JP7659967B2 - OCT equipment - Google Patents

Description

This disclosure relates to an OCT device that acquires OCT data of tissue in a subject's eye.

In recent years, optical coherence tomography (OCT), a device that captures tomographic images of tissues in the subject's eye, has been attracting attention in the field of ophthalmology.

In SD-OCT, which is relatively common in ophthalmology, the effective imaging range in the depth direction is about 2 to 3 mm from the origin position (zero delay position) in the OCT data.

When photographing the fundus using OCT, the optical path length difference between the measurement light and the reference light must be adjusted according to the axial length of the test eye. For example, in Patent Document 1, when capturing OCT data, the optical path length difference is roughly adjusted as follows. That is, while changing the optical path length difference, a predetermined evaluation value is obtained based on the OCT data acquired at each optical path length difference, and the optical path length difference is adjusted to the value that maximizes the evaluation value. After that, the optical path length difference is further fine-tuned.

On the other hand, various attempts are being made to improve the depth of penetration in OCT data (i.e., to expand the imaging range in the depth direction).

In recent years, it has been reported in non-patent literature 1 and elsewhere that the imaging range can be significantly improved by improving the light source, etc. Non-patent literature 1 reports that, for example, using a light source that emits light with a long coherence length, known as a VCSEL, as the OCT light source is effective in improving the penetration depth.

JP 2010-12111 A

Ireneusz Grulkowski. et al. (2013) High-precision, high-accuracy ultralong-range swept-source optical coherence tomography using vertical cavity surface emitting laser light source, Opt Lett. 2013 Mar 1; 38(5): 673-675.

The subject needs to keep their eyes open while the optical path length difference is being adjusted. This places a burden on the subject depending on the time required for the adjustment. In response to this, the inventors have investigated an adjustment method that reduces the burden on the subject in OCT, which has a wider imaging range in the depth direction than conventional OCT.

This disclosure was made based on the problems of the conventional technology, and the technical objective is to provide an OCT device that reduces the burden on the subject associated with adjusting the optical path length difference.

The OCT device according to a first aspect of the present disclosure includes an OCT optical system that detects a spectral interference signal between a measurement light and a reference light guided to a tissue of a test eye, the OCT optical system being capable of acquiring OCT data in an imaging range of 10 mm or more in a depth direction, and detecting the OCT data of the test eye based on the spectral interference signal output from the OCT optical system. The device is equipped with an image processor that acquires CT data, an optical path length difference adjustment unit that changes the optical path length difference between the measurement light and the reference light in order to adjust the depth position at which the OCT data is acquired, and a control means that executes an adjustment process that at least adjusts the depth position and a capture process that captures the OCT data, wherein the control means sets, as an initial position of the depth position in the adjustment process, a position that is included in a predetermined section in the OCT data from a first fundus position, which is the fundus position assumed in a short-axis long eye or a long-axis long eye, to a second fundus position, which is the fundus position assumed in an average axial long eye, and if a fundus image is located within the predetermined section when the depth position is the initial position, the adjustment of the depth position is skipped regardless of the position of the fundus image and the capture process is executed.

This disclosure reduces the burden on the subject associated with adjusting the optical path length difference.

1 is a diagram showing a schematic configuration of an OCT system according to an embodiment. FIG. 2 is a diagram showing an OCT optical system according to an embodiment. FIG. 2 is a diagram for explaining OCT data. 11 is a flowchart illustrating operations up to photographing. FIG. 2 is a diagram showing the state of wavelength sweeping at each sweep frequency. 11A and 11B are diagrams illustrating a first technique (technique in an embodiment) for adjusting the depth position at which OCT data is acquired. FIG. 13 is a diagram showing a second technique (a modified technique from the embodiment) for adjusting the depth position at which OCT data is acquired. 10 is a flowchart showing a process flow relating to display of captured OCT data. FIG. 2 is a diagram showing an example of a viewer screen. FIG. 10 is a diagram showing a viewer screen in a state in which the extraction area has been changed in comparison with that in FIG. 9 . FIG. 13 is a diagram showing an example of a viewer screen when an anterior segment OCT is displayed. 13 is a diagram showing a display form of extracted OCT data according to a modified example. FIG.

