JP2018068578A - OCT apparatus and OCT control program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an OCT apparatus and an OCT control program which efficiently correct the misalignment of an image caused by a movement of a subject eye.SOLUTION: There is provided an OCT apparatus which captures a tomographic image of a subject using optical interference between measurement light and reference light, the OCT apparatus comprising: scan means for scanning the subject with the measurement light; and control means for controlling the scan means such that each time a scan cycle to scan the measurement light along a scan path is repeated a plurality of times at the same position, the position of the scan path is changed within an imaging range, with the scan path before and after the change overlapping each other in at least one point.SELECTED DRAWING: Figure 3

Description

  The present disclosure relates to an OCT apparatus that acquires a tomographic image using optical interference between measurement light and reference light, and an OCT control program.

  Divides the light from the light source into measurement light and reference light, acquires the interference light of the measurement light and reference light irradiated to the test object, and processes the acquired interference signal to acquire the tomographic image of the test object An OCT apparatus is known (see Patent Document 1).

JP 2006-212153 A

  In the OCT apparatus as described above, if the subject moves during imaging, the image may shift. In such a case, an image shift may be corrected by taking images of the same part a plurality of times and synthesizing these images. However, taking an image a plurality of times increases the imaging time, which is a burden on the subject.

  In view of the above problems, it is an object of the present disclosure to provide an OCT apparatus and an OCT control program that efficiently correct image shift due to movement of a subject.

  In order to solve the above problems, the present disclosure is characterized by having the following configuration.

(1) An OCT apparatus that obtains a tomographic image of a subject using optical interference between measurement light and reference light, the scanning means for scanning the measurement light with respect to the subject, and controlling the scanning means And a control means for changing the position of the scanning path within the imaging range each time a scanning cycle for scanning the measurement light along the scanning path is repeated a plurality of times at the same position, and the control means comprises: The position of the scanning path is changed so that the scanning paths before and after the change overlap at least one point.
(2) An OCT apparatus that obtains a tomographic image of a subject using optical interference between measurement light and reference light, the scanning means for scanning the measurement light with respect to the subject, and controlling the scanning means Each time a scanning cycle for scanning the measurement light along the scanning path is repeated, a control unit that changes the position of the scanning path within an imaging range, and an arithmetic unit that acquires OCT data based on the interference light The control means changes the position of the scanning path so that the scanning paths before and after the change overlap at least at one point, and the calculation means obtains redundantly in the overlapping portion where the scanning paths overlap. Analyzing the overlapped OCT data to estimate the movement of the subject, and the control means corrects the position of the scanning path based on the estimated movement of the eye to be examined. To do.
(3) An OCT control program that is executed in an OCT apparatus that obtains a tomographic image of a subject using optical interference between measurement light and reference light, and is executed by a processor to A scanning step for controlling the scanning means for scanning the measurement light and scanning the measurement light a plurality of times along the same scanning path, and each time the scanning step is repeated, the scanning path is at least one point before and after the change. And a scanning position changing step of changing the position of the scanning path so as to overlap with each other.
(4) An OCT control program that is executed in an OCT apparatus that obtains a tomographic image of a subject using optical interference between measurement light and reference light, and is executed by a processor so that the subject A scanning step for scanning the measuring light and scanning the measuring light along the scanning path, and each time the scanning step is repeated, the scanning path overlaps at least one point before and after the change. A scanning position changing step for changing the position of the scanning path; an estimation step for estimating the movement of the subject by analyzing overlapping OCT data obtained by overlapping in an overlapping portion where the scanning paths overlap; and A correction step of correcting the position of the scanning path based on the movement of the eye to be examined estimated in the estimation step; It is made to perform.

It is the schematic which shows the internal structure of an OCT apparatus. It is a flowchart which shows the control operation of an OCT apparatus. It is a figure which shows the scanning path | route of a Lissajous scan. It is a figure which shows the A scan profile of an overlapping point. It is a figure which shows the imaging region on a fundus. It is a figure which shows the example of a change of a scan pattern.

<Embodiment>
Hereinafter, embodiments according to the present disclosure will be described. The present embodiment is an OCT apparatus that obtains a tomographic image of a subject using interference between measurement light and reference light. The OCT apparatus (for example, the OCT apparatus 1) mainly includes, for example, a scanning unit (for example, the scanning unit 108) and a control unit (for example, the control unit 70). For example, the scanning unit scans the measurement light with respect to the test object. For example, a galvano scanner or the like is used as the scanning unit.

