Image processing apparatus, optical tomographic imaging apparatus including the same, and computer program

Abstract

To provide a technique for efficiently specifying optical axes of birefringence in various directions in a measuring object.SOLUTION: An image processing device includes an acquisition unit that acquires a plurality of tomographic images indicating polarization characteristics of a measurement object in cross sections at different positions of the measurement object, and a calculation unit that generates an image indicating a direction of an optical axis of birefringence using the plurality of tomographic images. The calculation unit specifies a shape of a portion included in the measurement object, and corrects a direction of an optical axis of birefringence of each pixel in each tomographic image so as to follow the specified shape.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to an image processing device, an optical tomographic imaging apparatus including the image processing device, and a computer program, and more particularly to a technology for processing a tomographic image of a measurement object (e.g., an eye to be examined). [Background technology]

[0002] Optical tomography is non-invasive and non-contact, and is therefore widely used in ophthalmologic devices and other devices as a method for obtaining tomographic images of biological tissues. Optical tomography measures the intensity distribution of backscattered light resolved in the depth direction. In recent years, polarization-sensitive optical tomography, a type of multifunctional optical tomography, has been developed. Polarization-sensitive optical tomography measures the intensity distribution of backscattered light resolved in the depth direction and is also capable of making measurements using the polarization characteristics of living organisms. Birefringence is an example of the polarization characteristics of living organisms. For example, nerve fibers and collagen fibers exhibit birefringence. Using a polarization-sensitive optical tomography device, it is possible to measure the birefringence distribution within a living organism in three dimensions.

[0003] The birefringence is characterized by its optical axis. The slow axis and fast axis are known as optical axes. The incident polarized light for which a medium (e.g., a test eye) exhibits maximum or minimum birefringence is called eigenpolarization. In the case of birefringence in fibrous tissue, there are two eigenpolarizations, which are linearly polarized light that are orthogonal to each other. The vibration directions of the eigenpolarizations for which a medium exhibits maximum or minimum birefringence are called the slow axis and fast axis, respectively. In biological fibrous tissue, it is known that the slow axis generally coincides with the orientation of the fibers.

[0004] A polarization-sensitive optical tomography apparatus can only measure the birefringence component projected in a plane perpendicular to the propagation direction of the probe light of the polarization-sensitive optical tomography apparatus. Therefore, if the optical axis of birefringence of a medium does not lie in a plane perpendicular to the propagation direction of the probe light, the optical axis of birefringence has a component in the same direction as the propagation direction of the probe light, and this component cannot be measured by a polarization-sensitive optical tomography apparatus. For example, Non-Patent Documents 1 to 4 disclose techniques for detecting the optical axes of birefringence in various directions in a test eye, which is an example of a measurement object. In Non-Patent Documents 1 to 4, the test eye is measured multiple times by changing the angle at which the probe light of a polarization-sensitive optical tomography apparatus is incident on the test eye, and the optical axes of birefringence in various directions in the test eye are detected using the data from the multiple measurements. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Ugryumova N, Gangnus SV, Matcher SJ. Three-dimensional optic axis determination using variable-incidence-angle polarization-optical coherence tomography. Opt Lett 2006; 31:2305-2307. [Non-patent document 2] Lu Z, Kasaragod DK, Matcher SJ. Optic axis determination by fiber-based polarization-sensitive swept-source optical coherence tomography. Phys Med Biol 2011; 56:1105. [Non-patent document 3] Lu Z, Kasaragod D, Matcher SJ. Conical scan polarization-sensitive optical coherence tomography. Biomed Opt Express 2014; 5:752-762. [Non-patent document 4] Liu CJ, Black AJ, Wang H, Akkin T. Quantifying three-dimensional optic axis using polarization-sensitive optical coherence tomography. J Biomed Opt 2016; 21:070501. Summary of the Invention [Problem to be solved by the invention]

[0006] The methods described in Non-Patent Documents 1 to 4 can detect the optical axes of birefringence in various directions in a subject's eye, which is an example of a measurement object. However, these methods require measuring the measurement object multiple times by changing the angle at which the probe light is incident on the measurement object. This poses a problem of long measurement times.

[0007] This specification discloses a technique for efficiently identifying the optical axes of birefringence in various directions within a measurement object. [Means for solving the problem]

[0008] In a first aspect of the technology disclosed in this specification, an image processing device includes an acquisition unit that acquires multiple tomographic images showing polarization characteristics of a measurement object at cross sections at different positions on the measurement object, and a calculation unit that generates an image showing the direction of the optical axis of birefringence using the multiple tomographic images. The calculation unit identifies the shape of a portion included in the measurement object, and corrects the direction of the optical axis of birefringence of each pixel in each tomographic image so that it follows the identified shape.

[0009] In the image processing device described above, when generating an image showing the direction of the birefringence optic axis of a measurement object, the direction of the birefringence optic axis is corrected to conform to the shape of the tissue within the measurement object. For example, in tissue within a living organism, many of the fibers within the measurement object run along the shape of the tissue. By correcting the direction of the birefringence optic axis to conform to the shape of the tissue within the measurement object, it is possible to appropriately correct (estimate) the birefringence optic axis that does not lie in a plane perpendicular to the direction of propagation of the light irradiated onto the measurement object. Therefore, it is possible to generate an image depicting the birefringence optic axis in various directions within the measurement object without measuring the measurement object multiple times by changing the angle at which the light irradiated onto the measurement object is incident on the measurement object.

[0010] In addition, the optical tomographic imaging device disclosed in this specification includes an imaging unit that captures tomographic images at cross sections of different positions on the object to be measured, and any of the image processing devices described above that processes the multiple tomographic images captured by the imaging unit.

[0011] The optical tomographic imaging apparatus includes any one of the image processing devices described above, and therefore can achieve the same effects as those of the image processing device described above.

