JP2024052025A - OCT device and OCT imaging control method - Google Patents

Abstract

[Problem] To provide an OCT apparatus and an OCT imaging control method capable of more appropriately suppressing the influence when the stability of the signal acquisition state decreases. [Solution] In a signal set acquisition step, a control unit acquires a signal set including a plurality of OCT signals by performing a process of scanning the same scanning line on the tissue with measurement light a plurality of times. As a quality determination step for determining the quality of the acquisition state of the signal set, the control unit executes an OCT determination step for determining the quality of the acquisition state of the signal set based on a comparison result of at least two OCT signals included in the signal set acquired in the signal set acquisition step. When it is determined in the OCT determination step that the acquisition state of the signal set is not good, the control unit resets the position of the next scanning line to the same position on the tissue as the scanning line used when acquiring the signal set determined to be not good. [Selected Figure] Figure 4

Description

This disclosure relates to an OCT device that captures images of tissue based on the principles of optical coherence tomography (OCT) by scanning measurement light over the tissue of a subject, and an OCT imaging control method.

The OCT device guides measurement light split from the OCT light to the tissue of a subject (e.g., a test eye), while guiding reference light to a reference optical system, and is capable of capturing an image of the tissue (e.g., a tomographic image, etc.) based on an interference signal obtained by combining the measurement light reflected by the tissue and the reference light. The OCT device can be used, for example, to obtain images of biological tissues such as the eyeball or skin.

During imaging by the OCT device, if an event occurs that reduces the stability of the OCT signal acquisition state (e.g., tissue movement during imaging), an appropriate image may not be obtained. Therefore, techniques have been proposed to suppress the effects of a decrease in the stability of the signal acquisition state. For example, the OCT device described in Patent Document 1 detects the positional deviation of multiple front images of a subject acquired by a front observation optical system. Based on the detection result of the positional deviation of the front image, the quality of multiple OCT signals acquired for the same scanning area is determined. If the multiple OCT signals are determined to be poor, multiple OCT signals are reacquired for the same scanning area.

Patent No. 6544071

According to the technology described in Patent Document 1, the stability of the acquisition state of the OCT signal is detected based on the positional deviation of multiple front images. However, in recent years, it has become possible to increase the acquisition rate of the OCT signal (i.e., the number of times per unit time that the OCT signal is acquired each time the measurement light is scanned once on the scanning line) compared to the conventional method. As a result of the increase in the number of times that the OCT signal is acquired while one front image is captured, it has become difficult to adequately detect the stability of the acquisition state of the OCT signal based on the front image. Therefore, a technology that can more appropriately suppress the influence when the stability of the signal acquisition state decreases is desired.

A typical objective of the present disclosure is to provide an OCT device and an OCT imaging control method that can more appropriately suppress the effects of a decrease in the stability of the signal acquisition state.

An OCT device provided by a typical embodiment of the present disclosure includes an OCT light source, a branching optical element that branches light emitted from the OCT light source into measurement light and reference light, an optical scanning unit that scans the measurement light branched by the branching optical element on tissue of a subject, a light receiving element that detects an interference signal for acquiring an OCT signal by receiving a combined light of the measurement light reflected by the tissue and the reference light branched by the branching optical element, and a control unit, wherein the control unit performs a process of scanning the measurement light multiple times on the same scanning line on the tissue, or a process of scanning the measurement light on each of multiple adjacent scanning lines, thereby performing a signal set acquisition step of acquiring a signal set including multiple OCT signals, and a process of scanning the signal set. A quality determination step for determining whether the acquisition state is good or bad, and a next scan position setting step for setting the position on the tissue of the scanning line along which the measurement light will be scanned in the next signal set acquisition step are repeatedly executed, and as the quality determination step, an OCT determination step is executed for determining whether the acquisition state of the signal set is good or bad based on a comparison result of at least two OCT signals included in the signal set acquired in the signal set acquisition step, and in the next scan position setting step, if the acquisition state of the signal set is determined to be not good in the OCT determination step, the position of the next scan line is reset to the same position on the tissue as the scanning line when the signal set determined to be not good was acquired.

An OCT imaging control method provided by a typical embodiment of the present disclosure is an OCT imaging control method executed in an OCT device, the OCT device comprising an OCT light source, a branching optical element that branches light emitted from the OCT light source into measurement light and reference light, an optical scanning unit that scans the measurement light branched by the branching optical element on tissue of a subject, and a light receiving element that detects an interference signal for acquiring an OCT signal by receiving a combined light of the measurement light reflected by the tissue and the reference light branched by the branching optical element, and a signal set acquisition unit that acquires a signal set including a plurality of OCT signals by performing a process of scanning the measurement light multiple times on the same scanning line on the tissue, or a process of scanning the measurement light on each of a plurality of adjacent scanning lines. The method repeatedly executes a signal acquisition step, a quality determination step for determining whether the acquisition state of the signal set is good or bad, and a next scan position setting step for setting the position on the tissue of the scanning line along which the measurement light will be scanned in the next signal set acquisition step. As the quality determination step, an OCT determination step is executed for determining whether the acquisition state of the signal set is good or bad based on a comparison result of at least two OCT signals included in the signal set acquired in the signal set acquisition step. In the next scan position setting step, if the acquisition state of the signal set is determined to be not good in the OCT determination step, the position of the next scan line is reset to the same position on the tissue as the scan line at the time of acquisition of the signal set determined to be not good.

The OCT device and OCT imaging control method disclosed herein more appropriately suppress the effects of a decrease in the stability of the signal acquisition state.

1 is a block diagram showing a schematic configuration of an OCT apparatus 1. FIG. 1 is a diagram showing an example of a state in which a plurality of scanning lines 58 are set on the fundus tissue of the subject's eye E shown in a front image 40 captured by the front observation optical system 23. FIG. FIG. 4 is a diagram showing an example of a two-dimensional tomographic image 41 acquired by processing each OCT signal. 4 is a timing chart showing an example of the flow of various processes executed by the OCT apparatus 1 of the present embodiment. 4 is a flowchart of an OCT imaging process executed by the OCT apparatus 1. 13 is a flowchart of a front image determination process executed during an OCT imaging process. 11 is an explanatory diagram for explaining the contents of a front image determination process; FIG. 11 is an explanatory diagram for explaining a method of OCT signal determination processing according to an acquisition rate of the OCT signal. FIG.

＜Overview＞
The OCT device exemplified in the present disclosure includes an OCT light source, a branching optical element, an irradiation optical system, a light receiving element, and a control unit. The OCT light source emits OCT light. The branching optical element branches the light emitted from the OCT light source into a measurement light and a reference light. The light receiving element detects an interference signal for acquiring an OCT signal by receiving a composite light of the measurement light reflected by the tissue and the reference light branched by the branching optical element. The control unit controls the OCT device. The control unit repeatedly executes a signal set acquisition step, a pass/fail determination step, and a next scan position setting step. In the signal set acquisition step, the control unit acquires a signal set including a plurality of OCT signals by performing a process of scanning the same scan line on the tissue with the measurement light multiple times, or a process of scanning each of a plurality of adjacent scan lines with the measurement light. In the pass/fail determination step, the control unit performs a pass/fail determination of the acquisition state of the signal set. In the next scan position setting step, the control unit sets a position on the tissue of the scan line on which the measurement light is scanned in the next signal set acquisition step. The control unit executes an OCT determination step of determining whether the acquisition state of the signal set is good or bad based on a comparison result of at least two OCT signals included in the signal set acquired in the signal set acquisition step as a pass/fail determination step. In the next scanning position setting step, if the acquisition state of the signal set is determined to be bad in the OCT determination step, the control unit resets the position of the next scanning line to the same position on the tissue as the scanning line used when acquiring the signal set determined to be bad.

If no events (e.g., tissue movement, etc.) that impair the stability of the signal acquisition state occur while the measurement light is scanned multiple times on the same scanning line on the tissue to acquire a signal set of multiple OCT signals, the correlation between the multiple OCT signals included in the acquired signal set will be high. On the other hand, if the stability of the signal acquisition state decreases while the signal set is acquired, the correlation between the multiple OCT signals included in the signal set will be low. The same is true when a signal set is acquired by scanning the measurement light on each of multiple adjacent (i.e., close) scanning lines. Therefore, by comparing the multiple OCT signals included in the acquired signal set, the quality of the signal acquisition state when the signal set was acquired (the quality of the acquired signal set) can be appropriately determined.

