An OCT imaging method and device based on Airy light sheet line scanning

Abstract

The present invention discloses an OCT imaging method and system based on Airy light sheet line scanning. The method includes: splitting the light emitted by a light source into a first light ray and a second light ray; based on the azimuthal phase diagram of a spatial light modulator or a phase mask, and based on a first beam splitter, a high-speed galvanometer, and a first objective lens, performing phase modulation and Fourier transform on the first light ray to generate an Airy light sheet; based on the Airy light sheet, obtaining object light reflected by a first reflection optical path including a sample to be measured; based on the second light ray and a reflector, obtaining a sheet-shaped reference light reflected by a second reflection optical path including the reflector; and based on the object light and the sheet-shaped reference light, obtaining an image of the sample to be measured. The present invention can use a low-cost LED light source, modulate incident light with a spatial light modulator or a phase mask to generate an Airy light sheet, improve the focal depth and penetration depth of the incident light, increase the signal acquisition speed, and achieve high-cost-performance OCT three-dimensional fast tomographic imaging.

Description

Technical Field

[0001] This specification relates to the field of OCT imaging technology, and in particular to an OCT imaging method and system based on Airy light sheet line scanning. Background Art

[0002] Optical Coherence Tomography (OCT) is a new imaging technology developed on the basis of the interference principle of low-coherence light and combined with computer image processing technology. In 1991, Huang et al. first successfully obtained the fine structure of the human eye retina and the structure of the coronary artery wall using OCT technology. With the continuous development of technology and the in-depth application, further improving the imaging depth has become a research trend of OCT. Due to the self-recovery characteristic of non-diffracting light, Airy light can effectively suppress scattering and improve the signal-to-noise ratio and imaging depth of the image if it is used for OCT tomography imaging under the condition of scattering media. Some scholars have proposed spectral domain OCT based on Airy light illumination. This system uses a superluminescent diode SLD (or SLED) as the light source, and uses the main lobe of Airy light as the scanning beam to generate the corresponding A-Scan image, which improves the imaging depth on the basis of making full use of the characteristics of non-diffracting light. However, the SLD light source used in this system is relatively expensive, and since the illumination light selects the main lobe of Airy light rather than the entire light sheet, the scanning method is the same as that of traditional spectral domain OCT, which is line-by-line (A-line) scanning rather than parallel scanning.

[0003] Traditional OCT systems mostly use Gaussian convergent beams to perform point scanning or line scanning on the sample tissue to construct three-dimensional images. However, the focal depth of the Gaussian beam in the focusing area is limited. Especially in the case of using an objective lens with a high numerical aperture, the short focal depth will significantly reduce the imaging resolution in the defocused area. At this time, it is necessary to longitudinally scan the sample on the sample arm along the optical axis to obtain a three-dimensional tomographic image with stable resolution at all depths. In addition, when the Gaussian beam propagates in a scattering tissue filled with tiny particles, its effective penetration depth is restricted by the light wave diffraction effect. Summary of the Invention

[0004] The purpose of the embodiments of this specification is to provide an OCT imaging method and system based on Airy light sheet line scanning. In the present invention, a phase-type spatial light modulator (SLM) or a high-precision phase mask is used as the phase modulation surface. At this input surface, the incident light field is phase-modulated to generate an Airy light sheet (expanded in the horizontal direction), and under the action of an electrically controlled pitching and deflecting stage (or diffraction of the phase grating on the phase-type spatial light modulator SLM), the Airy light sheet is scanned along the direction perpendicular to the desktop to achieve three-dimensional scanning tomography of time-domain OCT. It can not only achieve fast parallel scanning imaging, but also utilize the characteristics of the Airy light sheet such as non-diffraction and self-recovery to suppress scattering while increasing the depth of focus and signal-to-noise ratio of the OCT imaging system.

[0005] To achieve the above object, on the one hand, the embodiments of this specification provide an OCT imaging method based on Airy light sheet line scanning, including:

[0006] Dividing the light emitted by the light source into a first light ray and a second light ray;

[0007] Based on the vertical phase diagram of the spatial light modulator or the phase mask, and based on the first beam splitter, the high-speed galvanometer, and the first objective lens, performing phase modulation and Fourier transform on the first light ray to generate an Airy light sheet;

[0008] Based on the Airy light sheet, obtaining the object light reflected by the first reflection optical path including the sample to be measured;

[0009] Based on the second light ray and the mirror, obtaining the sheet-shaped reference light reflected by the second reflection optical path including the mirror;

[0010] Based on the object light and the sheet-shaped reference light, recording the double-beam interference signal and obtaining the image of the sample to be measured.

[0011] On the other hand, the embodiments of this specification also provide an OCT imaging system based on Airy light sheet line scanning, including:

[0012] A light source and a light source light beam splitter, which are respectively used for emitting light source light rays and dividing the light source light rays into a first light ray and a second light ray;

[0013] An Airy light sheet generation optical path, including a spatial light modulator or a phase mask, a first beam splitter, a high-speed galvanometer, and a first objective lens sequentially arranged along the propagation direction of the first light ray, for generating an Airy light sheet;

[0014] An object light acquisition optical path, for acquiring the object light reflected by the first reflection optical path including the sample to be measured;

[0015] A sheet-shaped reference light acquisition optical path for acquiring a sheet-shaped reference light that is generated based on the second light beam and a reflecting mirror and is reflected by a second reflection optical path including the reflecting mirror;

[0016] A device for acquiring an image of a sample to be measured, configured to record a double-beam interference signal based on the object light and the sheet-shaped reference light, and acquire an image of the sample to be measured.

