JP7332131B2 - Optical tomography system - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act May 19, 2018, 2nd Annual General Meeting of the Japanese Society of Nearsightedness, Knowledge Capital Congress Convention Center (3-1 Ofukacho, Kita-ku, Osaka, Grand Front Osaka North Building B2F) [Published] Materials] February 3, 2019, Photonics West 2019, Moscone Center (747 Howard Street, San Francisco, CA, USA)

The technology disclosed in the present specification relates to a polarization-sensitive optical tomography apparatus.

2. Description of the Related Art Optical tomographic imaging apparatuses are non-invasive and non-contact, and are widely used in ophthalmic apparatuses and the like as a method for acquiring tomographic images of living tissue.

Birefringence that changes the polarization state occurs in a structure in which molecules or fibers are arranged in a certain direction. In the retina of the fundus, strong birefringence exists in the retinal nerve fiber layer, retinal pigment epithelium layer, blood vessel wall, sclera, and cribriform plate. In order to visualize these tissues using this birefringence, a polarization-sensitive optical tomographic imaging apparatus, which is one of functional optical tomographic imaging apparatuses, has been developed. For example, Patent Document 1 discloses an example of a polarization-sensitive optical tomography apparatus.

JP 2016-57197 A

This specification discloses a technique that contributes to new image diagnosis using a polarization-sensitive optical tomography apparatus.

The optical tomography apparatus disclosed in this specification is a polarization-sensitive optical tomography apparatus. An optical tomography apparatus includes an imaging unit that captures a tomographic image of an eye to be inspected, and a computing unit. The tomographic images are a first tomographic image captured by irradiating the eye to be inspected with a first polarized wave and a tomographic image by irradiating the eye to be inspected with a second polarized wave having a vibration direction different from that of the first polarized wave. and a second tomographic image taken at. The calculation unit is configured to be capable of executing identification processing for identifying a running mode of fibers in at least the sclera and cribriform plate of the subject's eye based on the first tomographic image and the second tomographic image.

In the optical tomography apparatus described above, it is possible to specify the running mode of fibers in at least the sclera and cribriform plate of the subject's eye 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 cribriform plate of the subject's eye, which can contribute to new diagnostic imaging.

1 is a diagram showing a schematic configuration of an optical system of an optical tomography apparatus according to an embodiment; FIG. 1 is a block diagram showing a control system of an optical tomography apparatus according to an embodiment; FIG. FIG. 2 is a block diagram showing the configuration of a sampling trigger/clock generator; FIG. 4 is a flow chart showing an example of a process for identifying a running mode of fibers in the sclera of an eye to be examined. FIG. 4 is a diagram for explaining properties of wavelength bands of light output from a light source; (a) is a tomographic image of the fundus of the eye to be examined, (b) is an En-face image of the retina of the eye to be examined and the running mode of retinal fibers, and (c) is the En-face of the sclera of the eye to be examined. The image and the running state of the scleral fibers are shown.

The main features of the embodiments 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 as of the filing. do not have.

(Feature 1) The optical tomography apparatus disclosed in the present specification may further include a display unit that displays an Amphas image of the sclera of the subject's eye. The display unit may display the Amphas image of the sclera of the eye to be inspected together with the running mode superimposed on the corresponding position of the Amphas image of the sclera. With such a configuration, the examiner can more easily grasp the running mode of the scleral fibers of the eye to be examined.

(Feature 2) The optical tomographic imaging apparatus disclosed in the present specification, when an amphas image of the sclera and the running mode are superimposed and displayed on the display unit, shows the depth direction of the eye to be inspected in the displayed image. may further include a designating portion that designates the position of the cross section of the . The display unit may display a cross-sectional image of the fundus of the subject's eye at the specified cross-sectional position when the cross-sectional position in the depth direction is specified by the specifying unit. According to such a configuration, the examiner can easily check the cross-sectional image corresponding to the region of interest in the running mode of the scleral fibers of the eye to be examined. Therefore, it is possible to more accurately grasp the condition of the subject's eye.

(Feature 3) In the optical tomographic imaging apparatus disclosed in this specification, the imaging unit may image the fundus of the subject's eye using light with a wavelength of 980 nm or more and 1120 nm or less. With such a configuration, the fundus of the subject's eye can be photographed favorably.

(Feature 4) In the optical tomography apparatus disclosed in this specification, the imaging unit may irradiate the subject's eye with a first polarized wave and a second polarized wave of circularly polarized light. According to such a configuration, the measurement can be performed regardless of the direction in which the fibers of the sclera and cribriform plate are oriented, and the running direction of the fibers can be more reliably specified.