Here, the time required to acquire an OCT signal for one scanning line is shorter than the time required to capture one two-dimensional front image of the tissue. In other words, the acquisition rate of the OCT signal is higher than the capture rate of the front image. Therefore, the control unit can precisely detect the stability of the signal acquisition state by determining whether the signal acquisition state is good or bad based on the comparison result of multiple OCT signals included in the acquired signal set. Therefore, according to the technology disclosed herein, the stability of the signal acquisition state can be easily detected appropriately even when the acquisition rate of the OCT signal is increased.

Furthermore, according to the technology disclosed herein, when it is determined in the OCT determination step that the signal acquisition state is not good, the position of the next scan line is reset to the same position on the tissue as the scan line when the signal set for which the acquisition state was determined to be not good was acquired. As a result, it becomes easier to reacquire a signal set for a scan line for which a good signal set was not obtained at an early stage. Therefore, the effect of a decrease in the stability of the signal acquisition state is more appropriately suppressed.

For example, after the acquisition of signal sets for multiple positions is completed, only the signal sets for which the signal acquisition state is determined to be poor are reacquired, thereby improving the overall accuracy of the OCT signal. However, in a method of reacquiring only the signal sets for which the signal acquisition state is poor after the acquisition of multiple signal sets, the difference between the conditions when the multiple signal sets are acquired (e.g., tissue position and angle, etc.) and the conditions when some signal sets are reacquired becomes large, and the quality of the entire signal is likely to deteriorate (e.g., a defect in which the part where the signal set was reacquired stands out in the image obtained based on the acquired OCT signal). In contrast, according to the technology disclosed herein, the signal sets for the scanning lines for which a good signal set was not obtained are reacquired at an early stage. Therefore, the entire OCT signal is more likely to be acquired with high accuracy.

In addition, when a movement of tissue during imaging is detected due to a positional shift between multiple two-dimensional front images, it is possible to improve the overall accuracy of the OCT signal by reacquiring the OCT signal acquired during imaging of the front image. However, as described above, the time required for imaging each front image is often longer than the time required for acquiring each OCT signal. In particular, in recent years, it has become possible to increase the acquisition rate of the OCT signal compared to the conventional method. As a result, the imaging rate of the front image tends to be even lower than the acquisition rate of the OCT signal compared to the conventional method. In a method for reacquiring an OCT signal when a positional shift occurs between multiple front images, the lower the imaging rate of the front image compared to the acquisition rate of the OCT signal, the more likely it is that the number of positions at which the OCT signal is reacquired will increase. In contrast, according to the technology disclosed herein, the quality of the signal acquisition state (quality of the signal set) is determined by the OCT signal that can be acquired in a short time, and the signal set for the scanning line where a good signal set was not obtained is reacquired at an early stage. As a result, the number of positions at which the signal set needs to be reacquired is reduced compared to the above-mentioned method. The technology disclosed herein also has the advantage that poor signal sets can be more easily and accurately identified from among successively acquired signal sets.

In the next scanning position setting step, if the acquisition state of the signal set is determined to be good in the pass/fail judgment, the control unit may set the position of the next scanning line to the position on the tissue where the signal set is scheduled to be acquired next to the position where the signal set was previously acquired (i.e., a new position where the measurement light has not yet been scanned). In this case, if the signal acquisition state is good, the acquisition of signal sets at multiple planned positions is smoothly repeated.

The specific method for determining whether the signal acquisition state (signal set) is good or bad based on the multiple OCT signals can be appropriately selected. For example, the control unit may acquire a tomographic image by processing each of at least two OCT signals included in the signal set, and may determine whether the signal acquisition state (signal set) is good or bad based on the correlation value of the acquired multiple tomographic images. In this case, the control unit may determine that the signal acquisition state is good if the correlation value is equal to or greater than a threshold value, and may determine that the signal acquisition state is not good if the correlation value is lower than the threshold value. By using the correlation value of the tomographic image, it becomes easier to perform the good or bad determination with high accuracy. In addition, the control unit may determine whether the signal acquisition state is good or bad by comparing at least two OCT signals included in the signal set. A known method, such as a method using a correlation value (similarity) obtained by phase-only correlation, may be used as a method for comparing OCT signals (for example, between tomographic images generated based on OCT signals).

In the next scanning position setting step, when the acquisition of the signal set in the previous signal set acquisition step is completed, the control unit may provisionally set the position of the next scanning line regardless of whether the pass/fail judgment of the signal set in the OCT judgment step is completed. In the signal acquisition step, the control unit may start scanning of the measurement light on the provisionally set scanning line regardless of whether the pass/fail judgment in the OCT judgment step is completed. Furthermore, the control unit may change the scanning line on which the measurement light is scanned to the re-set scanning line when the position of the scanning line is reset to a position different from the provisionally set position after starting scanning of the measurement light on the provisionally set scanning line. If the scanning of the measurement light is stopped until the pass/fail judgment of the signal acquisition state based on the OCT signal is completed, it becomes difficult to shorten the acquisition time of the entire plurality of OCT signals. In addition, if the driving of the light scanning unit is stopped once, it takes more time to resume driving. In response to this, the control unit provisionally sets the next scanning line and starts scanning of the measurement light regardless of whether the pass/fail judgment based on the OCT signal is completed, thereby making it possible to appropriately shorten the acquisition time of the multiple OCT signals.

In addition, if the provisionally set scanning line is not changed and is maintained as it is, the control unit may continue scanning the measurement light onto the scanning line as if it were the original scanning line, with the provisionally set scanning line as the original scanning line. In this case, the acquisition time for multiple OCT signals is appropriately shortened.

In addition, when the control unit resets the position of the scanning line to a position different from the provisionally set position, the control unit may exclude the signal (OCT signal, etc.) acquired for the provisionally set scanning line from being stored in the storage device. In this case, the problem of an inappropriate signal being adopted is suppressed.

In the OCT judgment step, the control unit may change the number of pairs of OCT signals to be compared to determine whether the signal acquisition state is good or bad, among the multiple OCT signals included in the signal set, according to the number of times the OCT signal is acquired per unit time when the signal set is acquired (i.e., the number of times the OCT signal is acquired per unit time each time the measurement light is scanned once on the scanning line). The more pairs of OCT signals included in the signal set are compared, the higher the accuracy of the determination of the signal acquisition state (signal set). On the other hand, the more pairs of OCT signals are compared to perform the determination, the longer the time required for the determination. If the time required for the determination of the signal acquisition state is too long, the quality of the acquired OCT signal may be reduced. Therefore, when increasing the number of times per unit time that the OCT signal is acquired each time the measurement light is scanned once on the scanning line (which can also be expressed as the "OCT signal acquisition rate"), the acquisition time for the signal set is shortened, and it is therefore desirable to shorten the time required to determine whether the signal acquisition state is good or bad. Therefore, by changing the number of OCT signal pairs used to determine whether the signal acquisition state is good or bad according to the OCT signal acquisition rate, it becomes easier to perform an appropriate pass/fail determination according to the OCT signal acquisition rate.

The specific method for changing the number of OCT signal pairs used to determine the quality of the signal acquisition state according to the acquisition rate of the OCT signal can be selected as appropriate. For example, when the acquisition rate of the OCT signal is equal to or higher than a threshold, the control unit may reduce the number of OCT signal pairs used to determine the quality of the signal acquisition state compared to when the acquisition rate is less than the threshold.

In the OCT judgment step, the control unit may always include a pair of the first acquired OCT signal and the last acquired OCT signal among the multiple OCT signals included in the signal set in the pair used for determining whether the signal acquisition state is good or bad, regardless of the OCT signal acquisition rate. The influence of the stability of the signal acquisition state while the signal set is being acquired (e.g., the presence or absence of tissue movement, etc.) is likely to appear between the pair of the first acquired OCT signal and the last acquired OCT signal among the multiple OCT signals included in the signal set. Therefore, by including the pair of the first and last OCT signals in the pair used for determining whether the signal acquisition state is good or bad, the accuracy of the determination is likely to be improved.

However, it is also possible to exclude the first and last OCT signal pairs from the pairs used for pass/fail judgment among the multiple OCT signals included in the signal set. In this case, the control unit can perform pass/fail judgment without waiting for the completion of acquisition of the last OCT signal in the signal set. Furthermore, even if the number of OCT signal pairs used for pass/fail judgment is constant regardless of the OCT signal acquisition rate, the impact of a decrease in the stability of the signal acquisition state is appropriately suppressed.