[0012] This specification also discloses a computer program for processing a plurality of tomographic images showing polarization characteristics of a measurement object at cross sections at different positions on the measurement object. The computer program causes a computer to function as an acquisition unit that acquires the plurality of tomographic images, an identification unit that identifies the shape of a portion included in the measurement object, a correction unit that corrects the direction of the optical axis of birefringence of each pixel in each tomographic image so that it conforms to the shape identified by the identification unit, and a generation unit that generates an image showing the direction of the optical axis of birefringence corrected by the correction unit. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of an optical system of an optical tomographic imaging apparatus according to an embodiment. [Figure 2] FIG. 2 is a block diagram showing a control system of the optical tomographic imaging apparatus according to the embodiment. [Figure 3] FIG. 1 is a block diagram showing the configuration of a sampling trigger / clock generator. [Figure 4] 10 is a flowchart showing an example of a process for correcting the running direction of fibers in a subject's eye (an example of a measurement object). [Figure 5] (a) is an intensity tomographic image of the area near the temporal angle of the anterior segment of the right eye of the subject's eye, and (b) is a two-dimensional topographic map. [Figure 6] 10 shows maps showing the gradient of the surface shape calculated using a two-dimensional topographic map, where (a) shows the gradient in the horizontal direction and (b) shows the gradient in the vertical direction. [Figure 7] FIG. 10 is a diagram for explaining a method for correcting the tilt of the optical axis of birefringence, showing the rotation of a vector in the αβ plane. [Figure 8] FIG. 10 is a diagram for explaining a method for correcting the tilt of the optical axis of birefringence, showing the rotation of a vector in the βγ plane. [Figure 9] These are three-dimensional images of the birefringence optical axis of the lower part of the measurement range of the test eye viewed from diagonally above, where (a) shows a three-dimensional image of the birefringence optical axis before correction, and (b) shows a three-dimensional image of the birefringence optical axis after correction. [Figure 10] These are three-dimensional images of the birefringence optical axis when the lower part of the measurement range of the test eye is viewed from the side, where (a) shows a three-dimensional image of the birefringence optical axis before correction, and (b) shows a three-dimensional image of the birefringence optical axis after correction. [Figure 11] These are three-dimensional images of the birefringence optical axis when viewed from directly to the side on the nasal side of the measurement range of the test eye, where (a) shows a three-dimensional image of the birefringence optical axis before correction, and (b) shows a three-dimensional image of the birefringence optical axis after correction. [Figure 12] Three-dimensional images of the birefringence optical axis, with a fixed thickness of 406 μm removed from the surface of the anterior segment, are shown as en-face images, displayed from the surface side of the anterior segment. (a) shows the en-face image of the birefringence optical axis before correction, and (b) shows the en-face image of the birefringence optical axis after correction. DETAILED DESCRIPTION OF THE INVENTION

[0014] The main features of the embodiments described below are listed below. Note that the technical elements described below are independent technical elements that exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing.

[0015] In a second aspect of the technology disclosed in this specification, in the first aspect described above, the tomographic image may be a tomographic image showing the polarization characteristics of tissue in a living body. The direction of the optical axis of birefringence may be the direction in which fibers run. The shape may be the surface shape of the tissue. The calculation unit may correct the direction of the optical axis of birefringence so that it follows the surface shape. Most fibers in a living body run along the surface shape. Therefore, it is possible to preferably execute a process for correcting the direction of the optical axis of birefringence (i.e., the direction in which fibers run).

[0016] In a third aspect of the technology disclosed in this specification, in the second aspect, the calculation unit may calculate the tilt of the surface shape and correct the direction of the optical axis of birefringence using the calculated tilt. With this configuration, it is possible to preferably execute the process of correcting the direction of the optical axis of birefringence.

[0017] In a fourth aspect of the technology disclosed in the present specification, in any one of the first to third aspects described above, the calculation unit may identify the shape of the tissue of the measurement object from the multiple tomographic images acquired by the acquisition unit, and correct the direction of the optical axis of birefringence so that it conforms to the identified shape. With this configuration, the shape of the tissue can be identified using the tomographic images captured to generate an image indicating the direction of the optical axis of birefringence. Therefore, the process of correcting the direction of the optical axis of birefringence can be performed without capturing and acquiring a separate image for identifying the shape of the tissue.

[0018] In a fifth aspect of the technology disclosed in the present specification, in any one of the first to fourth aspects, the image processing device may further include a display unit that displays an image indicating the direction of the optical axis of birefringence corrected by the calculation unit. With this configuration, the image indicating the direction of the optical axis of birefringence corrected can be presented to the examiner, and the user can visually grasp the direction of the optical axis of birefringence of the measurement object.

[0019] In a sixth aspect of the technology disclosed in the present specification, in any one of the first to fifth aspects, the calculation unit may be configured to generate an en-face image of an image showing the direction of the optical axis of birefringence after correction. With this configuration, the image showing the direction of the optical axis of birefringence after correction can be grasped two-dimensionally by the en-face image. [Example]

[0020] An optical tomographic imaging apparatus according to an embodiment will be described with reference to the drawings. The optical tomographic imaging apparatus of this embodiment is a polarization-sensitive OCT (PS-OCT) apparatus that uses a wavelength-swept Fourier-domain method (swept-source optical coherence tomography: SS-OCT) that uses a wavelength-swept light source and is capable of capturing the polarization characteristics of a measurement object. In this embodiment, the measurement object will be described as an eye to be examined.

[0021] As shown in Figure 1, the optical tomographic imaging apparatus of this embodiment includes a light source 11, a measurement light generation unit (21-29, 31, 32) that generates measurement light from the light of the light source 11, a reference light generation unit (41-46, 51) that generates reference light from the light of the light source 11, interference light generation units 60, 70 that generate interference light by combining reflected light from the test eye 500 generated by the measurement light generation unit with reference light generated by the reference light generation unit, and interference light detection units 80, 90 that detect the interference light generated by the interference light generation units 60, 70.

[0022] (light source) The light source 11 is a wavelength sweep type light source, and the wavelength (wave number) of the emitted light changes at a predetermined cycle. Because the wavelength of the light irradiated onto the subject's eye 500 changes (sweeps), the intensity distribution of the light reflected from each part in the depth direction of the subject's eye 500 can be obtained by Fourier analysis of a signal obtained from the interference light between the reflected light from the subject's eye 500 and the reference light.

[0023] The light source 11 is connected to a polarization control device 12 and a fiber coupler 13, and the fiber coupler 13 is connected to a PMFC (polarization-maintaining fiber coupler) 14 and a sampling trigger / clock generator 100. Therefore, the light output from the light source 11 is input to the PMFC 14 and the sample trigger / clock generator 100 via the polarization control device 12 and the fiber coupler 13. The sampling trigger / clock generator 100 uses the light from the light source 11 to generate sampling triggers and sampling clocks for signal processors 83 and 93, which will be described later.

[0024] (Measurement light generation section) The measurement light generation unit (21 to 29, 31, 32) includes a PMFC 21 connected to the PMFC 14, two measurement optical paths S1 and S2 branching from the PMFC 21, a polarization beam combiner / splitter 25 connecting the two measurement optical paths S1 and S2, and a collimator lens 26, galvanometer mirrors 27 and 28, and a lens 29 connected to the polarization beam combiner / splitter 25. An optical path length difference generation unit 22 and a circulator 23 are disposed in the measurement optical path S1. Only a circulator 24 is disposed in the measurement optical path S2. Therefore, the optical path length difference ΔL between the measurement optical paths S1 and S2 is generated by the optical path length difference generation unit 22. The optical path length difference ΔL may be set longer than the measurement range in the depth direction of the eye 500 to be examined. This prevents interference light with different optical path length differences from overlapping. The optical path length difference generating unit 22 may be, for example, an optical fiber or an optical system such as a mirror or a prism. In this embodiment, a 1 m PM fiber is used for the optical path length difference generating unit 22. The measurement light generating unit further includes PMFCs 31 and 32. PMFC 31 is connected to circulator 23. PMFC 32 is connected to circulator 24.