[0017] As can be seen from the technical solutions provided in the embodiments of this specification above, the present invention can use a low-cost LED light source, modulate incident light with a spatial light modulator or a phase mask plate to generate an Airy light sheet, improve the depth of focus and penetration depth of the incident light; improve the signal acquisition speed, and achieve high-cost-performance OCT three-dimensional fast tomographic imaging. Description of the Drawings

[0018] Figure 1 It is a flowchart of an OCT imaging method based on Airy light sheet line scanning according to some embodiments of this specification.

[0019] Figure 2 It is a design diagram of an OCT imaging system based on Airy light sheet line scanning according to some embodiments of this specification.

[0020] Figure 3 It is a light intensity distribution diagram of an Airy light sheet according to some embodiments of this specification.

[0021] Figure 4 It is a double-beam interference diagram of an imaging system according to some embodiments of this specification.

[0022] Figure 5 It is a composite phase distribution diagram according to some embodiments of this specification.

[0023] Figure 6 It is a scanning interference diagram under the action of a blazed grating according to some embodiments of this specification.

[0024] Figure 7 It is a four-step phase-shift interference experimental diagram according to some embodiments of this specification.

[0025] Figure 8 It is the phase and amplitude distribution of the object light extracted by the four-step phase-shift technique according to some embodiments of this specification. Detailed Embodiments

[0026] To enable those skilled in the art to better understand the technical solutions in this specification, the following will clearly and completely describe the technical solutions in the embodiments of this specification in conjunction with the accompanying drawings in the embodiments of this specification. Obviously, the described embodiments are only a part of the embodiments of this specification, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in this specification without creative efforts shall fall within the scope of protection of this specification.

[0027] As Figure 1 shown, in some embodiments of this specification, an OCT imaging method based on Airy light sheet line scanning is provided, and the method includes the following steps:

[0028] S102. Divide the light emitted by the light source into a first light beam and a second light beam; based on the azimuthal phase diagram of the spatial light modulator or the phase mask plate, and based on the first beam splitter, the high-speed galvanometer, and the first objective lens, perform phase modulation and Fourier transform on the first light beam to generate an Airy light sheet;

[0029] S104. Based on the Airy light sheet, obtain the object light reflected by the first reflection optical path including the sample to be measured;

[0030] S106. Based on the second light beam and the mirror, obtain the sheet-like reference light reflected by the second reflection optical path including the mirror;

[0031] S108. Based on the object light and the sheet-like reference light, record the double-beam interference signal and obtain the image of the sample to be measured.

[0032] In some embodiments of this specification, based on the azimuthal phase diagram of the spatial light modulator or the phase mask plate, and based on the first beam splitter, the high-speed galvanometer, and the first objective lens, perform phase modulation and Fourier transform on the first light beam to generate an Airy light sheet. Specifically, it includes performing transverse scanning and longitudinal scanning on the sample to be measured based on the angle control of the high-speed galvanometer and / or the first beam splitter and the movement control of the sample to be measured.

[0033] In some embodiments of this specification, based on the azimuthal phase diagram of the spatial light modulator or the phase mask plate, and based on the first beam splitter, the high-speed galvanometer, and the first objective lens, perform phase modulation and Fourier transform on the first light beam to generate an Airy light sheet. Specifically, it further includes scanning the sample to be measured based on the phase-type blazed grating with different grating periods loaded on the spatial light modulator or the phase mask plate.

[0034] In some embodiments of this specification, based on the azimuthal phase diagram of a spatial light modulator or a phase mask, and based on a first beam splitter, a high-speed galvanometer, and a first objective lens, phase modulation and Fourier transform are performed on the first light ray to generate an Airy light sheet. Specifically, it further includes obtaining, based on the camera photosensitive surface, the object light reflected by the sample to be measured, which first passes through the first objective lens and the high-speed galvanometer, then passes through the first beam splitter, then is converged by the first lens, and finally is reflected by the second beam splitter and enters the camera photosensitive surface.

[0035] In some embodiments of this specification, a quasi-4f imaging system is constituted based on the sample to be measured, the first objective lens, the first lens, and the camera photosensitive surface.

[0036] In some embodiments of this specification, based on the second light ray and a mirror, a sheet-like reference light reflected by a second reflection optical path including the mirror is obtained. Specifically, it includes collimating the second light ray based on a second lens, and then obtaining, based on a third beam splitter, a second objective lens, the mirror, a plane mirror, and a cylindrical lens, the sheet-like reference light reflected by the mirror.

[0037] In some embodiments of this specification, based on the third beam splitter, the second objective lens, the mirror, the plane mirror, and the cylindrical lens, the sheet-like reference light reflected by the mirror is obtained. Specifically, the scattered second light ray is focused on the mirror after passing through the third beam splitter and the second objective lens, and then the sheet-like reference light reflected by the mirror, which first passes through the second objective lens, the third beam splitter, and the plane mirror in sequence, then passes through the cylindrical lens, the second beam splitter, and the slit of a one-dimensional camera, is obtained.