The OCT device may further include a front observation optical system that captures front images of the subject's tissue at an imaging rate (i.e., the number of times front images are captured per unit time) that is lower than the number of times OCT signals are acquired per unit time (i.e., the acquisition rate of the OCT signal described above). In the signal set acquisition step, the control unit may adjust the scanning position of the measurement light based on the latest front image captured by the front observation optical system, thereby causing the measurement light to scan a scanning line set on the tissue. In this case, even if the tissue moves, the measurement light is more likely to be scanned on an appropriate scanning line on the tissue based on the latest front image. This makes it easier to improve the accuracy of the acquired OCT signal.

The specific method for adjusting the scanning position of the measurement light based on the latest front image can also be selected as appropriate. For example, the control unit may detect a positional shift between the latest front image and a front image (reference image) captured before the latest front image, and adjust the scanning position of the measurement light for scanning the measurement light on the next scanning line based on the detected positional shift (e.g., the amount and direction of the positional shift).

The control unit may further execute a front image determination step in which, as a pass/fail determination step, the control unit determines whether the acquisition state of the signal set is good or bad based on a comparison result between the latest front image captured by the front observation optical system and a front image captured before the latest front image (for example, a front image captured immediately before the latest front image). In the next scanning position setting step, while the acquisition state of the signal set is determined to be poor in at least one of the front image determination step and the OCT determination step, the control unit may reset the position of the next scanning line to a position on the tissue that is the same as the scanning line at the time of acquisition of any signal set whose acquisition state is determined to be poor. In this case, the position of the next scanning line is set taking into consideration not only the determination result of the signal acquisition state based on the OCT signal, but also the determination result of the signal acquisition state based on the front image. Therefore, the influence when the stability of the signal acquisition state decreases is further likely to be suppressed.

However, the control unit can also set the position of the next scan line by referring only to the judgment result of the signal acquisition result in the OCT judgment step, without executing the front image judgment step. Even in this case, it becomes easier to reacquire a signal set at an early stage for a scan line for which a good signal set was not obtained.

In the front image determination step, the control unit may acquire a second positional deviation amount, which is a positional deviation amount between the latest front image and a reference front image captured before the latest front image, in addition to a first positional deviation amount, which is a positional deviation amount between the latest front image and a previous front image captured before the latest front image. When both the first positional deviation amount and the second positional deviation amount are acquired, the control unit may determine that the acquisition state is not good if at least one of the first positional deviation amount and the second positional deviation amount exceeds a threshold value. Once the control unit determines that the acquisition state is not good, the control unit may replace the reference front image with a newly captured front image. In this case, even if the tissue is moving slowly, by referring to both the first positional deviation amount and the second positional deviation amount, it is possible to detect with higher accuracy that the signal acquisition state has deteriorated due to the movement of the tissue.

Once the control unit determines that the signal set acquisition state is not good, the control unit may continue to determine that the signal acquisition state is not good at least until the next front image is captured by the front observation optical system. While the control unit determines that the signal set acquisition state is not good, the control unit may repeat the acquisition of the signal set in the signal set acquisition step and exclude the acquired signal set from the target to be stored in the storage device. If the signal acquisition state determination result is determined to be not good, it is highly likely that the tissue has already moved. Therefore, even if the signal set acquisition state is restored before the next front image is captured, the acquired signal set may be a signal set at a position different from the planned position. Therefore, by excluding the acquired signal set from the target to be stored at least until the next front image is captured after the signal acquisition state is determined to be not good, the possibility of using an OCT signal acquired at an inappropriate position is appropriately reduced.

Furthermore, as described above, once the driving of the optical scanning unit is stopped, it takes time to restart the driving, making it difficult to shorten the acquisition time of the multiple OCT signals. In response to this, the control unit can prevent the acquisition time of the multiple OCT signals from becoming longer by repeating the acquisition of the signal set in the signal set acquisition step even while it is determined that the acquisition state of the signal set is not good.

In the next scanning position setting step, the control unit may reset the position of the next scanning line to the same position on the tissue as the scanning line at the time of acquiring the signal set for which the signal acquisition state was determined to be poor, and then repeatedly set the position of the next scanning line to the same position as the previous time, at least until the next front image is captured. In this case, when the signal acquisition state is restored, the signal set acquisition process is more likely to be resumed from the position where the signal acquisition state was no longer good. As a result, the acquisition time for multiple OCT signals is more likely to be shortened.

The control unit may repeat the determination of the quality of the acquisition state of the signal set in the OCT determination step even while it is determined that the acquisition state of the signal set is not good. In this case, the stability of the signal acquisition state is detected in detail regardless of whether the acquired signal set is adopted or not. Therefore, the stability of the signal acquisition state is detected with high accuracy.

However, once the control unit determines that the acquisition state of the signal set is not good, the control unit may suspend the determination of the quality of the acquisition state of the signal set in the OCT determination step at least until the next capture of a front image by the front observation optical system is completed. In this case, the amount of processing by the control unit is likely to be reduced.

In addition, once the control unit determines that the signal set acquisition state is not good, it may execute a process of simply repeating the scanning of the measurement light on the set scanning line, instead of the signal set acquisition process in the signal set acquisition step, at least until the next front image capture by the front observation optical system is completed. In this case, when the signal acquisition state is restored, the normal signal set acquisition process is likely to be resumed immediately. As a result, the acquisition time for multiple OCT signals is likely to be further shortened.

The control unit may reduce the number of OCT signals acquired as a signal set in the signal set acquisition step while it is determined that the acquisition state of the signal set is not good, compared to when the acquisition state is determined to be good. In this case, the acquisition time of each signal set while it is determined that the signal acquisition state is not good is shortened. Therefore, the stability of the signal acquisition state is detected in more detail.

The control unit may acquire motion contrast data (OCT angiographic data) of the subject's tissue by processing a plurality of OCT signals (signal sets) acquired by scanning the same scanning line on the tissue multiple times with the measurement light. The motion contrast data is data generated by arithmetically processing at least two OCT signals acquired at different times for the same position on the subject's tissue. The motion contrast data includes perfusion information of the vascular network in the tissue, and is useful for diagnosis, etc. An OCT angiographic image showing a two-dimensional distribution of perfusion information of the vascular network when the tissue is viewed from the front (in the direction along the optical axis of the OCT measurement light) is generated by the motion contrast data acquired for each scanning line. By utilizing the technology in the present disclosure, it becomes easier to appropriately acquire motion contrast data in which the influence of an unstable signal acquisition state is suppressed.

<Embodiment>
A typical embodiment according to the present disclosure will be described below. As an example, the OCT device 1 of this embodiment can acquire and process an OCT signal of the fundus tissue of the subject eye E as a specimen. Based on the acquired OCT signal, it is possible to generate an OCT angio image, a two-dimensional tomographic image, a three-dimensional tomographic image, and the like. However, even when processing an OCT signal of a tissue other than the fundus in the subject eye E (e.g., the anterior segment of the subject eye E, etc.) or a specimen other than the subject eye E (e.g., skin, digestive organs, brain, blood vessels (including cardiovascular vessels), or teeth, etc.), at least a part of the technology exemplified in this disclosure can be applied. The OCT signal is a signal acquired based on the principle of optical coherence tomography (OCT).

The schematic configuration of the OCT device 1 of this embodiment will be described with reference to FIG. 1. The OCT device 1 includes an OCT section 10 and a control unit 30. The OCT section 10 includes an OCT light source 11, a coupler (light splitter) 12, a measurement optical system 13, a reference optical system 20, a light receiving element 22, and a front observation optical system 23.

The OCT light source 11 emits light (OCT light) for acquiring an OCT signal. The coupler 12 splits the OCT light emitted from the OCT light source 11 into measurement light and reference light. The coupler 12 of this embodiment combines the measurement light reflected by the tissue of the subject (the fundus of the subject's eye E in this embodiment) with the reference light generated by the reference optical system 20 to cause interference. In other words, the coupler 12 of this embodiment serves as a branching optical element that branches the OCT light into measurement light and reference light, and a combining optical element that combines the reflected light of the measurement light with the reference light. It is also possible to change the configuration of at least one of the branching optical element and the combining optical element. For example, an element other than a coupler (e.g., a circulator, a beam splitter, etc.) may be used.

