optical path length at the location along the axial direction changes over time. If it is determined that the comparison value is not equal to or greater than the threshold, the data processing device may be arranged to set the corresponding indication of tissue velocity at the location along the axial direction to indicate zero velocity, the generated data may include one or more sets of equal consecutive values, and the data processing device may be further arranged to smooth the generated data by replacing one or more values ​​in one of the one or more sets of equal consecutive values ​​in the generated data with one or more estimated values, the one or more estimated values ​​being calculated based on adjacent values ​​adjacent to the set of equal consecutive values.

[0018] The data processing device may also be arranged to process the phase values ​​at the position along the axial direction in the A-scan of the first OCT image in the set and the phase values ​​at the position along the axial direction in the corresponding A-scan of the second OCT image in the set before calculating the corresponding indication of tissue velocity at the position along the axial direction to compensate for the overall movement of the common portion of the retina during the acquisition of the series of OCT images by the Fourier domain OCT imaging system.

[0019] According to a seventh exemplary aspect of the present disclosure, there is provided a Fourier domain OCT imaging system comprising a data processing apparatus as described in any of the aforementioned aspects. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Example embodiments will now be explained in detail, by way of non-limiting example only, with reference to the accompanying drawings described below.Unless otherwise indicated, like reference numerals appearing in different figures of the drawings may represent the same element or a functionally similar element.

[0021] Figure 1 is a schematic diagram of a system including a Fourier domain OCT imaging system 30 and a data processing apparatus 100 according to an example embodiment herein.

[0022] Figure 2 is a schematic diagram of an example implementation of the data processing apparatus 100 in programmable signal processing hardware.

[0023] Figure 3 is a flow chart illustrating a method by which an OCT image is processed to generate an indication of tissue velocity according to a first example embodiment herein.

[0024] Figure 4A The first pair of B-scans that are highly correlated are shown.

[0025] Figure 4B Shows the Figure 4A Calculate the cross-correlation of the B-scans.

[0026] Figure 5A A second pair of B-scans that are not highly correlated is shown.

[0027] Figure 5B Shows the Figure 5A Calculate the cross-correlation of the B-scans.

[0028] Figure 6A Shown is the sinusoidal bulk oscillation added to the oscillatory movement of the two model retinal layers.

[0029] Figure 6BShown is the effect of removing global motion on the temporal variation of the phase angle of light reflected from two model retinal layers.

[0030] Figure 7 An example of a concatenation of velocity profiles that may be generated by the data processing device 100 is shown.

[0031] Figure 8 A graph showing the change in optical path length over time ΔOPL is shown, which has been calculated by the data processing apparatus of an example embodiment for selected positions in a velocity profile in a cascade of velocity profiles.

[0032] Figure 9 A graph showing an example ORG signal generated by a data processing apparatus according to an example embodiment of the present invention is shown.

[0033] Figure 10 Shows smooth Figure 9 The result of the ORG signal in .

[0034] Figure 11 is a flow chart illustrating an optional process that may be performed by the data processing apparatus 100 of the embodiments described herein.

[0035] Figure 12 is a flow chart illustrating a method by which an OCT image is processed to generate an indication of tissue velocity according to a second example embodiment herein. Detailed Description of Example Embodiments

[0036] A core part of the process of generating ORG data from a collection of repeated B-scans (or other OCT images) that have been acquired by an FD-OCT imaging system after application of light stimulation is processing each subset of the B-scans to generate a corresponding indication of tissue velocity at one or more locations along the axial direction in the B-scan. The inventors have recognized that some indications of tissue velocity calculated using conventional ORG processing techniques may be unreliable and adversely affect the ORG data or other final processed results. Furthermore, the inventors have devised a scheme for identifying source B-scans (or other OCT images) that produce such unreliable indications, and the scheme is used to prevent any unreliable indications of tissue velocity from entering the processing pipeline in order to improve the ORG data or other final processed results. Example embodiments will now be described in detail with reference to the accompanying drawings.

[0037] First exemplary embodiment

[0038] Figure 1is a schematic diagram of a data processing apparatus 100 according to a first exemplary embodiment. The data processing apparatus 100 is arranged to process complex OCT data generated by a Fourier domain OCT (FD-OCT) imaging system having phase resolution capability. More specifically, the data processing apparatus 100 is arranged to process each set of OCT images, including a first OCT image 10-1 and a second OCT image 10-2, in a series of OCT images 10 of a common portion of the retina of an eye 20 captured by a Fourier domain OCT imaging system 30, to generate a respective indication of tissue velocity v at one or more locations in the OCT images 10 along an axial direction z (i.e., a direction along which the elements of the component A-scan of the OCT image are arranged in any OCT image (e.g., a B-scan or a C-scan)).

[0039] As in the present example embodiment, the FD-OCT imaging system 30 may be a swept source OCT (SS-OCT) system. However, the FD-OCT imaging system 30 need not be provided in this form and may, for example, take the alternative form of spectral domain OCT (SD-OCT). More specifically, the example embodiments may be provided as any form of FD-OCT imaging system with phase resolution capability that is capable of generating complex OCT data, i.e., a Fourier transform of individual spectral interference patterns (interference spectra) representing complex A-scan information obtained for each scan position at which an OCT measurement is taken during a scan. Such complex OCT data encodes phase information from the acquired OCT measurements, which phase information may be used by the data processing apparatus 100 as described herein to calculate tissue velocity in a common portion of the retina.

[0040] The FD-OCT imaging system 30 may include well-known components, including a scanning system, a photodetector, OCT data processing hardware, and a beam generator (not shown). The scanning system may be arranged to perform one-dimensional and / or two-dimensional point scanning of a light beam across the retina and collect light that has been scattered by the retina during the point scanning. The scanning system is therefore arranged to acquire A-scans at various scanning locations distributed on the surface of the retina by sequentially illuminating the scanning locations with a light beam (one scanning location at a time) and collecting at least a portion of the light scattered by the retina at each scanning location. The scanning system may acquire OCT images in the form of repeated B-scans by performing point scanning using a linear scanning pattern, wherein a set of overlapping scan lines is followed during scanning. Although in this exemplary embodiment, the scanning system is arranged to acquire repeated B-scans by performing point scanning, in other exemplary embodiments, the scanning system may alternatively be arranged to acquire repeated B-scans by performing line scanning using hardware well known to those skilled in the art. The FD-OCT imaging system 30 may alternatively be arranged to acquire OCT images in the form of C-scans by performing point scanning or line scanning using techniques well known to those skilled in the art, or by employing a full-field setup.

[0041] like Figure 1 As shown, as in this exemplary embodiment, the first OCT image described above may be in the form of a first OCT B-scan 10-1, and the second OCT image may be in the form of a second OCT B-scan 10-2. However, the form of the first and second OCT images is not limited thereto, and, for example, the first and second OCT images may be corresponding OCT C-scans. As in this exemplary embodiment, the first B-scan 10-1 and the second B-scan 10-2 of a common portion of the retina may be adjacent to each other in one set of B-scans in a series of OCT B-scans 10, or they may be separated by n intermediate B-scans, where n is ≥ 1 but is sufficiently small so that the B-scans have a sufficiently high degree of phase correlation with each other due to the absence of significant relative movement of the eye 20 relative to the FD-OCT imaging system 30.