[0038] In some embodiments of this specification, based on the second light ray and the mirror, the sheet-like reference light reflected by the second reflection optical path including the mirror is obtained. Specifically, based on the control of the position movement of the reference mirror platform including the second objective lens and the mirror along the optical axis, the interference image is captured after the phase of the reference light is changed.

[0039] In some embodiments of this specification, the phase of the reference light is changed by λ / 4 each time. When the phase of the reference light is changed three times, the corresponding interference images are recorded, and based on the interference images, the corresponding phase and amplitude of the object light are obtained.

[0040] In some embodiments of this specification, before the step of splitting the light emitted by the light source into the first light ray and the second light ray, it further includes collimating the light emitted by the light source. Specifically, the light emitted by the light source is collimated based on a single-mode optical fiber, or the light emitted by the light source passes through a first aspherical lens, a ground glass, and a second aspherical lens arranged at a preset distance in sequence, and the ground glass is set on the focal plane of the first aspherical lens and the second aspherical lens.

[0041] In some embodiments of the present specification, the light source further includes an Airy laser, or a femtosecond laser, or a supercontinuum light source, or a swept-frequency laser.

[0042] Some embodiments of the present specification also provide an OCT imaging system based on Airy light sheet line scanning, the system includes:

[0043] A light source and a light source beam splitter, which are respectively used for emitting light source rays and splitting the light source rays into a first ray and a second ray;

[0044] An Airy light sheet generation optical path, including a spatial light modulator or a phase mask plate, a first beam splitter, a high-speed galvanometer, and a first objective lens arranged in sequence along the propagation direction of the first ray, for generating an Airy light sheet;

[0045] An object light acquisition optical path, for acquiring the object light reflected by the first reflection optical path including the sample to be measured;

[0046] A sheet-like reference light acquisition optical path, for acquiring the sheet-like reference light based on the second ray and a reflector and reflected by the second reflection optical path including the reflector;

[0047] A device for acquiring an image of the sample to be measured, for recording a double-beam interference signal based on the object light and the sheet-like reference light, and acquiring an image of the sample to be measured.

[0048] In some embodiments of the present specification, the Airy light sheet generation optical path further includes a first collimating lens and a first plane mirror arranged upstream of the spatial light modulator or the phase mask plate along the propagation direction of the first ray, the first collimating lens is used for collimating the first ray, and the first plane mirror is used for reflecting the collimated first ray.

[0049] In some embodiments of the present specification, the first reflection optical path includes, in sequence along the propagation direction of light, the sample to be measured, the first objective lens, the first high-speed galvanometer, the first beam splitter, the second beam splitter, the first lens, and the camera. The sample to be measured, the first objective lens, the first lens, and the camera photosensitive surface form a quasi-4f imaging system. The first lens is used for converging light, and the camera is used for receiving the object light.

[0050] In some embodiments of the present specification, the sheet-like reference light acquisition optical path includes a second lens, a third beam splitter, a second objective lens, and a second reflection optical path arranged along the propagation direction of the second ray. The second lens is used for collimating the second ray;

[0051] In some embodiments of the present specification, the second reflection optical path includes, in sequence along the propagation direction of the reflected light, a reflector, the second objective lens, the third beam splitter, the second plane mirror, the cylindrical lens, the second beam splitter, and the camera.

[0052] In some embodiments of this specification, the OCT imaging system based on Airy light sheet line scanning further includes a control system for controlling the angles of the high-speed galvanometer and / or the first beam splitter, controlling the movement of the sample to be measured, performing transverse scanning and longitudinal scanning on the sample to be measured, and controlling the position movement of the reference mirror platform of the second objective lens and the mirror along the optical axis.

[0053] In some embodiments of this specification, phase-type blazed gratings with different grating periods are loaded on the spatial light modulator or the phase mask plate.

[0054] In some embodiments of this specification, the light source includes a near-infrared LED light source with spatial incoherence.

[0055] In some embodiments of this specification, the OCT imaging system based on Airy light sheet line scanning further includes an LED light source collimation device. The LED light source collimation device includes a single-mode optical fiber or a collimation optical path. The collimation optical path includes a first aspherical lens, a ground glass, and a second aspherical lens. The ground glass is located between the first aspherical lens and the second aspherical lens and is disposed on the focal planes of the first aspherical lens and the second aspherical lens.

[0056] The following specifically explains the corresponding design methods and systems in combination with Figure 2 the design drawings in.

[0057] The system of the present invention can use a near-infrared LED (or femtosecond laser, supercontinuum light source, swept laser) as the illumination light source. The light emitted by the light source passes through a single-mode polarization-maintaining optical fiber and an optical fiber beam splitter and is divided into a reference light and an object light. The reference light becomes collimated light through a lens, and after passing through a beam splitter and an objective lens, it is focused on a flat mirror. The reflected light first passes through the objective lens, the beam splitter, and the flat mirror, then passes through a cylindrical lens to become a sheet light, and finally passes through the slit of a one-dimensional camera to become a sheet reference light. The object light is first collimated through a lens, modulated by a cubic phase pattern on a phase plate or a spatial light modulator after passing through a flat mirror, then enters the objective lens through a beam splitter and a high-speed galvanometer, and a one-dimensional linear array Airy light sheet is generated at the focal plane of the objective lens. The object light reflected from the sample first passes through the objective lens and the galvanometer, then passes through the beam splitter and is converged by a lens, and finally is reflected by the beam splitter and enters the camera photosensitive surface. In the reflection optical path in the object light arm, the sample layer, the objective lens, the lens, and the camera photosensitive surface can be regarded as a quasi-4f imaging system. In addition, to obtain an OCT three-dimensional tomographic image, the high-speed galvanometer and the sample translation stage can be automatically controlled by a computer to achieve transverse scanning and longitudinal scanning of the sample.