[0025] One of the beams (i.e., the measurement beam) branched by the PMFC 14 is input to the measurement beam generator (21-29, 31, 32). The PMFC 21 splits the measurement beam input from the PMFC 14 into a first measurement beam and a second measurement beam. The first measurement beam split by the PMFC 21 is guided to the measurement beam path S1, and the second measurement beam is guided to the measurement beam path S2. The first measurement beam guided to the measurement beam path S1 passes through the optical path length difference generator 22 and the circulator 23 and is input to the polarization beam combiner / splitter 25. The second measurement beam guided to the measurement beam path S2 passes through the circulator 24 and is input to the polarization beam combiner / splitter 25. The PM fiber 304 is connected to the polarization beam combiner / splitter 25 rotated 90 degrees circumferentially with respect to the PM fiber 302. As a result, the second measurement light input to the polarized beam combiner / splitter 25 becomes light having a polarization component orthogonal to that of the first measurement light. Because the optical path length difference generating unit 22 is provided in the measurement light path S1, the first measurement light is delayed relative to the second measurement light by the distance of the optical path length difference generating unit 22 (i.e., an optical path length difference ΔL is generated). The polarized beam combiner / splitter 25 superimposes the input first measurement light and second measurement light. The light output from the polarized beam combiner / splitter 25 (light obtained by superimposing the first measurement light and the second measurement light) is irradiated onto the test eye 500 via a collimator lens 26, galvanometer mirrors 27 and 28, and a lens 29. The light irradiated onto the test eye 500 is scanned in the x and y directions by the galvanometer mirrors 27 and 28.

[0026] Light irradiated onto the eye 500 is reflected by the eye 500. The light reflected by the eye 500 is scattered on the surface and inside the eye 500. The reflected light from the eye 500 passes through the lens 29, galvanometer mirrors 28 and 27, and collimator lens 26 in the opposite direction to the incident path, and is then input to the polarization beam combiner / splitter 25. The polarization beam combiner / splitter 25 splits the input reflected light into two polarized components that are orthogonal to each other. For convenience, these are referred to here as horizontally polarized reflected light (horizontally polarized component) and vertically polarized reflected light (vertically polarized component). The horizontally polarized reflected light is then guided to the measurement optical path S1, and the vertically polarized reflected light is guided to the measurement optical path S2.

[0027] The optical path of the horizontally polarized reflected light is changed by the circulator 23 and input to the PMFC 31. The PMFC 31 splits the input horizontally polarized reflected light and inputs it to the PMFCs 61 and 71. Therefore, the horizontally polarized reflected light input to the PMFCs 61 and 71 contains a reflected light component due to the first measurement light and a reflected light component due to the second measurement light. The optical path of the vertically polarized reflected light is changed by the circulator 24 and input to the PMFC 32. The PMFC 32 splits the input vertically polarized reflected light and inputs it to the PMFCs 62 and 72. Therefore, the vertically polarized reflected light input to the PMFCs 62 and 72 contains a reflected light component due to the first measurement light and a reflected light component due to the second measurement light.

[0028] (Reference light generation section) The reference light generation unit (41 to 46, 51) includes a circulator 41 connected to the PMFC 14, reference delay lines (42, 43) connected to the circulator 41, a PMFC 44 connected to the circulator 41, two reference light paths R1 and R2 branching from the PMFC 44, a PMFC 46 connected to the reference light path R1, and a PMFC 51 connected to the reference light path R2. An optical path length difference generation unit 45 is disposed in the reference light path R1. No optical path length difference generation unit is provided in the reference light path R2. Therefore, the optical path length difference ΔL′ between the reference light paths R1 and R2 is generated by the optical path length difference generation unit 45. For example, an optical fiber is used for the optical path length difference generation unit 45. The optical path length ΔL′ of the optical path length difference generation unit 45 may be the same as the optical path length ΔL of the optical path length difference generation unit 22. By making the optical path length differences ΔL and ΔL′ equal, the depth positions of a plurality of interference lights, which will be described later, become the same with respect to the subject's eye 500. In other words, it is not necessary to align the positions of a plurality of tomographic images to be acquired.

[0029] The other light (i.e., reference light) branched by the PMFC 14 is input to the reference light generating unit (41 to 46, 51). The reference light input from the PMFC 14 passes through a circulator 41 and is input to a reference delay line (42, 43). The reference delay line (42, 43) is composed of a collimator lens 42 and a reference mirror 43. The reference light input to the reference delay line (42, 43) is irradiated onto the reference mirror 43 via the collimator lens 42. The reference light reflected by the reference mirror 43 is input to the circulator 41 via the collimator lens 42. Here, the reference mirror 43 is movable in a direction toward or away from the collimator lens 42. In this embodiment, before starting measurement, the position of the reference mirror 43 is adjusted so that the signal from the subject's eye 500 falls within the measurement range of the OCT in the depth direction.

[0030] The reference light reflected by reference mirror 43 has its optical path changed by circulator 41 and is input to PMFC 44. PMFC 44 splits the input reference light into a first reference light and a second reference light. The first reference light is guided to reference optical path R1, and the second reference light is guided to reference optical path R2. The first reference light passes through optical path length difference generating unit 45 and is input to PMFC 46. The reference light input to PMFC 46 is split into a first split reference light and a second split reference light. The first split reference light passes through collimator lens 47 and lens 48 and is input to PMFC 61. The second split reference light passes through collimator lens 49 and lens 50 and is input to PMFC 62. The second reference light is input to PMFC 51 and split into a third split reference light and a fourth split reference light. The third split reference light passes through collimator lens 52 and lens 53 and is input to PMFC 71. The fourth branched reference light passes through a collimator lens 54 and a lens 55 and is input to the PMFC 72 .

[0031] (Interference light generation unit) The interference light generation units 60 and 70 include a first interference light generation unit 60 and a second interference light generation unit 70. The first interference light generation unit 60 includes PMFCs 61 and 62. As described above, PMFC 61 receives horizontally polarized reflected light from the measurement light generation unit and receives the first branched reference light (light having an optical path difference ΔL′) from the reference light generation unit. The horizontally polarized reflected light includes a reflected light component due to the first measurement light (light having an optical path difference ΔL) and a reflected light component due to the second measurement light (light without an optical path difference ΔL). Therefore, PMFC 61 combines the reflected light component due to the first measurement light (light having an optical path difference ΔL) and the first branched reference light to generate the first interference light (horizontally polarized component).

[0032] Furthermore, PMFC 62 receives vertically polarized reflected light from the measurement light generator and second branched reference light (light having an optical path difference ΔL′) from the reference light generator. The vertically polarized reflected light includes a reflected light component due to the first measurement light (light having an optical path difference ΔL) and a reflected light component due to the second measurement light (light without an optical path difference ΔL). Therefore, PMFC 62 combines the reflected light component due to the first measurement light (light having an optical path difference ΔL) and the second branched reference light to generate second interference light (vertically polarized component).

[0033] The second interference light generation unit 70 has PMFCs 71 and 72. As described above, PMFC 71 receives the horizontally polarized reflected light from the measurement light generation unit and the third branched reference light (light without optical path difference ΔL′) from the reference light generation unit. Therefore, in PMFC 71, the reflected light component of the horizontally polarized reflected light due to the second measurement light (light without optical path difference ΔL) and the third branched reference light are combined to generate the third interference light (horizontally polarized component).