An optical tomography apparatus according to an embodiment will be described below. The optical tomography apparatus of the present embodiment can capture the polarization characteristics of a test object by a wavelength sweeping Fourier domain method (swept-source optical coherence tomography: SS-OCT) using a wavelength sweeping light source. A possible polarization-sensitive OCT (PS-OCT) device.

As shown in FIG. 1, the optical tomography 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 from the light source 11, and the light source 11. A reference light generator (41 to 46, 51) that generates reference light from light, and the reflected light from the subject's eye 500 generated by the measurement light generator and the reference light generated by the reference light generator are combined. and interference light generators 60 and 70 for generating interference light, and interference light detectors 80 and 90 for detecting the interference light generated by the interference light generators 60 and 70 .

(light source)
The light source 11 is a wavelength swept light source, and the wavelength (wave number) of emitted light changes at a predetermined cycle. Since the wavelength of the light irradiated to the subject's eye 500 changes (sweeps), the signal obtained from the interference light between the reflected light from the subject's eye 500 and the reference light is subjected to Fourier analysis to obtain the depth direction of the subject's eye 500. It is possible to obtain the intensity distribution of the light reflected from each part of .

A polarization controller 12 and a fiber coupler 13 are connected to the light source 11 , and a PMFC (Polarization Maintaining 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 controller 12 and the fiber coupler 13, respectively. The sampling trigger/clock generator 100 uses light from the light source 11 to generate sampling triggers and sampling clocks for signal processors 83 and 93, which will be described later.

(Measurement light generator)
Measurement light generators (21 to 29, 31, 32) include PMFC 21 connected to PMFC 14, two measurement optical paths S1 and S2 branched from PMFC 21, and a polarization beam combiner / It comprises a splitter 25 , a collimator lens 26 connected to the polarization beam combiner/splitter 25 , an optical path extender 306 , galvanomirrors 27 , 28 and a lens 29 . An optical path length difference generator 22 and a circulator 23 are arranged in the measurement optical path S1. Only the circulator 24 is arranged in the measuring 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 generator 22 . The optical path length difference ΔL may be set longer than the measurement range of the subject's eye 500 in the depth direction. As a result, it is possible to prevent overlapping of interference lights with different optical path length differences. For the optical path length difference generator 22, for example, an optical fiber may be used, or an optical system such as a mirror or a prism may be used. In the present embodiment, a 1 m PM fiber is used for the optical path length difference generator 22 . In addition, the measurement light generator further includes PMFCs 31 and 32 . PMFC 31 is connected to circulator 23 . PMFC 32 is connected to circulator 24 .

One light branched by the PMFC 14 (that is, the measurement light) is input to the measurement light generators (21 to 29, 31, 32). The PMFC 21 splits the measurement light input from the PMFC 14 into first measurement light and second measurement light. The first measurement light split 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 polarization beam combiner/splitter 25 through the optical path length difference generator 22 and the circulator 23 . The second measurement light guided to the measurement optical path S2 passes through the circulator 24 and enters the polarization beam combiner/splitter 25 . PM fiber 304 is connected to polarizing beam combiner/splitter 25 circumferentially rotated 90 degrees with respect to PM fiber 302 . As a result, the second measurement light input to the polarization beam combiner/splitter 25 has a polarization component orthogonal to that of the first measurement light. Since the optical path length difference generator 22 is provided in the measurement light path S1, the first measurement light is delayed from the second measurement light by the distance of the optical path length difference generator 22 (that is, the optical path difference ΔL is occurring). The polarization beam combiner/splitter 25 superimposes the input first measurement light and second measurement light. The light output from the polarization beam combiner/splitter 25 (light in which the first measurement light and the second measurement light are superimposed) is applied to the subject's eye 500 via the collimator lens 26, the galvanometer mirrors 27 and 28, and the lens 29. be. The light applied to the eye 500 to be examined is scanned in the xy direction by the galvanomirrors 27 and 28 .