[0058] Since the signal acquisition methods of the OCT system are divided into time domain and frequency domain (which can be further divided into spectral domain and swept frequency), this solution takes into account the needs of both systems. If a low-coherence light source such as near-infrared LED or femtosecond laser, supercontinuum light source (the latter two are more expensive) is used, it means that the system is a time domain system. At this time, the phase shift method (such as the four-step phase shift method) or the optical delay line method is required to realize the extraction of the complex amplitude of the object light; in the phase shift method, the reflector on the reference arm (or object light arm) needs to be precisely stepped and displaced. By recording several interference patterns corresponding to the step displacement position and performing post-processing calculations, the complex amplitude information of the time domain coherence layer can be extracted. If a swept frequency light source (more expensive) is used, the swept frequency interference signal needs to be analyzed by Fourier analysis to extract the layered information. In principle, the sample does not need to be scanned longitudinally at this time.

[0059] Compared with point scanning confocal, line scanning imaging is faster, the optical path structure is relatively simple, and the cost is lower. The lateral resolution of the imaging system is the same as the thickness of the Airy light sheet, and is directly related to the wavelength of the light source and the numerical aperture of the objective lens used, which is about 10 microns. The longitudinal resolution of the system is the same as that of traditional OCT, which depends on the coherence length of the LED light source (determined by the central wavelength and spectral width), which is about 10-20 microns. The imaging frame rate of the system (with the B scan two-dimensional image of traditional OCT as a reference) depends on the camera sensitivity and the longitudinal scanning rate of the object light arm. The imaging field size depends on the length of the Airy light sheet stretched and the distance range of the line scan. Compared with lasers, light-emitting diode (LED) light sources are cheaper. With the advancement of LED technology, high-power, high-brightness LED light sources can replace laser light sources to a certain extent, thereby reducing system costs. Based on the non-diffraction Airy light sheet as the light source, a low-cost, high-penetration depth OCT system was constructed.

[0060] The detailed description of the method for generating the Airy light sheet is as follows:

[0061] Airy light is a non-diffracting beam. Compared with traditional Gaussian beams, non-diffracting light has the characteristics of self-bending, self-recovery, and long depth of focus. It can maintain a stable ballistic trajectory over a long transmission distance and can thus be used as an illumination source for biological scattering tissues. The work of combining Airy light with an imaging system began with light-sheet fluorescence microscopy. In light-sheet fluorescence microscopy, the illumination direction and the detection direction are at 90 degrees. A two-dimensional light sheet with a long depth of focus is used to illuminate the focal plane of the detection lens, and then the fluorescence signal of the focal plane is detected by the detection lens in a wide-field manner. Due to its fast three-dimensional imaging ability, low phototoxicity (only illuminating the plane of interest), and high contrast, light-sheet fluorescence microscopy is very suitable for application scenarios in tumor biology and neuroscience. Compared with traditional Gaussian-beam-based fluorescence microscopes, light-sheet fluorescence microscopy can obtain higher resolution within a larger field of view, while under the illumination conditions of traditional light sources, these two often restrict each other and are difficult to achieve both at the same time.

[0062] Ideal Airy light is a beam with non-diffracting characteristics. Different from traditional beams, it can maintain a basically unchanged light intensity distribution over a long propagation range. Compared with other diffracting beams, Airy light also has the characteristics of self-bending and self-recovery (when encountering obstacles). If it is used for internal imaging of scattering media, it can effectively suppress scattering and improve the signal-to-noise ratio of the image.

[0063] To achieve light-sheet line scanning, the present invention first needs to modulate the quasi-Gaussian beam emitted by the LED into an Airy beam. There are many methods to generate an Airy beam, which can be generated by a liquid crystal spatial light modulator, a second-order nonlinear photonic crystal, a surface plasmon generated by a liquid crystal cell with a binary phase diagram electrode, or directly generated by an Airy laser, and no special limitation is made here. Generating an Airy light sheet based on a spatial light modulator has the advantages of low energy consumption, easy control, high resolution, fast response speed, etc. By loading the calculated phase distribution map onto the spatial light modulator, when the LED light source irradiates and is reflected by the spatial light modulator, after the Fourier transform of the objective lens, the outgoing light is modulated into an Airy light sheet.

[0064] After the Airy beam is generated, it illuminates the sample in the form of a linear light sheet. To achieve three-dimensional imaging, in addition to using an electronically controlled deflection stage to control the pitch angle of the beam splitter to achieve the line scanning of the light sheet, different grating period phase-type blazed gratings can also be loaded onto the spatial light modulator based on a cubic phase diagram to synthesize a composite phase distribution film. The blazed grating can diffract the modulated Airy light to different diffraction angles, and thus the deflection control of the Airy light sheet can also be achieved. In addition, the scanning of the light sheet can also be achieved by using a motor to control the pitch of the beam splitter.