[0042] As described in more detail below, the data processing apparatus 100 is arranged to process at least a portion of the phase component of the first B-scan 10-1 and at least a portion of the phase component of the second B-scan 10-2 to calculate a velocity profile P comprising values ​​of the velocity v, the variations of which in the velocity profile as a function of position are indicative of the distribution of the velocity v among points along the axial direction z in a common portion of the retina, e.g. Figure 1. Thus, as in this example embodiment, the velocity profile P may be a two-dimensional data structure in which values ​​of velocity v are associated with corresponding values ​​of position. The velocity profile P may more generally be a two-dimensional data structure in which values ​​indicative of velocity v (e.g., calculated changes in phase or optical path length) are associated with corresponding values ​​of position. However, the data processing apparatus 100 is not required to calculate the velocity profile P and may be limited to calculating, for each set of B-scans in a plurality of sets of two or more B-scans, a corresponding indication of tissue velocity v at a single common position along the axial direction z.

[0043] The data processing device 100 may be provided in any suitable form, for example as Figure 2The programmable signal processing hardware 200 is provided as schematically shown in FIG. The programmable signal processing hardware 200 includes a communication interface (I / F) 210 for receiving a B-scan (or another form of OCT image, such as a C-scan) from the FD-OCT imaging system 30 and outputting a calculated indication of tissue velocity and / or a graphical representation thereof on a display (such as a computer screen). The signal processing hardware 200 also includes a processor 220 (e.g., a central processing unit (CPU) and / or a graphics processing unit (GPU), a working memory 230 (e.g., a random access memory), and an instruction storage device 240 storing a computer program 245. The computer program 245 includes computer-readable instructions that, when executed by the processor 220, cause the processor 220 to perform various functions of the data processing device 100 described herein. The working memory 230 stores information used by the processor 220 during execution of the computer program 245. The instruction storage device 240 may include a ROM (e.g., in the form of an electrically erasable programmable read-only memory (EEPROM) or flash memory) preloaded with computer-readable instructions. Alternatively, the instruction storage device 240 may include RAM or a similar type of memory, and the computer-readable instructions of the computer program 245 may be input to the instruction storage device 240 from a computer program product (e.g., a non-transitory computer-readable storage medium 250 in the form of a CD-ROM, DVDROM, or the like) or a computer-readable signal 260 carrying the computer-readable instructions. In any case, the computer program 245, when executed by the processor 220, causes the processor 220 to perform the functions of the data processing apparatus 100 described herein. Thus, the data processing apparatus 100 of the example embodiment may include a computer processor 220 and a memory 240 storing computer-readable instructions that, when executed by the processor 220, cause the processor 220 to process each set of OCT images in a plurality of different sets of OCT images in a series of OCT images 10 of a common portion of the retina of the eye 20 to generate a corresponding indication of tissue velocity v at a location in the OCT image 10 along the axial direction z (i.e., the direction along which the elements of the component A-scan of the OCT image are arranged in any OCT image (e.g., a B-scan or a C-scan)).

[0044] However, it should be noted that the data processing apparatus 100 may alternatively be implemented in non-programmable hardware (such as an ASIC, FPGA or other integrated circuit dedicated to performing the functions of the data processing apparatus 100 described herein), or in a combination of such non-programmable hardware and the above-referenced Figure 2 The system is implemented in a combination of programmable signal processing hardware 200 as described.

[0045] The data processing apparatus 100 may be provided as a standalone product or as part of a system 1000 comprising an FD-OCT imaging system 30 that is arranged to acquire a series of OCT images 10 of a common portion of the retina of the eye 20, typically before and after stimulation of the common portion by an optical stimulus 40 generated by a light source 45 (e.g., an LED). The data processing apparatus 100 is arranged to process at least a portion of a phase component of a first OCT image 10-1 and at least a portion of a phase component of a second OCT image 10-2 in the series of OCT images 10 acquired by the FD-OCT imaging system 30 using the techniques described herein.

[0046] Figure 3 is a flow chart showing a method by which the data processing apparatus 100 processes data from Figure 1 Each set of B-scans in a plurality of sets of B-scans in a series of B-scans 10 of a common portion of the retina shown (e.g., a pair of B-scans including a first B-scan 10-1 and a second B-scan 10-2) is used to generate a corresponding indication of tissue velocity v at a position along the axial direction z in the B-scan 10.

[0047] exist Figure 3 In process S10, the data processing device 100 calculates a comparison value based on a first OCT image (B-scan 10-1 in this example embodiment) and a second OCT image (B-scan 10-2 in this example embodiment). The comparison value may be a value of an image quality metric or attribute calculated based on at least one of the amplitude component of the first B-scan 10-1 and the amplitude component of the second B-scan 10-2. The image quality metric (attribute) may take the form of a dynamic range, contrast, signal-to-noise ratio, or sharpness function value derived from the B-scan. A measure of the success of intensity-based segmentation of the B-scan is another example of an image quality metric that may be used. Alternatively, the comparison value may be the value of an image similarity metric that provides a measure of the degree of similarity between the images, the image similarity metric being calculated based on the first B-scan 10-1 and the second B-scan 10-2. As in this example embodiment, the image similarity metric may take the form of the maximum value of the cross-correlation between the first B-scan 10-1 and the second B-scan 10-2. Other image similarity metrics that may be used alternatively include sum of squared differences, mutual information, normalized mutual information, and Kullback-Leibler distance.

[0048] The cross-correlation between two complex functions f(t) and g(t) of a real variable t is denoted as f*g and is defined as where * denotes convolution, and is the complex conjugate of f(t).

[0049] The maximum value of the cross-correlation between two B-scans is a good measure of how closely the B-scans are related to each other. For example, Figure 4A The two B-scans shown in FIG are highly correlated with each other, and the cross-correlation calculated between these B-scans has a value of approximately 3·10 4 The peak value, such as Figure 4B shown.

[0050] For comparison, Figure 5A Two dissimilar B-scans are shown. This dissimilarity could be caused by factors such as eye movement, for example, and would result in poor image registration. Figure 4A For the B-scan shown in Figure 5A For the example B-scans shown in FIG, the maximum value of the calculated cross-correlation between the B-scans is much lower and is approximately 1·10 4 ,like Figure 5B shown.