"overview"
The following describes embodiments of the present disclosure. Items grouped in <> below may be used independently or in association with each other. For example, in a certain embodiment, a plurality of items may be appropriately combined. Also, for example, an item described with respect to a certain embodiment may be applied to other embodiments.

First Embodiment
First, a first embodiment will be described. According to the OCT apparatus according to the first embodiment, good OCT data can be obtained at different sweep frequencies.

<OCT optical system>
The OCT optical system (see FIG. 2) is used to capture OCT data of the subject's eye and detects a spectral interference signal between the measurement light and the reference light guided to the tissue of the subject's eye.

The OCT optical system may be suitable for obtaining OCT data with high depth of penetration (in other words, wide range). For example, the OCT optical system according to the first embodiment is a wavelength-swept OCT (SS-OCT) optical system. In this case, the OCT optical system is provided with a wavelength-swept light source (wavelength-scanning light source) as an OCT light source, which is a light source of the measurement light and the reference light. The wavelength-swept light source changes the emission wavelength at high speed in time. For example, since a VCSEL-type wavelength-swept light source has a long coherence length, it is possible to capture wide-range OCT data in the depth direction by using it as an OCT light source. For example, a shooting range of about 10 mm or more can be realized. This makes it possible to shoot multiple tissues at different depth positions in the test eye in a single shot. As a specific example, both the fundus and the translucent body can be shot in a single shot. In addition, it is preferable that the wavelength-swept light source performs wavelength sweeping in the so-called 1 μm band (wavelength sweeping is performed around about 1050 nm). The so-called 1 μm band is known to have greater penetration into the tissues of the test eye than other wavelength bands.

The sweep frequency in the wavelength swept light source of the first embodiment can be changed at least between a first frequency and a second frequency. The second frequency is a value smaller than the first frequency. For example, the sweep frequency is changed by changing either the speed or the duty ratio of an optical element built into the light source that is driven to sweep the wavelength.

The OCT optical system according to the first embodiment includes at least a light splitting unit and a detector. The OCT optical system may additionally include a scanning unit (also called an optical scanner). The light splitting unit splits light from an OCT light source into a measurement light and a reference light. The scanning unit is a device for scanning the measurement light on the tissue of the test eye. The scanning unit may be, for example, a combination of two optical scanners with different scanning directions. The detector outputs a spectral interference signal by receiving the measurement light and the reference light guided to the test eye. The OCT optical system may scan the measurement light along a plurality of predetermined scan lines on the tissue of the test eye and capture OCT data for each of the plurality of scan lines. The scan lines may be set at any position based on an instruction from the examiner. In addition, a scan line corresponding to the scan pattern may be set by selecting one of a plurality of predetermined scan patterns. Various scan patterns such as line, cross, multi, map, radial, and circle are known.

<Conversion section>
The converter samples the spectral interference signal output from the detector. As the wavelength is swept, the spectral interference signal is detected as a beat signal. The converter also converts the spectral interference signal output from the detector from an analog signal to a digital signal. The converter may be a digitizer with an adjustable sampling frequency.

<Image processor>
The image processor processes the spectral interference signal output from the OCT optical system to obtain OCT data of the subject's eye. More specifically, the spectral interference signal converted into a digital signal by the converter is arithmetically processed by the image processor. In this way, the OCT data of the subject's eye is obtained.

<OCT data>
The OCT data may be signal data or visualized image data. For example, the OCT data may be at least one of tomographic image data showing reflection intensity characteristics of the test eye, OCT angiographic data (e.g., OCT motion contrast data) of the test eye, Doppler OCT data showing Doppler characteristics of the test eye, and polarization characteristic data showing polarization characteristics of the test eye.