  The control unit controls the scanning unit. For example, the control unit changes the position of the scanning path within the imaging range every time the scanning cycle is repeated a plurality of times. In addition, a scanning cycle is a cycle which scans once along a scanning path | route, for example. The scanning path is, for example, a trajectory when scanning the measurement light. For example, after repeating a certain scanning cycle a predetermined number of times, the control unit changes the position of the scanning path and repeats the scanning cycle a predetermined number of times again in the changed scanning path. Note that when changing the position of the scanning path, the control unit changes the position of the scanning path so that the scanning paths before and after the change overlap at least one point. For example, the control unit changes the position of the scanning path so that the scanning path in a certain scanning cycle and the scanning path in another scanning cycle overlap at least at one point. For example, every time the position of the scanning path is changed, the control unit changes the position of the scanning path so that the scanning paths before and after the change overlap at least one point. Thereby, the OCT data of the common part can be acquired in different scanning cycles. The OCT data of the common part can be used as a comparison target when comparing the OCT data for each scanning cycle.

  In addition, it may be the case where it cross | intersects and it may be the case where it has touched. The scanning paths may be regarded as substantially overlapping. For example, if the deviation is within one pixel or the deviation within the spot diameter of the measurement light, it can be regarded as substantially overlapping.

  Note that the OCT apparatus may include a calculation unit (for example, the control unit 70). For example, the calculation unit acquires a motion contrast based on the OCT data. In this case, a plurality of time-dependent OCT data obtained by repeating a scanning cycle for scanning the measurement light along the scanning path of the same position (may be a nearby position) a plurality of times at the same (or nearby) position. Is used.

  For example, the calculation unit may estimate the movement of the subject by analyzing the overlapping OCT data. Duplicate OCT data is, for example, OCT data acquired in duplicate at overlapping portions (common parts) where scanning paths overlap. For example, the calculation unit may estimate the movement of the subject by comparing a plurality of overlapping OCT data acquired in each scanning cycle. In this case, the calculation unit may calculate an evaluation value of the duplicate OCT data. The evaluation value may be, for example, a similarity or a difference. Examples of the similarity include NCC (Normalized Cross-Correlation), ZNCC (Zero-mean Normalized Cross-Correlation), and the like. Examples of the difference include SSD (sum of squared difference) or SAD (sum of absolute difference).

  For example, the calculation unit may calculate the evaluation value of the overlapped OCT data, determine that the subject has moved when the correlation between the OCT data cannot be obtained, and perform alignment of the OCT data so that the correlation can be obtained. The calculation unit may calculate the amount of movement of the eye to be examined based on the amount of movement of the OCT data at this time. The analysis position may be a measurement point in the vicinity of the overlapping portion in addition to the overlapping portion. If the scanning paths are substantially the same, the correlation of the OCT data of the entire scanning path may be analyzed.

  The calculation unit may edit the OCT data based on the estimated movement of the subject. For example, the calculation unit may discard inappropriate OCT data, correct position information of some OCT data, correct a measured value of OCT data, and obtain it by re-imaging. Replacement with OCT data may be performed. Thus, the calculation unit can acquire a good OCT image by editing the OCT data.

  Note that the control unit may correct the position of the scanning path based on the estimated movement of the subject. For example, the position of the scanning path is shifted by the distance moved by the eye calculated by the calculation unit. Thereby, even when the subject has moved, the position of the next scanning path can be made to follow the desired position of the subject.

  Note that the control unit may control the scanning unit so that a scanning path in a certain scanning cycle and a scanning path in another scanning cycle overlap at two or more points. In this case, the calculation unit may compare the OCT data acquired at each overlapping point, and analyze the movement of the subject and the amount of rotation based on the deviation amount. The calculation unit may correct the shift of the OCT data between each scanning cycle based on these pieces of information.

  Note that the processor (for example, the CPU 71) of the control unit may execute an OCT control program stored in the storage unit or the like. The OCT control program includes a scanning step and a scanning position changing step. The scanning step is a step of controlling the scanning unit to scan the measurement light along the same scanning path. The scanning position changing step is a step of changing the position of the scanning path so that the scanning path overlaps at least one point before and after the change every time the scanning step is repeated.

  The OCT control program may include an estimation step and a correction step. The estimation step is, for example, a step of estimating the motion of the subject by analyzing overlapping OCT data acquired in an overlapping portion where the scanning paths overlap. The correction step is a step of correcting the position of the scanning path based on the movement of the subject estimated in the estimation step.

