JP2020156909A - Optical tomographic image capturing apparatus - Google Patents

Abstract

To provide a technology that contributes to new diagnostic imaging by polarization-sensitive optical tomographic image capturing apparatus.SOLUTION: An optical tomographic image capturing apparatus is a polarization-sensitive optical tomographic image capturing apparatus. The optical tomographic image capturing apparatus includes an image capturing part for capturing a tomographic image of an eye to be examined, and an arithmetic part. The tomographic image includes a first tomographic image captured by irradiating the eye to be examined with a first polarized wave, and a second tomographic image captured by irradiating, with a second polarized wave having a vibration direction different from that of the first polarized wave, the eye to be examined. The arithmetic part is configured so as to execute specification processing for specifying a running mode of a fiber at least in the sclera and the cribrosa lamina of the eye to be examined based on the first tomographic image and the second tomographic image.SELECTED DRAWING: Figure 1

Description

The technique disclosed herein relates to a polarized light sensitive optical tomography apparatus.

Since the optical tomography apparatus is non-invasive and non-contact, it is widely used in ophthalmic apparatus and the like as a method for acquiring a tomographic image of a living tissue.

Birefringence that changes the polarization state occurs in a structure in which molecular and fibrous structures are arranged in a certain direction. In the retina at the fundus, strong birefringence is present in the retinal nerve fiber layer, retinal pigment epithelial layer, blood vessel wall, sclera, and lamina cribrosa. In order to visualize these tissues using this birefringence, a polarization-sensitive optical tomography imaging device, which is one of the functional optical tomography imaging devices, has been developed. For example, Patent Document 1 discloses an example of a polarization-sensitive optical tomography imaging apparatus.

Japanese Unexamined Patent Publication No. 2016-57197

The present specification discloses a technique that contributes to a new image diagnosis by a polarization-sensitive optical tomography imaging apparatus.

The optical tomography imaging device disclosed in the present specification is a polarization-sensitive optical tomography imaging device. The optical tomography imaging apparatus includes an imaging unit that captures a tomographic image of the eye to be inspected and a calculation unit. The tomographic image is a first tomographic image taken by irradiating the eye to be inspected with a first polarized wave, and a second tomographic image to be irradiated with a second polarized wave having a vibration direction different from that of the first polarized wave. Includes the second tomographic image taken in. The calculation unit is configured to be able to execute a specific process for specifying at least the traveling mode of the fibers in the sclera and the sieve plate of the eye to be inspected based on the first tomographic image and the second tomographic image.

In the above-mentioned optical tomographic imaging apparatus, it is possible to identify at least the traveling mode of the fibers in the sclera and the lamina cribrosa of the eye to be inspected based on the first tomographic image and the second tomographic image. As a result, it is possible to grasp the running mode of the fibers in the sclera and the lamina cribrosa of the eye to be inspected, which can contribute to a new diagnostic imaging.

The figure which shows the schematic structure of the optical system of the optical tomography imaging apparatus which concerns on Example. The block diagram which shows the control system of the optical tomography imaging apparatus which concerns on Example. A block diagram showing a configuration of a sampling trigger / clock generator. The flowchart which shows an example of the process which specifies the running mode of a fiber in the sclera of the eye to be examined. The figure for demonstrating the nature of the wavelength band of the light output from a light source. (A) is a tomographic image of the fundus of the eye to be inspected, (b) shows an En-face image of the retina of the inspected eye and a running mode of fibers of the retina, and (c) is an En-face of the sclera of the inspected eye. The image and the running mode of the scleral fibers are shown.

The main features of the examples described below are listed. It should be noted that the technical elements described below are independent technical elements and exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Absent.

(Feature 1) The optical tomography imaging apparatus disclosed in the present specification may further include a display unit for displaying an amphas image of the sclera of the eye to be inspected. The display unit may superimpose the traveling mode on the corresponding position of the scleral amphas image of the eye to be inspected and the sclera amphiscera image. With such a configuration, the examiner can more easily grasp the running mode of the scleral fibers of the eye to be inspected.

(Feature 2) The optical tomographic imaging apparatus disclosed in the present specification is the depth direction of the eye to be inspected in the displayed image when the scleral amphas image and the traveling mode are superimposed on the display unit. It may further include a designated portion for designating the position of the cross section of. When the position of the cross section in the depth direction is designated by the designated unit, the display unit may display a cross-sectional image of the fundus of the eye to be inspected at the position of the designated cross section. With such a configuration, the examiner can easily confirm the cross-sectional image corresponding to the region of interest in the traveling mode of the scleral fibers of the eye to be inspected. Therefore, the state of the eye to be inspected can be grasped more accurately.

(Feature 3) In the optical tomography imaging apparatus disclosed in the present specification, the imaging unit may photograph the fundus of the eye to be inspected using light having a wavelength of 980 nm or more and 1120 nm or less. According to such a configuration, the fundus of the eye to be inspected can be suitably photographed.

(Feature 4) In the optical tomography imaging apparatus disclosed in the present specification, the imaging unit may irradiate the eye to be inspected with a first polarized wave and a second polarized wave due to circular polarization. With such a configuration, it is possible to measure the fibers of the sclera or the lamina cribrosa in any direction, and it is possible to more reliably identify the traveling direction of the fibers.