[0051] Reference again Figure 3 In process S20, the data processing device 100 calculates an indication of tissue velocity v at a position along the axial direction z using a phase value at a position along the axial direction in the A scan of the first OCT image (B scan 10-1) and a phase value at the same position along the axial direction z in a corresponding A scan of the second OCT image (B scan 10-2). The corresponding A scan of the B scan 10-2 has the same position along the x-axis of the B scan 10-2 as the position of the A scan considered in the B scan 10-1, along which the A scans of the B scan 10-2 are arranged. By Figure 3 S20 processes each set of B scans, and the data processing device 100 can calculate a corresponding indication of the tissue velocity v at a single common position along the axial direction z for each set of B scans, or as in the present example embodiment, calculate a corresponding velocity distribution map P indicating the distribution of the tissue velocity v within a common portion of the retina along the axial direction z for each set of B scans.

[0052] In more detail, Figure 3 In process S20, the data processing device 100 processes the phase component of the first B-scan 10-1 and the phase component of the second B-scan 10-2 to calculate a velocity profile P indicating the distribution of the velocity v in the common portion of the retina along the axial direction z. Thus, the data processing device 100 calculates the velocity profile P including, for example, values ​​of velocity v or values ​​of phase change or values ​​of optical path length change ΔOPL, which indicate the distribution of the velocity v of the retina (in the common portion) at corresponding points located on a line aligned with the axial direction as a function of position in the velocity profile P. The velocity profile P is thus a two-dimensional data structure in which the values ​​of the tissue velocity v (or the values ​​of a variable indicating the tissue velocity v, such as ΔOPL or phase change) are represented by the data. ) is associated with a corresponding value of the position, and the data structure can be used to store the velocity v (or or ΔOPL) can be visualized in the form of a graph, such as Figure 1 Schematically shown in FIG.

[0053] exist Figure 3 Before calculating the indication of tissue velocity v in process S20, the data processing device 100 can process the phase values ​​at the position along the axial direction z in the A scan of the first B scan 10-1 and the phase values ​​at the position along the axial direction z in the corresponding A scan of the second B scan 10-2 to compensate for the overall movement of the common part of the retina during the acquisition of a series of OCT images 10 by the Fourier domain OCT imaging system 30.

[0054] Figure 6A The overall oscillation of a sinusoidal waveform is shown added to the oscillatory movement of two model retinal layers. In this example, by adding the phase to model the overall motion, where Represents a fraction of a wavelength (in a two-way reflection, a half-wavelength shift is 2π). Figure 6A shows how the phase angle of light reflected from the first model retinal layer (layer 1) and the second model retinal layer (layer 2) varies with time while these layers undergo a common overall motion as well as their individual oscillations (i.e., Figure 6A Graphs labeled “Layer 1 + Whole” and “Layer 2 + Whole”). Figure 6A It also shows how the phase angle of light reflected from any model retinal layer changes with time while the layer is subjected only to bulk motion (i.e., Figure 6A ). Figure 6B Shown is the effect of removing global motion on the temporal variation of the phase angle of light reflected from two model retinal layers.

[0055] Used to generate Figure 6A and Figure 6B MATLAB plots in TM The code is as follows:

[0056] t=(0:1000);

[0057] A = 0.95;

[0058] B = 0.8;

[0059] RetinaBulkMovement=exp(j*cos(t*pi / sqrt(700)));

[0060] Layer1Movement=exp(j*cos(t*pi / sqrt(30)));

[0061] Layer2Movement=exp(j*cos(t*pi / sqrt(50)));

[0062] Layer1totalMovement=Layer1Movement.*RetinaBulkMovement;

[0063] Layer2totalMovement=Layer2Movement.*RetinaBulkMovement;

[0064] %%%%%%%%%%%%%%%%%

[0065] Layer1MovementDeduced=angle(Layer1totalMovement.*conj(RetinaBulkMovement));

[0066] Layer2MovementDeduced=angle(Layer2totalMovement.*conj(RetinaBulkMovement));

[0067] subplot(211);

[0068] plot(angle(Layer1totalMovement));hold

[0069] on;plot(angle(Layer2totalMovement));plot(angle(RetinaBulkMovement));legend('Layer1

[0070] +Bulk','Layer2+Bulk','Bulk');

[0071] xlim([300 400]);

[0072] subplot(212);

[0073] plot(Layer1MovementDeduced);hold on;plot(Layer2MovementDeduced);shg;hold off;

[0074] xlim([300 400]);

[0075] legend('Layer1','Layer2');

[0076] The data processing apparatus 100 may now be described as follows: Figure 3 An example of an S20 process, which is based on the velocity-based ORG technique described in Kari V. Vienola et al., “Velocity-based optoretinography for clinical applications,” Optica 9, pp. 1100-1108 (2022), the contents of which are incorporated herein by reference in their entirety.

[0077] As in this exemplary embodiment, the data processing device 100 may first flatten the first B-scan 10-1 and the second B-scan 10-2 so that the IS / OS and COST reflections are located at substantially the same height for each A-scan in each B-scan. The data processing device 100 may then register the second B-scan 10-2 relative to the first B-scan 10-1. The phase data of the two B-scans for each spatial coordinate pair (i.e., phase data at the same (x, z) coordinate in the B-scan) may then be unfolded in the time dimension to minimize the magnitude of the phase difference between the datasets of the two B-scans 10-1 and 10-2. After unfolding and processing the phase components of the first B-scan 10-1 and the second B-scan 10-2 to compensate for the overall motion of the retina during imaging, the difference between the corresponding phase values ​​in the B-scans 10-1 and 10-2 is calculated for each spatial location specified by the corresponding coordinate pair, and then the instantaneous velocity for that spatial location is calculated using the difference between the acquisition times of the B-scans. As in this example embodiment, these instantaneous velocities can be averaged in the lateral dimension (ie, along the x-axis) to give an instantaneous, depth-dependent measure of velocity along the z-axis, ie Figure 1 A one-dimensional velocity profile P of the type shown schematically in FIG1 indicates the distribution of velocity v in the axial direction (z-axis) within the common portion of the retina covered by the first B-scan 10-1 and the second B-scan 10-2. The B-scan amplitudes can also be averaged in the transverse dimension (x-axis) if desired to provide an instantaneous, depth-dependent measure of backscatter. It should be noted that averaging in the transverse dimension is not necessary, and a two-dimensional velocity profile can instead be generated that indicates the distribution of velocity v in both the axial direction (z-axis) and the transverse direction (x-axis) within the common portion of the retina covered by the first B-scan 10-1 and the second B-scan 10-2.

[0078] The tissue velocity v in a portion of the velocity profile P corresponding to the photoreceptors OS in the retina varies (usually monotonically) from a maximum velocity vmax Change to minimum speed v min , which corresponds in the velocity profile P to the first position z of the IS-OS junction at a given position on the retina max The minimum velocity corresponds to the second position z of COST at the given position on the retina in the velocity distribution map P. min Place, such as Figure 1 Schematically shown in FIG.