[0034] Furthermore, PMFC 72 receives vertically polarized reflected light from the measurement light generation unit and receives fourth branched reference light (light without optical path difference ΔL′) from the reference light generation unit. Therefore, PMFC 72 combines the reflected light component (light without optical path difference ΔL) of the vertically polarized reflected light due to the second measurement light with the fourth branched reference light to generate fourth interference light (vertically polarized component). The first interference light and second interference light correspond to the measurement light that has passed through measurement optical path S1, and the third interference light and fourth interference light correspond to the measurement light that has passed through measurement optical path S2.

[0035] (Interference light detection unit) The interference light detection units 80, 90 include a first interference light detection unit 80 that detects the interference light (first interference light and second interference light) generated by the first interference light generation unit 60, and a second interference light detection unit 90 that detects the interference light (third interference light and fourth interference light) generated by the second interference light generation unit 70.

[0036] The first interference light detection unit 80 includes balanced photodetectors 81 and 82 (hereinafter simply referred to as "detectors 81 and 82") and a signal processor 83 connected to the detectors 81 and 82. The PMFC 61 is connected to the detector 81, and the signal processor 83 is connected to the output terminal of the detector 81. The PMFC 61 splits the first interference light into two interference lights with a phase difference of 180 degrees and inputs them to the detector 81. The detector 81 performs differential amplification and noise reduction processing on the two interference lights with a phase difference of 180 degrees input from the PMFC 61, converts them into an electrical signal (first interference signal), and outputs the first interference signal to the signal processor 83. That is, the first interference signal is an interference signal HH between the horizontally polarized reflected light from the test eye 500 and the reference light due to the horizontally polarized measurement light. Similarly, the PMFC 62 is connected to the detector 82, and the signal processor 83 is connected to the output terminal of the detector 82. The PMFC 62 splits the second interference light into two interference lights with a phase difference of 180 degrees, and inputs them to the detector 82. The detector 82 performs differential amplification and noise reduction processing on the two interference lights with a phase difference of 180 degrees, converts them into an electrical signal (second interference signal), and outputs the second interference signal to the signal processor 83. That is, the second interference signal is an interference signal HV between the vertically polarized reflected light from the subject's eye 500 and the reference light due to the horizontally polarized measurement light.

[0037] The signal processor 83 includes a first signal processing unit 84 to which the first interference signal is input, and a second signal processing unit 85 to which the second interference signal is input. The first signal processing unit 84 samples the first interference signal based on a sampling trigger and a sampling clock input from a sampling trigger / clock generator 100 to the signal processor 83. The second signal processing unit 85 samples the second interference signal based on a sampling trigger and a sampling clock input from the sampling trigger / clock generator 100 to the signal processor 83. The first interference signal and the second interference signal sampled by the first signal processing unit 84 and the second signal processing unit 85 are input to a calculation unit 202, which will be described later. A known data acquisition device (so-called DAQ) can be used as the signal processor 83.

[0038] Similar to the first interference light detecting unit 80, the second interference light detecting unit 90 includes balanced photodetectors 91 and 92 (hereinafter also simply referred to as "detectors 91 and 92") and a signal processor 93 connected to the detectors 91 and 92. The PMFC 71 is connected to the detector 91, and the signal processor 93 is connected to the output terminal of the detector 91. The PMFC 71 splits the third interference light into two interference lights with a phase difference of 180 degrees and inputs them to the detector 91. The detector 91 performs differential amplification and noise reduction processing on the two interference lights with a phase difference of 180 degrees, converts them into an electrical signal (third interference signal), and outputs the third interference signal to the signal processor 93. That is, the third interference signal is an interference signal VH between the horizontally polarized reflected light from the subject's eye 500 and the reference light due to the vertically polarized measurement light. Similarly, the PMFC 72 is connected to the detector 92, and the signal processor 93 is connected to the output terminal of the detector 92. The PMFC 72 splits the fourth interference light into two interference lights with a phase difference of 180 degrees, and inputs them to the detector 92. The detector 92 performs differential amplification and noise reduction processing on the two interference lights with a phase difference of 180 degrees, converts them into an electrical signal (fourth interference signal), and outputs the fourth interference signal to the signal processor 93. That is, the fourth interference signal is an interference signal VV between the vertically polarized reflected light of the test eye 500 resulting from the vertically polarized measurement light and the reference light.

[0039] The signal processor 93 includes a third signal processing unit 94 to which the third interference signal is input and a fourth signal processing unit 95 to which the fourth interference signal is input. The third signal processing unit 94 samples the third interference signal based on a sampling trigger and a sampling clock input from a sampling trigger / clock generator 100 to the signal processor 93. The fourth signal processing unit 95 samples the fourth interference signal based on a sampling trigger and a sampling clock input from the sampling trigger / clock generator 100 to the signal processor 93. The third interference signal and the fourth interference signal sampled by the third signal processing unit 94 and the fourth signal processing unit 95 are input to a calculation unit 202 (described later). A known data acquisition device (DAQ) can also be used for the signal processor 93. This configuration allows for acquisition of interference signals representing four polarization characteristics of the subject's eye 500. Note that, although the present embodiment uses signal processors 83 and 93 each having two signal processing units, the present invention is not limited to such a configuration. For example, one signal processor having four signal processing sections may be used, or four signal processors each having one signal processing section may be used.

[0040] Next, the configuration of the control system of the optical tomographic imaging apparatus according to this embodiment will be described. As shown in FIG. 2, the optical tomographic imaging apparatus is controlled by a calculation device 200. The calculation device 200 is composed of a calculation unit 202, a first interference light detection unit 80, and a second interference light detection unit 90. The first interference light detection unit 80, the second interference light detection unit 90, and the calculation unit 202 are connected to the measurement unit 10. The calculation unit 202 outputs a control signal to the measurement unit 10 and drives the galvanometer mirrors 27 and 28 to scan the incident position of the measurement light on the subject's eye 500. The first interference light detection unit 80 acquires first sampling data based on the sampling clock 1 input from the measurement unit 10, using a sampling trigger 1 as a trigger, in response to the interference signals (interference signals HH and HV) input from the measurement unit 10, and outputs the first sampling data to the calculation unit 202. The calculation unit 202 performs calculation processing such as Fourier transform processing on the first sampling data to generate HH tomographic images and HV tomographic images. The second interference light detection unit 90 acquires second sampling data based on a sampling clock 2 input from the measurement unit 10 in response to interference signals (interference signals VH and VV) input from the measurement unit 10, using a sampling trigger 2 as a trigger, and outputs the second sampling data to the calculation unit 202. The calculation unit 202 performs calculation processing such as Fourier transform processing on the second sampling data to generate VH tomographic images and VV tomographic images. Here, the HH tomographic image, VH tomographic image, HV tomographic image, and VV tomographic image are tomographic images of the same position. Therefore, the calculation unit 202 can generate tomographic images of four polarization characteristics (HH, HV, VH, VV) that represent the Jones matrix of the subject's eye 500.

[0041] 3, the sampling trigger / clock generator 100 includes a fiber coupler 102, sampling trigger generators (140 to 152), and sampling clock generators (160 to 172). Light from a light source 11 is input to the sampling trigger generator 140 and the sampling clock generator 160 via the fiber coupler 13 and the fiber coupler 102, respectively.