[0065] Airy light can be generated by a coherent light source through phase modulation (the cubic phase diagram loaded onto the spatial light modulator or the phase mask) and the Fourier transform of a lens.

[0066] Its light intensity distribution pattern consists of a main lobe with a relatively large intensity and multiple side lobes with relatively small intensities, as Figure 2 shown. When the Airy beam is used for dynamic scanning of a sample, its main lobe can form a sheet-like light under the action of a high-speed galvanometer scanner, which is also called an Airy beam light sheet.

[0067] Compared with the light sheet formed by a common Gaussian beam (scanned by a galvanometer scanner), when illuminating a sample with an Airy beam light sheet, the light intensity distribution across the beam cross-section remains unchanged (i.e., the spot size remains constant) over a long propagation distance. This enables the imaging system based on the Airy beam light sheet to maintain the best resolution axially. Due to the long depth of focus, the irradiance peak of the Airy beam light sheet can be set very low, so that it can penetrate deeper samples while reducing the photobleaching effect, and generate high-quality three-dimensional images on the basis of high acquisition rate, high resolution, and low phototoxicity. Because of the low phototoxicity, the system can set a longer exposure time to detect the sample, making in vivo fluorescence imaging possible. In contrast, if other technical solutions (such as a laser scanning confocal microscope or a traditional fluorescence microscope) are adopted, an overly long exposure time will lead to high phototoxicity, which will seriously damage the sample. In addition, the field of view of the Airy beam light sheet microscope not only increases significantly, but also does not lose the high resolution of the Gaussian beam.

[0068] Compared with the Bessel beam, which is also a non-diffracting beam, the ratio of the main lobe power to the total power of the Airy beam can reach more than 50%, while the corresponding power ratio of the Bessel beam is only about 20%. This makes the Airy beam have a higher signal-to-noise ratio when used for light sheet scanning imaging. The Bessel beam can produce a finer light sheet, but without using two-photon excitation, the transverse annular side lobe structure of the Bessel beam will generate background fluorescence, thus reducing the axial resolution. In contrast, the annular structure around the Airy beam lobe is not obvious, and the beam lobe can pass through the sample field in a uniform and thin form, ensuring the optical uniformity (isotropy) of the imaging quality, even approaching the diffraction limit. However, because the ballistic trajectory of the Airy beam itself is curved, this will cause obvious distortion in the obtained microscopic image. On the other hand, precisely because the Airy beam is transmitted in the form of a ballistic rather than a beam, it can avoid the defocus blur effect of the Gaussian beam, thereby increasing the imaging field of view. In addition, introducing a high-efficiency algorithm to perform deconvolution on the distorted image can obtain a uniform image across the entire field of view.

[0069] Regarding the acquisition of the reference light, the detailed description is as follows:

[0070] The acquisition of the reference light mainly relies on the four-step phase-shifting method, which is a phase interference measurement method that combines optical interference technology and digital phase-shifting technology. Its measurement principle is as follows: by gradually changing the phase of the reference light, four interference fringes are obtained on the CCD / CMOS camera, and the four interference fringes are respectively processed by a computer to generate the corresponding complex amplitude distribution. Then, the complex amplitude distribution is processed by Fresnel transform or Fourier transform in the computer, and the image can be reconstructed.

[0071] The reconstructed image can not only extract the amplitude and phase of the object light, but more importantly, for a low-coherence interference system, this method can remove the background signal of the incoherent layer and achieve tomographic imaging of time-domain OCT. Based on the need of four-step phase-shifting, in the reference optical path, a stepping motor is used to accurately move the reference mirror platform (including the objective lens) along the optical axis position, so that the phase of the reference light changes 3 times. An interference pattern is taken at each position, and a total of four interference images are obtained.

[0072] Let and be the complex amplitudes of the plane reference light wave and the object light wave respectively, x and y are the pixel positions in the CMOS camera, and are the initial phases of the reference light and the object light respectively, A R is the amplitude of the reference light. Generally, the reference light is a parallel light, so A R can be considered a constant, and A is the amplitude of the object light. If the phase of the reference light is used as the independent variable, the interference light intensity on the two-dimensional camera is:

[0073]

[0074] By stepwise changing the phase of the reference light, the corresponding interference intensity patterns are recorded on the camera respectively. Let the initial phase of the reference light After calculation, the phase and amplitude formulas are as follows:

[0075] The phase of the object light is:

[0076]

[0077] The amplitude of the object light is:

[0078]

[0079] For a one-dimensional linear array camera, y = 0 can be taken. Each time the stepping motor changes the distance by λ / 8, the corresponding phase changes by λ / 4. When the phase is changed three times, that is, one four-step phase shift is completed, the corresponding interference images are recorded in the camera. The four interference images are calculated by the computer through the above algorithm, and the corresponding phase and amplitude of the object light can be obtained, that is, the extraction of the OCT complex amplitude is completed.