The light irradiated to the subject's eye 500 is reflected by the subject's eye 500 . Here, the light reflected by the eye 500 to be examined scatters on the surface and inside the eye 500 to be examined. Reflected light from the subject's eye 500 passes through the lens 29 , the galvanometer mirrors 28 and 27 and the collimator lens 26 in the reverse direction of the incident path, is input to the SMFC 26 , and is input to the polarization beam combiner/splitter 25 . Polarization beam combiner/splitter 25 splits the incoming reflected light into two mutually orthogonal polarization components. Here, for convenience, they are referred to as horizontally polarized reflected light (horizontal polarized component) and vertically polarized reflected light (vertically polarized component). 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 horizontally polarized reflected light has its optical path changed by the circulator 23 and is input to the PMFC 31 . The PMFC 31 splits the input horizontally polarized reflected light and inputs the split light to the PMFCs 61 and 71, respectively. Therefore, the horizontally polarized reflected light input to the PMFCs 61 and 71 contains a reflected light component of the first measurement light and a reflected light component of the second measurement light. The vertically polarized reflected light has its optical path changed by the circulator 24 and is input to the PMFC 32 . The PMFC 32 splits the input vertically polarized reflected light and inputs the split light to the PMFCs 62 and 72 . Therefore, the vertically polarized reflected light input to the PMFCs 62 and 72 contains a reflected light component of the first measurement light and a reflected light component of the second measurement light.

(Reference beam generator)
The reference light generators (41 to 46, 51) include 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, and branches from the PMFC 44. A PMFC 46 connected to the reference optical path R1 and a PMFC 51 connected to the reference optical path R2 are provided. An optical path length difference generator 45 is arranged in the reference optical path R1. An optical path length difference generator is not provided in the reference optical path R2. 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 generator 45. FIG. For example, an optical fiber is used for the optical path length difference generator 45 . The optical path length ΔL′ of the optical path length difference generator 45 may be the same as the optical path length ΔL of the optical path length difference generator 22 . By making the optical path differences ΔL and ΔL′ the same, the depth positions of a plurality of interfering light beams to be examined 500 become the same. In other words, it is not necessary to align a plurality of tomographic images to be acquired.

The other light (that is, the reference light) branched by the PMFC 14 is input to the reference light generators (41 to 46, 51). The reference light input from PMFC 14 passes through circulator 41 and is input to reference delay lines (42, 43). A reference delay line (42, 43) is composed of a collimator lens 42 and a reference mirror 43. FIG. 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 is movable in a direction to approach or separate from the collimator lens 42 . In this embodiment, before starting the measurement, the position of the reference mirror 43 is adjusted so that the signal from the eye 500 to be examined falls within the depth-direction measurement range of OCT.

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

(interference light generator)
The interference light generators 60 and 70 include a first interference light generator 60 and a second interference light generator 70 . The first interference light generator 60 has PMFCs 61 and 62 . As described above, the PMFC 61 receives the horizontally polarized reflected light from the measurement light generator and the first branched reference light (the light having the optical path difference ΔL′) from the reference light generator. Here, the horizontally polarized reflected light includes a reflected light component of the first measurement light (light having the optical path difference ΔL) and a reflected light component of the second measurement light (light having no optical path difference ΔL). ing. Therefore, in the PMFC 61, the reflected light component (the light having the optical path difference ΔL) from the first measuring light in the horizontally polarized reflected light and the first branched reference light are combined to form the first interference light (horizontally polarized component). is generated.

The PMFC 62 also receives the vertically polarized reflected light from the measurement light generator and the second branched reference light (the light having the optical path difference ΔL′) from the reference light generator. Here, the vertically polarized reflected light includes a reflected light component of the first measurement light (light having the optical path difference ΔL) and a reflected light component of the second measurement light (light having no optical path difference ΔL). ing. Therefore, in the PMFC 62, the reflected light component (the light having the optical path difference ΔL) from the first measurement light in the vertically polarized reflected light and the second branched reference light are combined to form the second interference light (vertically polarized component). is generated.

The second interference light generator 70 has PMFCs 71 and 72 . As described above, the PMFC 71 receives the horizontally polarized reflected light from the measurement light generator and the third branched reference light (light without the optical path difference ΔL′) from the reference light generator. Therefore, in the PMFC 71, the reflected light component (light having no optical path difference ΔL) of the second measurement light among the horizontally polarized reflected light and the third branched reference light are combined to form the third interference light (horizontal polarized component ) is generated.

The PMFC 72 also receives the vertically polarized reflected light from the measurement light generator and the fourth branched reference light (light without the optical path difference ΔL′) from the reference light generator. Therefore, in the PMFC 72, the reflected light component of the second measuring light (the light having no optical path difference ΔL) among the vertically polarized reflected light and the fourth branched reference light are combined to form the fourth interference light (vertically polarized component ) is generated. The first interference light and the second interference light correspond to the measurement light passing through the measurement optical path S1, and the third interference light and the fourth interference light correspond to the measurement light passing through the measurement optical path S2.

(interference light detector)
Interference light detection units 80 and 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 generation unit. A second interference light detection section 90 is provided to detect the interference light (the third interference light and the fourth interference light) generated by the section 70 .