The measurement optical system 13 guides the measurement light split by the coupler 12 to the subject and returns the measurement light reflected by the subject to the coupler 12. The measurement optical system 13 includes an optical scanning unit 14, an irradiation optical system 16, and a focus adjustment unit 17. The optical scanning unit 14 is driven by the driving unit 15 to scan (deflect) the measurement light in a two-dimensional direction intersecting the optical axis of the measurement light. In this embodiment, two galvanometer mirrors capable of deflecting the measurement light in different directions are used as the optical scanning unit 14. However, another device that deflects light (for example, at least one of a polygon mirror, a resonant scanner, an acousto-optical element, etc.) may be used as the optical scanning unit 14. The irradiation optical system 16 is provided downstream of the optical path (i.e., on the subject side) from the optical scanning unit 14, and irradiates the measurement light to the tissue of the subject. The focus adjustment unit 17 adjusts the focus of the measurement light by moving an optical member (e.g., a lens) of the irradiation optical system 16 in a direction along the optical axis of the measurement light.

The reference optical system 20 generates reference light and returns it to the coupler 12. In this embodiment, the reference optical system 20 generates reference light by reflecting the reference light split by the coupler 12 using a reflective optical system (e.g., a reference mirror). However, the configuration of the reference optical system 20 can also be changed. For example, the reference optical system 20 may transmit the light incident from the coupler 12 without reflecting it and return it to the coupler 12. The reference optical system 20 includes an optical path length difference adjustment unit 21 that changes the optical path length difference between the measurement light and the reference light. In this embodiment, the optical path length difference is changed by moving the reference mirror in the optical axis direction. Note that the configuration for changing the optical path length difference may be provided in the optical path of the measurement optical system 13.

The light receiving element 22 receives interference light, which is a composite light of the measurement light and the reference light generated by the coupler 12, and detects an interference signal for obtaining an OCT signal. In this embodiment, the principle of Fourier domain OCT is adopted. In Fourier domain OCT, the spectral intensity of the interference light (spectral interference signal) is detected by the light receiving element 22, and a complex OCT signal is obtained by Fourier transforming the spectral intensity data. The OCT signal is obtained by processing the complex OCT signal (for example, a process of calculating the absolute value of the amplitude in the complex OCT signal). Examples of Fourier domain OCT that can be adopted include Spectral-domain-OCT (SD-OCT) and Swept-source-OCT (SS-OCT). It is also possible to adopt, for example, Time-domain-OCT (TD-OCT).

In this embodiment, SD-OCT is used. In the case of SD-OCT, for example, a low-coherent light source (broadband light source) is used as the OCT light source 11, and a spectroscopic optical system (spectrometer) that separates the interference light into each frequency component (each wavelength component) is provided near the light receiving element 22 in the optical path of the interference light. In the case of SS-OCT, for example, a wavelength scanning light source (wavelength tunable light source) that changes the emission wavelength at high speed over time is used as the OCT light source 11. In this case, the OCT light source 11 may include a light source, a fiber ring resonator, and a wavelength selection filter. The wavelength selection filter includes, for example, a filter that combines a diffraction grating and a polygon mirror, and a filter that uses a Fabry-Perot etalon.

The front observation optical system 23 is provided to capture a front image (for example, the front image 40 shown in FIG. 2) of the tissue of the subject (the fundus of the subject's eye E in this embodiment) in real time. The front image in this embodiment is a two-dimensional image of the tissue when viewed from the direction along the optical axis of the OCT measurement light (front direction). In this embodiment, a scanning laser ophthalmoscope (SLO) is used as the front observation optical system 23. The SLO captures a front image of the tissue by scanning a laser light on the tissue of the subject and receiving the return light of the laser light from the tissue. For example, the SLO may be a so-called line scan type device. In this case, a line-shaped light beam is scanned on the observation surface. The front observation optical system 23 in this embodiment repeatedly captures a front image of the tissue at a capture rate lower than the acquisition rate of the OCT signal. The acquisition rate of the OCT signal is the number of times per unit time that the OCT signal is acquired each time the OCT measurement light is scanned once on the scanning line. The imaging rate of the front observation optical system 23 is the number of times a two-dimensional front image is captured per unit time. In recent years, it has become possible to increase the acquisition rate of the OCT signal compared to the past. In this embodiment, if the acquisition rate of the OCT signal is increased as much as possible, the acquisition rate of the OCT signal becomes about eight times the imaging rate of the front observation optical system 23. Note that the configuration of the front observation optical system 23 may be a configuration other than an SLO (for example, an infrared camera that captures a front image by irradiating a two-dimensional imaging range with infrared light all at once).

The control unit 30 is responsible for various controls of the OCT device 1. The control unit 30 includes a CPU 31, a RAM 32, a ROM 33, and a non-volatile memory (NVM) 34. The CPU 31 is a controller that performs various controls. The RAM 32 temporarily stores various information. The ROM 33 stores programs executed by the CPU 31 and various initial values, etc. The NVM 34 is a non-transient storage medium that can retain the stored contents even if the power supply is cut off. An OCT imaging control program for executing the OCT imaging process (see FIG. 3) described later may be stored in the NVM 34.

A microphone 36, a monitor 37, and an operation unit 38 are connected to the control unit 30. The microphone 36 inputs sound. The monitor 37 is an example of a display unit that displays various images. The operation unit 38 is operated by a user to input various operation instructions to the OCT device 1. The operation unit 38 can be various devices such as a mouse, a keyboard, a touch panel, a foot switch, etc. Note that various operation instructions may be input to the OCT device 1 by inputting sound to the microphone 36. In this case, the CPU 31 may determine the type of operation instruction by performing voice recognition processing on the input sound.

In this embodiment, an integrated OCT device 1 in which the OCT section 10 and the control unit 30 are built into a single housing is illustrated. However, it goes without saying that the OCT device 1 may include multiple devices with different housings. For example, the OCT device 1 may include an optical device that includes the OCT section 10, and a PC that is connected to the optical device by wire or wirelessly. In this case, the control unit of the optical device and the control unit of the PC may both function as the control unit 30 of the OCT device 1.

(Example of a method for acquiring an OCT signal)
An example of an acquisition method (photographing method) of an OCT signal in this embodiment will be described with reference to Fig. 2 and Fig. 3. Fig. 2 shows an example of a state in which a plurality of scanning lines 58 are set on the fundus tissue of the subject's eye E shown in the front image 40 photographed by the front observation optical system 23. In this embodiment, the measurement light spot is scanned in a two-dimensional target area 55 on the tissue by the light scanning unit 14, and an OCT signal in the target area 55 is acquired. In detail, in this embodiment, motion contrast data (OCT angiographic data) in the target area 55 is acquired (photographed). The motion contrast data is generated by arithmetically processing at least two OCT signals acquired at different times for the same position of the subject. The motion contrast data includes perfusion information of the vascular network in the tissue, and is therefore useful for diagnosis and the like.

2, the OCT device 1 of this embodiment sets multiple scanning lines 58 at equal intervals to scan the measurement light spot within a two-dimensional target region 55 that spreads in a direction intersecting the optical axis of the measurement light. In the example shown in FIG. 2, the scanning lines 58 are arranged at equal intervals in the order of the first scanning line 581, the second scanning line 582, the third scanning line 583, and the fourth scanning line 584, and the last scanning line is the Kth scanning line 58K. The OCT device 1 scans each scanning line 58 on the tissue with the measurement light spot multiple times (for example, in this embodiment, in principle, four times each) to obtain multiple (in this embodiment, in principle, four) signal sets of OCT signals for each scanning line 58. The multiple OCT signals included in the signal set for each scanning line 58 are arithmetically processed to obtain motion contrast data for each scanning line 58.

As shown in FIG. 3, the OCT device 1 processes each OCT signal acquired by irradiating the scanning line 58 with the measurement light once each, thereby acquiring a two-dimensional tomographic image 41 extending in the depth direction of the tissue from the scanning line 58. As will be described in detail later, when the OCT device 1 judges whether the OCT signal acquisition state (hereinafter, sometimes simply referred to as the "signal acquisition state") is good or bad based on a plurality of OCT signals, it uses the correlation value between the two-dimensional tomographic images 41 acquired by processing each OCT signal. The signal acquisition state deteriorates, particularly when tissue movement occurs while the OCT signal is being acquired.

The process executed by the OCT device 1 of this embodiment will be described in detail below. As described above, the process exemplified in this embodiment is a process for acquiring motion contrast data of the fundus of the subject eye E by the method exemplified in FIG. 2. However, at least a part of the process described below can also be applied to capturing data other than motion contrast data (e.g., three-dimensional tomographic image data, or arithmetic average image data obtained by averaging multiple two-dimensional tomographic images, etc.).