The OCT data may be at least one of B-scan data (e.g., B-scan tomographic image data, two-dimensional OCT angiogram data, etc.), en face data (e.g., OCT en face data, en face motion contrast data, etc.), three-dimensional data (e.g., three-dimensional tomographic image data, three-dimensional OCT angiogram data, etc.), etc.

<Application of full-range technology>
A full-ranging technique may be applied to the OCT data. Various techniques for removing virtual images in OCT data are called full-ranging techniques. In the present embodiment, any of the full-ranging techniques may be applied, and this may enable acquisition of a wider range of OCT data from which virtual images have been selectively removed.

Examples of full-range technologies include a technology that uses additional hardware to remove virtual images (also called mirror images) (see, for example, Non-Patent Document 2), and a technology that uses software to make corrections without using additional hardware (see, for example, Patent Document 2).

Wojtkowski, M. et al. (2002) Full range complex spectral optical coherence tomography technique in eye imaging, Optics Letters, 27(16), p. 1415.

Special Publication No. 2015-506772

In addition, in an application filed by the present applicant (Patent Application No. 2019-014771), a further full-range technology has been proposed in which, based on multiple OCT data sets with different optical path lengths when detecting spectral interference signals, at least an interpolation process is performed on the overlapping area between the real image and the virtual image in the OCT data, and the OCT data that has been subjected to the interpolation process is generated. This may be applied to the present embodiment.

<Calculation control unit>
The arithmetic and control unit is a processor that controls the operation of the entire OCT apparatus. The arithmetic and control unit may be configured with, for example, a CPU, a RAM, and a ROM. The arithmetic and control unit may also function as an image processor.

In the first embodiment, the sweep frequency of the wavelength swept light source is controlled by the calculation control unit. The control unit changes the sweep frequency at least between a first frequency and a second frequency that is smaller than the first frequency. This allows multiple conditions in the OCT data to be changed. The multiple conditions include the signal-to-noise ratio of the spectral interference signal, the imaging range in the depth direction, and the correspondence between the sampling timing and the wavelength of the light emitted from the light source.

Details will be given later in the Examples, but the signal-to-noise ratio of the spectral interference signal can be greater at the second frequency than at the first frequency.

In SD-OCT, the interference fringes between the measurement light and the reference light are detected by a spectrometer to detect the spectral interference signal. For this reason, in SD-OCT, the noise in the spectral interference signal can be suppressed by controlling the exposure time of the camera (line sensor). On the other hand, the concept of exposure time does not exist in SS-OCT, so the method of SD-OCT cannot be adopted. Furthermore, even if the amount of measurement light incident on the test eye is increased to suppress noise, there is a limit from the perspective of safety. For this reason, in SS-OCT, changing the sweep frequency is considered to be meaningful in adjusting the signal-to-noise ratio of the spectral interference signal.

In addition, in SS-OCT, if the sampling rate of the spectral interference signal is constant, the smaller the sweep frequency, the wider the imaging range in the depth direction in the OCT data.

In a wavelength swept light source, the inclination of the phase slope may change depending on the sweep frequency. In other words, the correspondence between the sampling timing and the wavelength of the light emitted from the light source may change nonlinearly between the first frequency and the second frequency. For this reason, in order to properly obtain OCT data at both the first frequency and the second frequency, the conditions for mapping the sampled spectral interference signal into wavelength space must be changed for each sweep frequency.

<Correction Processing>
In response to this, the calculation control unit of the first embodiment executes a correction process in which at least one of the control of the OCT optical system and the calculation process of the spectral interference signal by the image processor is corrected according to the sweep frequency so that changes in some of the above conditions according to the sweep frequency are suppressed.

<Correction regarding the shooting range in the depth direction>
The calculation and control unit may maintain the imaging range in the depth direction in the OCT data before and after changing the sweep frequency by using any of the following methods in the correction process. For example, the imaging range may be maintained by adjusting the number of samples per A-scan to be equal between when the sweep frequency is the first cycle and when the sweep frequency is the second cycle by any of the following methods.