The first interference light detection section 80 includes balanced photodetectors 81 and 82 (hereinafter also simply referred to as “detectors 81 and 82”) and a signal processor 83 connected to the detectors 81 and 82. . A PMFC 61 is connected to the detector 81 , and a signal processor 83 is connected to an 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 input from the PMFC 61 whose phases differ by 180 degrees, converts them into electrical signals (first interference signals), and converts the first interference signals into electrical signals (first interference signals). Output to the signal processor 83 . That is, the first interference signal is the interference signal HH between the horizontally polarized light reflected from the eye 500 by the horizontally polarized measurement light and the reference light. Similarly, PMFC 62 is connected to detector 82 , and signal processor 83 is connected to the output terminal of 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 interfering lights whose phases differ by 180 degrees, converts them into electrical signals (second interference signals), and converts the second interference signals into signal processors 83 output to That is, the second interference signal is the interference signal HV between the vertically polarized light reflected from the eye 500 by the horizontally polarized measurement light and the reference light.

The signal processor 83 includes a first signal processing section 84 to which the first interference signal is input, and a second signal processing section 85 to which the second interference signal is input. The first signal processor 84 samples the first interference signal based on the sampling trigger and sampling clock input from the sampling trigger/clock generator 100 to the signal processor 83 . Also, the second signal processing unit 85 samples the second interference signal based on the sampling trigger and 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 section 84 and the second signal processing section 85 are input to the calculation section 202, which will be 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 and 92 (hereinafter also simply referred to as “detectors 91 and 92”) and detectors 91 and 92. It has 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 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 interfering lights whose phases differ by 180 degrees, converts them into electrical signals (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 between the horizontally polarized light reflected from the eye 500 by the vertically polarized measurement light and the reference 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 interfering lights whose phases are different by 180 degrees, converts them into electrical signals (fourth interference signals), and converts the fourth interference signals to the signal processor 93. output to That is, the fourth interference signal is the interference signal VV between the vertically polarized light reflected from the subject's eye 500 from the vertically polarized measurement light and the reference light.

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

Next, the configuration of the control system of the optical tomography apparatus according to this embodiment will be described. As shown in FIG. 2, the optical tomography apparatus is controlled by an arithmetic unit 200. FIG. The computing device 200 is composed of a computing section 202 , a first interference light detection section 80 and a second interference light detection section 90 . The first interference light detection section 80 , the second interference light detection section 90 and the calculation section 202 are connected to the measurement section 10 . The calculation unit 202 outputs a control signal to the measurement unit 10 and drives the galvanomirrors 27 and 28 to scan the incident position of the measurement light on the eye 500 to be examined. The first interference light detection unit 80 detects the interference signals (interference signal HH and interference signal HV) input from the measurement unit 10 using the sampling trigger 1 as a trigger, and 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 calculation processing such as Fourier transform processing on the first sampling data to generate an HH tomographic image and an HV tomographic image. Triggered by the sampling trigger 2, the second interference light detection unit 90 responds to the interference signals (interference signal VH and interference signal VV) input from the measurement unit 10 by using the sampling clock 2 input from the measurement unit 10. Based on this, it acquires the second sampling data 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 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 of 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 examined.

As shown in FIG. 3, the sampling trigger/clock generator 100 comprises a fiber coupler 102, sampling trigger generators (140-152), and sampling clock generators (160-172). Light from the light source 11 is input to the sampling trigger generator 140 and the sampling clock generator 160 through the fiber couplers 13 and 102, respectively.

(sampling trigger generator)
The sampling trigger generator 140 may generate sampling triggers using, for example, an FBG (Fiber Bragg Grating) 144 . As shown in FIG. 3, the FBG 144 reflects only specific wavelengths of light incident from the light source 11 to generate sampling triggers. The generated sampling trigger is input to distributor 150 . Distributor 150 distributes the sampling triggers to sampling trigger 1 and sampling trigger 2 . The sampling trigger 1 is input to the calculation section 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 serves as a trigger signal for interference signals (first interference signal and second interference signal) input from the first interference light detector 80 to the calculator 202 . Sampling trigger 2 serves as a trigger signal for the interference signals (the third interference signal and the fourth interference signal) input from the second interference light detector 90 to the calculator 202 . The signal delay circuit 152 is designed so that the sampling trigger 1 is delayed with respect to the sampling trigger 2 by the optical path length difference ΔL of the optical path length difference generator 22 . As a result, the frequency at which sampling of the interference signal input from the first interference light detection section 80 is started can be the same as the frequency at which sampling of the interference signal input from the second interference light detection section 90 is started. . Here, only sampling trigger 1 may be generated. Since the optical path difference ΔL is known, when sampling the interference input from the second interference light detector 90, sampling may be started with a time delay of the optical path difference ΔL from the sampling trigger 1. .