(Processing Overview)
First, referring to FIG. 4, the flow of various processes executed by the OCT apparatus 1 of the present embodiment will be outlined. FIG. 4 is a timing chart showing an example of the flow of various processes executed by the OCT apparatus 1 of the present embodiment. In the example shown in FIG. 4, "front image capture" in the figure indicates the timing at which the front image 40 of the tissue is continuously captured by the front observation optical system 23. "Front image judgment result" in the figure indicates the timing at which the signal acquisition state is judged to be good or bad based on the captured front image 40. "Signal set acquisition" in the figure indicates the timing at which a signal set of a plurality of OCT signals is continuously acquired for each scanning line 58. "OCT signal judgment result" in the figure indicates the timing at which the signal acquisition state is judged to be good or bad based on the OCT signal included in the acquired signal set. "Signal acquisition state" in the figure indicates the timing at which the signal acquisition state is switched to good or bad as grasped by a state deterioration flag described later. In the "front image judgment result" and "OCT signal judgment result", the judgment result of the signal acquisition state is indicated by "◯" when it is good, and by "×" when it is not good. In "signal set acquisition", the actual signal acquisition state when the signal set was acquired is indicated as "good" by "o" and not good by "x". Furthermore, the period when the signal acquisition state grasped by the state deterioration flag is good is indicated as "o", and the period when it is not good is indicated as "x".

The OCT device 1 of this embodiment repeatedly executes each of the signal set acquisition process, the signal acquisition state quality judgment process, and the next scanning position setting process (omitted in FIG. 4). In the signal set acquisition process, the OCT measurement light is scanned multiple times (in this embodiment, in principle, four times) on the same scanning line 58 set at that time to acquire a signal set of multiple OCT signals. In the signal acquisition state quality judgment process, the signal acquisition state quality is basically judged based on the OCT signal included in the acquired signal set each time acquisition of a signal set is completed. The stability of the signal acquisition state is detected in detail according to the quality judgment of the signal acquisition state based on the OCT signal. Furthermore, in the signal acquisition state quality judgment process of this embodiment, quality judgment is also performed based on the comparison result between the latest front image 40 and the front image 40 captured before the latest front image 40. In the next scanning position setting process, the position on the tissue of the scanning line 58 on which the OCT measurement light will be scanned next time is set.

The OCT device 1 adjusts the scanning position of the OCT measurement light based on the latest captured front image 40, thereby scanning the OCT measurement light along the set scanning line 58 on the tissue. As a result, even if the tissue moves, the OCT measurement light is more likely to scan the appropriate scanning line 58 on the tissue based on the latest front image 40.

When the result of the signal acquisition state determination based on the OCT signal is poor, the OCT device 1 sets the deterioration state flag, which indicates whether the signal acquisition state is good or bad, to "ON" indicating that the state is not good. In the example shown in FIG. 4, the acquisition state of the fifth acquired signal set is determined to be poor, and as a result, the deterioration state flag is set to "ON". In addition, the OCT device 1 of this embodiment also sets the deterioration state flag to "ON" when the result of the signal acquisition state determination based on the front image is poor. Note that in the example shown in FIG. 4, the result of the signal acquisition state determination based on the third and fourth captured front images is poor, but since the deterioration state flag is already "ON", the deterioration state flag remains "ON".

When the signal acquisition state is judged to be good, the OCT device 1 stores the acquired signal set in a storage device (e.g., NVM 34, etc.). In the example shown in FIG. 4, when the first to fourth acquired signal sets are acquired and when the twelfth to fourteenth acquired signal sets are acquired, both the judgment of the signal acquisition state based on the OCT signal and the signal acquisition state grasped by the state deterioration flag are good. Therefore, the first to fourth and twelfth to fourteenth acquired signal sets are stored in the storage device. Furthermore, when the signal acquisition state is judged to be good, the OCT device 1 sets the position of the next scan line to the position on the tissue where the next signal set is to be acquired after the position (scan line 58) where the signal set was previously acquired. As a result, signal sets for each of the multiple scan lines are acquired and stored sequentially.

On the other hand, when the result of the judgment of the signal acquisition state based on the OCT signal is bad, the OCT device 1 resets the position of the next scanning line 58 to the same position on the tissue as the scanning line 58 at the time of acquisition of the signal set for which the signal acquisition state was judged to be bad. (In FIG. 7, after the acquisition of the fifth signal set, the position of the next scanning line 58 is reset to the same position as the previous time.) As a result, the signal set for the scanning line 58 for which a good signal set was not obtained is likely to be reacquired at an early stage. Note that, when the result of the judgment of the signal acquisition state based on the OCT signal is bad, the OCT device 1 excludes the signal set for which the signal acquisition state is judged to be bad from the targets to be stored in the storage device. As a result, the possibility of adopting a signal set with poor quality decreases. In the example shown in FIG. 7, when the fifth acquired signal set is acquired, the result of the judgment of the signal acquisition state based on the OCT signal is bad. Therefore, the fifth acquired signal set is excluded from the targets to be stored in the storage device.

In addition, while the OCT device 1 is determined to be in a poor signal acquisition state (i.e., while the deterioration flag is set to "ON"), the OCT device 1 repeats acquisition of the signal set and excludes the acquired signal set from the targets to be stored in the storage device. As a result, the possibility of adopting a signal set of poor quality is reduced. In the example shown in FIG. 7, when the sixth to eleventh acquired signal sets are acquired, the signal acquisition state is determined to be poor (i.e., the deterioration flag is set to "ON"), and therefore the sixth to eleventh acquired signal sets are excluded from the targets to be stored in the storage device. Note that, even while the signal acquisition state is determined to be poor, the acquisition of the signal set is repeated, thereby shortening the time required to resume driving the optical scanning unit 14. As a result, the acquisition time of multiple OCT signals is easily shortened. In addition, once the OCT device 1 resets the position of the next scan line 28 to the same position as the previous time, it repeatedly sets the position of the next scan line 58 to the same position as the previous time until the signal set for the reset scan line 58 is acquired in a good signal acquisition state. As a result, after the signal acquisition state is restored, the signal set acquisition process is more likely to be resumed from an appropriate position. In the example shown in FIG. 7, the setting position of the next scan line 58 reset after the acquisition of the fifth signal set continues to be the same position until the acquisition of the twelfth signal set is completed.

In addition, once the OCT device 1 of this embodiment determines that the signal acquisition state is not good, the state deterioration flag is set to "ON" until at least the next front image 40 is captured, thereby continuing the determination result that the signal acquisition state is not good. If the signal acquisition state determination result is determined to be not good, it is highly likely that the tissue has already moved. Therefore, even if the acquisition state of the signal set is restored before the next front image 40 is captured, it is difficult to adjust the scanning position of the measurement light based on the latest front image 40. In other words, after the signal acquisition state is once determined to be not good, the signal set acquired at least until the next front image 40 is captured may be a signal set at a position different from the planned position. Therefore, by continuing the determination result that the signal acquisition state is not good until at least the next front image 40 is captured, the possibility of a signal set with poor quality being adopted is reduced.

In detail, once the OCT device 1 of this embodiment determines that the signal acquisition state is not good, it continues the determination result that the signal acquisition state is not good until the result of the signal acquisition state determination based on the front image becomes good (i.e., it continues the state deterioration flag "ON" state). As a result, it becomes easier to appropriately reacquire a signal set whose quality is not good. Note that in the example shown in FIG. 7, the signal acquisition state is determined to be not good when the fifth signal set is acquired, but for the eighth and subsequent signal sets, the result of the signal acquisition state determination based on the OCT signal is restored. However, the OCT device 1 reduces the possibility that a signal set whose quality is not good will be adopted by continuing the determination result that the signal acquisition state is not good even when the eighth to eleventh signal sets are acquired.

As shown in FIG. 7, the OCT device 1 of this embodiment repeats the determination of the quality of the signal acquisition state based on the OCT signal even while it is determined that the acquisition state of the signal set is not good (i.e., while the acquired signal set is excluded from the target to be stored in the storage device). Therefore, regardless of whether the acquired signal set is adopted or not, the stability of the signal acquisition state is precisely detected.

(OCT imaging processing)
5 to 8, an OCT imaging process executed by the OCT apparatus 1 of the present embodiment will be described. The CPU 31 of the OCT apparatus 1 executes the OCT imaging process shown in FIG.

As shown in FIG. 5, in the OCT imaging process of this embodiment, the process related to the front image 40 (S1 to S4) and the process related to the OCT signal (S21 to S38) are executed in parallel. First, the process related to the front image 40 (S1 to S4) will be described. When the OCT imaging process is started, the CPU 31 executes continuous imaging of the front image 40 by the front observation optical system 23.