<Example>
The OCT apparatus 1 of the present embodiment will be described. FIG. 1 is a schematic diagram showing the internal configuration of the OCT apparatus 1. As shown in FIG. 1, the OCT apparatus 1 includes an OCT optical system 100, an observation optical system 200, a fixation target projection unit 300, a control unit 70, and the like.

<OCT optical system>
Hereinafter, an outline of the OCT optical system 100 will be described. In the present embodiment, for example, an OCT optical system 100 that irradiates the eye E with measurement light and acquires an OCT signal acquired by the reflected light and the measurement light will be described as an example. For example, the OCT optical system 100 captures a tomographic image of the eye E by acquiring an OCT signal.

  The OCT optical system 100 is a so-called optical coherence tomography (OCT) optical system. The OCT optical system 100 divides light emitted from the measurement light source 102 into measurement light (sample light) and reference light by a coupler (light splitter) 104. Then, the OCT optical system 100 guides the measurement light to the fundus oculi Ef of the eye E by the measurement optical system 106. The measurement optical system 106 includes, for example, a scanning unit (for example, an optical scanner) 108. For example, the scanning unit 108 changes the scanning position of the measurement light on the eye to be examined in order to change the imaging position on the eye to be examined. The OCT optical system 100 guides the reference light to the reference optical system 110. Thereafter, the detector 120 receives interference light obtained by combining the measurement light reflected by the eye E and the reference light.

  The detector 120 detects an interference state between the measurement light and the reference light. In the case of Fourier domain OCT, the spectral intensity of the interference light is detected by the detector 120, and a depth profile (A scan signal) in a predetermined range is obtained by Fourier transform on the spectral intensity data. Examples include Spectral-domain OCT (SD-OCT) and Swept-source OCT (SS-OCT). Moreover, Time-domain OCT (TD-OCT) may be used.

  In the case of SD-OCT, a low-coherent light source (broadband light source) is used as the light source 102, and the detector 120 is provided with a spectroscopic optical system (spectrometer) that separates interference light into each frequency component (each wavelength component). . The spectrometer includes, for example, a diffraction grating and a line sensor.

  In the case of SS-OCT, a wavelength scanning light source (wavelength variable light source) that changes the emission wavelength at a high speed with time is used as the light source 102, and a single light receiving element is provided as the detector 120, for example. The light source 102 includes, for example, a light source, a fiber ring resonator, and a wavelength selection filter. Examples of the wavelength selection filter include a combination of a diffraction grating and a polygon mirror, and a filter using a Fabry-Perot etalon.

  The light emitted from the light source 102 is split into a measurement light beam and a reference light beam by the coupler 104. Then, the measurement light flux passes through the optical fiber and is then emitted into the air. The light beam is condensed on the fundus oculi Ef via the optical member of the measurement optical system 106. Then, the light reflected by the fundus oculi Ef is returned to the optical fiber through a similar optical path.

  The scanning unit 108 scans the measurement light in the XY direction (transverse direction) on the fundus. The scanning unit 108 is disposed at a position substantially conjugate with the pupil. For example, the scanning unit 108 is a galvano scanner having two galvanometer mirrors 51 and 52, and the reflection angle thereof is arbitrarily adjusted by the drive mechanism 50.

  Thereby, the reflection (advance) direction of the light beam emitted from the light source 102 is changed and scanned in an arbitrary direction on the fundus. Note that the scanning unit 108 may be configured to deflect light. For example, in addition to a reflective mirror (galvano mirror, polygon mirror, resonant scanner), an acousto-optic device (AOM) that changes the traveling (deflection) direction of light is used.

  The reference optical system 110 generates reference light that is combined with reflected light acquired by reflection of measurement light at the fundus oculi Ef. The reference optical system 110 may be a Michelson type or a Mach-Zehnder type. The reference optical system 110 is formed by, for example, a reflection optical system (for example, a reference mirror), and reflects light from the coupler 104 back to the coupler 104 by being reflected by the reflection optical system and guides it to the detector 120. As another example, the reference optical system 110 is formed by a transmission optical system (for example, an optical fiber), and guides the light from the coupler 104 to the detector 120 by transmitting the light without returning.