(sampling clock generator)
The sampling clock generator may, for example, consist of a Mach-Zehnder interferometer. As shown in FIG. 3, the sampling clock generator uses a Mach-Zehnder interferometer to generate equal-frequency sampling clocks. A sampling clock generated by the Mach-Zehnder interferometer is input to the distributor 172 . The distributor 172 distributes the sampling clock to sampling clock 1 and sampling clock 2 . The sampling clock 1 is input to the first interference light detection section 80 through the signal delay circuit 174 . The sampling clock 2 is directly input to the second interference light detector 90 . The signal delay circuit 174 is designed to delay time by the optical path length difference ΔL of the optical path length difference generator 22 . As a result, the interference light delayed by the optical path length difference generator 22 can be sampled at the same timing. Thereby, it is possible to prevent positional deviation of the plurality of tomographic images to be acquired. 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. Alternatively, a light source having a sampling clock generator may be used as the light source to generate the sampling lock.

Next, processing for identifying the running mode of fibers in the sclera of the eye 500 to be examined will be described with reference to FIGS. 4 to 6. FIG. FIG. 4 is a flow chart showing an example of processing for identifying the running mode of fibers in the sclera of the subject's eye 500 using the optical tomography apparatus of this embodiment.

As shown in FIG. 4, first, the computing unit 202 acquires a tomographic image of the fundus of the subject's eye 500 (S12). The process of acquiring the tomographic image of the fundus of the subject's eye 500 is executed in the following procedure. First, the examiner operates an operation member such as a joystick (not shown) to align the optical tomography apparatus with respect to the eye 500 to be examined. That is, the calculation unit 202 drives a position adjustment mechanism (not shown) according to the operation of the operation member by the examiner. As a result, the position of the optical tomographic imaging apparatus with respect to the eye 500 to be examined is adjusted in the xy direction (longitudinal and horizontal directions) and in the z direction (forward and backward movement direction).

Next, the calculation unit 202 captures a tomographic image of the fundus of the eye 500 to be examined. Here, imaging conditions for the fundus of the subject's eye 500 in this embodiment will be described. In this embodiment, in order to specify the running mode of the fibers of the sclera of the subject's eye 500, when capturing a tomographic image of the fundus of the subject's eye 500, it is necessary to capture the sclera as well. To measure the sclera of the fundus, light must pass through the retina and choroid. Furthermore, it is desirable that the attenuation of light due to light absorption by water in the anterior chamber, crystalline lens, and vitreous body of the eye is low. As light wavelengths satisfying these conditions, a wavelength band around 800 nm and a wavelength band around 1060 nm are known. Here, a specific description will be given with reference to FIG. Graph G1 in FIG. 5 shows the relationship between the wavelength of light and the absorption coefficient of water, as indicated by arrows, and the graph G2, as indicated by the arrows, shows the wavelength of light and relative It shows the relationship of sensitivity (Log quantal luminosity efficiency). As shown in FIG. 5, the wavelength band around 800 nm (A) is a wavelength band of approximately 760 to 910 nm, and in the near-infrared light, the light absorption by water is small (see graph G1), so the light is good for the fundus. Since the light reaches the photoreceptor and the relative luminosity of the photoreceptor is small (see graph G2), the subject is less likely to perceive glare. In addition, in FIG. 5, the wavelength band (B) around 1060 nm is a wavelength band of approximately 980 to 1120 nm, and the light absorption by water is small in the longer wavelength band than (A) (see graph G1). does not sense light (see graph G2), the subject does not feel glare at all. Among these wavelength bands, it is known that the wavelength band around 1060 nm, which is the longer wavelength, has a lower light scattering intensity and therefore penetrates into living tissue more deeply. In particular, the wavelength band around 1060 nm is advantageous not only for normal OCT but also for polarized OCT in order to measure the fibrous scar tissue generated by the sclera of the fundus, the cribriform plate of the optic disc, and age-related macular degeneration. be. For this reason, in this embodiment, the light source 11 emits light with a center wavelength of 1060 nm, and a tomographic image of the fundus of the subject's eye 500 is captured.