[0042] (Sampling trigger generator) The sampling trigger generator 140 may generate a sampling trigger using, for example, an FBG (Fiber Bragg Grating) 144. As shown in FIG. 3 , the FBG 144 reflects only a specific wavelength of light incident from the light source 11 to generate a sampling trigger. The generated sampling trigger is input to the distributor 150. The distributor 150 distributes the sampling trigger into sampling trigger 1 and sampling trigger 2. The sampling trigger 1 is input to the calculation unit 202 via a signal delay circuit 152. The sampling trigger 2 is input directly to the calculation unit 202. The sampling trigger 1 serves as a trigger signal for the interference signals (first interference signal and second interference signal) input from the first interference light detection unit 80 to the calculation unit 202. The sampling trigger 2 serves as a trigger signal for the interference signals (third interference signal and fourth interference signal) input from the second interference light detection unit 90 to the calculation unit 202. The signal delay circuit 152 is designed so that sampling trigger 1 is delayed in time relative to sampling trigger 2 by the optical path length difference ΔL of the optical path length difference generation unit 22. This makes it possible to make the frequency at which sampling of the interference signal input from the first interference light detection unit 80 starts the same as the frequency at which sampling of the interference signal input from the second interference light detection unit 90 starts. Here, only sampling trigger 1 may be generated. Because the optical path length difference ΔL is known, when sampling the interference input from the second interference light detection unit 90, sampling can be started so as to be delayed in time by the optical path length difference ΔL from sampling trigger 1.

[0043] (Sampling clock generator) The sampling clock generator may be configured, for example, with a Mach-Zehnder interferometer. As shown in FIG. 3, the sampling clock generator generates sampling clocks of equal frequency using a Mach-Zehnder interferometer. The sampling clock generated by the Mach-Zehnder interferometer is input to a distributor 172. The distributor 172 distributes the sampling clock into sampling clock 1 and sampling clock 2. Sampling clock 1 is input to the first interference light detector 80 via a signal delay circuit 174. Sampling clock 2 is input directly to the second interference light detector 90. The signal delay circuit 174 is designed to delay the time by the optical path length difference ΔL of the optical path length difference generator 22. This allows sampling of interference light delayed by the optical path length difference generator 22 at the same timing. This prevents misalignment of multiple acquired tomographic images. In this embodiment, a Mach-Zehnder interferometer is used to generate the sampling clock. However, a Michelson interferometer or an electrical circuit may be used to generate the sampling clock, or a light source equipped with a sampling clock generator may be used to generate the sampling clock.

[0044] Next, a process for correcting the direction of fibers in the subject's eye 500 will be described. While a polarization-sensitive optical tomographic imaging device can measure the optical axis of birefringence (i.e., the direction of fibers) in the subject's eye 500, the polarization-sensitive optical tomographic imaging device can only measure the birefringence component projected in a plane perpendicular to the direction of propagation of light emitted from the light source 11 of the polarization-sensitive optical tomographic imaging device (hereinafter also referred to as probe light). Therefore, if the optical axis of birefringence does not exist in a plane perpendicular to the direction of propagation of the probe light, the optical axis of birefringence has a component in the same direction as the direction of propagation of the probe light, and this component is not measured by the polarization-sensitive optical tomographic imaging device. For example, by measuring the subject's eye 500 multiple times while changing the incident angle of the probe light and constructing the optical axis of birefringence three-dimensionally using the data from the multiple measurements, the optical axis of birefringence can be identified even in tissue that is tilted relative to the surface. However, if the eye 500 to be examined is measured multiple times, the measurement time becomes long and this places a burden on the examinee.

[0045] In this embodiment, we focus on the fact that most fibers run parallel to the layer structure. Fibrous tissue in living organisms is often layered, and fibers often run parallel to the layer structure. For example, optic nerve fibers and collagen fibers in the sclera and cornea run parallel to the layer structure in most regions. However, fibers do not run parallel to the layer structure in all regions. For example, tissues such as the anterior corneal stroma near the corneal epithelium are known to have not only fibers parallel to the layer structure but also fibers with vector components oblique to the depth direction. In the optic nerve head, optic nerve fibers change direction as they penetrate from the inside to the outside of the eyeball. Collagen fibers on the surface of the articular cartilage run parallel to the surface, while collagen fibers below the surface are known to run in an oblique direction relative to the surface. Although there are exceptions, fibers run parallel to the layer structure in most regions. Therefore, in this embodiment, the optical axis of birefringence (i.e., the fiber running direction) is corrected to conform to the shape of the tissue within the test eye 500. This makes it possible to correct the running direction of fibers running in various directions within the eye 500 without measuring the eye 500 multiple times by changing the incident angle of the probe light.

[0046] In this embodiment, a process for correcting the running direction of fibers in a tomographic image of the anterior segment of the subject's eye 500 will be described as an example. Note that the correction process of this embodiment is not limited to correcting the running direction of fibers in a tomographic image of the anterior segment of the subject's eye 500, but can also be applied to correcting the running direction of fibers in a tomographic image of a portion other than the anterior segment of the subject's eye 500 (for example, the fundus, etc.). In this embodiment, for simplicity of explanation, it is assumed that the fibrous tissue runs parallel to the surface shape.

[0047] As shown in FIG. 4, first, the calculation unit 202 acquires a tomographic image showing the running direction of fibers in the subject's eye 500 (S12). The process of acquiring a tomographic image showing the running direction of fibers in the subject's eye 500 is performed as follows: First, the examiner operates an operating member such as a joystick (not shown) to align the optical tomographic imaging apparatus with respect to the subject's eye 500. That is, the calculation unit 202 drives a position adjustment mechanism (not shown) in response to the examiner's operation of the operating member. This adjusts the position of the optical tomographic imaging apparatus in the x- and y-directions (vertical and horizontal directions) and the z-direction (direction of forward and backward movement) relative to the subject's eye 500. Next, the calculation unit 202 captures a tomographic image of the subject's eye 500 (in this embodiment, the anterior segment of the subject's eye 500). In this embodiment, this is performed using a raster scan method. In the raster scan method, the tomographic image is captured with the B-scan direction set horizontally relative to the subject's eye 500 and the C-scan direction set vertically. This allows a tomographic image of the anterior segment of the subject's eye 500 to be acquired over the entire area. The method for capturing a tomographic image of the anterior segment of the subject's eye 500 is not limited to the raster scan method. Any method may be used as long as a tomographic image of the anterior segment of the subject's eye 500 can be acquired over the entire area, and for example, the image may be captured by a radial scan method. In the radial scan method, the B scan direction is set in a radial direction from the corneal apex of the subject's eye 500, and the C scan direction is set in a circumferential direction to capture a tomographic image.