[0080] Regarding the collimation design of the LED light source, the detailed description is as follows:

[0081] Since the selected LED light source is a divergent light source, in order to make it have the coherence like a laser, it is necessary to collimate the light source first. Generally, if a point light source is exactly at the focus of an ordinary plano-convex lens, after passing through the plano-convex lens, a collimated (parallel) light beam can be obtained on the other side. However, each point on the LED light-emitting surface can be regarded as a point light source, which is equivalent to a surface light source. In the direction perpendicular to the light propagation direction, point light sources at different positions pass through the plano-convex lens. Although each beam of light is a parallel light, the beam synthesized by multiple light-emitting points must be divergent. At this time, it is very difficult to change it into collimated light with an ordinary plano-convex lens. Two methods can be adopted. One is the single-mode fiber transmission method, directly obtaining the single-mode output light that has been coupled well from the manufacturer. The advantage of this method is that the acquisition of the single-mode output light is simple and direct, and the disadvantage is that the coupling efficiency of the LED light in the fiber is relatively low, which will reduce the utilization rate of the system light energy. In addition, a pair of aspherical lenses can also be used to make the emitted light of the LED become approximately collimated light. Placing a ground glass at the focal plane position can effectively remove the grid structure of the LED light source itself, making the emitted light beam uniform and its cross-sectional intensity approximately Gaussian distribution.

[0082] Combined Figures 3 to 8 with respect to the experimental and verification effects of some embodiments of the solution of the present invention, the detailed description is as follows:

[0083] For the generation of an Airy light sheet, after setting up the system in the laboratory, a cubic phase diagram is loaded on the spatial light modulator. The incident light will be diffracted and laterally expanded in two directions after phase modulation. By introducing a diaphragm between the SLM and the objective lens of the object light arm to block one of the diffracted components in one direction, an Airy light sheet can be obtained on the focal plane of the objective lens, as Figure 3 shown. As can be seen from Figure 3 , the spatial light modulator generates a one-dimensional Airy light sheet on the focal plane of the objective lens after diffraction by loading a cubic phase diagram. By repeatedly loading cubic phase diagrams with different parameters (such as fringe spacing, modulation depth, etc.) for testing, a relatively ideal parameter range can be found.

[0084] For the optical path adjustment and interference experiment of the imaging system, before generating the Airy light sheet, it is necessary to debug the optical path of the LED low-coherence interference system to make it interfere. In order to better observe the fringes in the interference phenomenon, first temporarily remove the line array camera in the optical path system and replace it with an ordinary two-dimensional camera. At the same time, remove the cylindrical lens in the reference arm and the imaging lens in front of the camera of the object light arm. By controlling the movement of the electric translation stage of the sample arm through software, the reflector of the sample arm can be driven to move back and forth. When the optical path difference between the sample arm and the reference arm reaches the coherence length, interference fringes can be observed on the photosensitive surface of the two-dimensional camera at this time, as Figure 4As shown, it can be seen that the fringe contrast of the Airy interference pattern is clear, indicating that the optical path difference between the object light and the reference light is small enough, proving that the interference system based on low-coherence LED light source illumination can produce classical interference fringes.

[0085] Regarding the scanning experiment of the composite phase diagram, for the spatial light modulator, when a phase grating with different parameters (grating constant, phase modulation depth, etc.) is superimposed on the cubic phase diagram, a synthesized composite phase distribution diagram can be obtained. Based on this composite phase diagram, the scanning of the Airy light sheet can be realized. The combined results of multiple scanning images constitute a complete scan of the Airy light sheet. To test the scanning effect, based on the above-mentioned double-beam interference experiment, a partial composite phase distribution diagram was loaded on the spatial light modulator, as Figure 5 shown, and the corresponding interference experiment intensity distribution diagram is as Figure 5 shown. The scanning interference pattern under the action of the grating is as Figure 6 shown. Figure 5 In it, a to d are the composite phase distribution diagrams with grating constants of 0.064, 0.048, 0.032, and 0.016 respectively, e is the cubic phase diagram at the center position without the grating for scanning loaded, and f to i are the composite phase distribution diagrams with grating constants of 0.016, 0.032, 0.048, and 0.064 respectively. Figure 6 In it, (a)-(i) are the interference patterns corresponding to the composite phase diagrams loaded on the spatial light modulator Figure 6 in (a)-(i) respectively. As can be seen from Figure 6 , the object light modulated by the spatial light modulator is diffracted to different diffraction angles under the action of different gratings. Reflected in the interference pattern, it is a series of interference light fields that gradually intersect, coincide, and then separate.

[0086] Regarding the verification experiment of the four-step phase shifting technique, the detailed explanation is as follows:

[0087] To experimentally verify the effect of extracting the complex amplitude of the light field by the four-step phase shifting of this system, based on the above-mentioned experiment, the concave mirror was replaced with a plane mirror, and the plane mirror was used instead of the scattering medium as the sample, and four interference patterns were obtained as Figure 7 shown. Figure 7 The four diagrams in it are the interference patterns with an optical path difference of 1 / 4λ (202.5μm) collected by the camera. Due to the reflection characteristics of the optical path, each time the platform where the reference mirror is located is moved a distance of 1 / 8λ (101.25μm), and after three consecutive movements, the four-step phase shift is completed. The above-mentioned interference fringes are the equal-thickness interference fringes obtained after slightly tilting the plane mirror of the object light arm. Using MATLAB to calculate the four interference patterns through the formula, the phase and amplitude diagrams corresponding to the object light can be extracted, as Figure 8 shown. Figure 8Among them, (a) is the phase distribution diagram, and (b) is the amplitude distribution diagram. From the experimental results in the above figure, it can be seen that the (wrapped) phase distribution extracted by calculation in Figure (a) is relatively clear and can effectively reflect the gradient phase distribution brought by the subtle angle (due to the angle between the object light and the reference light) to the object light. The reason why there are still fringe structures in the object light amplitude extracted by calculation in Figure (b) is, on the one hand, due to mirror errors and measurement errors; on the other hand, it is also because considering the display needs, the image is gray-normalized in the later image processing, and after normalization, the originally unobvious fringe structures are displayed with a greater contrast. Since a plane mirror is tested on the object light arm in this experiment, if it is replaced with a real biological sample, the fringe structures brought by such mirror and measurement errors will not be obvious. In summary, through experimental verification, using the four-step phase-shifting technique in this system can effectively extract the amplitude and phase of the object light in the interference layer.