As a first method for maintaining the imaging range in the depth direction, the calculation control unit may change the sampling rate in the conversion unit according to the sweep frequency. When the sweep frequency is constant, the higher the sampling rate, the wider the imaging range in the depth direction. Therefore, the sampling rate may be increased together with the sweep frequency to maintain the imaging range before and after the sweep frequency is changed.

As a second method for maintaining the imaging range in the depth direction, the calculation control unit may thin out the sampled spectral interference signal in accordance with the sweep frequency, either before or after analog-to-digital conversion. For example, when the sweep frequency is a smaller second frequency, the interference signal is thinned out, thereby making the imaging range in the depth direction equal to that when the sweep frequency is a larger first frequency.

As a third method for maintaining the imaging range in the depth direction, the calculation control unit may perform interpolation on the spectral interference signal obtained by sampling either before or after analog/digital conversion. For example, by interpolating the sampling results when the sweep frequency is a higher first frequency, the imaging range in the depth direction can be made equal to that when the sweep frequency is a lower second frequency.

<Mapping correction>
The calculation control unit may change mapping information for mapping the spectral interference signals obtained by each sampling into a wavelength space according to the sweep frequency. The mapping information indicates a correspondence relationship between the sampling timing and the wavelength of the light emitted from the light source (i.e., mapping conditions). As a calibration, a change over time in the wavelength of the emitted light may be measured for each sweep frequency, and mapping information for each sweep frequency may be obtained based on the measurement results. The mapping information may be, for example, a look-up table. By changing such mapping information according to the sweep frequency, appropriate OCT data can be obtained based on calculation processing of the spectral interference signals at each sweep frequency.

<Light intensity correction>
When the sweep frequency is changed, the duty ratio is changed according to the sweep frequency. As a result, it is considered that the sensitivity of the spectral interference signal is reduced. In response to this, the calculation and control unit may change the amount of light emitted from the wavelength swept light source for each sweep frequency.

<How to select the sweep frequency>
The sweep frequency of the swept light source may be selected based on an operation input from an examiner. In this case, the OCT apparatus may include an input receiving unit that receives the operation input.

The operation input may be an operation input for setting any one of the measurement site, the measurement range, and the scan pattern. That is, the sweep frequency may be automatically set according to any one of the measurement site, the measurement range, and the scan pattern that are set based on the operation input. For example, a first scan pattern and a second scan pattern that scans a narrower range than the first scan pattern may be prepared as the scan pattern. In this case, when the first scan pattern is selected, the first value may be selected as the sweep frequency, and when the second scan pattern is selected, the second value may be selected as the sweep frequency. This makes it possible to reduce the measurement time when scanning a wider range, and to obtain high-quality OCT data when scanning a narrower range.

When acquiring OCT data of the fundus, the sweep frequency of the wavelength swept light source may be changed depending on the degree of opacity of the optical medium in the test eye. In this case, the OCT device may have a detection means for detecting opacity of the optical medium in the test eye. The calculation and control unit may change the sweep frequency of the light source depending on the degree of opacity detected.

There are various possible methods for detecting opacity in the optical body of the test eye. For example, the optical body may be photographed using an OCT optical system or a separate optical system, and opacity may be detected from the photographed image. Alternatively, a fundus image may be acquired, and the presence or absence of significant opacity may be determined based on the fundus image (i.e., opacity detection may be performed). Of course, if the image quality of the fundus image is low, there may be factors other than opacity, but even if there are factors other than opacity, improvement can be expected.

Second Embodiment
Next, a second embodiment will be described.

The OCT device of the second embodiment reduces the burden on the subject associated with adjusting the optical path length difference.

The OCT device according to the second embodiment includes at least an OCT optical system, an image processor, an optical path length difference adjustment unit, and an arithmetic control unit (control means in the embodiment). The OCT device according to the second embodiment is also suitable for acquiring wide-area OCT data in the depth direction. Additionally, the OCT device according to the second embodiment may have a focus adjustment unit.