[0079] By following Figure 2 The velocity profile P calculated from the OCT images in each set of OCT images from the series of OCT images 10 (or in other example embodiments, an indication of tissue velocity v at a single common location along the axial direction z) of process S20 can be used for various purposes. For example, the velocity profiles (or the aforementioned indication of tissue velocity) can be cascaded, and the cumulative sum of the values ​​in the resulting cascade can be calculated to generate ORG data indicative of the response of the retina to an applied optical stimulus, as described below. Additionally or alternatively, the velocity profiles (or the aforementioned indication of tissue velocity) can be processed using the velocity-based segmentation method described in co-pending European application with reference number 253 989 to determine the position of one or both of the boundaries of the OS or other layers L of the retina that change in response to the applied optical stimulus (e.g., the position of the rod outer segment tip (ROST) or the retinal pigment epithelium (RPE)). For example, for z>z min , the velocity profile P can have a Figure 1 The data processing apparatus 100 in this example embodiment can be configured to generate a z-axis velocity distribution map P by first determining the candidate first position z in the velocity distribution map P. i and the candidate second position z in the velocity profile P j All combinations of (z i ,z j ) for each combination of the candidate first position and the candidate second position in the calculation of the combination (z i ,z j ) in the candidate first position z i The corresponding speed v i and candidate second position z j The corresponding velocity v j The difference between ij The corresponding value of the calculated velocity profile P determines the first position z of at least one of the calculated velocity profiles P. max and the second position z min Then, the data processing device 100 identifies the candidate first position z of the following combinations among the plurality of combinations: i and candidate second position zj As the first position z max and the second position z min : For this combination in multiple combinations, the calculated difference D ij The value of is the largest of the calculated differences.

[0080] Once the boundaries of the OS are identified as described above, their corresponding velocities can be extracted from the velocity profile P, and the difference between the extracted velocities provides the contraction / elongation of the OS when the B scans 10-1 and 10-2 are acquired by the FD-OCT imaging system 30, which can be used to generate ORG data indicating the response of the retina to the applied stimulus in the common portion.

[0081] Regardless of the purpose for which the velocity profile P or the aforementioned indication of tissue velocity is subsequently used, it is useful to measure their reliability and remove any unreliable velocity profiles (or unreliable indications of tissue velocity) from the processing pipeline to prevent these from adversely affecting the ORG data or other final results. The reliability of the velocity profile P or the aforementioned indication of tissue velocity will be affected by the image quality of the first B-scan 10-1 and the second B-scan 10-2, as well as the degree of correlation between the B-scans. The maximum value of the calculated cross-correlation between the two B-scans provides a good measure of the degree of correlation between the B-scans and, therefore, the reliability of the velocity profile P or the aforementioned indication of tissue velocity determined by the data processing device 100.

[0082] Reference again Figure 3 In process S30, the data processing device will Figure 3 The comparison value calculated in process S10 is compared with a threshold value to determine whether the comparison value is equal to or greater than the threshold value. In this exemplary embodiment, some pairs of B-scans produce comparison values ​​greater than or equal to the threshold value, and some other pairs of B-scans produce comparison values ​​less than the threshold value. Incidentally, please note that although Figure 3 The process S20 is shown and described herein as being performed after the process S10, but the order of execution of these processes may be reversed or they may be performed simultaneously. Alternatively, the process S20 may be performed simultaneously with the process S10. Figure 3 The process S30 in is executed simultaneously.

[0083] The value of the threshold in process S30 can depend on the subsequent use of the velocity profile P or the aforementioned tissue velocity indication and can be selected by trial and error so that retaining only the velocity profile P (or the aforementioned tissue velocity indication) associated with comparison values ​​that equal or exceed the selected threshold reduces or prevents degradation that would otherwise occur to the ORG data or other processing results.

[0084] For example, where one or more of the velocity profiles are used in the velocity-based segmentation technique described in co-pending European application with reference number 253 989, the threshold value may be set by comparing the segmentation result from the data processing apparatus 100 (i.e., the boundaries of the layer L determined by the data processing apparatus 100) with the layer segmentation from the user's review of the source B-scans, taking into account the maximum cross-correlation values ​​calculated for the source B-scans. In this way, it may be determined that, when the B-scans are processed by the data processing apparatus 100 as described herein, pairs of B-scans between which the maximum cross-correlation calculated is below a certain threshold value tend to produce unreliable values ​​for the indication of the layer boundary, whereas pairs of B-scans between which the maximum cross-correlation calculated is equal to or above the threshold value tend to produce reliable values ​​for the indication of the layer boundary.

[0085] For example, it can be found that Figure 4A The B-scans shown in yield layer boundary indications that compare favorably with manual segmentation of the OS performed by inspecting these B-scans, while Figure 5A The B-scans shown in produce significantly different layer boundary indications than the manual segmentation of OS performed by examining these B-scans. In this case, it may be appropriate to set the threshold to Figure 4B and Figure 5B The maximum values ​​of the cross-correlations shown (i.e., approximately 3·10 4 and 1.10 4 ), for example, about 1.4·10 4 The value of Figure 5B This is shown by the horizontal black line in . B-scans that produce maximum cross-correlation values ​​below this threshold can be considered not allowing reliable segmentation to be performed.

[0086] exist Figure 3 In the case where it is determined in process S30 that the comparison value is equal to or greater than the threshold value ( Figure 3 "Yes" at S40 in the data processing apparatus 100, the data processing apparatus 100 retains (stores) the data in Figure 3 The velocity profile P at the position along the axial direction z calculated in the process S20 or more generally retains (stores) an indication of the tissue velocity v.

[0087] On the other hand, Figure 3 In the case where it is determined in the process S30 that the comparison value is not equal to or greater than the threshold value, the data processing apparatus 100 discards the Figure 3 The velocity profile P at the position along the axial direction z calculated in process S20 or more generally the indication of the tissue velocity v is discarded and thus not used in subsequent processing operations. For example, the data processing device 100 may erase or overwrite the calculated indication (or velocity profile, as the case may be). Figure 3 In the case of calculating the velocity profile P in the process S20, as in the present exemplary embodiment, the data processing apparatus 100 may Figure 3 After the negative determination in S40, a zero velocity distribution map indicating zero velocity v at all positions along the axial direction z or, more generally, an indication of zero tissue velocity at positions along the axial direction is retained in the storage device (i.e., the memory) to replace the calculated velocity distribution map P (or, more generally, the calculated indication of tissue velocity at positions along the axial direction z) for subsequent use.

[0088] exist Figure 3 After the process S50, as in the present exemplary embodiment, the data processing apparatus 100 may Figure 3 The retained velocity profile P or more generally the retained tissue velocity indication calculated in process S20 is the same as that in Figure 3 Any zero velocity profiles (or, more generally, indications of zero tissue velocity) generated after a negative determination in S40 are concatenated together. The resulting concatenation indicates how the tissue velocity v varies with time.