Hereinafter, the optical tomography imaging apparatus according to the embodiment will be described. The optical coherence tomography apparatus of this embodiment can capture the polarization characteristics of a test object by a wavelength sweep type Fourier domain method (swept-source optical coherence tomography: SS-OCT) using a wavelength sweep type light source. It is a possible polarized light-sensitive OCT (polarization-sensitive OCT: PS-OCT) device.

As shown in FIG. 1, the optical tomographic imaging apparatus of this embodiment includes a light source 11, measurement light generation units (21 to 29, 31, 32) that generate measurement light from the light of the light source 11, and light source 11. The reference light generator (41 to 46, 51) that generates the reference light from the light, the reflected light from the eye 500 to be inspected generated by the measurement light generator, and the reference light generated by the reference light generator are combined. It is provided with interference light generation units 60 and 70 that generate interference light, and interference light detection units 80 and 90 that detect interference light generated by the interference light generation units 60 and 70.

(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. Since the wavelength of the light applied to the eye 500 to be inspected changes (sweeps), the signal obtained from the interference light between the reflected light from the eye 500 to be inspected and the reference light is subjected to Fourier analysis by Fourier analysis in the depth direction of the eye 500 to be inspected. The intensity distribution of the light reflected from each part of the above can be obtained.

A polarization control device 12 and a fiber coupler 13 are connected to the light source 11, and a PMFC (polarization holding fiber coupler) 14 and a sampling trigger / clock generator 100 are connected to the fiber coupler 13. 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 of the light source 11 to generate a sampling trigger and a sampling clock for each of the signal processors 83 and 93, which will be described later.

(Measurement light generator)
The measurement light generators (21 to 29, 31, 32) are a polarized beam combiner that connects the PMFC21 connected to the PMFC14, the two measurement optical paths S1 and S2 branched from the PMFC21, and the two measurement optical paths S1 and S2. It includes a splitter 25, a collimator lens 26 connected to the polarizing beam combiner / splitter 25, an optical path extension 306, galvanometer mirrors 27 and 28, and a lens 29. An optical path length difference generation unit 22 and a circulator 23 are arranged in the measurement optical path S1. Only the circulator 24 is arranged in the measurement optical path S2. Therefore, the optical path length difference ΔL between the measurement optical path S1 and the measurement optical path 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 inspected. As a result, it is possible to prevent interference lights having different optical path length differences from overlapping. For the optical path length difference generation unit 22, for example, an optical fiber may be used, or an optical system such as a mirror or a prism may be used. In this embodiment, a 1 m PM fiber is used for the optical path length difference generation unit 22. Further, the measurement light generation unit further includes PMFCs 31 and 32. The PMFC 31 is connected to the circulator 23. The PMFC 32 is connected to the circulator 24.

One of the lights branched by the PMFC 14 (that is, the measurement light) is input to the measurement light generation unit (21 to 29, 31, 32). The PMFC 21 divides the measurement light input from the PMFC 14 into a first measurement light and a second measurement light. The first measurement light divided by the PMFC 21 is guided to the measurement optical path S1, and the second measurement light is guided to the measurement optical path S2. The first measurement light guided to the measurement optical path S1 is input to the polarized beam combiner / splitter 25 through the optical path length difference generation unit 22 and the circulator 23. The second measurement light guided to the measurement optical path S2 is input to the polarized beam combiner / splitter 25 through the circulator 24. The PM fiber 304 is connected to the polarizing beam combiner / splitter 25 in a state of being rotated 90 degrees in the circumferential direction 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 the first measurement light. Since the optical path length difference generation unit 22 is provided in the measurement optical path S1, the first measurement light is delayed by the distance of the optical path length difference generation unit 22 with respect to the second measurement light (that is, the optical path length difference ΔL is large. Is happening). The polarized beam combiner / splitter 25 superimposes the input first measurement light and the second measurement light. The light output from the polarized beam combiner / splitter 25 (light in which the first measurement light and the second measurement light are superimposed) is applied to the eye 500 to be inspected through the collimator lens 26, the galvanometer mirrors 27 and 28, and the lens 29. To. The light emitted to the eye 500 to be inspected is scanned by the galvanometer mirrors 27 and 28 in the xy direction.

The light applied to the eye 500 to be inspected is reflected by the eye 500 to be inspected. Here, the light reflected by the eye 500 to be inspected is scattered on or inside the eye 500 to be inspected. The reflected light from the eye 500 to be inspected passes through the lens 29, the galvanometer mirrors 28, 27 and the collimator lens 26, and is input to the SMFC 26, and is input to the polarized beam combiner / splitter 25, contrary to the incident path. The polarized beam combiner / splitter 25 divides the input reflected light into two polarized components that are orthogonal to each other. Here, for convenience, they are referred to as horizontally polarized reflected light (horizontally polarized light component) and vertically polarized light reflected light (vertically polarized light component). Then, the horizontally polarized reflected light is guided to the measurement optical path S1, and the vertically polarized reflected light is guided to the measurement optical path S2.