The OCT optical system in the second embodiment is an OCT optical system that detects a spectral interference signal between the measurement light and the reference light guided to the tissue of the test eye. The OCT optical system in the second embodiment is also capable of acquiring wide-range OCT data in the depth direction. However, the OCT optical system does not necessarily have to be an SS-OCT optical system, and may be an SD-OCT optical system. However, if it is an SD-OCT optical system, it is desirable that it has a sufficient imaging range in the depth direction to the extent that the present invention can be implemented. In this case, full-range processing may be used.

In the second embodiment, wide-area OCT data is acquired by an image processor based on the spectral interference signal output from the OCT optical system.

<Optical path length difference adjustment unit>
The optical path length difference adjustment unit changes the optical path length difference between the measurement light and the reference light. This adjusts the depth position at which the OCT data is acquired. For example, the optical path length of at least one of the measurement optical path and the reference optical path may be changed, and as a result, the optical path length difference may be changed. The optical path length difference adjustment unit may change the optical path length difference by moving an optical member arranged in at least one of the measurement optical path and the reference optical path by a drive unit. Furthermore, the optical path length difference adjustment unit may change the optical path length difference by adjusting the working distance between the subject's eye and the device.

<Calculation control unit>
In the second embodiment, the arithmetic and control unit executes an adjustment process and a capture process (capture of OCT data).

<Adjustment process (adjustment step)>
The adjustment process will be described in detail. In the first embodiment, the adjustment process adjusts at least the depth position at which OCT data is acquired. The depth position is adjusted by adjusting the optical path length difference. In the second embodiment, the adjustment process adjusts the depth position (and the optical path length difference) so that a fundus image (a signal corresponding to the fundus image) is included in a predetermined section (described in detail later) in the OCT data.

Unless otherwise specified, the specified section refers to data on one side that is predetermined with respect to the zero delay position in the OCT data (in FIG. 3, one of the first image data G1 and the second image data G2 that is predetermined). However, when full-range processing is performed, this is not the case, and the entire OCT data (in FIG. 3, both the first image data G1 and the second image data G2) may be the specified section.

In addition, other conditions such as focus and polarization may be adjusted in the adjustment process. The adjustment of each condition may be performed in order (i.e., sequentially) or in parallel.

As the initial depth position, a position is set such that the first fundus position to the second fundus position are included in a predetermined section in the OCT data. Here, the first fundus position is the fundus position assumed in a short-axis long eye or a long-axis long eye. The second fundus position is the fundus position assumed in an average long-axis long eye. Here, the fundus position assumed in a short-axis long eye may be the fundus position assumed in a child (e.g., less than 22 mm from the cornea). Also, the fundus position assumed in a long-axis long eye may be, for example, the fundus position assumed in a highly myopic eye (e.g., 26 mm or more from the cornea).

In this embodiment, the specified section in the OCT data is required to be sufficiently long relative to the distance from the first fundus position to the second fundus position.

Here, although there is variation in the average axial length value depending on the statistics, a value of around 24 mm is commonly used. Also, a value of about 16 mm has been reported in cases where the axial length is extremely short. The difference between the two is about 8 mm. Therefore, when the fundus position assumed for a short axial long eye is adopted as the first fundus position, the interval from the first fundus position to the second fundus position may be, for example, 8 mm or more. When the first fundus position and the second fundus position are assumed in this way, it is required that a predetermined section in the OCT data be secured to be 8 mm or more.

In the adjustment process, OCT data is acquired when the depth position is the initial position. A detection process for a fundus image (and a signal corresponding to the fundus image) may be performed on the OCT data acquired at this time. If the result of the detection process indicates that the fundus image is included within a specified section of the OCT data, a capture process may be executed.

The specified section is a section that is to be output, such as an image output, and may be a portion of the OCT data or the entire section. If the fundus image is located within the specified section, the capture process may be performed regardless of the position of the fundus image. In this case, the capture process may be performed without changing the depth position of the shooting range from the initial position.