  The reference optical system 110 has a configuration in which the optical path length difference between the measurement light and the reference light is changed by moving an optical member in the reference optical path. For example, the reference mirror is moved in the optical axis direction. The configuration for changing the optical path length difference may be arranged in the measurement optical path of the measurement optical system 106.

<Observation optics>
The observation optical system 200 is provided to obtain a front image of the fundus oculi Ef. The observation optical system 200 includes, for example, an optical scanner that two-dimensionally scans the fundus of measurement light (for example, infrared light) emitted from a light source, and a confocal aperture that is disposed at a position substantially conjugate with the fundus. And a second light receiving element for receiving the fundus reflection light, and has a so-called ophthalmic scanning laser ophthalmoscope (SLO) device configuration.

  Note that the configuration of the observation optical system 200 may be a so-called fundus camera type configuration. The OCT optical system 100 may also serve as the observation optical system 200. That is, the front image may be acquired using data forming a tomographic image obtained two-dimensionally (for example, an integrated image in the depth direction of the three-dimensional tomographic image, at each XY position). The integrated value of the spectrum data.

<Fixed target projection unit>
The fixation target projecting unit 300 includes an optical system for guiding the line-of-sight direction of the eye E. The projection unit 300 has a fixation target presented to the eye E, and can guide the eye E in a plurality of directions.

  For example, the fixation target projection unit 300 includes a visible light source that emits visible light, and changes the presentation position of the target two-dimensionally. Thereby, the line-of-sight direction is changed, and as a result, the imaging region is changed. For example, when the fixation target is presented from the same direction as the imaging optical axis, the center of the fundus is set as the imaging site. When the fixation target is presented upward with respect to the imaging optical axis, the upper part of the fundus is set as the imaging region. That is, the imaging region is changed according to the position of the target with respect to the imaging optical axis.

  As the fixation target projection unit 300, for example, a configuration in which the fixation position is adjusted based on the lighting positions of LEDs arranged in a matrix, light from a light source is scanned using an optical scanner, and fixation is performed by lighting control of the light source. Various configurations such as a configuration for adjusting the position are conceivable. The projection unit 300 may be an internal fixation lamp type or an external fixation lamp type.

<Control unit>
For example, the control unit 70 is realized by a general CPU (Central Processing Unit) 71, a ROM 72, a RAM 73, and the like. The ROM 72 of the control unit 70 has an OCT signal processing program for processing an OCT signal, various programs for controlling the operation of a device (for example, the OCT optical system 100) connected to the OCT signal processing apparatus 1, and an initial value. Values are stored. The RAM 73 temporarily stores various information. The control unit 70 may be configured by a plurality of control units (that is, a plurality of processors).

  As shown in FIG. 1, for example, a storage unit (for example, a non-volatile memory) 74, an operation unit 76, a display unit 75, and the like are electrically connected to the control unit 70. The storage unit 74 is a non-transitory storage medium that can retain stored contents even when power supply is interrupted. For example, a hard disk drive, a flash ROM, a removable USB memory, or the like can be used as the storage unit 74.

  Various operation instructions by the examiner are input to the operation unit 76. The operation unit 76 outputs a signal corresponding to the input operation instruction to the CPU 71. For the operation unit 76, for example, at least one of user interfaces such as a mouse, a joystick, a keyboard, and a touch panel may be used.

  The display unit 75 may be a display mounted on the apparatus main body or a display connected to the main body. A display of a personal computer (hereinafter referred to as “PC”) may be used. A plurality of displays may be used in combination. The display unit 75 may be a touch panel. When the display unit 75 is a touch panel, the display unit 75 functions as the operation unit 76. The display unit 75 displays, for example, image data obtained by processing the OCT signal acquired by the OCT optical system 100.

<Control action>
The control operation of the OCT apparatus 1 as described above will be described based on the flowchart of FIG. Although the case where the eye E is measured will be described, it may be another part of the living body. Note that the steps shown in FIG. 2 are not necessarily performed in the order described below.

(Step S1: Alignment)
First, the CPU 71 performs alignment of the optical system with respect to the eye to be examined. For example, the CPU 71 controls the fixation target projection unit 300 to project the fixation target onto the subject. Then, the CPU 71 automatically controls the drive unit (not shown) so that the measurement optical axis comes to the center of the pupil of the eye E based on the anterior ocular segment observation image captured by the anterior segment imaging camera (not shown). Align.