[0089] Figure 7 An example of a cascade 300 of velocity profiles P generated by the data processing device 100 is shown. Each velocity profile P is along Figure 7 The y-axis in FIG. 1 (labeled “OCT depth layer”) extends along the y-axis, and the velocity profiles calculated for adjacent pairs of B-scans in the series of B-scans 10 are plotted along the y-axis. Figure 7 The x-axis (labeled as "Time (ms)") in the diagram is arranged. Figure 7 The optical path length change ΔOPL (which provides an indication of velocity v) is shown as a function of position in each velocity profile P derived from a B-scan acquired after application of the optical stimulus at time t=200 ms. The optical path length change ΔOPL is shown as a function of position (i.e., along the Figure 7 y-axis in FIG) varies from a minimum ΔOPL of approximately -300 (arbitrary units) to a maximum ΔOPL of approximately +250 (arbitrary units).

[0090] In this example embodiment, the data processing apparatus 100 may also integrate the respective portions of the velocity profile P in the concatenation of velocity profiles, which portions have the same position along the axial direction z, to generate ORG data indicating a temporal change in the optical path length at a position along the axial direction z. More generally, the data processing apparatus 100 may integrate the portions of the velocity profile P in the concatenation of velocity profiles to generate ORG data indicating a temporal change in the optical path length at a position along the axial direction z. Figure 3 The indication of the tissue velocity at the location is retained in the process S50 and in Figure 3The data processing apparatus 100 may integrate (i.e., calculate a cumulative sum or running total) any alternative indications of zero velocity that may have been generated after the negative determination in S40 to generate ORG data indicating how the optical path length at a position along the axial direction z changes over time. The data processing apparatus 100 may process each velocity profile P in the concatenated set of velocity profiles by selecting portions (segments or data elements) of the velocity profile P that are disposed at predetermined positions along the axial direction z of the velocity profile P, and then integrate the selected (co-located) portions by calculating a cumulative sum (or running total) of the velocity values ​​in these portions, the cumulative sum indicating how the optical path length of the optical path of the OCT sample beam that ends at a position in the retina corresponding to the predetermined position in the velocity profile P changes over time.

[0091] Figure 8 A graph of the optical path length versus time ΔOPL is shown, which has been calculated by the data processing device 100 for selected positions in the velocity profiles in the cascade of velocity profiles. Figure 8 The graph in shows how the ΔOPL at a common location varies from one B-scan to the next in a series of B-scans 10 .

[0092] Figure 9 A graph showing the cumulative change in optical path length over time is referred to as an ORG signal (or ORG data). The ORG signal is obtained by calculating the cumulative sum of the optical path length changes for selected positions in the velocity profiles in the cascade of velocity profiles. Figure 9 As shown, the ORG signal becomes negative shortly after the stimulus is applied, then increases to become positive, and finally levels off at a value of approximately 250 nm in this example. Figure 9 It is also shown that the ORG signal has several plateaus, which are caused by replacing the velocity profile calculated using the B-scan with a velocity profile indicating zero velocity (i.e., a zero velocity profile) as described above, which did not produce a sufficiently high maximum cross-correlation value.

[0093] Thus, the ORG data may include one or more sets of equal consecutive values, and the data processing apparatus 100 may be arranged to smooth the generated ORG data by replacing one or more values ​​in at least one of the one or more sets of equal consecutive values ​​with one or more estimated values, the one or more estimated values ​​being calculated based on adjacent values ​​adjacent to the set of equal consecutive values ​​in the ORG data. The data processing apparatus 100 may perform this smoothing by using a moving median or moving average, for example, where the median or average of a specified number of points on either side of a missing data point is calculated and then assigned to the missing point. Alternatively, the data processing apparatus 100 may, for example, detect each set of equal consecutive values ​​in the ORG data and replace the values ​​in each detected set with a corresponding estimated value obtained by (e.g., linearly) interpolating between a first value in the ORG data that is adjacent to the first of the equal consecutive values ​​in the detected set and a second value in the ORG data that is adjacent to the last of the equal consecutive values ​​in the detected set.

[0094] The result of smoothing the ORG signal using the moving average is as follows: Figure 10 Before smoothing is applied, most of the data show that the OPL variation is zero, as shown in Figure 9 , and therefore generally underestimate the actual values ​​that will be observed. Using the method described herein, equivalent values ​​are replaced with estimated values ​​(e.g. Figure 10 ), which more accurately represents the changes in OPL.

[0095] Optional further processing that may be performed by the data processing apparatus 100 of this example embodiment is described in Figure 11 In summary.

[0096] exist Figure 11 In process S70 , the data processing apparatus 100 generates a cascade 300 of the generated indications of the tissue velocity v, such that the cascade 300 indicates how the tissue velocity v at a position along the axial direction z varies over time.

[0097] exist Figure 11 In the process S80 , the data processing device 100 integrates the cascade 300 to generate data indicating a change in the optical path length at a position along the axial direction z over time.

[0098] exist Figure 3 Process S40 (or the second exemplary embodiment described below) Figure 12In the case where it is determined in process S130 in , that the comparison value is not equal to or greater than the threshold value, as in the present example embodiment, the corresponding indication of the tissue velocity v at the position along the axial direction z can be set to indicate zero velocity, and the generated data can include one or more sets of equal continuous values, as described above.

[0099] exist Figure 11 In process S90, the data processing device 100 smoothes the generated data by replacing one or more values ​​in one or more sets of equal continuous values ​​in the generated data with one or more estimated values, which are calculated based on adjacent values ​​adjacent to the set of equal continuous values.

[0100] Although the data processing apparatus 100 processes adjacent pairs of B-scans in a series of B-scans 10 (i.e., one pair of B-scans in the series is adjacent to another pair of B-scans) sequentially to generate a velocity profile P, or more generally, an indication of tissue velocity at a position along the axial direction z, the data processing apparatus 100 may alternatively generate these by processing adjacent pairs of B-scans in parallel, thereby significantly speeding up processing. Furthermore, while processing pairs of B-scans that are adjacent to each other in a series of B-scans 10 (i.e., consecutive B-scans in the series), the data processing apparatus 100 may alternatively process pairs of B-scans in the series where, for example, the B-scans of each pair are separated from each other by one or more intermediate B-scans.

[0101] Furthermore, although the data processing apparatus 100 of this example embodiment has been described as processing pairs of B-scans, it may more generally be configured to process sets of more than two B-scans in a series of B-scans 10, which may be consecutive B-scans in the series or individual B-scans in the series separated from each other by one or more intermediate B-scans that do not form part of the set. A respective set of (e.g., five) B-scans may be selected by sliding a window selection function along the series of B-scans 10, wherein Figure 3 In each implementation of the process, the window selection function selects, for example, all B-scans in a windowed portion of a series of B-scans 10 or every other B-scan in a windowed portion, and the selected set may have one or more B-scans in common.