On the other hand, if the image of the fundus is not included within the specified interval when the depth position is at the initial position, the depth position is changed from the initial position.

<First Method>
For example, when the depth position is at the initial position, if the center of a specified section is offset from the second fundus position, the depth position may be changed by the following first method. That is, in the first method, the depth position is changed from the initial position to the back side if the aforementioned first fundus position is the fundus position expected in a short axis long eye, and to the front side if the first fundus position is the fundus position expected in a long axis long eye.

In the first technique, the position that is shifted by one step from the initial position is referred to as the second position for convenience. The second position is a position that includes the third fundus position within a specified interval. The third fundus position is the other of the fundus position assumed in a short-axis long eye and the fundus position assumed in a long-axis long eye, which is the first fundus position.

The adjustment of the depth position by the first method is shown in FIG. 6. In FIG. 6, a predetermined section in the OCT data is shown as region G1. The first fundus position, the second fundus position, and the third fundus position are shown as symbols Er1, Er2, and Er3, respectively. As shown in FIG. 6, when the first fundus position is the fundus position expected in a short-axis long eye, and the third fundus position is the fundus position expected in a short-axis long eye, the predetermined section is displaced in one step from the initial position, as shown in FIG. 6(a) ⇒ FIG. 6(b).

If the fundus image is located within a predetermined interval when the depth position is changed to the second position, the capture process may be performed regardless of the position of the fundus image.

According to the first method, for most test eyes, OCT data capture can be started with adjustment of one step or less (in other words, with only one change from the initial value). As a result, OCT data can be captured quickly regardless of the axial length of the test eye.

The overlap amount of the specified section between the initial position and the second position (indicated by symbol D in FIG. 6) may be less than half of the specified section. Because the imaging range of the OCT data is wide in the depth direction, even if the overlap amount is less than half of the specified section, it is easy to adjust the depth position so that the fundus image is properly detected.

<Second Method>
Furthermore, for example, when the second fundus position is located approximately in the center of a predetermined section when the depth position is at the initial position, the depth position may be changed by the following second method.

Here, in the second method, the positions that are changed within two steps from the initial position are referred to as the third position and the fourth position, respectively, for convenience.

In the second technique, the depth position is sequentially changed from the initial position to a third position closer to the subject and a fourth position farther from the subject. However, when the fundus image is located within a predetermined range at either the third or fourth position, the capture process is executed regardless of the position of the fundus image.

The axial length of normal eyes, including mild myopic and hyperopic eyes, shows a normal distribution with the second fundus position (approximately 0D) at the approximate center. Eyes with pathological abnormalities in axial length, such as severe myopic eyes, do not follow the above normal distribution, but their number is relatively small compared to the parameter of the normal distribution (normal eyes). Therefore, according to the second method, the second fundus position is positioned at the center of a specified interval at the initial position, so that capture can be performed for a larger number of test eyes without necessarily requiring adjustment from the initial position. As a result, the time required for adjusting the depth position is likely to be shortened.

The adjustment of the depth position by the second method is shown in FIG. 7. In FIG. 7, as in FIG. 6, a predetermined section is indicated by the symbol G1. The first fundus position, the second fundus position, and the third fundus position are indicated by the symbols Er1, Er2, and Er3, respectively. In the second method, the predetermined section is displaced within two steps from the initial position, as in FIG. 7(a) ⇒ FIG. 7(b) ⇒ FIG. 7(c), or FIG. 7(a) ⇒ FIG. 7(c) ⇒ FIG. 7(d).

It is possible to capture an image of the area from 16 mm to 32 mm from the cornea in one shot by using an OCT light source with high penetration depth (for example, a VCSEL type wavelength swept light source), or by using an OCT light source with high penetration depth in combination with full range processing. In this case, capture can be started for most test eyes without necessarily needing to change the depth position from the initial position.

<Capture process (capture step)>
The capture process captures the OCT data. For example, the measurement light is scanned along a predetermined scan line on the tissue of the subject's eye, and the OCT data of each of the multiple scan lines is acquired as imaging data. The imaging data is stored in a memory.