(Step S2: Measurement)
When the alignment is completed, the CPU 71 controls the OCT optical system 100 to perform measurement. In the following description, scanning the measurement light in the optical axis direction of the measurement light is referred to as “A scan”, and scanning the measurement light in a direction intersecting the optical axis direction of the measurement light is “B scan”. Call it.

As shown in FIG. 3A, in this embodiment, the CPU 71 performs a B scan on the fundus oculi Ef along the Lissajous curve. The Lissajous curve is, for example, a curve represented by the following formula (1).

Here, _{f A} A line rate of the OCT, # A is A number of lines per B-scan cycle, _{t i} is the time of the i-th A scan.

  For example, the CPU 71 operates a X-axis and a Y-axis of the scanning unit 108 with a sine wave or a cosine wave whose phase difference changes with time as in Expression (1), thereby scanning along the Lissajous curve (Lissajous scan and Call). For example, when the phase difference is 0 or π, the measurement light is scanned on a diagonal line of the imaging region, and when the phase difference is π / 2, the measurement light is scanned in a circular shape. For example, the CPU 71 changes the phase difference to gradually change the shape of the scanning path as shown in FIGS. By performing the Lissajous scan, the scanning paths having different shapes are overlapped, and the measurement points are overlapped (for example, overlap points P1 to P4 in FIG. 3C). The OCT signals acquired at these overlapping points are used in step S3 described later.

  The CPU 71 may repeat the B-scan cycle a plurality of times to obtain at least two OCT signals that are temporally different with respect to the same position on the eye to be examined. By using these OCT signals, the CPU 71 can acquire motion contrast that captures blood flow, movement of an object, or changes.

  For example, the CPU 71 acquires four temporally different OCT signals by repeating the scanning path Q1 four times with a time interval and performing a B scan. At this time, if the correlation between the B scans is low, the acquired OCT signal may be discarded or retaken, assuming that the eye to be examined has moved. For example, in the profile of the A scan signal shown in FIG. 4, if the correlation is obtained as shown in FIGS. 4A and 4B, the CPU 71 determines that the eye to be examined has not moved. On the other hand, as shown in FIGS. 4A and 4C, if there is no correlation, the CPU 71 determines that the eye to be examined has moved, and abandons or re-shoots the OCT signal. Thereby, even when the eye E moves, a good measurement result can be left.

  Note that, as an evaluation value for evaluating the correlation, for example, a degree of difference such as SSD (sum of squares of differences in luminance values), SAD (sum of absolute values of differences in luminance values), or the like is calculated. Good. In this case, the smaller the difference is, the more correlation is obtained. As the evaluation value, a similarity such as normalized cross-correlation (NCC, ZNCC, etc.) may be calculated. In this case, the closer the similarity is to 1, the more correlation is obtained.

  When the CPU 71 repeats the B scan four times for the scanning path Q1, the CPU 71 repeats the B scan cycle four times for the next scanning path Q2. As described above, the CPU 71 repeats the B-scan cycle four times for all the scanning paths (Q1, Q2,..., Qn) of the Lissajous curve, and acquires four OCT signals that are temporally different in each scanning path. The CPU 71 acquires the OCT signal detected by the detector 120 while scanning the measurement light. The OCT data acquired for each scanning path is stored in the storage unit 74.

(Step S3: Motion correction)
The CPU 71 corrects the deviation of the OCT data between the scanning paths caused by the movement of the eye to be examined during measurement. For example, the CPU 71 obtains an evaluation value of a measurement point that overlaps with another scanning path, and corrects the OCT data of each scanning path so that the evaluation value becomes the highest. Note that the OCT data used for correction may be one of four OCT data obtained by four scans, or may be obtained by integrating four OCT data such as an average value. .

  For example, the CPU 71 first corrects the deviation in the XY directions. At this time, the alignment may be performed based on the two-dimensional data generated from the volume data instead of the volume data. For example, the CPU 71 generates a front image for each OCT data acquired in the imaging region. Here, the front image is an image when the at least part of the living tissue is viewed from the optical axis direction (for example, z direction) of the measurement light (so-called “En face image”). In addition, as a method of generating the front image from the OCT data, for example, the front image may be generated using the brightness value of the OCT data extracted for at least a partial region in the depth direction. By aligning the position of the two-dimensional front image, volume data alignment information may be obtained.