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

(Reference light generator)
The reference optical generators (41 to 46, 51) are branched from the circulator 41 connected to the PMFC 14, the reference delay line (42, 43) connected to the circulator 41, the PMFC 44 connected to the circulator 41, and the PMFC 44. It includes two reference optical paths R1 and R2, a PMFC 46 connected to the reference optical path R1, and a PMFC 51 connected to the reference optical path R2. An optical path length difference generation unit 45 is arranged in the reference optical path R1. The reference optical path R2 is not provided with an optical path length difference generation unit. Therefore, the optical path length difference ΔL'between the reference optical path R1 and the reference optical path 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 difference ΔL and ΔL'the same, the depth positions of the plurality of interference lights described later with respect to the eye 500 to be inspected become the same. That is, it is not necessary to align the acquired tomographic images.

The other light branched by the PMFC 14 (that is, the reference light) is input to the reference light generation unit (41 to 46, 51). The reference light input from the PMFC 14 is input to the reference delay lines (42, 43) through the circulator 41. 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 lines (42, 43) is applied to 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 can move in a direction closer to or away from the collimator lens 42. In this embodiment, the position of the reference mirror 43 is adjusted so that the signal from the eye 500 to be inspected falls within the measurement range in the depth direction of the OCT before starting the measurement.

The optical path of the reference light reflected by the reference mirror 43 is changed by the circulator 41 and input to the PMFC 44. The PMFC 44 branches the input reference light into a first reference light and a second reference light. The first reference light is guided to the reference optical path R1, and the second reference light is guided to the reference optical path R2. The first reference light is input to the PMFC 46 through the optical path length difference generation unit 45. The reference light input to the PMFC 46 is branched into a first branch reference light and a second branch reference light. The first branch reference light is input to the PMFC 61 through the collimator lens 47 and the lens 48. The second branch reference light is input to the PMFC 62 through the collimator lens 49 and the lens 50. The second reference light is input to the PMFC 51 and is divided into a third branch reference light and a fourth branch reference light. The third branch reference light is input to the PMFC 71 through the collimator lens 52 and the lens 53. The fourth branch reference light is input to the PMFC 72 through the collimator lens 54 and the lens 55.

(Interference light generator)
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 has PMFCs 61 and 62. As described above, the horizontally polarized light reflected from the measurement light generation unit is input to the PMFC 61, and the first branch reference light (light having an optical path length difference ΔL') is input from the reference light generation unit. Here, the horizontally polarized reflected light includes a reflected light component (light having an optical path length difference ΔL) due to the first measurement light and a reflected light component (light having no optical path length difference ΔL) due to the second measurement light. ing. Therefore, in the PMFC 61, the reflected light component (light having an optical path length difference ΔL) of the first measurement light and the first branch reference light are combined to form the first interference light (horizontal polarized light component). Is generated.

Further, vertically polarized reflected light is input to the PMFC 62 from the measurement light generation unit, and second branch reference light (light having an optical path length difference ΔL') is input from the reference light generation unit. Here, the vertically polarized reflected light includes a reflected light component (light having an optical path length difference ΔL) due to the first measurement light and a reflected light component (light having no optical path length difference ΔL) due to the second measurement light. ing. Therefore, in the PMFC 62, the reflected light component (light having an optical path length difference ΔL) of the first measurement light and the second branch reference light of the vertically polarized reflected light are combined to form the second interference light (vertically polarized light). Is generated.

The second interference light generation unit 70 has PMFCs 71 and 72. As described above, the horizontally polarized light reflected from the measurement light generation unit is input to the PMFC 71, and the third branch reference light (light having no optical path length difference ΔL') is input from the reference light generation unit. Therefore, in the PMFC 71, the reflected light component (light having no optical path length difference ΔL) by the second measurement light and the third branch reference light of the horizontally polarized reflected light are combined to form the third interference light (horizontal polarized light component). ) Is generated.

Further, vertically polarized reflected light is input to the PMFC 72 from the measurement light generation unit, and fourth branch reference light (light having no optical path length difference ΔL') is input from the reference light generation unit. Therefore, in the PMFC 72, the reflected light component (light having no optical path length difference ΔL) by the second measurement light and the fourth branch reference light among the vertically polarized reflected light are combined to form the fourth interference light (vertically polarized light component). ) Is generated. The first interference light and the second interference light correspond to the measurement light passing through the measurement light path S1, and the third interference light and the fourth interference light correspond to the measurement light passing through the measurement light path S2.

(Interference light detector)
The interference light detection units 80 and 90 include a first interference light detection unit 80 that detects the interference light (first interference light and the second interference light) generated by the first interference light generation unit 60, and a second interference light generation unit. A second interference light detection unit 90 for detecting the interference light (third interference light and fourth interference light) generated by the unit 70 is provided.

The first interference light detection unit 80 includes balanced photodetectors 81, 82 (hereinafter, also simply referred to as “detectors 81, 82”) and a signal processor 83 connected to the detectors 81, 82. .. A PMFC 61 is connected to the detector 81, and a signal processor 83 is connected to the output terminal of the detector 81. The PMFC 61 branches the first interference light into two interference lights having 180 degrees out of phase and inputs the first interference light to the detector 81. The detector 81 performs differential amplification and noise reduction processing on two interference lights input from the PMFC 61 whose phases differ by 180 degrees, converts them into an electric signal (first interference signal), and converts the first interference signal into an electric signal (first interference signal). Output to the signal processor 83. That is, the first interference signal is the interference signal HH of the horizontally polarized light reflected light from the eye 500 to be inspected and the reference light by the horizontally polarized light 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 branches the second interference light into two interference lights having 180 degrees out of phase, and inputs the second interference light to the detector 82. The detector 82 performs differential amplification and noise reduction processing on two interference lights having 180 degrees out of phase, converts them into an electric signal (second interference signal), and converts the second interference signal into the signal processor 83. Output to. That is, the second interference signal is the interference signal HV of the vertically polarized light reflected from the eye 500 to be examined and the reference light by the horizontal polarization measurement light.