[0088] In summary, this system uses a near-infrared LED light as the light source and uses the method of line scanning with an Airy light sheet to obtain OCT tomographic images. Using an LED as the illumination light source can effectively eliminate the speckle interference brought by the laser imaging method while reducing the cost. The incident light is modulated into a non-diffracting Airy light sheet by a spatial light modulator or a phase template, which can effectively increase the penetration depth of the incident light and the imaging depth in the scattering sample. Compared with the traditional time-domain point-scanning OCT system, the signal acquisition method of line array scanning and line array parallelism introduced by the light sheet illumination can effectively improve the efficiency and speed of signal acquisition. In addition, compared with the time-domain full-field illumination OCT system, the one-dimensional slit retained in the light sheet illumination design of the present invention can play a role in filtering and denoising in a confocal system and can effectively improve the signal-to-noise ratio of the imaging system.

[0089] Although the process flow described above includes multiple operations that appear in a specific order, it should be clearly understood that these processes can include more or fewer operations, and these operations can be executed sequentially or in parallel (for example, using a parallel processor or a multi-threaded environment). The present invention is described with reference to the flowcharts and / or block diagrams of methods according to embodiments of the present invention.

[0090] It should also be noted that the term "comprising", "including" or any other variant thereof is intended to cover a non-exclusive inclusion, so that a process, method or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the existence of another identical element in the process, method or device comprising the element.

[0091] Each embodiment in this specification is described in a progressive manner. For the same or similar parts among the embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments. In particular, for method embodiments, since they are basically similar to apparatus embodiments, the description is relatively simple, and for the relevant parts, reference can be made to the corresponding parts in the apparatus embodiments. The above is only the embodiments of this specification and is not intended to limit this specification. For those skilled in the art, various modifications and changes can be made to this specification. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this specification shall be included within the scope of the claims of this specification.

Claims

1. An OCT imaging method based on Airy light sheet line scanning, characterized in that, The method includes: Dividing the light emitted by a light source into a first light beam and a second light beam; Based on the azimuthal phase diagram of a spatial light modulator or a phase mask, and based on a first beam splitter, a high-speed galvanometer, and a first objective lens, performing phase modulation and Fourier transform on the first light beam to generate an Airy light sheet; Based on the Airy light sheet, obtaining an object light reflected by a first reflection optical path including a sample to be measured; Based on the second light beam and a reflector, obtaining a sheet-shaped reference light reflected by a second reflection optical path including the reflector; Based on the object light and the sheet-shaped reference light, recording a double-beam interference signal and obtaining an image of the sample to be measured; The step of, based on the azimuthal phase diagram of a spatial light modulator or a phase mask, and based on a first beam splitter, a high-speed galvanometer, and a first objective lens, performing phase modulation and Fourier transform on the first light beam to generate an Airy light sheet, specifically further includes: Based on the camera photosensitive surface, obtaining the object light reflected by the sample to be measured, which first passes through the first objective lens and the high-speed galvanometer, then passes through the first beam splitter, and then is converged by a first lens and finally is reflected by a second beam splitter and enters the camera photosensitive surface; Based on the sample to be measured, the first objective lens, the first lens, and the camera photosensitive surface, constituting a quasi-4f imaging system; The step of, based on the second light beam and a reflector, obtaining a sheet-shaped reference light reflected by a second reflection optical path including the reflector, specifically includes: Collimating the second light beam by a second lens, and then based on a third beam splitter, a second objective lens, a reflector, a plane mirror, and a cylindrical lens, obtaining the sheet-shaped reference light reflected by the reflector; The step of, based on the third beam splitter, the second objective lens, the reflector, the plane mirror, and the cylindrical lens, obtaining the sheet-shaped reference light reflected by the reflector, specifically is: Focusing the scattered second light beam onto the reflector through the third beam splitter and the second objective lens, and then obtaining the sheet-shaped reference light reflected by the reflector, which first sequentially passes through the second objective lens, the third beam splitter, and the plane mirror, and then passes through the cylindrical lens, the second beam splitter, and the slit of a one-dimensional camera; 2. The OCT imaging method based on Airy light sheet line scanning according to claim 1, characterized in that, The step of, based on the azimuthal phase diagram of a spatial light modulator or a phase mask, and based on a first beam splitter, a high-speed galvanometer, and a first objective lens, performing phase modulation and Fourier transform on the first light beam to generate an Airy light sheet, specifically includes: Based on the angle control of the high-speed galvanometer and / or the first beam splitter and the movement control of the sample to be measured, performing transverse scanning and longitudinal scanning on the sample to be measured; 3. The OCT imaging method based on Airy light sheet line scanning according to claim 1, characterized in that, The step of, based on the azimuthal phase diagram of a spatial light modulator or a phase mask, and based on a first beam splitter, a high-speed galvanometer, and a first objective lens, performing phase modulation and Fourier transform on the first light beam to generate an Airy light sheet, specifically further includes: Based on a phase-type blazed grating with different grating periods loaded on the spatial light modulator or the phase mask, scanning the sample to be measured; 4. The OCT imaging method based on Airy light sheet line scanning according to claim 1, characterized in that, The step of, based on the second light beam and a reflector, obtaining a sheet-shaped reference light reflected by a second reflection optical path including the reflector, specifically is: Based on the control of the position movement of the reference mirror platform including the second objective lens and the mirror along the optical axis, the phase of the reference light is changed and the corresponding interference image is captured.