[0048] As described above, the optical tomography apparatus of this embodiment is a polarization-sensitive optical tomography apparatus, and therefore can simultaneously acquire a tomographic image captured by irradiating the test eye 500 with a vertical wave and a tomographic image captured by irradiating the test eye 500 with a horizontal wave. By using these two types of tomographic images, the calculation unit 202 can generate not only a tomographic image showing the tissue in the test eye 500 based on the scattering intensity (so-called a normal tomographic image), but also a tomographic image showing the direction of fiber travel within the test eye 500. In this embodiment, the tomographic image showing the direction of fiber travel is generated using four interference signals HH, HV, VH, and VV. The tomographic image showing the direction of fiber travel can be generated using a known method. For example, the tomographic image showing the direction of fiber travel can be generated by calculating the optical axis of birefringence, thereby identifying the direction of birefringence and visualizing the direction of fiber travel within the test eye 500. When calculating the optical axis of birefringence, a local phase delay indicating the magnitude of birefringence may also be calculated. Furthermore, the optical axis of birefringence can be calculated using known methods (e.g., Ohno-Matsui K, Igarashi-Yokoi T, Azuma T, et al. Polarization-Sensitive OCT Imaging of Scleral Abnormalities in Eyes With High Myopia and Dome-Shaped Macula. JAMA Ophthalmol 2024;142:310-319, etc.), so detailed explanations will be omitted.

[0049] Next, the calculation unit 202 identifies the surface shape of the tissue in each tomographic image (S14). In this embodiment, the "surface shape of the tissue" refers to the surface shape of the tissue on the light source 11 side (the side irradiated with light). Most fibers run along the surface shape of the tissue. Therefore, in this embodiment, the calculation unit 202 identifies the surface shape of the tissue in each tomographic image. Specifically, the calculation unit 202 detects (segments) the boundaries of the tissue in the subject's eye 500 for each tomographic image and identifies the surface of each tissue. Note that segmentation can be performed using a known method, for example, as disclosed in Japanese Patent Application Laid-Open No. 2019-88957, and therefore detailed description thereof will be omitted. Then, the calculation unit 202 generates a two-dimensional topographic map to identify the surface shape of the tissue.

[0050] Fig. 5(a) is a tomographic image (hereinafter also referred to as an intensity tomographic image) showing the intensity distribution near the temporal angle of the anterior segment of the right eye of the subject's eye 500, and Fig. 5(b) is a two-dimensional topographic map obtained by segmenting the surface of the volume data of the tomographic image. Note that Fig. 5(b) shows that the surface protrudes as the color changes from white to black. The calculation unit 202 generates a two-dimensional topographic map as shown in Fig. 5(b).

[0051] Next, the calculation unit 202 calculates the gradient of the surface shape identified in step S14 (S16). Specifically, the calculation unit 202 performs noise reduction processing on the 2D topographic map generated in step S14 using a median filter, and then generates a gradient map of the surface shape using a Prewitt filter. Note that the method for calculating the gradient of the surface shape is not particularly limited to the above method. For example, the calculation unit 202 may calculate the gradient of the surface shape by polynomial approximation of the surface shape and differentiating the polynomial. Also, an image differentiation filter other than a Prewitt filter (e.g., a Sobel filter) may be used. When an image differentiation filter such as a Prewitt filter or a Sobel filter is used, generally, only one-directional differentiation can be obtained with one filtering. For this reason, the calculation unit 202 uses image differentiation filters for the β-axis direction and the γ-axis direction, which will be described later, respectively, to calculate the gradient for each direction. Note that a well-known image differentiation filter can be used, and detailed description thereof will be omitted.

[0052] Figures 6(a) and 6(b) are maps showing the slope of the surface shape calculated using the two-dimensional topographic map shown in Figure 5(b). Figure 6(a) shows the horizontal slope (angle φ, described below), and Figure 6(b) shows the vertical slope (angle θ, described below). In Figures 6(a) and 6(b), the slope is expressed as an angle between -π / 2 and +π / 2, and is shown in grayscale from black to white.

[0053] Next, the calculation unit 202 corrects the tilt of the optical axis of birefringence for each pixel for each tomographic image (S18). A method for correcting the tilt of the optical axis of birefringence will be described below. The tilt of the optical axis of birefringence is expressed using a three-dimensional Cartesian coordinate system defined by the α-axis, β-axis, and γ-axis. In this embodiment, a right-handed coordinate system is used, but a left-handed coordinate system may also be used. In this embodiment, the axis in the depth direction is defined as the α-axis. The direction of the α-axis is defined to coincide with the incident direction of the probe light. Two axes perpendicular to the α-axis are defined as the β-axis and γ-axis. The β-axis is defined to coincide with the horizontal scanning direction of the B-scan. The γ-axis is defined so that the α-axis, β-axis, and γ-axis form a right-handed coordinate system. By defining the coordinate system in this way, the optical axis of birefringence in the tomographic image can be represented by a vector in the βγ plane. In this embodiment, the tilt of the optical axis of birefringence of each pixel is corrected by rotating the vector in the βγ plane and converting it into a vector in a three-dimensional space including the α-axis direction.

[0054] The method of conversion into vectors in three-dimensional space will be further explained. First, rotation within the αβ plane, i.e., the plane of a B-scan tomographic image, will be explained. Figure 7 shows the αβ plane. The γ axis faces the front direction perpendicular to the αβ plane, and the three axes intersect at the origin 0. When point A rotates by an angle φ around the γ axis as the rotation axis and moves to point A', the rotation matrix R is γ (φ) is expressed by the following formula 1.

[0055]

number

[0056] The coordinates of point A are A=(A α ,A β ,A γ ) t The coordinates of point A' can be expressed as A'=(A' α ,A' β ,A' γ ) t The superscript t indicates transposition. The rotation from point A to point A' is expressed by the following formula (2).

[0057]

number

[0058] If the vector OA from the origin 0 to point A is defined as a unit vector representing the optical axis of birefringence of the subject's eye 500, the vector OA exists in the βγ plane, and therefore, A α =0. In addition, Figure 7 shows the α Note that this is a generalized diagram for the case where has a value other than 0. If the tilt of the layer structure of the fibrous tissue of the subject's eye 500 in the αβ plane, i.e., in the plane of the B-scan tomographic image, is considered to be angle φ, then the vector 0A' from the origin 0 to point A' is a vector tilted by angle φ in the αβ plane so that the optical axis of the birefringence of the subject's eye 500 is aligned with the layer structure.

[0059] Next, we will explain the rotation in the γα plane, i.e., the tomographic image plane perpendicular to the B-scan. Figure 8 shows the γα plane. The β axis faces the front direction perpendicular to the γα plane, and the three axes intersect at the origin 0. When point A rotates by an angle θ around the β axis as the rotation axis and moves to point A″, the rotation matrix R β (θ) is expressed by the following formula 3.

[0060]

number

[0061] The coordinates of point A" are A" = (A" α ,A” β ,A” γ ) t The rotation from point A to point A" can be expressed as the following equation (4).

[0062]

number

[0063] If the inclination of the layer structure of the fibrous tissue of the test eye 500 in the γα plane, i.e., in the tomographic image plane perpendicular to the B-scan, is considered to be angle θ, then the vector 0A″ from the origin 0 to point A″ is a vector tilted by angle θ in the γα plane following the above-mentioned αβ plane, with the optical axis of the birefringence of the test eye 500 aligned with the layer structure.

[0064] Therefore, A" obtained by the above two rotations can be expressed by the following formula (5). In the formula (5), A α =0 is used.