  For example, the CPU 71 aligns the front images generated from the OCT data in the scanning path Q1 and the scanning path Q2. For example, the CPU 71 shifts the position of the two front images one pixel at a time, and aligns the images so that the two images are the best match (the correlation is the highest). Since the scanning path Q1 and the scanning path Q2 overlap at the point P1, the point P2, the point P3, and the point P4, the positions of the images are aligned so that these points coincide with each other. Subsequently, the CPU 71 aligns the front image generated from the OCT data of the scanning path Q3 with respect to the combined front images of the scanning path Q1 and the scanning path Q2, as described above. The CPU 71 repeats this alignment for each scanning path, and aligns the entire OCT data in the XY directions.

  After correcting the deviation in the XY directions, the CPU 71 next corrects the deviation in the Z direction (optical axis direction). For example, the CPU 71 obtains the evaluation value of the A-scan profile with the same XY coordinates in the volume data of each scanning path, and aligns each volume data in the Z direction so that the evaluation value becomes the highest. For example, when the volume data of the scanning path Q1 and the scanning path Q2 are aligned, the evaluation value of the A scan profile at or near the same overlapping point (for example, point P1, point P2, point P3, point P4) of the XY coordinates And the alignment in the Z direction is performed so that the value becomes the highest. The CPU 71 aligns the entire OCT data in the Z direction by performing this alignment on the volume data of each scanning path.

(Step S4: Calculation of motion contrast)
The CPU 71 calculates the motion contrast based on the four volume data aligned between the scanning paths as described above. For example, the CPU 71 processes a plurality of OCT signals stored in the storage unit 74 and acquires a complex OCT signal. For example, the CPU 71 performs a Fourier transform on the OCT signal. For example, if the signal at the nth (x, z) position in N OCT images is represented by An (x, z), the CPU 71 obtains a complex OCT signal An (x, z) by Fourier transform. The complex OCT signal An (x, z) includes a real component and an imaginary component.

  The CPU 71 processes the acquired complex OCT signal and acquires motion contrast. As a method of processing the complex OCT signal, for example, a method of calculating an intensity difference of the complex OCT signal, a method of calculating a phase difference of the complex OCT signal, a method of calculating a vector difference of the complex OCT signal, a level of the complex OCT signal, and the like. A method of multiplying a phase difference and a vector difference, a method of using signal correlation (correlation mapping), a method of calculating decorrelation of signal strength, a method of using a ratio between the maximum value and the minimum value of the strength, etc. In this embodiment, a method for calculating a phase difference will be described as an example.

First, the CPU 71 calculates a phase difference with respect to the complex OCT signal A (x, z) acquired at least at two different times at the same position. The CPU 71 calculates the change in phase using, for example, the following equation (2). For example, when performing the measurement of the different time T over N times, the time _{T 1} and time _{T 2,} the time _{T 2} and time _T 3, · · ·, the time _{T (N-1)} and time _{T N} meter (N -1) calculation is performed, and (N-1) pieces of data are calculated. Of course, the combination of time is not limited to the above, and the combination may be changed as long as the time is different. In the equation, An indicates a signal acquired at time _TN , and * indicates a complex conjugate.

  As described above, the CPU 71 acquires the phase difference profile in the depth direction (A scan direction) related to the phase difference of the complex OCT signal. For example, the CPU 71 acquires a luminance profile whose luminance is determined according to the size of the phase difference profile, and acquires a motion contrast image in which the luminance profiles are arranged in the B scan direction.

(Step S5: Synthesis)
In this embodiment, OCT data is acquired in a plurality of imaging regions on the fundus, and a wide range of OCT images are acquired by combining them. For example, as shown in FIG. 5, the CPU 71 performs the above-described Lissajous scan in the area A1, area A2, area A3, and area A4 on the fundus and acquires OCT data in each imaging area. The CPU 71 calculates the motion contrast based on the OCT data acquired in each region and synthesizes them. For example, the CPU 71 synthesizes images based on the correlation of the overlapping portions of the areas A1, A2, A3, and A4.

  Note that image alignment methods include, for example, a phase-only correlation method, a method using various correlation functions, a method using Fourier transform, a method based on feature point matching, an alignment method including affine transformation, and distortion correction (for example, Various image processing techniques such as non-rigid registration, etc.) may be used.

  As described above, it is possible to correct the shift of the scanning position due to the movement of the eye to be examined by scanning the measurement light so that at least one point overlaps in each scanning path and analyzing the overlapped OCT data. . For example, the imaging time is shorter than when the same image is captured a plurality of times to correct the movement of the eye to be examined.