[0102] exist Figure 3 In a modified form of the process S10 in FIG. 1 , the data processing apparatus 100 calculates a comparison value for one of a plurality of different sets of consecutive B-scans in the series of B-scans 10. The comparison value may take any of the different forms described above. The data processing apparatus 100 then calculates the comparison value based on Figure 3A modified form of process S20 processes the phase components of at least some of the B-scans in the set to generate a velocity profile P indicative of a distribution, or more generally of tissue velocity v at locations along the axial direction z. Here, the data processing apparatus 100 may first flatten the B-scans of the set so that for each A-scan in each B-scan, the IS / OS and COST reflections are located at substantially the same height. The data processing apparatus 100 may then register the B-scans relative to each other. The phase data cube θ(x, z, t) is then generated by flattening the B-scans at θ(x, z, t). p , z q , t r ) by adding or subtracting 2π to minimize |θ(x p , z q , t r )-θ(x p , z q , t r-1 )| to expand in the time dimension, where t r and t r-1 represents a continuous phase B scan. For each spatial coordinate pair (x p ,z q ) performs this step. The phase change rate for each coordinate pair is calculated by performing a least squares linear fit with respect to t, given The unit is rad / s. Therefore, the instantaneous velocity of each spatial location can be calculated as where λ is the wavelength of the OCT light used, and n is the nominal refractive index of the eye 20. These instantaneous velocities can be averaged in the lateral dimension (i.e., along the x-axis) to give an instantaneous, depth-dependent measure of velocity along the z-axis, i.e. Figure 1 A one-dimensional velocity profile P of the type shown schematically in FIG is indicative of the distribution of velocities v in the axial direction (z-axis) within the common portion of the retina covered by the repeated B-scans. The B-scan amplitudes may also be averaged over the transverse dimension (x-axis) if desired to give an instantaneous, depth-dependent measure of backscatter. It should be noted that averaging over the transverse dimension is not necessary and a two-dimensional velocity profile may instead be generated indicating the distribution of velocities v in both the axial direction (z-axis) and the transverse direction (x-axis) within the common portion of the retina covered by the repeated B-scans. The process is then based on Figure 3 S30 or S60.

[0103] Second exemplary embodiment

[0104] In the first example embodiment described above, a respective indication of tissue velocity at one or more positions along the axial direction z is calculated for each of a plurality of sets of B-scans in the series of B-scans 10, and each calculated indication is retained or discarded depending on the result of comparing the associated comparison value with a threshold value. However, in the present example embodiment, the calculation of the indication of tissue velocity v is selectively performed (i.e., not necessarily for each set of B-scans) depending on the result of comparing the comparison value calculated for the set of OCT images with the threshold value, as will now be described with reference to FIG. Figure 12 Described in more detail.

[0105] Figure 12 is a flow chart showing a method by which the data processing apparatus 100 of this exemplary embodiment processes data from Figure 1 Each set of B-scans in a plurality of sets of B-scans in a series of B-scans 10 of a common portion of the retina shown (e.g., a pair of B-scans including a first B-scan 10-1 and a second B-scan 10-2) is used to generate a corresponding indication of tissue velocity v at a position along the axial direction z in the B-scan 10.

[0106] Figure 12 The processes S110 to S130 are respectively the same as those described in detail above. Figure 3 The processes S10, S30 and S40 are the same.

[0107] In the case where the data processing apparatus 100 determines that the comparison value is equal to or greater than the threshold value (in Figure 12 In S130, the answer is "Yes". Figure 12 In process S140, in calculating the corresponding indication of the tissue velocity v at the position along the axial direction z, the data processing device 100 uses the phase value of the OCT data element at the position along the axial direction z in the A scan of the first B scan 10-1 in the set and the phase value at the same position along the axial direction z in the corresponding A scan of the second B scan 10-2 in the set.

[0108] In the case where the data processing apparatus 100 determines that the comparison value is not equal to or greater than the threshold value (in Figure 12 In S130, the answer is "No". Figure 12 In the process S150, in calculating the corresponding indication of the tissue velocity v at the position along the axial direction z, the data processing device 100 ignores the phase value at the position along the axial direction z in the A scan of the first B scan 10-1 in the set and the phase value at the same position along the axial direction z in the corresponding A scan of the second B scan 10-2 in the set. Figure 12Following the negative determination in S130 , the data processing apparatus 100 may generate a zero velocity profile indicating zero velocity v at all positions along the axial direction z, or more generally, an indication of zero tissue velocity at positions along the axial direction.

[0109] Similar to the first exemplary embodiment, the data processing device 100 can then process the calculated velocity profile P or more generally the velocity profile already in Figure 12 The calculated indication of the tissue velocity calculated in process S140 is the same as that in Figure 12 Any zero velocity profiles (or, more generally, indications of zero tissue velocity) generated after a negative determination in S130 are concatenated together. The resulting concatenation indicates how the tissue velocity v varies with time.

[0110] In this example embodiment, the data processing apparatus 100 may further integrate corresponding portions of the velocity profile P in the concatenation of velocity profiles, the portions having the same position along the axial direction z (or, more generally, the portions already in the concatenation of velocity profiles) to generate ORG data indicating temporal changes in the optical path length at positions along the axial direction z. Figure 12 The tissue velocity indication calculated in process S140 and in Figure 12 The data processing apparatus 100 may process each velocity profile P in the concatenated set of velocity profiles by selecting portions (segments or data elements) of the velocity profile P that are disposed at predetermined positions along the axial direction z of the velocity profile P, and then integrating the selected (co-located) portions by calculating a cumulative sum (or cumulative total) of the velocity values ​​in the portions, the cumulative sum indicating how the optical path length of the optical path of the OCT sample beam that ends at the position in the retina corresponding to the predetermined position in the velocity profile P changes over time.

[0111] Thus, the ORG data may include one or more sets of equal consecutive values, and the data processing apparatus 100 may be arranged to smooth the generated ORG data by replacing one or more values ​​in at least one of the one or more sets of equal consecutive values ​​with one or more estimated values ​​calculated based on neighboring values ​​adjacent to the set of equal consecutive values ​​in the ORG data. The data processing apparatus 100 may perform this smoothing by using a moving median or moving average, for example, where the median or average of a specified number of points on either side of a missing data point is calculated and then assigned to the missing point. Alternatively, the data processing apparatus 100 may, for example, detect each set of equal consecutive values ​​in the ORG data and replace the values ​​in each detected set with corresponding estimated values ​​obtained by (e.g., linearly) interpolating between a first value in the ORG data that is adjacent to the first of the equal consecutive values ​​in the detected set and a second value in the ORG data that is adjacent to the last of the equal consecutive values ​​in the detected set.

[0112] It will be appreciated that at least some modifications of the first exemplary embodiment described above may also be made to this exemplary embodiment.

[0113] In the foregoing description, example aspects have been described with reference to several example embodiments. Therefore, the description should be regarded as illustrative rather than restrictive. Similarly, the figures shown in the accompanying drawings, which highlight the features and advantages of the example embodiments, are presented for illustrative purposes only. The architecture of the example embodiments is sufficiently flexible and configurable that it can be utilized in ways other than those shown in the accompanying drawings.