[0065]

number

[0066] The calculation unit 202 corrects the tilt of the optical axis of birefringence for each pixel by substituting the tilt of the surface shape identified in step S16 into the equation expressed by Equation 5 above. As described above, FIGS. 6(a) and 6(b) show the tilt of the surface shape calculated using the 2D topographic map shown in FIG. 5(b), where FIG. 6(a) shows the horizontal tilt (angle φ) and FIG. 6(b) shows the vertical tilt (angle θ). The calculation unit 202 corrects the tilt of the optical axis of birefringence for each pixel by substituting the tilts φ and θ of the surface shape calculated using the 2D topographic map into the equation expressed by Equation 5 above. As described above, in this embodiment, for simplicity of explanation, it is assumed that the fibrous tissue runs parallel to the shape. Therefore, the calculation unit 202 can rotate the optical axis of birefringence depending only on the β-axis and γ-axis directions in the horizontal direction, without depending on the α-axis in the depth direction. This makes it possible to correct the optical axis of birefringence (i.e., the direction of fiber travel). In other words, by rotating the birefringence component (optical axis) projected onto a plane perpendicular to the direction of travel of the probe light (light emitted from the light source 11) so that it follows the surface shape, the direction of birefringence (optical axis) can be corrected.

[0067] Next, the calculation unit 202 generates an image showing the fiber running direction corrected in step S18 (S20). Specifically, the calculation unit 202 generates a three-dimensional image showing the birefringence optical axis (hereinafter also referred to as a three-dimensional image of the birefringence optical axis) using the tomographic image in which the tilt of the birefringence optical axis has been corrected in step S18. By generating a three-dimensional image of the birefringence optical axis, it is possible to visualize the streamline of the birefringence optical axis (i.e., the fiber running direction). Here, the calculation unit 202 may also calculate a local phase delay indicating the magnitude of birefringence, and only when the local phase delay is greater than a certain amount, may the calculation unit 202 display the birefringence optical axis of a portion corresponding to the spatial pixel or position in the three-dimensional image. The calculation unit 202 may also generate an en-face image showing the fiber running direction. Then, the calculation unit 202 displays the image showing the corrected fiber running direction generated in step S20 on the monitor 120 (S22).

[0068] 9(a) and 9(b) show three-dimensional images of the birefringence optical axis of the lower portion of the measurement range of the subject's eye 500 viewed obliquely from above. FIG. 9(a) is a three-dimensional image of the birefringence optical axis generated from the tomographic image shown in FIG. 4 on which the tilt correction process for the birefringence optical axis has not been performed (hereinafter, also referred to as the three-dimensional image of the birefringence optical axis before correction). FIG. 9(b) is a three-dimensional image of the birefringence optical axis generated from the tomographic image shown in FIG. 4 on which the tilt correction process for the birefringence optical axis has been performed (hereinafter, also referred to as the three-dimensional image of the birefringence optical axis after correction). As shown in FIG. 9(a), in the three-dimensional image of the birefringence optical axis before correction, the streamline of the birefringence optical axis in the shallow sclera layer is discontinuous. On the other hand, as shown in FIG. 9(b), in the three-dimensional image of the birefringence optical axis after correction, the streamline of the birefringence optical axis in the shallow sclera layer is depicted smoothly with almost no discontinuities.

[0069] 10(a) and 10(b) show three-dimensional images of the birefringence optical axis when the lower part of the measurement range of the test eye 500 is viewed from the side. FIG. 10(a) shows a three-dimensional image of the birefringence optical axis before correction, and FIG. 10(b) shows a three-dimensional image of the birefringence optical axis after correction. As shown in FIG. 10(a), in the three-dimensional image of the birefringence optical axis before correction, the streamlines of the birefringence optical axis are all oriented in a substantially horizontal direction. On the other hand, as shown in FIG. 10(b), in the three-dimensional image of the birefringence optical axis after correction, the streamlines of the birefringence optical axis are inclined along the surface shape and are smoothly depicted.

[0070] 11(a) and 11(b) show three-dimensional images of the birefringence optical axis as viewed directly from the nasal side of the measurement range of the subject's eye 500. That is, FIGS. 11(a) and 11(b) show the birefringence optical axis from the inside of the anterior chamber to the angle side. FIG. 11(a) shows a three-dimensional image of the birefringence optical axis before correction, and FIG. 11(b) shows a three-dimensional image of the birefringence optical axis after correction. As shown in FIG. 11(a), in the three-dimensional image of the birefringence optical axis before correction, the streamlines of the birefringence optical axis are all directed substantially horizontally, similar to FIG. 10(a). On the other hand, as shown in FIG. 11(b), in the three-dimensional image of the birefringence optical axis after correction, the streamlines of the birefringence optical axis are inclined along the surface shape and are smoothly depicted, similar to FIG. 10(b).

[0071] In this embodiment, by correcting the tilt of the optical axis of birefringence, it is possible to draw a smooth streamline of the optical axis of birefringence in three dimensions. Therefore, it is possible to generate an image showing the running direction of fibers that allows the structure of fibrous tissue to be grasped without having to measure the subject's eye 500 multiple times by changing the incident angle of the probe light.

[0072] Furthermore, in this embodiment, by generating a three-dimensional image of the birefringence optical axis, it is possible to grasp the birefringence optical axis (i.e., the direction of fiber travel) at a desired depth position in the subject's eye 500. Figures 12(a) and 12(b) show en-face images in which a three-dimensional image of the birefringence optical axis is displayed from the surface side of the anterior eye segment after a fixed thickness of 406 μm has been removed from the surface of the anterior eye segment. Figure 12(a) shows an en-face image based on a three-dimensional image of the birefringence optical axis before correction, and Figure 12(b) shows an en-face image based on a three-dimensional image of the birefringence optical axis after correction.

[0073] At a depth of 406 μm from the surface of the anterior segment, scleral fibers running radially from the limbus are present in the arc-shaped range shown as region A in Figures 12(a) and 12(b). As shown in Figure 12(a), in the 3D image of the birefringence optical axis before correction, the streamlines of the birefringence optical axis are short and fragmented, making it difficult to accurately grasp the scleral fibers running radially from the limbus. On the other hand, as shown in Figure 12(b), in the 3D image of the birefringence optical axis after correction, the scleral fibers running radially from the limbus are depicted smoothly.

[0074] Furthermore, at a depth of 406 μm from the surface of the anterior segment, a ring-shaped structure existing in a range deeper than 406 μm is seen at the position indicated by arrow B in FIGS. 12(a) and 12(b), and a ring-shaped structure is also seen at the position indicated by arrow C. Although not shown, the intensity tomographic image shows a structure estimated to be a luminal structure at the center of the ring-shaped structure indicated by arrows B and C. Therefore, it is estimated that a luminal structure such as a collecting duct, vein, or artery exists at the center of the ring-shaped structure indicated by arrows B and C. As shown in FIG. 12(a), in the 3-dimensional image of the birefringence optical axis before correction, the streamline of the birefringence optical axis is short and fragmented, and the radial fiber distribution around the ring-shaped structure indicated by arrows B and C is not sufficiently depicted. On the other hand, as shown in FIG. 12(b), in the 3-dimensional image of the birefringence optical axis after correction, the radial fiber distribution around the ring-shaped structure indicated by arrows B and C is sufficiently depicted.