<Display of shooting results>
In the OCT data captured as described above, the image of the fundus is depicted in a narrow range of the entire imaging range. Therefore, if the entire imaging range is displayed on the screen as is, it is considered that it is difficult to observe the tissue of the fundus. In contrast, in this embodiment, when displaying the OCT data, the following <setting step> and <display control step> may be executed.

<Setup steps>
In the setting step, an extraction region is set for a partial depth region in the OCT data.

Now, the extraction region in this embodiment will be described with reference to FIG. 3. FIG. 3 shows image data G of a tomographic image, which is an example of visualized OCT data. The image data G is made up of first image data G1 corresponding to the back side of the zero delay position Z and second image data G2 corresponding to the front side of the zero delay position Z, and the images are symmetrical with respect to the zero delay position Z. In detail, a real image and a virtual image of the fundus are formed symmetrical with respect to the zero delay position Z.

In the setting step, an extraction region is set for data in one direction from the zero delay position Z (in FIG. 3, either the first image data G1 or the second image data G2). At that time, a depth region including the image position of the tissue is set as the extraction region. In other words, the distance between the zero delay position and one or both of the upper and lower ends of the extraction region is adjusted so that the image position of the tissue is included between the upper and lower ends of the extraction region.

Here, in the setting step, the image position of the tissue in the OCT data may be detected. In this case, the distance between the zero delay position and one or both of the upper and lower ends of the extraction region may be adjusted based on the detected image position. In this case, for example, by adjusting the relationship between the reference position in the extraction region and the image position of the tissue in the OCT data, the distance between the zero delay position and one or both of the upper and lower ends of the extraction region may be adjusted.

When observing the area from the retinal surface to the choroid at the center of the fundus (between the macula and the optic disc), a shooting range in the depth direction of about several millimeters (e.g., 2 mm to 3 mm) is sufficient, whereas with swept-wavelength OCT, a shooting range more than twice that (shooting range in one direction from the zero delay position) can be realized. In this case, when the center of the fundus is displayed in extracted OCT data, it is preferable that the length in the depth direction of the extracted region is half or less of the shooting range of the OCT data from which it is extracted.

The full-range technique may also be applied to the OCT data according to the second embodiment. In other words, it may be possible to obtain a wider range of OCT data from which virtual images have been selectively removed. In this case, an extraction region can be set at any depth position from the combined region of the first image data G1 and the second image data G2.

<Display control step>
In the display control step, the extracted OCT data corresponding to the extraction region is extracted from the OCT data and displayed in a predetermined display region on the monitor. Therefore, in this embodiment, even if OCT data with high penetration depth is acquired, a depth region including the image position of the tissue is extracted from the OCT data and displayed, not the entire OCT data. Therefore, the image of the tissue of the test eye is displayed in a more enlarged manner relative to the predetermined display region. As a result, the state of the tissue of the test eye can be easily grasped through the extracted OCT data.

<Display of information indicating the position of the extracted area>
In the display control step, information indicating a positional relationship of the extracted region with respect to the OCT data from which the extraction was made may be displayed on the monitor together with the extracted OCT data. By displaying such information, for example, the position of the tissue of the subject's eye included in the extracted OCT data can be easily grasped.

The information indicating the positional relationship of the extraction region with respect to the OCT data from which the extraction was made may be displayed, for example, as a graphic, as text, or as a combination of both. The graphic may be a thumbnail image of the OCT data from which the extraction was made, or may be something else. When a thumbnail image of the OCT data is displayed, the extraction region may be further highlighted on the thumbnail image. The graphic may also indicate the positional relationship between the tissue included in the OCT data from which the extraction was made and the extraction region (for example, see FIG. 9). The graphic may also be, for example, an indicator such as the following. The indicator is a bar or number line indicating the imaging range of the OCT data, and the range corresponding to the extraction region is highlighted in a manner that makes it identifiable from other ranges. The graphic may also be an indicator that indicates the positional relationship between the tissue included in the OCT data from which the extraction was made and the extraction region by color. For example, the color of the indicator may be changed to green when the extraction region includes tissue, and to red when the extraction region does not include tissue.