[0114] In one example embodiment, some aspects of the examples given herein, such as reference Figure 3 、 Figure 11 and Figure 12The processing methods described herein may be provided as a computer program or software, such as one or more programs having instructions or instruction sequences, contained in or stored on an article of manufacture, such as a machine-accessible or machine-readable medium, instruction storage, or computer-readable storage device, each of which may be non-transitory. The program or instructions on the non-transitory machine-accessible medium, machine-readable medium, instruction storage, or computer-readable storage device may be used to program a computer system or other electronic device. Machine-readable or computer-readable media, instruction storage, and storage devices may include, but are not limited to, floppy disks, optical disks, magneto-optical disks, or other types of media / machine-readable media / instruction storage / storage devices suitable for storing or transmitting electronic instructions. The techniques described herein are not limited to any particular software configuration. They may be employed in any computing or processing environment. As used herein, the terms "computer-readable," "machine-accessible medium," "machine-readable medium," "instruction storage," and "computer-readable storage device" shall include any medium capable of storing, encoding, or transmitting instructions or instruction sequences for execution by a machine, computer, or computer processor, and causing the machine / computer / computer processor to perform any of the methods described herein. Furthermore, it is common in the art to refer to software in one form or another (e.g., program, procedure, process, application, module, unit, logic, etc.) as taking an action or causing a result. Such expressions are merely a shorthand way of stating that execution of the software by a processing system causes the processor to perform an action to produce a result.

[0115] Some or all of the functionality of the OCT data processing hardware 130 may also be implemented by preparing application specific integrated circuits, field programmable gate arrays, or by interconnecting an appropriate network of conventional component circuits.

[0116] The computer program product may be provided in the form of one or more storage media, instruction storage means, or storage devices having stored thereon or therein instructions that can be used to control or cause a computer or computer processor to perform any of the processes of the example embodiments described herein. The storage media / instruction storage means / storage devices may include, by way of example and without limitation, optical disks, ROM, RAM, EPROM, EEPROM, DRAM, VRAM, flash memory, flash memory cards, magnetic cards, optical cards, nanosystems, molecular memory integrated circuits, RAID, remote data storage / archiving / warehousing devices, and / or any other type of device suitable for storing instructions and / or data.

[0117] For storage on any one of one or more computer-readable media, instruction storage devices, or storage devices, some embodiments include hardware for controlling the system and software for enabling the system or microprocessor to utilize the results of the example embodiments described herein to interact with a human user or other mechanism. Such software may include, without limitation, device drivers, operating systems, and user applications. Ultimately, as described above, such computer-readable media or storage devices also include software for performing example aspects of the present invention.

[0118] Software modules for implementing the processes described herein are included in the system's programming and / or software. In some example embodiments herein, the modules include software, but in other example embodiments herein, the modules include hardware or a combination of hardware and software.

[0119] Although various exemplary embodiments of the present invention have been described above, it should be understood that they have been presented by way of example and not limitation. It will be apparent to those skilled in the relevant art that various changes in form and detail may be made. Therefore, the present invention should not be limited by any of the above exemplary embodiments, but should be defined only in accordance with the appended claims and their equivalents.

[0120] Although this specification contains many specific embodiment details, these should not be understood as limitations on the scope of any invention or what may be claimed, but rather as descriptions of features specific to the particular embodiments described herein. Certain features described in this specification in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented in multiple embodiments individually or in any suitable subcombination. Furthermore, although features may be described above as acting in a particular combination and even initially claimed as such, one or more features from the claimed combination may in some cases be deleted from the combination, and the claimed combination may be directed to subcombinations or variations of subcombinations.

[0121] In some cases, multitasking and parallel processing may be advantageous. In addition, the separation of the various components in the above embodiments should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products.

[0122] Now that some illustrative embodiments and implementations have been described, it will be apparent that the foregoing embodiments are illustrative rather than restrictive and have been presented by way of example. In particular, although many of the examples presented herein involve specific combinations of devices or software elements, these elements can be combined in other ways to achieve the same objectives. Actions, elements, and features discussed in connection with only one embodiment are not intended to be excluded from similar roles in that embodiment or other embodiments.

Claims

1. A computer-implemented method for processing each set of OCT images, including a first OCT image (10-1) and a second OCT image (10-2), in a series of OCT images (10) of a common portion of a retina of an eye (20) acquired by a Fourier domain optical coherence tomography (OCT) imaging system (30) to generate a respective indication of tissue velocity (v) at a position along an axial direction (z) in the OCT images (10), the method comprising performing, for each of the sets of OCT images: Calculate (S10) a corresponding comparison value as one of the following: a value of an image quality metric, the value of the image quality metric being calculated based on at least one of the first OCT image (10-1) in the set and the second OCT image (10-2) in the set; and a value of an image similarity metric, the image similarity metric providing a measure of the degree of similarity between images, the value of the image similarity metric being calculated based on the first OCT image (10-1) in the set and the second OCT image (10-2) in the set; calculating (S20) a respective indication of tissue velocity (v) at the position along the axial direction (z) using a phase value at the position along the axial direction (z) in an A-scan of the first OCT image (10-1) in the set and a phase value at the position along the axial direction (z) in a corresponding A-scan of the second OCT image (10-2) in the set; comparing the comparison value with a threshold value (S30) to determine whether the comparison value is equal to or greater than the threshold value; retaining ( S50 ) a corresponding indication of the tissue velocity (v) at the position along the axial direction (z) in case the comparison value is determined to be equal to or greater than the threshold value; and In case it is determined that the comparison value is not equal to or greater than the threshold value, the corresponding indication of the tissue velocity (v) at the position along the axial direction (z) is discarded (S60).

2. A computer-implemented method for processing each set of OCT images, including a first OCT image (10-1) and a second OCT image (10-2), in a series of OCT images (10) of a common portion of a retina of an eye (20) acquired by a Fourier domain optical coherence tomography (OCT) imaging system (30) to generate a respective indication of tissue velocity (v) at a position along an axial direction (z) in the OCT images (10), the method comprising performing, for each of the sets of OCT images: A corresponding comparison value is calculated (S110) as one of: a value of an image quality metric, the value of the image quality metric being calculated based on at least one of the first OCT image (10-1) in the set and the second OCT image (10-2) in the set; and a value of an image similarity metric, the image similarity metric providing a measure of the degree of similarity between images, the value of the image similarity metric being calculated based on the first OCT image (10-1) in the set and the second OCT image (10-2) in the set; comparing the comparison value with a threshold value ( S120 ) to determine whether the comparison value is equal to or greater than the threshold value; In case it is determined that the comparison value is equal to or greater than the threshold value, using (S140) a phase value at the position along the axial direction (z) in an A-scan of the first OCT image (10-1) in the set and a phase value at the position along the axial direction (z) in a corresponding A-scan of the second OCT image (10-2) in the set in calculating a corresponding indication of tissue velocity (v) at the position along the axial direction (z); and In the event that it is determined that the comparison value is not equal to or greater than the threshold value, in the calculation of the corresponding indication of the tissue velocity (v) at the position along the axial direction (z), the phase value at the position along the axial direction (z) in the A scan of the first OCT image (10-1) in the set and the phase value at the position along the axial direction (z) in the corresponding A scan of the second OCT image (10-2) in the set are ignored (S150).