[0075] In this way, by displaying the optical axis of birefringence (i.e., the running direction of the fibers) at a desired depth position of the subject's eye 500, it is possible to more accurately grasp the running direction of the fibers at a desired depth position of the subject's eye 500. For example, it is possible to accurately grasp the running direction of the fibers near a luminal structure present at a desired depth position of the subject's eye 500. In other words, it is possible to appropriately grasp the fibrous structure of the sclera near a luminal structure present at a desired depth position of the subject's eye 500.

[0076] In this embodiment, the optical axis of birefringence (i.e., the fiber direction) is corrected using the inclination of the surface shape of the tissue in the tomographic image. However, the present invention is not limited to this configuration. For example, the calculation unit 202 may correct the optical axis of birefringence for each tomographic image so that it follows the boundary between adjacent tissues in the subject's eye 500. Specifically, the calculation unit 202 identifies (by segmentation) the boundary between adjacent tissues in the subject's eye 500 for each tomographic image. The calculation unit 202 may then correct the optical axis of birefringence by linearly interpolating between the two adjacent boundary lines. Alternatively, the calculation unit 202 may determine the center of gravity of the intensity signal for each A-scan, generate a depth map of the center of gravity of the entire volume, and use the generated depth map instead of the above-mentioned two-dimensional topographic map. When the depth map is used, the segmentation process can be omitted.

[0077] In this embodiment, the tilt of the optical axis of birefringence (i.e., the fiber running direction) is calculated from the tomographic image and the calculated tilt of the optical axis is corrected, but this configuration is not limited to this. For example, the tomographic image may be deformed in advance so that the tilt of the tissue shape in the tomographic image is flattened, and then an en-face image of the birefringence optical axis (an image of a plane perpendicular to the direction of travel of the probe light deformed to match the tissue shape) may be created using this deformed tomographic image, and streamlines of the birefringence optical axis may be drawn within the en-face image plane. Displaying the birefringence optical axis in this manner omits three-dimensional information including the depth direction, but instead allows the birefringence optical axis to be effectively displayed by limiting it to two-dimensional information within the en-face image plane at a certain depth. Alternatively, two-dimensional streamlines of the optical axis within the en-face image plane at each depth may be created in this manner, and the two-dimensional streamlines may be deformed to restore the tissue shape, thereby creating three-dimensional streamlines of the optical axis. In this case, it is not necessary to perform calculations for streamline rendering on the entire volume data at once, but it is sufficient to repeatedly perform calculations for two-dimensional streamline rendering within the en-face image plane at each depth, thereby saving memory required for calculations in the calculation unit 202. Furthermore, when the depth within the tissue at which the optical axis is to be displayed is limited, the amount of calculations can be effectively reduced by performing streamline rendering only for the limited depth range in the above method.

[0078] In addition, in this embodiment, the tilt of the tissue surface shape in the tomographic image is determined using a tomographic image captured by the optical tomographic imaging apparatus, but this configuration is not limited to this. As long as the surface shape of the subject's eye 500 can be determined, the tilt of the tissue surface shape may be determined using an image other than the tomographic image captured by the optical tomographic imaging apparatus of this embodiment. For example, the calculation unit 202 may determine the tilt of the tissue surface shape using a corneal topography generated from an image captured by a Mayerling image.

[0079] In this embodiment, the measurement object imaged by the optical tomography apparatus is the subject's eye, but this is not limited to this configuration. For example, the measurement object may be a living tissue other than the subject's eye. The measurement object may also be an object having birefringence other than a living body (e.g., a suture thread). In this case, for example, the tilt of the optical axis of birefringence may be corrected so as to follow the surface shape of the birefringent portion of the object.

[0080] In addition, in this embodiment, the calculation unit 202 executes the process of correcting the optical axis of birefringence, but the present invention is not limited to this configuration. For example, another calculation device provided outside the optical tomographic imaging apparatus of this embodiment may acquire a tomographic image of the subject's eye 500 captured by the optical tomographic imaging apparatus of this embodiment, and the other calculation device may execute the process of correcting the optical axis of birefringence.

[0081] Although specific examples of the technology disclosed in this specification have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. Furthermore, the technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technology exemplified in this specification or drawings simultaneously achieves multiple objectives, and achieving one of those objectives itself has technical utility. [Explanation of symbols]

[0082] 10: Measuring part 11:Light source 43: Reference mirror 60, 70: interference light generating unit 80, 90: Interference light detection section 81, 82, 91, 92: Balanced photodetectors 83, 93: Signal processor 84, 85, 94, 95: Signal processing section 100: Sampling trigger / clock generator 140: Sampling trigger generator 160: Sampling clock generator 200: Arithmetic device 202: Arithmetic section 500: Subject's eye S1, S2: Measurement optical path R1, R2: Reference optical path

Claims

1. an acquisition unit that acquires a plurality of tomographic images showing polarization characteristics of a measurement object at cross sections at different positions of the measurement object; a calculation unit that generates an image indicating the direction of the optical axis of birefringence using the plurality of tomographic images, The image processing device wherein the calculation unit identifies a shape of a portion included in the measurement object, and corrects a direction of an optical axis of birefringence of each pixel in each tomographic image so as to conform to the identified shape.

2. the tomographic image is a tomographic image showing polarization characteristics of tissue in a living body, the direction of the optical axis of the birefringence is the direction of fiber travel, the shape is a surface shape of the tissue; The image processing device according to claim 1 , wherein the calculation unit corrects the direction of the optical axis of the birefringence so as to conform to the surface shape.

3. The image processing device according to claim 2 , wherein the calculation unit calculates a tilt of the surface shape and corrects the direction of the optical axis of the birefringence using the calculated tilt.

4. 2. The image processing device according to claim 1, wherein the calculation unit identifies the shape of the tissue of the measurement object from the plurality of tomographic images acquired by the acquisition unit, and corrects the direction of the optical axis of the birefringence so as to conform to the identified shape.

5. The image processing device according to claim 1 , further comprising a display unit that displays an image indicating the direction of the optical axis of the birefringence corrected by the calculation unit.

6. 2. The image processing device according to claim 1, wherein the calculation unit is configured to be capable of generating an en-face image of an image indicating the direction of the optical axis of birefringence after correction.

7. an imaging unit that captures tomographic images at cross sections at different positions of the object to be measured; An optical tomographic imaging apparatus comprising: the image processing device according to any one of claims 1 to 6, which processes a plurality of tomographic images captured by the imaging unit.

8. 1. A computer program for processing a plurality of tomographic images showing polarization characteristics of a measurement object at cross sections at different positions of the measurement object, comprising: Computer, an acquisition unit that acquires the plurality of tomographic images; an identification unit that identifies the shape of a portion included in the measurement object; a correction unit that corrects the direction of the optical axis of birefringence of each pixel in each tomographic image so that the direction is in accordance with the shape identified by the identification unit; a generating unit that generates an image indicating the direction of the optical axis of birefringence corrected by the correcting unit.

Images