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 the sampling trigger and the sampling clock input from the sampling trigger / clock generator 100 to the signal processor 83. Further, the second signal processing unit 85 samples the second interference signal based on the sampling trigger and the 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 the calculation unit 202 described later. A known data acquisition device (so-called DAQ) can be used for the signal processor 83.

Similar to the first interference light detection unit 80, the second interference light detection unit 90 includes balanced photodetectors 91, 92 (hereinafter, also simply referred to as “detectors 91, 92”) and detectors 91, 92. It includes a connected signal processor 93. A PMFC 71 is connected to the detector 91, and a signal processor 93 is connected to the output terminal of the detector 91. The PMFC 71 branches the third interference light into two interference lights having 180 degrees out of phase and inputs the third interference light to the detector 91. The detector 91 performs differential amplification and noise reduction processing on two interference lights having 180 degrees out of phase, converts them into an electric signal (third interference signal), and converts the third interference signal into a signal processor 93. Output to. That is, the third interference signal is the interference signal VH of the horizontally polarized light reflected from the eye 500 to be inspected and the reference light by the vertical polarization 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 branches the fourth interference light into two interference lights having 180 degrees out of phase, and inputs the fourth interference light to the detector 92. The detector 92 performs differential amplification and noise reduction processing on two interference lights having 180 degrees out of phase, converts them into an electric signal (fourth interference signal), and converts the fourth interference signal into a signal processor 93. Output to. That is, the fourth interference signal is the interference signal VV of the vertically polarized light reflected light of the eye 500 to be inspected and the reference light from the vertically polarized light measurement light.

The signal processor 93 includes a third signal processing unit 94 to which a third interference signal is input and a fourth signal processing unit 95 to which a fourth interference signal is input. The third signal processing unit 94 samples the third interference signal based on the sampling trigger and the sampling clock input from the sampling trigger / clock generator 100 to the signal processor 93. Further, the fourth signal processing unit 95 samples the fourth interference signal based on the sampling trigger and the 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 the calculation unit 202 described later. A known data acquisition device (so-called DAQ) can also be used for the signal processor 93. According to such a configuration, it is possible to acquire an interference signal representing the four polarization characteristics of the eye 500 to be inspected. In this embodiment, signal processors 83 and 93 including two signal processing units are used, but the configuration is not limited to this. For example, one signal processor having four signal processing units may be used, or four signal processing devices including one signal processing unit may be used.

Next, the configuration of the control system of the optical tomography imaging device according to this embodiment will be described. As shown in FIG. 2, the optical tomography imaging device is controlled by the arithmetic unit 200. The arithmetic unit 200 includes an arithmetic 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 eye 500 to be inspected. The first interference light detection unit 80 triggers the sampling trigger 1 with respect to the interference signals (interference signal HH and interference signal HV) input from the measurement unit 10 to the sampling clock 1 input from the measurement unit 10. Based on this, the first sampling data is acquired, and the first sampling data is output to the calculation unit 202. The calculation unit 202 performs arithmetic processing such as Fourier transform processing on the first sampling data to generate an HH tomographic image and an HV tomographic image. The second interference light detection unit 90 uses the sampling trigger 2 as a trigger to set the sampling clock 2 input from the measurement unit 10 to the interference signal (interference signal VH and interference signal VV) input from the measurement unit 10. Based on this, the second sampling data is acquired, and the second sampling data is output to the calculation unit 202. The calculation unit 202 performs arithmetic processing such as Fourier transform processing on the second sampling data to generate a VH tomographic image and a VV tomographic image. Here, the HH tomographic image, the VH tomographic image, the HV tomographic image, and the VV tomographic image are tomographic images at the same position. Therefore, the calculation unit 202 can generate a tomographic image of four polarization characteristics (HH, HV, VH, VV) representing the Jones matrix of the eye 500 to be inspected.

As shown in FIG. 3, the sampling trigger / clock generator 100 includes a fiber coupler 102, a sampling trigger generator (140 to 152), and a sampling clock generator (160 to 172). The light from the light source 11 is input to the sampling trigger generator 140 and the sampling clock generator 160, respectively, via the fiber coupler 13 and the fiber coupler 102.

(Sampling trigger generator)
The sampling trigger generator 140 may generate a sampling trigger by 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 to the sampling trigger 1 and the sampling trigger 2. The sampling trigger 1 is input to the calculation unit 202 via the signal delay circuit 152. The sampling trigger 2 is input to the calculation unit 202 as it is. The sampling trigger 1 is a trigger signal for 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 is a trigger signal for 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 the sampling trigger 1 delays the sampling trigger 2 by the amount of the optical path length difference ΔL of the optical path length difference generation unit 22. As a result, the frequency at which sampling of the interference signal input from the first interference light detection unit 80 is started can be made the same as the frequency at which sampling of the interference signal input from the second interference light detection unit 90 is started. .. Here, only the sampling trigger 1 may be generated. Since the optical path length difference ΔL is known, when sampling the interference input from the second interference light detection unit 90, sampling may be started so as to delay the time by the optical path length difference ΔL from the sampling trigger 1. ..