In this embodiment, a tomographic image of the fundus is captured, but the technique of this embodiment can also be used to capture an image for identifying fibrous tissue of the eyeball other than the fundus. For example, it is possible to measure fibrous tissue in the anterior segment of the eye 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 corneal stroma, trabecular meshwork, conjunctival stroma, sclera, extraocular muscle, pupillary sphincter muscle, pupillary dilator muscle, and ciliary muscle. Fibrous tissue in diseased eyes includes pterygium and scar tissue of filtering bleb formed by trabeculectomy. Materials having birefringence are sometimes used in artificial objects such as resin implants used in glaucoma filtration surgery and resin artificial intraocular lenses used in cataract surgery, which can be measured by polarization OCT. In addition, smooth muscle, elastic fiber, and collagen fiber generally exist in the blood vessel wall regardless of the site of the anterior segment or fundus, and the birefringence of these fiber tissues can be measured by polarization OCT.

In addition, as the principle of OCT, OCT using each wavelength band described above is implemented in all of the time domain method that scans the optical path length of the reference light, the spectral domain method that uses a spectrometer, and the swept source method that uses a wavelength swept light source. It is possible.

The light emitted from the light source 11 is incident on the subject's eye 500 as clockwise or counterclockwise circularly polarized light. If right-handed or left-handed circularly polarized light is used as the incident polarization state to the eye 500 to be inspected, the birefringence of the fibers of the object to be measured (that is, the sclera) can be measured regardless of the orientation of the fibers. This is because, in the case of circularly polarized light, when the polarized light is decomposed into a component parallel to the axis of the birefringence of the fiber and a component perpendicular to the axis of the birefringence of the fiber, each component obtained by decomposing the polarized light in both axial directions has the same amplitude. This is because the phase delay occurring between the polarization components can be reliably measured.

In this example, since the sclera of the fundus is measured, the incident polarization state is changed by the cornea and optic nerve fibers before the light reaches the sclera, and the incident polarization state coincides with or is perpendicular to the fiber direction of the sclera. It can 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 generally can occur in measurements of any part of the living body. To eliminate the above possibilities, there are methods of measuring the Jones matrix of an object using two or more different incident polarizations. By measuring the Jones matrix with polarization OCT, it is possible to reliably measure the birefringence of an object regardless of the incident polarization state.

Also, in this embodiment, a tomographic image of the fundus is captured using raster scanning. Note that the method of taking a tomographic image of the fundus for measuring the fibers of the sclera of the fundus is not limited to raster scanning. For example, a radial scan, a concentric scan, or any other lateral scan may be used, but preferably a scan that includes the vicinity of the optic nerve head where the scleral fibers are oriented in the circumferential direction. It is known that the optic nerve fibers and the sclera near the optic nerve head have radial and concentric fiber orientations, respectively, centered on the optic nerve head. In addition, since Henle's fibers in the vicinity of the normal central retinal malformation have radial fiber directions centered on the central retinal malformation, the retinal central malformation may be included in the scanning range. By including a region where the fiber direction is anatomically clear in the scanning range, 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 processing for identifying the sclera is executed in the following procedure. In order to measure the birefringence and fiber running of the retina, it is first necessary to determine the inner limiting membrane of the retina and the junction between the inner and outer segments of the photoreceptors from the polarized OCT data. In order to measure the birefringence and fiber running of the sclera, it is necessary to first determine the junction between the inner and outer segments of the photoreceptors and the choroid/scleral interface of the retina from the polarized OCT data. Specifically, by applying binarization to the OCT intensity image using the image intensity gradient and threshold, and applying an appropriate particle filter to the image, the above-mentioned tissues and interfaces can be obtained. .

Note that 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 tissue/interface described above, supervised machine learning may be performed using a technique such as deep learning, and an arbitrary OCT intensity image may be automatically segmented. .

Alternatively, differences in the properties of the choroid and sclera can be used to determine the choroid/sclera interface. For example, the viable choroid is filled with blood and there is constant blood flow, while the interior of the sclera is not filled with blood. When the B-scan of the polarized OCT is repeatedly performed at the same position of the fundus, the OCT speckle pattern changes with time in the choroid where blood flow exists. This change over time can be parameterized and imaged by the cross-correlation function of the OCT intensity or complex signal over time, and the choroid/sclera interface can be determined by applying image processing techniques similar to segmentation for OCT intensity images. Here, instead of the cross-correlation function, the temporal change of the Jones vector or matrix measured by polarization OCT is represented by a covariance matrix, its temporal or spatial ensemble average is obtained, and the eigenvalues of the ensemble-averaged covariance matrix It is also possible to obtain the entropy from .

Also, the normal choroid contains melanin pigment, whereas the sclera contains little melanin pigment. Melanin pigments may be used to determine the choroid/scleral interface since they have depolarizing properties that randomize the polarization state. Depolarization can be defined and visualized by parameters such as the degree of polarization uniformity defined by the Stokes parameter and the polarization entropy, which is an index indicating the disorder of the Jones matrix calculated by the Cloude-Pottier decomposition.