  In this embodiment, since the photographing density (μm / pixel) and the time interval (time interval of B scan) are set to the same level as the raster scan (17 μm / pixel, 6 ms, respectively), the angle of view of 1.5 mm is overlapped. While shooting, images are taken in four shooting areas, and they are combined. As described above, when a plurality of images obtained by the Lissajous scan are combined, the A-scan measurement points near the center of the image can be made denser than when the images are not combined.

<Transformation example>
Note that the scan is not limited to the Lissajous scan described above, and may be any scan in which at least one measurement point overlaps. For example, as shown in FIG. 6A, there is a method of shooting while shifting the circle scan. In this case, two measurement points overlap in each scan. Further, as shown in FIG. 6B, the scanning path may be trochoidal. Also in this case, two measurement points overlap in each scan.

  Further, as shown in FIG. 6C, the scanning path may be an 8-digit Arabic numeral. In this case, for example, scanning may be performed while rotating the scanning path around the center intersection (number 8 intersection) of the scanning path. As a result, the number of measurement points in the central portion of the imaging region increases, and the resolution of the central portion of the image can be increased as compared with the Lissajous scan. In addition, the movement of the subject in one scanning cycle can be estimated by providing an intersection in the scanning path within one scanning cycle.

  Further, the scanning path may be an arbitrary free curve as shown in FIG. 6D as long as it can cover the measurement points in the imaging region. In this case as well, measurement points can be overlapped every scanning cycle by photographing while shifting the scanning path of the curve.

  In the Lissajous scan, the trajectory of the scan changes as the phase difference changes with time, but if the parameters are determined in advance, the scan paths of all cycles are determined. For example, in the case of FIG. 3, the scanning path of 256 patterns is scanned, but the above-described motion correction can be performed because there is always an intersection regardless of the scanning order. Therefore, the scanning order of the scanning path is arbitrary.

  In the above embodiment, the movement of the eye to be examined is estimated only from the OCT image. However, the movement of the eye to be examined is combined with other images such as an IR image (infrared image), an SLO image, and a fundus camera image. It may be estimated. As a result, the movement of the eye to be examined can be corrected more accurately.

  In the present embodiment, the CPU 71 estimates the movement of the eye to be examined and corrects the OCT data after imaging, but the present invention is not limited to this. For example, the CPU 71 may correct the scanning position in real time by estimating the movement of the eye to be examined at high speed. Accordingly, it is possible to perform scanning while following the movement of the eye to be examined using only the OCT image without estimating the movement of the eye to be examined from the observation image (for example, SLO image) of the fundus. In this case, the scanning paths may be overlapped in successive scanning cycles. Thereby, the shift of the OCT data from the immediately preceding scanning cycle can be detected, and the movement of the eye to be examined can be quickly followed. Of course, the scan paths may be overlapped between spaced scan cycles.

  Note that when acquiring the motion contrast as in this embodiment, it is not always necessary to scan the same locus, and the image may be taken with a slight shift. In this case, the CPU 71 may calculate a motion contrast by collecting a plurality of OCT signals acquired at nearby scanning positions.

  In the above description, the motion contrast is calculated based on the OCT data obtained by repeating the scanning cycle of each scanning path a plurality of times. However, the scanning paths may be overlapped in normal tomographic image capturing. . Also in this case, similarly to the motion contrast, the OCT data may be corrected based on the movement of the eye to be examined obtained by comparing the OCT data at the overlapping points.

  In the image alignment, position information of the imaging regions A1, A2, A3, and A4 of each OCT data may be used. For example, alignment by image processing may be performed in a state where the position of each image is specified to some extent based on the position information of the imaging region. In this case, the CPU 71 may obtain the position information of the imaging region based on information such as the scanning position of the measurement light when each OCT data is acquired and the fixation position of the fixation target presented to the eye E. . In this way, by using the position information of the imaging region of each OCT data, the processing speed of image alignment can be increased.

  In the above description, the motion correction is performed based on the OCT volume data before calculating the motion contrast. However, the motion correction may be performed based on the motion contrast data.

  Alternatively, raster scan may be performed using the volume data after motion correction as a reference, and the position may be aligned with the reference.

  Note that when imaging is performed by Lissajous scanning or the like, the measurement points near the center of the image may become rough and the measurement points near the edge of the image may become dense. In such a case, the control unit may increase the number of measurement points near the center of the image, for example, by slowing down the speed of moving the galvano scanner near the center of the image or increasing the scan rate near the center of the image. .