The CPU 31 judges whether or not one front image 40 has been captured (S1). The judgment of S1 is repeated until the capture of the front image 40 is completed (S1: NO), and a standby state is entered. When the capture of the front image 40 is completed (S1: YES), the CPU 31 executes a front image judgment process (S2). In the front image judgment process, a judgment is made as to whether the signal acquisition state is good or bad based on the comparison result between the latest front image 40 captured in S1 and a front image 40 captured before the latest front image 40.

6, in the front image determination process, the CPU 31 acquires a first positional deviation amount, which is a positional deviation amount between the latest front image 40 that has been shot in S1 (see FIG. 5) and the immediately preceding front image 40 that was shot immediately before the latest front image 40 (S11). Next, the CPU 31 judges whether the latest front image 40 is a reference front image 40 or not (S12). The reference front image 40 is an image that is a target for acquiring a positional deviation amount between the latest front image 40 and one or more front images 40 shot before the immediately preceding front image 40 described above. If the latest front image 40 is the reference front image 40 (S12: YES), the process proceeds directly to S15. On the other hand, if an image different from the latest front image 40 is set as the reference front image 40 (S12: NO), the CPU 31 acquires a second positional deviation amount, which is a positional deviation amount between the latest front image 40 and the reference front image 40 (S13), and the process proceeds to S15. In addition, known image processing, etc. may be used to obtain the amount of positional deviation between the front images in S11 and S13.

The CPU 31 judges whether the signal acquisition state is good or bad based on the positional deviation amount acquired in S11 to S13 (S15). In detail, when only the first positional deviation amount has been acquired, the CPU 31 judges that the signal acquisition state is good if the acquired first positional deviation amount is less than a threshold value. When the first positional deviation amount and the second positional deviation amount have been acquired, the CPU 31 judges that the signal acquisition state is good if both the first positional deviation amount and the second positional deviation amount are less than a threshold value. On the other hand, when at least one of the first positional deviation amount and the second positional deviation amount exceeds a threshold value, the CPU 31 judges that the signal acquisition state is not good.

When the CPU 31 determines that the signal acquisition state is not good (poor) (S15: NO), it sets the state deterioration flag, which indicates whether the OCT signal acquisition state at that time is good or not, to "ON" indicating that the signal acquisition state is not good (S17). Note that in S17, if the state deterioration flag is already "ON", it remains "ON".

When the CPU 31 determines that the signal acquisition state is good (S15: YES), it determines whether the state deterioration flag is "OFF" indicating that the signal acquisition state is good (S17). If the state deterioration flag is "OFF" (S17: YES), the process returns to the OCT imaging process (see FIG. 5). If the state deterioration flag is "ON" (S17: NO), the signal acquisition state has returned from a bad state to a good state. Therefore, the CPU 31 changes the state deterioration flag from "ON" to "OFF" (see timing T2 in FIG. 4). As a result, the process of acquiring the signal set and storing it in the storage device is resumed. Furthermore, the CPU 31 replaces the reference front image 40 with either the latest front image or the immediately preceding front image (as an example, in this embodiment, the immediately preceding front image) for which the first positional deviation amount was acquired in S11 (S19).

With reference to FIG. 7, the front image determination process in this embodiment will be described based on a specific example. In FIG. 7, six front images S1 to S6 are arranged in the order in which they were captured. In addition, the arrows indicate the front images to which each of the front images from S2 onwards is compared when determining whether the signal acquisition state is good or bad. The arrow indicating the acquisition target of the first positional deviation amount is marked with "1", and the arrow indicating the acquisition target of the second positional deviation amount is marked with "2". In the example shown in FIG. 7, a positional deviation between the front images occurs due to tissue movement between the completion of capturing the third front image S3 and the completion of capturing the fourth front image S4.

In the example shown in FIG. 7, the first captured front image S1 is set as the reference front image. When the second front image S2 is captured, only the first positional deviation between S2 and the immediately preceding front image S1 is acquired. Since no tissue movement occurs during the capture of S1 to S2, no positional deviation is detected when capture of S2 is completed, and the reference front image remains S1.

When the third front image S3 is captured, a first positional deviation amount between S3 and S2, which is the immediately preceding front image, is obtained. Furthermore, a second positional deviation amount between S3 and S1, which is the reference front image, is obtained. Since no tissue movement occurs during the capture of S2 to S3, no positional deviation is detected even when capture of S3 is completed, and the reference front image remains S1.

When the fourth front image S4 is captured, a first positional deviation amount between S4 and S3, which is the immediately preceding front image, is obtained. Furthermore, a second positional deviation amount between S4 and S1, which is the reference front image, is obtained. Since tissue movement occurs during the capture of S3 to S4, a positional deviation between the front images is detected when the capture of S4 is completed, and the signal acquisition state is determined to be poor. Furthermore, after the signal acquisition state is determined to be poor when the capture of S4 is completed, the reference front image is replaced from S1 to the newly captured front image. In detail, when the fifth front image S5 is captured, a first positional deviation amount between S5 and S4, which is the immediately preceding front image, is obtained. Since no tissue movement occurs during the capture of S4 to S5, the signal acquisition state returns from a poor state to a good state (i.e., the state deterioration flag is changed from "ON" to "OFF". At this point, the reference front image is replaced from S1 to S4, which is the immediately preceding front image. Thereafter, the same process is repeated.

As described above, according to the front image determination process of this embodiment, for example, when tissue moves slowly during imaging of S1 to S4, even if the positional deviation amount between S3 and S4 is less than the threshold, if the positional deviation amount between S1 and S4 is equal to or greater than the threshold, a poor signal acquisition state due to tissue movement is appropriately detected. Therefore, a deterioration in the signal acquisition state due to tissue movement is detected with higher accuracy.

Returning to the explanation of FIG. 5, when the front image determination process (S2) is completed, the CPU 31 adjusts the scanning position of the OCT measurement light controlled in S21 to S38 based on the latest front image 40 captured in S1, thereby scanning the measurement light on the scanning line 58 set on the tissue (S3). Therefore, even if the tissue moves, the measurement light is likely to be scanned on an appropriate scanning line on the tissue based on the latest front image 40. In addition, in S3 of this embodiment, the CPU 31 detects a positional deviation between the latest front image 40 and a front image 40 (reference image) captured before the latest front image, and adjusts the scanning position of the measurement light for scanning the next scanning line 58 with the measurement light based on the detected positional deviation (e.g., the amount and direction of the positional deviation).

The CPU 31 determines whether acquisition of signal sets for all planned scanning lines 58 has been completed in the processes of S21 to S38 being performed in parallel (S4). If acquisition has not yet been completed (S4: NO), the process returns to S1. If acquisition of signal sets for all scanning lines 58 has been completed (S4: YES), the OCT imaging process ends.

Next, the processing related to the OCT signal (S21 to S38) will be described. When the CPU 31 starts the OCT imaging process, it sets the scanning line 58 on the tissue from which a signal set is to be acquired first, among the multiple scanning lines 58 on the tissue from which a signal set is to be acquired, as the scanning line 58 on which the OCT measurement light will be scanned next, and starts scanning the measurement light.

The CPU 31 determines whether acquisition of the signal set of multiple OCT signals for the set scanning line 58 is complete (S21). If not complete (S21: NO), the determination of S21 is repeated and the system enters a standby state. When acquisition of the signal set is complete (S21: YES), the CPU 31 starts the OCT signal determination process (S22). Note that the CPU 31 may start the OCT signal determination process when acquisition of at least two OCT signals out of the multiple OCT signals (in principle, four in this embodiment) included in the signal set is complete. In this case, it becomes easier to determine the quality of the signal acquisition state based on the OCT signals in a shorter time.

In the OCT signal determination process, the CPU 31 determines whether the signal acquisition state is good or bad based on the comparison result of at least two OCT signals included in the acquired signal set. If no event (e.g., tissue movement, etc.) that inhibits the stability of the signal acquisition state occurs while the measurement light is scanned multiple times on the same scanning line 58 on the tissue to acquire a signal set of multiple OCT signals, the correlation between the multiple OCT signals included in the acquired signal set will be high. On the other hand, if the stability of the signal acquisition state decreases while acquiring the signal set, the correlation between the multiple OCT signals included in the signal set will be low. Therefore, by comparing the multiple OCT signals included in the acquired signal set, the quality of the signal acquisition state when the signal set is acquired (the quality of the acquired signal set) is appropriately determined. Also, as described above, the acquisition rate of the OCT signal (i.e., the number of acquisitions per unit time of the OCT signal acquired each time the OCT measurement light is scanned once on the scanning line 58) is higher than the shooting rate of the front image 40 by the front observation optical system 23 (i.e., the number of shootings of the front image 40 per unit time). Therefore, the OCT signal evaluation process makes it possible to precisely detect the stability of the signal acquisition state.