(Sampling clock generator)
The sampling clock generator may be composed of, for example, a Mach-Zehnder interferometer. As shown in FIG. 3, the sampling clock generator uses a Mach-Zehnder interferometer to generate an equal frequency sampling clock. The sampling clock generated by the Mach-Zehnder interferometer is input to the distributor 172. The distributor 172 distributes the sampling clock to the sampling clock 1 and the sampling clock 2. The sampling clock 1 is input to the first interference light detection unit 80 through the signal delay circuit 174. The sampling clock 2 is directly input to the second interference light detection unit 90. The signal delay circuit 174 is designed so that the time is delayed by the optical path length difference ΔL of the optical path length difference generation unit 22. As a result, even the interference light delayed by the optical path length difference generation unit 22 can be sampled at the same timing. As a result, it is possible to prevent misalignment of a plurality of acquired tomographic images. In this embodiment, a Mach-Zehnder interferometer is used to generate the sampling clock. However, a Michelson interferometer may be used or an electric circuit may be used to generate the sampling clock. Further, a sampling lock may be generated by using a light source provided with a sampling clock generator as the light source.

Next, with reference to FIGS. 4 to 6, a process for specifying the traveling mode of the fibers in the sclera of the eye 500 to be inspected will be described. FIG. 4 is a flowchart showing an example of a process for specifying a traveling mode of fibers in the sclera of the eye 500 to be inspected using the optical tomography imaging apparatus of this embodiment.

As shown in FIG. 4, first, the calculation unit 202 acquires a tomographic image of the fundus of the eye 500 to be inspected (S12). The process of acquiring a tomographic image of the fundus of the eye 500 to be inspected is executed by the following procedure. First, the inspector operates an operating member such as a joystick (not shown) to align the optical tomography imaging device with respect to the eye 500 to be inspected. That is, the calculation unit 202 drives a position adjusting mechanism (not shown) in response to the operation of the operating member of the inspector. As a result, the position of the optical tomography imaging device with respect to the eye 500 to be inspected is adjusted in the xy direction (vertical and horizontal directions) and the position in the z direction (advance and retreat directions).

Next, the calculation unit 202 takes a tomographic image of the fundus of the eye 500 to be inspected. Here, the imaging conditions of the fundus of the eye 500 to be inspected in this embodiment will be described. In this embodiment, in order to specify the traveling mode of the sclera fibers of the eye 500 to be inspected, it is necessary to take a tomographic image of the fundus of the eye 500 to be examined so as to include the sclera. To measure the sclera of the fundus, light needs to pass through the retina and choroid. Furthermore, it is desirable that the anterior chamber of the eye, the crystalline lens, and the vitreous have low light attenuation due to water absorption. As the optical wavelength satisfying these conditions, a wavelength band of about 800 nm and a wavelength band of about 1060 nm are known. Here, a specific description will be given with reference to FIG. Graph G1 of FIG. 5 shows the relationship between the wavelength of light and the absorption coefficient of water as shown by the arrow, and graph G2 shows the wavelength and luminosity of light as shown by the arrow. It shows the relationship of sensitivity (Log quantal luminosity efficiency). As shown in FIG. 5, the wavelength band (A) of about 800 nm is a wavelength band of about 760 to 910 nm, and light absorption by water is small in near-infrared light (see graph G1), so that light is good for the fundus. Since it reaches and the relative luminosity of photoreceptor cells is small (see Graph G2), it has the property that the subject is less likely to feel glare. Further, in FIG. 5, the wavelength band (B) of about 1060 nm is a wavelength band of about 980 to 1120 nm, and the light absorption by water is smaller in the longer wavelength band than that of (A) (see graph G1), and further, photoreceptor cells. However, because it does not sense light (see Graph G2), the subject does not feel any glare. Of these wavelength bands, it is known that the longer wavelength band of around 1060 nm has a lower light scattering intensity and therefore has a higher depth of penetration into living tissues. In particular, in order to measure fibrous scar tissue generated by the sclera of the fundus, the optic disc, age-related macular degeneration, etc., a wavelength band of around 1060 nm is advantageous not only in normal OCT but also in polarized OCT. is there. Therefore, in this embodiment, light having a central wavelength of 1060 nm is emitted from the light source 11, and a tomographic image of the fundus of the eye 500 to be inspected is taken.

In this example, a tomographic image of the fundus is taken, but it is also possible to take an image for identifying the fibrous tissue of the eyeball other than the fundus by using the technique of this example. For example, it is possible to measure the fibrous tissue of the anterior segment using a wavelength band of 1310 nm, 1550 nm, 1700 nm, or a visible wavelength band.