3. The computer-implemented method of claim 1 or claim 2, wherein: The comparison value is a maximum value of the calculated cross-correlations between the first OCT image (10-1) and the second OCT image (10-2).

4. The computer-implemented method according to any one of claims 1 to 3, further comprising: generating (S70) a cascade (300) of the generated indications of tissue velocity (v), such that the cascade (300) indicates how the tissue velocity (v) at a position along the axial direction (z) varies with time; and The cascade (300) is integrated (S80) to generate data indicative of optical path length at a position along the axial direction (z) as a function of time.

5. The computer-implemented method of claim 4, wherein: in an event that the comparison value is determined not to be equal to or greater than the threshold value, setting the corresponding indication of tissue velocity (v) at the position along the axial direction (z) to indicate zero velocity, The generated data includes one or more sets of equal consecutive values, and The method also includes smoothing (S90) the generated data by replacing one or more values ​​in one of one or more sets of equal consecutive values ​​in the generated data with one or more estimated values, wherein the one or more estimated values ​​are calculated based on adjacent values ​​adjacent to the set of equal consecutive values.

6. A computer-implemented method according to any preceding claim, further comprising processing, prior to calculating the corresponding indication of tissue velocity (v) at the position along the axial direction (z), phase values ​​at the position along the axial direction (z) in the A-scan of the first OCT image (10-1) in the set and phase values ​​at the position along the axial direction (z) in the corresponding A-scan of the second OCT image (10-2) in the set to compensate for overall motion of the common portion of the retina during acquisition of the series of OCT images (10) by the Fourier domain OCT imaging system (30).

7. A computer program (245) comprising computer readable instructions which, when executed by a processor (220), cause the processor (220) to perform the method according to any one of claims 1 to 6.

8. A data processing apparatus (100) arranged to process each set of OCT images, including a first OCT image (10-1) and a second OCT image (10-2), in a series of OCT images (10) of a common portion of a retina of an eye (20) acquired by a Fourier domain optical coherence tomography (OCT) imaging system (30) to generate a respective indication of tissue velocity (v) at a position along an axial direction (z) in the OCT images (10), the data processing apparatus (100) being arranged to perform the following process for each of the sets of OCT images: Computes the corresponding comparison value as one of the following: a value of an image quality metric, the value of the image quality metric being calculated based on at least one of the first OCT image (10-1) in the set and the second OCT image (10-2) in the set; and a value of an image similarity metric, the image similarity metric providing a measure of the degree of similarity between images, the value of the image similarity metric being calculated based on the first OCT image (10-1) in the set and the second OCT image (10-2) in the set; calculating a respective indication of tissue velocity (v) at a location along the axial direction (z) using a phase value at a location along the axial direction (z) in an A-scan of the first OCT image (10-1) in the set and a phase value at a location along the axial direction (z) in a corresponding A-scan of the second OCT image (10-2) in the set; comparing the comparison value with a threshold value to determine whether the comparison value is equal to or greater than the threshold value; retaining a corresponding indication of a tissue velocity (v) at the location along the axial direction (z) in an event that the comparison value is determined to be equal to or greater than the threshold value; and In case it is determined that the comparison value is not equal to or greater than the threshold value, the corresponding indication of tissue velocity (v) at the position along the axial direction (z) is discarded.

9. A data processing apparatus (100) arranged to process each set of OCT images, comprising a first OCT image (10-1) and a second OCT image (10-2), in a series of OCT images (10) of a common portion of a retina of an eye (20) acquired by a Fourier domain optical coherence tomography (OCT) imaging system (30) to generate a respective indication of tissue velocity (v) at a position along an axial direction (z) in the OCT images (10), the data processing apparatus (100) being arranged to perform the following process for each of the sets of OCT images: Computes the corresponding comparison value as one of the following: a value of an image quality metric, the value of the image quality metric being calculated based on at least one of the first OCT image (10-1) in the set and the second OCT image (10-2) in the set; and a value of an image similarity metric, the image similarity metric providing a measure of the degree of similarity between images, the value of the image similarity metric being calculated based on the first OCT image (10-1) in the set and the second OCT image (10-2) in the set; comparing the comparison value with a threshold value to determine whether the comparison value is equal to or greater than the threshold value; upon determining that the comparison value is equal to or greater than the threshold, using, in calculation of a corresponding indication of tissue velocity (v) at the location along the axial direction (z), a phase value at the location along the axial direction (z) in an A-scan of the first OCT image (10-1) in the set and a phase value at the location along the axial direction (z) in a corresponding A-scan of the second OCT image (10-2) in the set; and In the event that it is determined that the comparison value is not equal to or greater than the threshold value, in the calculation of the corresponding indication of tissue velocity (v) at the position along the axial direction (z), the phase value at the position along the axial direction (z) in the A scan of the first OCT image (10-1) in the set and the phase value at the position along the axial direction (z) in the corresponding A scan of the second OCT image (10-2) in the set are ignored.

10. The data processing device (100) according to claim 8 or claim 9, wherein: The comparison value is a maximum value of the calculated cross-correlations between the first OCT image (10-1) and the second OCT image (10-2).

11. The data processing device (100) according to any one of claims 8 to 10, wherein: The data processing device (100) is further arranged to: generating a cascade (300) of generated indications of tissue velocity (v) such that the cascade (300) indicates how the tissue velocity (v) at a position along the axial direction (z) varies with time; and The cascade (300) is integrated to generate data indicative of optical path length at a position along the axial direction as a function of time.

12. The data processing device (100) according to claim 11, wherein: In case it is determined that the comparison value is not equal to or greater than the threshold value, the data processing device (100) is arranged to set the corresponding indication of the tissue velocity (v) at the position along the axial direction (z) to indicate zero velocity, The generated data includes one or more sets of equal consecutive values, and The data processing apparatus (100) is further arranged to smooth the generated data by replacing one or more values ​​in one of one or more sets of equal consecutive values ​​in the generated data with one or more estimated values, the one or more estimated values ​​being calculated based on adjacent values ​​adjacent to the set of equal consecutive values.

13. The data processing (100) according to any one of claims 8 to 12, wherein: The data processing device (100) is also arranged to process the phase values ​​at the position along the axial direction (z) in the A-scan of the first OCT image (10-1) in the set and the phase values ​​at the position along the axial direction (z) in the corresponding A-scan of the second OCT image (10-2) in the set before calculating the corresponding indication of the tissue velocity (v) at the position along the axial direction (z) to compensate for the overall movement of the common part of the retina during the acquisition of the series of OCT images (10) by the Fourier domain OCT imaging system (30).

14. A Fourier domain optical coherence tomography imaging system (30), comprising a data processing device (100) according to any one of claims 8 to 13.

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