In detail, in the OCT signal judgment process of this embodiment, the CPU 31 changes the number of pairs of OCT signals to be compared to judge the quality of the signal acquisition state among the multiple OCT signals included in the signal set according to the acquisition rate of the OCT signal when the signal set is acquired (i.e., the number of acquisitions per unit time of the OCT signal acquired each time the OCT measurement light is scanned once on the scanning line 58). The more pairs of OCT signals included in the signal set are compared, the higher the accuracy of the quality judgment of the signal acquisition state (signal set). On the other hand, the more pairs of OCT signals to be compared to judge the quality of the signal acquisition state (signal set) becomes, the longer the time required for the quality judgment becomes. If the time required for the quality judgment of the signal acquisition state becomes too long, the quality of the acquired OCT signal may decrease. Therefore, when the acquisition rate of the OCT signal is increased, the acquisition time of the signal set is shortened, and it is desirable to also shorten the time required for the OCT signal judgment process. Therefore, the CPU 31 changes the number of OCT signal pairs used to determine the quality of the signal acquisition state according to the acquisition rate of the OCT signals, thereby appropriately determining the quality according to the acquisition rate of the OCT signals.

With reference to FIG. 8, an example of a method of OCT signal judgment processing according to the acquisition rate of the OCT signal will be described. In FIG. 8, four OCT signals O1 to O4 included in the signal set are arranged in the order of acquisition time. In addition, pairs of OCT signals compared in the OCT signal judgment processing are connected by arrows. In this embodiment, the CPU 31 reduces the number of OCT signal pairs used for the quality judgment of the signal acquisition state as the OCT signal acquisition rate is increased. In the example shown in FIG. 8, when the OCT signal acquisition rate is at the lowest stage, three pairs of the first and second OCT signal pairs, the first and third OCT signal pairs, and the first and fourth OCT signal pairs, are used for the quality judgment of the signal acquisition state. In this case, the accuracy of the quality judgment is easily improved. In addition, when the OCT signal acquisition rate is at a medium stage, two pairs of the first and second OCT signal pairs and the first and fourth OCT signal pairs are used for the quality judgment of the signal acquisition state. If the OCT signal acquisition rate is at the highest stage, only the first and fourth OCT signal pairs are used to determine whether the signal acquisition state is good or bad. In this case, the time required for the OCT signal determination process is shortened. As shown in FIG. 8, the CPU 31 always includes the pair of the first (first) acquired OCT signal and the last (fourth) acquired OCT signal among the multiple OCT signals included in the signal set, regardless of the OCT signal acquisition rate, in the pair used to determine whether the signal acquisition state is good or bad. The effect of the stability of the signal acquisition state while the signal set is being acquired (for example, the presence or absence of tissue movement, etc.) is likely to appear between the pair of the first acquired OCT signal and the last acquired OCT signal. Therefore, by including the pair of the first and last OCT signals in the pair used to determine whether the signal acquisition state is good or bad, the accuracy of the pass/fail determination is easily improved.

In the OCT signal determination process of this embodiment, the CPU 31 acquires a tomographic image 41 (see FIG. 3) by processing each of at least two OCT signals included in the signal set, and determines whether the signal acquisition state (signal set) is good or bad based on the correlation value of the acquired multiple tomographic images 41. If the correlation value is equal to or greater than a threshold, the CPU 31 determines that the signal acquisition state is good, and if the correlation value is lower than the threshold, the CPU 31 determines that the signal acquisition state is not good. By using the correlation value of the tomographic image 41, it becomes easier to perform the good or bad determination with high accuracy. The CPU 31 may also determine whether the signal acquisition state is good or bad by comparing at least two OCT signals included in the signal set. A correlation value (similarity) calculated by phase-only correlation is used as a method for comparing OCT signals (for example, between tomographic images 41 generated based on OCT signals).

Returning to the explanation of FIG. 5, the OCT signal determination process takes a certain amount of time. Regardless of whether the OCT signal determination process based on the signal set acquired in S21 is completed or not, the CPU 31 determines whether the signal acquisition state at that point is considered to be good or not based on the state deterioration flag (S23).

When the status deterioration flag is set to "OFF" and it is determined that the OCT signal acquisition status at that time is good (S23: YES), the CPU 31 provisionally sets the position of the next scanning line 58 for acquiring the signal set to the position on the tissue where the signal set is to be acquired next to the position where the signal set was acquired last time (S25), regardless of whether the OCT signal judgment process is completed or not. Furthermore, the CPU 31 starts scanning the OCT measurement light to the provisionally set scanning line 58, regardless of whether the OCT signal judgment process is completed or not (S26). As a result, if the signal acquisition status is maintained as good, the signal set at the next scheduled position is smoothly acquired. In addition, if the scanning of the OCT measurement light is stopped until the judgment of the quality of the signal acquisition status based on the OCT signal (OCT signal judgment process) is completed, it becomes difficult to shorten the acquisition time of the entire plurality of OCT signals. In addition, if the driving of the optical scanning unit 14 is stopped once, it takes more time to resume driving. In contrast, in this embodiment, regardless of whether or not the pass/fail judgment based on the OCT signal is completed, the next scanning line 58 is provisionally set and scanning with the OCT measurement light is started. Thus, the acquisition time of multiple OCT signals is appropriately shortened. If the acquisition state of the OCT signal at that point is deemed good, the CPU 31 sets the number of OCT signals to be acquired as a signal set for the next scanning line 58 set in S25 to the normal number N1 ("4" in this embodiment).

Next, the CPU 31 judges whether the result of the signal acquisition state judgment based on the OCT signal (OCT signal judgment process) was good or not (S28). If the result of the OCT signal judgment process is good (S28: YES), the CPU 31 stores the signal set acquired in S21 in the storage device (S29). Furthermore, the CPU 31 maintains the next scanning line 58 provisionally set in S25 as the original scanning line 58, and continues the scanning of the OCT measurement light to the set scanning line 58 (S30). As a result, the acquisition time of multiple OCT signals (signal sets) is appropriately shortened. The CPU 31 judges whether the acquisition of the signal sets for all the scheduled scanning lines 58 has been completed (S31). When the acquisition of the signal sets for all the scanning lines 58 has been completed (S31: YES), the OCT imaging process ends. On the other hand, if the acquisition of the signal sets for all the scanning lines 58 has not yet been completed (S31: NO), the process returns to S21.

Also, if the result of the OCT signal determination process is not good (S28: NO), the CPU 31 changes the state deterioration flag, which indicates whether the OCT signal acquisition state at that time is good or not, to "ON" indicating that it is not good (S33). (See timing T1 in FIG. 4). After that, the process proceeds to S35. As described above, once the CPU 31 determines that the signal acquisition state is not good (S28: NO, S33), the state deterioration flag is maintained as "ON" at least until the next front image 40 is captured (in this embodiment, until the determination result of the signal acquisition state based on the front image 40 becomes good), thereby continuing the determination result that the signal acquisition state is not good. As a result, the possibility that a signal set with low accuracy will be adopted is reduced. Next, the CPU 31 resets the position of the next scanning line 58 to the same position on the tissue (i.e., the same position as the previous time) as the scanning line 58 at the time of acquisition of the signal set acquired in S21 (i.e., the signal set determined to have a bad signal acquisition state) (S35). As a result, the signal set for the scanning line 58 for which a good signal set was not obtained is likely to be reacquired at an early stage. In S35, the position of the scanning line 58 is reset to a position different from the position provisionally set in S26. In this case, the CPU 31 excludes (discards) the signal set acquired in S21 from the target to be stored in the storage device (S36). The CPU 31 starts scanning the OCT measurement light on the scanning line 58 reset in S35 (S37). Furthermore, the CPU 31 sets the number of OCT signals to be acquired for the next scanning line 58 reset in S35 to N2 ("2" in this embodiment) which is less than N1 ("4" in this embodiment) when the signal acquisition state is determined to be good (S38), and the process returns to S21. As a result, the acquisition time of the signal set is shortened while the determination result that the signal acquisition state is not good continues (i.e., while the state deterioration flag is set to "ON"). Therefore, the stability of the signal acquisition state is detected in more detail.