5. The OCT imaging method based on Airy light sheet line scanning according to claim 4, characterized in that, Each time the phase of the reference light is changed, when the phase of the reference light is changed three times, the corresponding interference image is recorded. Based on the interference image, the phase and amplitude of the object light are obtained.

6. The OCT imaging method based on Airy light sheet line scanning according to claim 1, characterized in that, The light source includes a near-infrared LED light source with spatial incoherence. Based on the phase modulation and the Fourier transform, the quasi-Gaussian beam emitted by the LED light source is modulated into an Airy beam.

7. The OCT imaging method based on Airy light sheet line scanning according to claim 1, characterized in that, Before the step of splitting the light emitted by the light source into a first light beam and a second light beam, it further includes: Collimating the light emitted by the light source. Specifically, collimating the light emitted by the light source based on a single-mode optical fiber, or making the light emitted by the light source sequentially pass through a first aspherical lens, a ground glass, and a second aspherical lens arranged at a preset spacing, and setting the ground glass at the focal plane of the first aspherical lens and the second aspherical lens.

8. The OCT imaging method based on Airy light sheet line scanning according to claim 1, characterized in that, The light source further includes an Airy laser or a femtosecond laser or a supercontinuum light source or a swept-frequency laser.

9. An OCT imaging system based on Airy light sheet line scanning, characterized in that, It includes: A light source and a light source beam splitter, which are respectively used for emitting light source light and splitting the light source light into a first light beam and a second light beam; An Airy beam generation optical path, including a spatial light modulator or a phase mask plate, a first beam splitter, a high-speed galvanometer, and a first objective lens sequentially arranged along the propagation direction of the first light beam, for generating an Airy beam; An object light acquisition optical path, for acquiring the object light reflected by the first reflection optical path including the sample to be measured; A sheet-shaped reference light acquisition optical path, for acquiring the sheet-shaped reference light generated based on the second light beam and the mirror and reflected by the second reflection optical path including the mirror; A sample to be measured image acquisition device, for recording a double-beam interference signal based on the object light and the sheet-shaped reference light and acquiring an image of the sample to be measured; The Airy beam generation optical path further includes a first collimating lens and a first plane mirror arranged upstream of the spatial light modulator or the phase mask plate along the propagation direction of the first light beam. The first collimating lens is used for collimating the first light beam, and the first plane mirror is used for reflecting the collimated first light beam; The first reflection optical path includes, in sequence along the propagation direction of light, the sample to be measured, the first objective lens, the high-speed galvanometer, the first beam splitter, the second beam splitter, the first lens, and the camera. The sample to be measured, the first objective lens, the first lens, and the camera photosensitive surface form a quasi-4f imaging system. The first lens is used for converging light, and the camera is used for receiving the object light; The sheet-shaped reference light acquisition optical path includes a second lens, a third beam splitter, and a second objective lens arranged along the propagation direction of the second light beam and the second reflection optical path. The second lens is used for collimating the second light beam; The second reflection optical path includes, in sequence along the propagation direction of the reflected light, a mirror, a second objective lens, a third beam splitter, a second plane mirror, a cylindrical lens, the second beam splitter, and the camera.

10. The OCT imaging system based on Airy light sheet line scanning according to claim 9, wherein, It further includes: A control system for controlling the angles of the high-speed galvanometer and / or the first beam splitter and for controlling the movement of the sample to be measured, for performing lateral scanning and longitudinal scanning on the sample to be measured, and for controlling the position movement of the reference mirror platform of the second objective lens and the mirror along the optical axis.

11. The OCT imaging system based on Airy light sheet line scanning according to claim 9, wherein, Phase-type blazed gratings with different grating periods loaded on the spatial light modulator or the phase mask.

12. The OCT imaging system based on Airy light sheet line scanning according to claim 9, wherein, The light source includes a near-infrared LED light source with spatial incoherence.

13. The OCT imaging system based on Airy light sheet line scanning according to claim 9, wherein, It further includes: An LED light source collimation device; The LED light source collimation device includes a single-mode optical fiber or a collimation optical path, and the collimation optical path includes a first aspherical lens, a ground glass, and a second aspherical lens. The ground glass is located between the first aspherical lens and the second aspherical lens and is disposed on the focal planes of the first aspherical lens and the second aspherical lens.

Images