Also, the sclera exhibits strong birefringence due to the collagen fiber bundles, whereas the choroid does not exhibit strong birefringence. Since the amount of phase delay measurable by polarization OCT differs between the choroid and the sclera, the contrast may be used to determine the choroid/sclera interface.

As described above, the inner limiting membrane, photoreceptor inner segment/outer segment junction, and choroid/scleral interface can be determined from various parameters and contrasts obtained by OCT or polarized OCT. A single image such as an OCT intensity image may be used for segmentation, or a combination of multiple images and data contrast may be used for segmentation.

The calculation unit 202 extracts a region indicating the specified sclera from the tomographic image, and generates an en-face image composed only of the sclera. Specifically, for the three-dimensional data, the maximum value, average value, etc. 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 identifies the running mode of fibers in the sclera identified in step S14 (S16). The process of identifying the running mode of 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 in Equation 1 below, and the Jones matrix of the junction between the inner and outer segments of the photoreceptors is defined as Equation 2 below. Define as

Here, J _in is a Jones matrix that represents all the polarization characteristics of polarized OCT light from the light source 11 until it irradiates the inner limiting film, and J _out is the reference light reflected or scattered from the inner limiting film. is a Jones matrix that represents all the polarization characteristics received until interference with . J _ILM is the Jones matrix representing the local polarization properties in the inner limiting membrane. J _PR is the Jones matrix representing the polarization properties from the inner limiting membrane to the junction of the inner and outer segments of photoreceptors. The superscript t represents matrix transpose.

At this time, the local Jones matrix from the inner limiting membrane to the junction between the inner and outer segments of photoreceptors is obtained as follows.

Here, U _PRILMin is a matrix composed of eigenvectors of (K _ILM ) ⁻¹ K _PR , and Λ _PR is a diagonal matrix composed of eigenvalues including the phase delay amount of JP _R . Both _UPRILMin and _ΛPR are obtained by _eigenvalue decomposition of ( _KILM ) ^-1KPR .

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

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

where U(x, y) is the matrix composed of the eigenvectors of U _PRILMin (x ₁ , y ₁ )(U _PRILMin ) ⁻¹ (x ₁ , y ₁ ), and Λ(x−x ₁ , yy ₁ ) is a diagonal matrix containing its relative birefringence axis θ in the form (exp(iθ),0;0,exp(-iθ)). As described above, without converting the Jones matrix into, for example, the Stokes parameter, which is a third-order rotation group, while maintaining the form of a second-order special unitary group, It is possible to determine the direction of the birefringence axis existing between

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

The local Jones matrix between the junction of the inner and outer photoreceptor segments to the sclera just below the choroid/scleral boundary membrane is obtained as follows.

Here, the following formula 8 holds.

Between the inner and outer photoreceptor junctions and the choroid/scleral boundary membrane, there is a retinal pigment cell layer with melanin pigment and the choroid. Backscattered light from melanin pigments is known to have depolarizing properties, but transmitted light does not. Therefore, the Jones matrix can be considered to be a unit matrix because the polarization state of light passing through the retinal pigment cell layer and the choroid does not change. 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/scleral limiting membrane can be obtained using the following equation. can be done.

As in the case of the photoreceptor inner segment-outer segment junction described above, the eigenvalues of the equation shown in Equation 9 above are the scleral complexes relative to an arbitrary position (x ₁ , y ₁ ) in the lateral direction. Indicates the direction of the axis of refraction.

In principle, it is possible to obtain the fiber direction and fiber run from the birefringence axis of the retina or sclera by the above-described method. However, since the Jones matrix raw data measured by polarization OCT contains speckle noise, it is desirable to apply noise reduction processing.

Cloude-Pottier decomposition, for example, can be used as Jones matrix noise reduction processing. In this method, each element of the Jones matrix is rearranged into a vector of 4 rows and 1 column, a covariance matrix of 4 rows and 4 columns is obtained from the vector, and the covariance matrix of pixels within a specified kernel size is Finding the ensemble average and finding the eigenvalues of the ensemble averaged covariance matrix allows maximum likelihood estimation of the Jones matrix within that kernel size. Alternatively, a method of finding the average of Jones matrices normalized by the global phase can also be used. In this embodiment, the average of the Jones matrices normalized by the global phase is first determined for K _ILM for a depth of 5 pixels and for K _Sc for a depth of 20 pixels. K _ILM , K _PR and K _Sc then denoise the Jones matrix using Cloude-Pottier decomposition with a kernel size of 21×11 pixels laterally on the en-face plane at each tissue depth. . The algorithm for calculating the birefringence axis described above is then applied to derive the fiber orientation.