Examples of the fibrous tissue of the anterior segment include the stroma, trabecular meshwork, conjunctival parenchyma, sclera, extraocular muscle, iris sphincter muscle, dilator muscle of the pupil, and ciliary muscle. Examples of the fibrous tissue of the diseased eye include pterygium and scar tissue of filter vesicles formed by trabeculectomy. In addition, a material having birefringence may be used for an artificial object such as a resin implant used in glaucoma filtration surgery or a resin artificial intraocular lens used in cataract surgery, and measurement can be performed by polarized OCT. In addition, smooth muscles, elastic fibers, and collagen fibers are generally present in the blood vessel wall regardless of the anterior segment of the eye or the fundus, and the birefringence of these fibrous tissues can be measured by polarized OCT.

In addition, as the principle of OCT, OCT using each of the above wavelength bands is implemented in all of the time domain method for scanning the optical path length of the reference light, the spectral domain method using a spectroscope, and the swept source method using a wavelength sweep light source. It is possible.

The light emitted from the light source 11 is incident on the eye 500 to be inspected by clockwise or counterclockwise circular polarization. When clockwise or counterclockwise circular polarization is used as the incident polarization state on the eye 500 to be inspected, the birefringence of the fibers can be measured regardless of the direction in which the fibers of the object to be measured (that is, the strong membrane) are oriented. This is because in the case of circularly polarized light, when polarized light is decomposed into a component parallel to the axis and a component perpendicular to the axis of the birefringence of the fiber, each component decomposed in both axial directions has the same amplitude, and in each axial direction. This is because the phase delay generated between the polarization components can be reliably measured.

In this embodiment, since the sclera of the fundus is measured, the incident polarization state is changed by the cornea and the optic nerve fiber before the light reaches the sclera, and the incident polarization state coincides with or is orthogonal to the sclera fiber direction. It may be linearly polarized. In that case, the birefringence of the sclera cannot be measured accurately. This phenomenon is not limited to the sclera of the fundus, but can generally occur in any part of the living body. To rule out the above possibility, there is a method of measuring the Jones matrix of an object using two or more different incident polarizations. By measuring the Jones matrix with polarized OCT, it is possible to reliably measure the birefringence of an object regardless of the incident polarization state.

Further, in this embodiment, a tomographic image of the fundus is taken by using a raster scan. The method of taking a tomographic image of the fundus to measure the scleral fibers of the fundus is not limited to raster scan. For example, any lateral scan such as a radial scan or a concentric scan may be used, but it is desirable that the scan includes the vicinity of the optic nerve head in which the scleral fibers are oriented in the circumferential direction. It is known that the optic nerve fibers and the sclera in the vicinity of the optic nerve head have radial and concentric fiber directions centered on the optic nerve head, respectively. In addition, since Henle's fiber near the normal central retinal defect has a radial fiber direction centered on the central defect, the central retinal defect may be included in the scan range. By including the site where the fiber direction is anatomically clear in the scan range in this way, it is possible to confirm whether or not there is a large error in the measurement.

Next, the calculation unit 202 identifies the sclera from the tomographic image acquired in step S12 (S14). The process of identifying the sclera is performed according to the following procedure. In order to measure birefringence and fiber running of the retina, it is first necessary to determine the inner limiting membrane of the retina and the inner segment outer segment junction of the photoreceptor cells from the polarized OCT data. In order to measure birefringence and scleral run of the sclera, it is first necessary to determine the photoreceptor inner segment outer segment junction of the retina and the choroid / sclera interface from the polarized OCT data. Specifically, the above-mentioned structures and interfaces can be obtained by applying binarization based on the intensity gradient and threshold value of the image to the OCT intensity image and applying an appropriate particle filter to the image. ..

The method for identifying the sclera is not limited to the above method. For example, the OCT intensity image may be manually segmented for each of the above-mentioned tissues / interfaces, supervised machine learning may be performed using a technique such as deep learning, and any OCT intensity image may be automatically segmented. ..

In addition, as another method, it is possible to utilize the difference in characteristics between the choroid and the sclera in order to determine the choroid / sclera interface. For example, a living choroid is filled with blood and blood flow is always present, while the sclera is not filled with blood. When the B scan of polarized OCT is repeated at the same position on the fundus, the speckle pattern of OCT changes with time in the choroid where blood flow exists. The choroid / sclera interface can be determined by parameterizing and imaging this change with time by the cross-correlation function of the OCT intensity or the complex signal over time and applying the same image processing technique as the segmentation to the OCT intensity image. Here, instead of the cross-correlation function, the change over time of the Jones vector or matrix measured by polarized OCT is represented by the covariance matrix, the temporal or spatial ensemble average is obtained, and the eigenvalue of the ensemble-averaged covariance matrix is obtained. It is also possible to obtain the entropy from and image it.

Also, the normal choroid contains melanin pigment, whereas the sclera contains almost no melanin pigment. Since the melanin dye has a depolarizing property that randomizes the polarization state, it may be used to determine the choroid / sclera interface. Depolarization property can be defined and visualized by parameters such as the degree of polarization uniformity defined by the Stokes parameter and polarization entropy, which is an index showing the disorder of the Jones matrix calculated by Cloude-Pottier decomposition.

In addition, the sclera shows strong birefringence due to collagen fiber bundles, whereas the choroid does not show strong birefringence. Since the amount of phase delay that can be measured by polarized OCT differs between the choroid and the sclera, the contrast may be used to determine the choroid / sclera interface.