  In FIG. 5, the regions A <b> 1 to A <b> 4 are regions that partially overlap, but may be continuous regions without overlapping. In this case, the OCT data may be combined so that the continuity of the OCT data acquired in each region is likely. For example, a feature region (for example, a blood vessel part) reflected in each OCT data may be detected, and image position information may be acquired so that the continuity of the feature region is maintained between the OCT data.

70 Control unit 71 CPU
72 ROM
73 RAM
74 Memory 75 Monitor 76 Operation Unit 100 OCT Optical System 108 Scanning Unit 200 Observation Optical System 300 Fixation Target Projection Unit

Claims (12)

An OCT apparatus that obtains a tomographic image of a subject using optical interference between measurement light and reference light,
Scanning means for scanning the measurement light with respect to the subject;
Control means for controlling the scanning means and changing the position of the scanning path within the imaging range each time a scanning cycle for scanning the measuring light along the scanning path is repeated a plurality of times at the same position, and
The OCT apparatus characterized in that the control means changes the position of the scanning path so that the scanning paths before and after the change overlap at least one point.   2. The OCT apparatus according to claim 1, further comprising a calculation unit that obtains motion contrast based on a plurality of temporally different OCT data obtained by repeating the scanning cycle a plurality of times at the same position.   The OCT apparatus according to claim 2, wherein the calculation unit estimates the movement of the subject by analyzing overlapping OCT data acquired in an overlapping portion where the scanning paths overlap.   The OCT apparatus according to claim 3, wherein the calculation unit calculates a similarity or a difference between the duplicate OCT data.   The OCT apparatus according to claim 3 or 4, wherein the calculation means edits OCT data based on the estimated movement of the subject.   6. The OCT apparatus according to claim 5, wherein the editing of the OCT data is at least one of discarding the OCT data, correcting position information, correcting measurement values, and re-imaging.   The OCT apparatus according to claim 3, wherein the control unit changes the position of the scanning path based on the estimated movement of the subject.   The OCT apparatus according to claim 1, wherein the control unit controls the scanning unit so that the scanning paths before and after the change overlap at two or more points. An OCT apparatus that obtains a tomographic image of a subject using optical interference between measurement light and reference light,
Scanning means for scanning the measurement light with respect to the subject;
Control means for controlling the scanning means and changing the position of the scanning path within the imaging range each time a scanning cycle for scanning the measuring light along the scanning path is repeated;
Computing means for obtaining OCT data based on the interference light,
The control means changes the position of the scanning path so that the scanning path before and after the change overlaps at least at one point,
The calculation means estimates the movement of the subject by analyzing overlapping OCT data acquired in an overlapping portion where the scanning paths overlap,
The OCT apparatus characterized in that the control means corrects the position of the scanning path based on the estimated movement of the subject. An OCT apparatus that obtains a tomographic image of a subject using optical interference between measurement light and reference light,
Scanning means for scanning the measurement light with respect to the subject;
Control means for controlling the scanning means;
Computing means for analyzing OCT data acquired based on the interference light,
The control means controls the scanning means so that the scanning paths overlap at least at one point in one scanning cycle,
The OCT apparatus is characterized in that the calculation means estimates the movement of the subject by analyzing overlapping OCT data acquired in an overlapping portion where the scanning paths overlap. An OCT control program that is executed in an OCT apparatus that obtains a tomographic image of a subject using optical interference between measurement light and reference light, and is executed by a processor,
A scanning step of controlling scanning means for scanning the subject with the measurement light, and scanning the measurement light a plurality of times along the same scanning path;
A scanning position changing step for changing the position of the scanning path so that the scanning path overlaps at least one point before and after the change each time the scanning step is repeated;
Is executed by the OCT apparatus. An OCT control program that is executed in an OCT apparatus that obtains a tomographic image of a subject using optical interference between measurement light and reference light, and is executed by a processor,
A scanning step of controlling scanning means for scanning the measurement light with respect to the subject and scanning the measurement light along a scanning path;
A scanning position changing step for changing the position of the scanning path so that the scanning path overlaps at least one point before and after the change each time the scanning step is repeated;
An estimation step of estimating the movement of the subject by analyzing overlapping OCT data acquired in duplicate in the overlapping portion where the scanning paths overlap;
A correction step of correcting the position of the scanning path based on the movement of the subject estimated in the estimation step;
Is executed by the OCT apparatus.