Next, the calculation unit 202 causes the monitor 120 to display the running mode of the scleral fibers identified in step S16 (S18). Specifically, as shown in FIG. 6(c), the calculation unit 202 specifies the position corresponding to the en-face image of the sclera generated in step S14 and the corresponding position of the en-face image of the sclera in step S16. The monitor 120 superimposes and displays the running state of the scleral fibers.

As a method of visualizing the birefringence axis direction as an image, it is possible to display the axis direction in correspondence with an arbitrary pseudo color map. However, it is not always easy to intuitively read the axial direction from the color map colors. Therefore, it is possible to draw a curve corresponding to the axial direction, a so-called streamline. Algorithms and software for rendering streamlines are generally readily available. For example, the Advanced Plotting Toolkit from Heliosphere Research LCC, which is provided as an add-on to LabVIEW from National Instruments, can be used to draw streamlines along the birefringence axis. Alternatively, similar processing may be performed using open source software Matplotlib. The streamline drawn in this manner can be presented as an image by itself, or it can be displayed superimposed on another polarization OCT image. In particular, it is effective for the photographer to intuitively understand the data by superimposing the streamline on the image in which the birefringence axis direction is visualized with 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 that position may be displayed. At this time, the corresponding tomographic image and the en-face image of the sclera may be displayed side by side on the monitor 120, or the display may be switched from the en-face image of the sclera to the corresponding tomographic image. By displaying the tomographic image of the designated position, the state of the cross section of the fundus can be confirmed for the position where a lesion or the like is suspected from the running pattern of the scleral fibers. Therefore, it is possible to more accurately grasp the state of the portion suspected of having a lesion.

In the above example, based on the fundus data measured by polarized OCT, each layer of the inner retinal limiting membrane, photoreceptor inner segment outer segment junction, choroid/scleral limiting membrane is segmented, and the inner retina and 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 cribriform plate inside the optic nerve head, the above-mentioned photoreceptor inner segment/outer segment junction is read as the optic nerve fiber/cribriform plate boundary, and the choroid/scleral boundary membrane is also optic nerve fiber /Boundary of the lamina cribrosa, the fiber running of the optic nerve fibers above the cribriform plate and the fiber running inside the cribriform plate can be visualized. Unlike the above example of the sclera, in the case of this example of the cribriform plate, the optic nerve fibers, which are fibers existing above the cribriform plate, are in contact with the lamina cribriformis. Two layers are sufficient instead of three layers.

Although specific examples of the technology disclosed in this specification have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. In addition, the technical elements described in this specification or in 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: Measurement unit 11: Light source 43: Reference mirrors 60, 70: Interference light generators 80, 90: Interference light detection units 81, 82, 91, 92: Balanced photodetectors 83, 93: Signal processors 84, 85 , 94, 95: Signal processing unit 100: Sampling trigger/clock generator 140: Sampling trigger generator 160: Sampling lock generator 200: Arithmetic unit 202: Arithmetic unit 500: Eyes to be examined S1, S2: Measurement optical paths R1, R2: reference path

Claims (5)

A polarization-sensitive optical tomography apparatus,
an imaging unit that captures a tomographic image of an eye to be inspected;
and a computing unit,
The tomographic images are a first tomographic image captured 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. and a second tomographic image taken by irradiating the
The computing unit is configured to be capable of executing a specific process for identifying a running mode of fibers in at least the sclera and cribriform plate of the eye to be examined based on the first tomographic image and the second tomographic image. Optical tomographic imaging device. further comprising a display unit for displaying an anphas image of the sclera of the subject's eye,
2. The optical tomographic imaging apparatus according to claim 1 , wherein the display unit displays the Amphas image of the sclera of the subject's eye and the running mode superimposed on a corresponding position of the Amphas image of the sclera. a designating unit for designating a cross-sectional position of the subject's eye in the depth direction in the displayed image when the anphas image of the sclera and the running mode are superimposed and displayed on the display unit; cage,
3. The display unit according to claim 2, wherein, when the position of the cross section in the depth direction is specified by the specifying unit, the display unit displays a cross-sectional image of the fundus oculi of the subject's eye at the specified position of the cross section. Optical tomographic imaging device. The optical tomographic imaging apparatus according to any one of claims 1 to 3, wherein the imaging unit images the fundus of the subject's eye using light with a wavelength of 980 nm or more and 1120 nm or less. The optical tomography apparatus according to any one of claims 1 to 4, wherein the imaging unit irradiates the eye to be inspected with the first polarized wave and the second polarized wave of circularly polarized light.