As described above, the internal limiting membrane, the photoreceptor inner segment outer segment junction, and the choroid / sclera interface can be determined from various parameters and contrasts obtained by OCT or polarized OCT. In the segmentation, only a single image, for example, an OCT intensity image may be used, or a plurality of images or data contrasts may be combined for the segmentation.

The calculation unit 202 extracts a region showing the specified sclera from the tomographic image and generates an En-face image composed of only the sclera. Specifically, for the three-dimensional data, the maximum value, the average value, and the like are calculated in the depth direction for each A scan, and the three-dimensional data is compressed into a two-dimensional En-face image.

Next, the calculation unit 202 specifies the traveling mode of the fibers with respect to the sclera identified in step S14 (S16). The process of identifying the running mode of the fibers in the sclera is performed by the following procedure.

The Jones matrix of the inner limiting membrane of the retina measured when identifying the sclera in step S14 above is defined as the following equation 1, and the Jones matrix of the photoreceptor inner segment outer segment junction is defined as the following equation 2. It is defined as.

Here, J _in is a Jones matrix representing all the polarization characteristics of the polarized OCT light from the light source 11 to irradiating the inner boundary film, and J _out is the reference light reflected or scattered from the inner boundary film. It is a Jones matrix that represents all the polarization characteristics that it receives before it interferes with. J _ILM is a Jones matrix that represents the local polarization properties of the inner limiting membrane. JP _R is a Jones matrix that represents the polarization properties between the inner limiting membrane and the photoreceptor inner segment outer segment junction. The superscript t represents matrix transpose.

At this time, the local Jones matrix from the inner limiting membrane to the inner segment outer segment junction of the photoreceptor cells is obtained as follows.

Here, U _PRILMin is, (K _ILM) is a matrix composed of eigenvectors of ^-1 K _PR, the lambda _PR, is a diagonal matrix composed of characteristic values including a phase delay amount of J _PR. U _PRILMin and lambda _PR is calculated by both (K _ILM) of ^-1 K _PR to eigenvalue decomposition.

Using the rotation matrix R _PR composed of the eigenvectors of J _PR , U _PRILMin can be described as follows.

The birefringence axis relative to an arbitrary position (x ₁ , y ₁ ) in the lateral direction at the depth of the inner segment outer segment junction of the photoreceptor can be obtained by using the following equation.

Here, U (x, y) is a matrix composed of eigenvectors of U _PRILMin (x ₁ , y ₁ ) (U _PRILMin ) ^-1 (x ₁ , y ₁ ), and is Λ (x − x ₁ , y). y-y ₁₎ is the relative birefringent axes θ (exp (iθ), 0 ; is a diagonal matrix containing at 0, exp (-iθ)) that form. As described above, the Jones matrix is not converted to, for example, the Stokes parameter, which is the third-order rotation group, and the inner limiting membrane to the photoreceptor inner segment outer segment junction, while maintaining the form of the second-order special unitary group. The direction of the birefringence axis existing between can be determined.

The birefringence axis of the sclera can also be obtained by an algorithm similar to the above. The Jones matrix of the sclera just below the choroid / sclera boundary membrane measured by polarized OCT is defined as follows.

The local Jones matrix between the inner segment of the photoreceptor and the sclera just below the choroid / sclera border membrane is determined as follows.

Here, the following equation 8 holds.

Between the inner segment and outer segment junction of the photoreceptor and the choroid / sclera border membrane, there is a retinal pigment cell layer with melanin pigment and a choroid. Backscattered light from a melanin dye is known to have depolarizing properties, but transmitted light does not. Therefore, the polarization state of the light transmitted through the retinal pigment cell layer and the choroid does not change, and the Jones matrix can be considered to be an identity matrix. The birefringence axis relative to an arbitrary position (x ₁ , y ₁ ) in the lateral direction at the depth where the sclera exists just below the choroid / sclera boundary membrane is calculated using the following equation. Can be done.

Similar to the case of the inner segment outer segment junction of the photoreceptor cells described above, the scleral compound in which the eigenvalue of the equation shown in the above equation 9 is relative to an arbitrary position (x ₁ , y ₁ ) in the lateral direction. Indicates the direction of the axis of refraction.

In principle, the fiber direction and fiber running can be obtained from the birefringence axis of the retina or sclera by the above method. However, since the raw data of the Jones matrix measured by polarized OCT contains speckle noise, it is desirable to apply noise reduction processing.

For example, Cloude-Pottier decomposition can be used as the noise reduction processing of the Jones matrix. In this method, each element of the Jones matrix is rearranged into a 4-by-1 vector, the 4-by-4 covariance matrix is obtained from that vector, and the covariance matrix is obtained for pixels within a specified kernel size. By finding the ensemble average and finding the eigenvalues of the ensemble-averaged covariance matrix, the Jones matrix within its kernel size can be estimated most likely. In addition, a method of finding the average of Jones matrices standardized by global phase can also be used. In this embodiment, the average of the Jones matrix first normalized by the global phase is calculated for K _ILM at a depth of 5 pixels and for K _Sc at a depth of 20 pixels. After that, K _ILM , K _PR, and K _Sc perform noise reduction processing of the Jones matrix using Cloude-Pottier decomposition in the range of kernel size 21 × 11 pixels in the horizontal direction on the En-face plane at each tissue depth. .. Then, the above-mentioned algorithm for calculating the birefringence axis is applied to derive the fiber direction.