In addition, when it is determined in the judgment of S23 that the status deterioration flag is "ON" and the acquisition status of the OCT signal at that time is poor (S23: NO), the CPU 31 repeatedly resets the position of the next scanning line 58 on the tissue to the same position as the previous time (S35). Therefore, when the signal acquisition status is restored, the acquisition process of the signal set is likely to be resumed from the position where the signal acquisition status is no longer good. As a result, the acquisition time of the multiple OCT signals is likely to be further shortened. Next, the CPU 31 excludes (discards) the signal set acquired in S21 while it is determined that the signal acquisition status is not good from the target to be stored in the storage device (S36). The CPU 31 starts scanning the OCT measurement light to the scanning line 58 reset in S35 (S37). In other words, even while the signal acquisition status is poor, the acquisition of the signal set is repeated. As a result, the acquisition time of the multiple OCT signals is suppressed from being prolonged compared to the case where the operation of the optical scanning unit 14 is temporarily stopped. The CPU 31 sets the number of OCT signals to be acquired for the next scan line 58 reset in S35 to N2 (<N1) (S38), and the process returns to S21. The CPU 31 repeats the determination of the quality of the signal acquisition state based on the OCT signal (S22) even while the acquisition state of the signal set is deemed poor (i.e., while the signal set is discarded). As a result, the stability of the signal acquisition state is precisely detected regardless of whether the signal set acquired in S21 is adopted. Therefore, the stability of the signal acquisition state is detected with high accuracy.

The technology disclosed in the above embodiment is merely an example. Therefore, it is possible to change the technology exemplified in the above embodiment. It is also possible to execute only a part of the multiple technologies exemplified in the above embodiment. For example, in the above embodiment, in addition to the judgment of the signal acquisition state based on the OCT signal (S22), the judgment of the signal acquisition state based on the front image (S2, see FIG. 6) is also executed. However, the judgment of the signal acquisition state based on the front image may be omitted. In this case, once the CPU 31 judges that the signal acquisition state is not good by the judgment of the signal acquisition state based on the OCT signal, the judgment result that the signal acquisition state is not good may be continued until the next front image 40 is captured (S1: YES). In other words, the CPU 31 may change the state deterioration flag from "ON" to "OFF" when the next front image 40 is captured (S1: YES). In this case, if the signal acquisition state has recovered, the signal set acquisition process is smoothly resumed when the next front image 40 is captured.

REFERENCE SIGNS LIST 1 OCT device 11 OCT light source 12 Coupler 14 Optical scanning unit 16 Irradiation optical system 20 Reference optical system 22 Light receiving element 23 Front observation optical system 31 CPU
34 NVM
40 Front image 58 Scan line

Claims (10)

An OCT light source;
A branching optical element that branches the light emitted from the OCT light source into a measurement light and a reference light;
an optical scanning unit that scans the measurement light branched by the branching optical element on tissue of a subject;
a light receiving element that receives a composite light of the measurement light reflected by the tissue and the reference light branched by the branching optical element to detect an interference signal for acquiring an OCT signal;
A control unit;
Equipped with
The control unit is
A signal set acquisition step of acquiring a signal set including a plurality of OCT signals by performing a process of scanning the measurement light multiple times on the same scanning line on the tissue or a process of scanning the measurement light on each of a plurality of adjacent scanning lines;
a quality determination step of determining whether an acquisition state of the signal set is good or bad;
a next scan position setting step of setting a position on the tissue of a scan line along which the measurement light is scanned in the next signal set acquisition step;
Repeatedly execute
As the quality determination step, an OCT determination step is executed to determine whether an acquisition state of the signal set is good or bad based on a comparison result of at least two OCT signals included in the signal set acquired in the signal set acquisition step;
The OCT device is characterized in that in the next scanning position setting step, when the acquisition state of the signal set is determined to be poor in the OCT judgment step, the position of the next scanning line is reset to a position on the tissue that is the same as the scanning line when the signal set determined to be poor was acquired. 2. The OCT apparatus according to claim 1,
The control unit is
In the next scanning position setting step,
When the acquisition of the signal set in the previous signal set acquisition step is completed, the position of the next scan line is provisionally set regardless of whether the pass/fail determination in the OCT determination step is completed or not;
In the signal acquisition step,
An OCT device characterized in that, regardless of whether the pass/fail judgment in the OCT judgment step is completed, scanning of the measurement light on the provisionally set scanning line is started, and when the position of the scanning line is reset to a position different from the provisionally set position, the scanning line along which the measurement light is scanned is changed to the reset scanning line. 2. The OCT apparatus according to claim 1,
The control unit is
An OCT device characterized in that, in the OCT judgment step, the number of pairs of OCT signals to be compared to make the pass/fail judgment among the multiple OCT signals included in the signal set is changed depending on the number of OCT signal acquisitions per unit time when the signal set is acquired. 2. The OCT apparatus according to claim 1,
The imaging apparatus further includes a front observation optical system that captures a front image of the tissue of the subject at an imaging rate lower than the number of times an OCT signal is acquired per unit time,
The control unit is
An OCT apparatus characterized in that, in the signal set acquisition step, the scanning position of the measurement light is adjusted based on the latest front image captured by the front observation optical system, thereby scanning the measurement light along a scanning line set on the tissue. 5. The OCT apparatus according to claim 4,
The control unit is
As the pass/fail determination step, a front image determination step is further executed to determine whether the acquisition state of the signal set is pass/fail based on a comparison result between the latest front image captured by the front observation optical system and a front image captured before the latest front image,
In the next scanning position setting step,
An OCT device characterized in that, in at least one of the front image determination step and the OCT determination step, while the acquisition state of the signal set is determined to be poor, the position of the next scanning line is reset to a position on the tissue that is the same as the scanning line at the time of acquisition of any of the signal sets whose acquisition state is determined to be poor. 6. The OCT apparatus according to claim 5,
The control unit, in the front image determination step,
In addition to a first positional shift amount which is a positional shift amount between a latest front image and a previous front image captured immediately before the latest front image,
a second positional deviation amount that is a positional deviation amount between the latest front image and a reference front image captured before the immediately preceding front image can be acquired;
When both the first positional deviation amount and the second positional deviation amount are acquired, if at least one of the first positional deviation amount and the second positional deviation amount exceeds a threshold value, it is determined that the acquisition state is not good;
An OCT apparatus characterized in that, once it is determined that the acquisition state is not good, the reference front image is replaced with a newly captured front image. 5. The OCT apparatus according to claim 4,
The control unit is
In the quality determination step, once it is determined that the acquisition state of the signal set is not good, the determination result that the acquisition state is not good is continued at least until the next front image is captured by the front observation optical system,
An OCT apparatus characterized in that while it is determined that the acquisition state of the signal set is not good, the acquisition of the signal set in the signal set acquisition step is repeated, and the acquired signal set is excluded from the targets to be stored in a storage device. 8. The OCT apparatus according to claim 7,
The control unit is
An OCT apparatus characterized in that, even while excluding the acquired signal set from the targets to be stored in a storage device, a quality judgment of the acquisition state of the signal set in the OCT judgment step is repeated. 8. The OCT apparatus according to claim 7,
The control unit is
An OCT device characterized in that while the acquisition state of the signal set is determined to be not good, the number of OCT signals acquired as the signal set in the signal set acquisition step is reduced compared to when the acquisition state is determined to be good. An OCT imaging control method executed in an OCT apparatus, comprising:
The OCT apparatus includes:
An OCT light source;
A branching optical element that branches the light emitted from the OCT light source into a measurement light and a reference light;
an optical scanning unit that scans the measurement light branched by the branching optical element on tissue of a subject;
a light receiving element that receives a composite light of the measurement light reflected by the tissue and the reference light branched by the branching optical element to detect an interference signal for acquiring an OCT signal;
Equipped with
A signal set acquisition step of acquiring a signal set including a plurality of OCT signals by performing a process of scanning the measurement light multiple times on the same scanning line on the tissue or a process of scanning the measurement light on each of a plurality of adjacent scanning lines;
a quality determination step of determining whether an acquisition state of the signal set is good or bad;
a next scan position setting step of setting a position on the tissue of a scan line along which the measurement light is scanned in the next signal set acquisition step;
Repeatedly execute
As the quality determination step, an OCT determination step is executed to determine whether an acquisition state of the signal set is good or bad based on a comparison result of at least two OCT signals included in the signal set acquired in the signal set acquisition step;
An OCT imaging control method characterized in that, in the next scanning position setting step, if the acquisition state of the signal set is determined to be poor in the OCT judgment step, the position of the next scanning line is reset to a position on the tissue that is the same as the scanning line when the signal set determined to be poor was acquired.

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