Next, the calculation unit 202 causes the monitor 120 to display the traveling mode of the scleral fibers identified in step S16 (S18). Specifically, as shown in FIG. 6C, the calculation unit 202 identifies the sclera En-face image generated in step S14 and the corresponding position of the sclera En-face image in step S16. The running mode of the scleral fibers is superimposed and displayed on the monitor 120.

As a method of visualizing the birefringence axis direction as an image, it is possible to display the axis direction corresponding to an arbitrary pseudo color map. However, it is not always easy to intuitively read the axial direction from the colors of the color map. Therefore, it is possible to draw a curve corresponding to the axial direction, a so-called streamline. In general, algorithms and software for drawing streamlines are readily available. For example, you can use Heliosphere Research LCC's Advanced Plotting Toolkit, which is provided as an add-on to National Instruments LabVIEW, to draw streamlines in the birefringence axis direction. Alternatively, the same processing may be performed using the open source software Matplotlib. The streamline drawn in this way can be presented as an image by itself, or can be superimposed and displayed on another polarized OCT image. In particular, it is effective for the photographer to intuitively understand the data when the streamline is superimposed and displayed on the image in which the birefringence axis direction is visualized by a pseudo color map.

Further, when a position in the En-face image of the sclera displayed on the monitor 120 is specified, a tomographic image corresponding to the position may be displayed. At this time, the corresponding tomographic image and the sclera En-face image may be displayed side by side on the monitor 120, or the display may be switched from the sclera En-face image to the corresponding tomographic image. By displaying the tomographic image of the specified position, it is possible to confirm the state of the cross section of the fundus at the position where a lesion or the like is suspected from the traveling mode of the scleral fiber. Therefore, the state of the suspected lesion can be grasped more accurately.

In the above example, based on the data of the fundus measured by polarized OCT, each layer of the inner limiting membrane, the inner segment of the photoreceptor, the choroid / sclera is segmented, and the inner retina and the sclera are segmented. An example of visualizing fiber running is shown. This technique can be applied to any fibrous tissue, not just the retinal lining and sclera. For example, when visualizing the fiber running of the lamina cribrosa inside the optic nerve head, the above-mentioned intraphalangeal extranode junction should be read as the optic nerve fiber / sieving plate boundary, and the choroid / scleral boundary membrane should also be the optic nerve fiber. / By reading the boundary of the optic disc, it is possible to visualize the optic nerve fiber running above the optic disc and the fiber running inside the optic disc. Unlike the sclera example described above, in the case of this sieve plate, the optic nerve fiber, which is a fiber existing above the sieve plate, is in contact with the sieve plate, so that the segmentation used for the calculation of fiber running is performed. It is sufficient to have two layers instead of three.

Although specific examples of the disclosed techniques have been described in detail in the present specification, these are merely examples and do not limit the scope of claims. The techniques described in the claims include various modifications and modifications of the specific examples illustrated above. In addition, the technical elements described in the present specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing.

10: Measuring unit 11: Light source 43: Reference mirror 60, 70: Interference light generation unit 80, 90: Interference light detection unit 81, 82, 91, 92: Balanced photodetector 83, 93: Signal processor 84, 85 , 94, 95: Signal processing unit 100: Sampling trigger / clock generator 140: Sampling trigger generator 160: Sampling lock generator 200: Arithmetic device 202: Arithmetic unit 500: Eyes to be inspected S1, S2: Measurement optical path R1, R2: Reference light path

Claims (5)

It is a polarized light-sensitive optical tomography imaging device.
The imaging unit that captures the tomographic image of the eye to be inspected,
It has a calculation unit and
The tomographic image includes a first tomographic image taken by irradiating the eye to be inspected with a first polarized wave and a second polarized wave having a vibration direction different from that of the first polarized wave in the eye to be inspected. Includes a second tomographic image taken by irradiating
Based on the first tomographic image and the second tomographic image, the calculation unit is configured to be capable of executing at least a specific process for specifying the traveling mode of the fibers in the sclera and the sieve plate of the eye to be inspected. Optical tomography imaging device. It is further provided with a display unit for displaying an unfussed image of the sclera of the eye to be inspected.
The display unit is an optical tomography imaging apparatus that superimposes the traveling mode on a corresponding position of the sclera amphas image of the eye to be inspected together with the sclera amphiscera image. When the sclera amphas image and the traveling mode are superimposed on the display unit, a designation unit for designating the position of the cross section of the eye to be inspected in the depth direction is further provided in the displayed image. Ori,
The display unit according to claim 2, wherein when the position of the cross section in the depth direction is designated by the designated unit, the display unit displays a cross-sectional image of the fundus of the eye to be inspected at the position of the designated cross section. Optical tomography imaging device. The optical tomography imaging apparatus according to any one of claims 1 to 3, wherein the imaging unit photographs the fundus of the eye to be inspected using light having a wavelength of 980 nm or more and 1120 nm or less. The optical tomographic imaging apparatus according to any one of claims 1 to 4, wherein the photographing unit irradiates the eye to be inspected with the first polarized wave and the second polarized wave due to circular polarization.