<Change steps>
In the changing step, an operation input for changing at least one of a depth position and a range of an extraction region for the OCT data is received, and at least one of a depth position and a range of the extraction region is changed based on the operation input.

Operational input may be entered via various input interfaces.

The graphic indicating the position of the extraction area may be used as a widget for receiving an operation input in the change step. In this case, the operation input for changing the extraction area may be input via the above-mentioned graphic. As one specific example, an operation for moving the highlighted portion on the thumbnail image or on the indicator may be input as an operation input for changing the extraction area. Note that the widget referred to here is a general term for GUI interface components (UI parts), and is also called a control. Specific examples of widgets that are well known include buttons, sliders, check boxes, text boxes, and other commonly used widgets.

If at least one of the depth position and range of the extraction region is changed by the change step, the extracted OCT data displayed in the specified display region is switched to that corresponding to the changed extraction region in the subsequent display control step.

This makes it possible to observe tissue contained in the OCT data at the desired depth on the monitor.

In addition, if at least one of the depth position and range of the extraction region is changed by the change step, the display mode of the extracted OCT data on the monitor may be changed in the subsequent display control step according to the changed extraction region.

In this embodiment, the change in the display mode may be realized, for example, by changing the layout of the extracted OCT data on the monitor. In this case, the layout may be changed by changing any one of the position, size, and shape of the display area in which the extracted OCT data is displayed. The display mode may also be changed by changing at least any one of the scale and aspect ratio of the extracted OCT data in the display area according to the extraction area. The display mode may also be changed by changing the coordinate system in the display area according to the extraction area. In this case, the extracted OCT data is converted (deformed) according to the coordinate system. Furthermore, some of the above examples may be combined.

In this embodiment, in the acquisition step, OCT data including images of multiple tissues at different depth positions in the subject's eye may be acquired. In this case, in the display control step, the display mode of the extracted OCT data may be changed depending on the type of tissue included in the extraction region. For example, the display mode may be changed at least between a case where the extraction region includes only fundus tissue and a case where the extraction region includes a transparent body. In addition, the display mode may be changed depending on the number of types of tissue included in the extraction region.

<Sequential display of OCT data from multiple scan lines>
In the acquiring step, a plurality of OCT data for each of a plurality of predetermined scan lines may be acquired. In order to capture the plurality of OCT data, the plurality of scan lines may be continuously scanned by the OCT optical system. The plurality of scan lines may be set at positions close to each other (e.g., positions spaced apart by approximately one pixel) by raster scanning.

In this case, in the setting step, a process of setting an extraction region for each OCT data may be performed so that the position of the extraction region relative to the image position of the subject coincides between the multiple OCT data. Also, in the display control step, extracted OCT extracted from each of the multiple OCT data may be displayed sequentially in the display area. At this time, the multiple extracted OCT data may be switched and displayed so that the position on the tissue displayed by the extracted OCT data transitions in one direction. Thereby, in the sequential display of the multiple extracted OCT data in the display area, the position of the tissue image is maintained relative to the display area.

However, this is not necessarily limited to this. In the setting step, a process of setting an extraction region for each OCT data may be performed so that the depth position of the extraction region is consistent between the multiple OCT data. When multiple extracted OCT data are switched and displayed so that the position on the tissue displayed by the extracted OCT data transitions in one direction, the image position of the tissue is displaced within the display area. As a result, the three-dimensional shape of the tissue can be easily grasped in the sequential display.

<Real-time display>
The real-time extracted OCT data may be displayed by the above-mentioned sequential display each time new OCT data is captured through the OCT optical system. In this case, for example, in the acquisition step, each time OCT data is generated by the image processor by scanning each scan line with the OCT optical system, the OCT data is acquired as new OCT data. In addition, an extraction region is set in the new OCT data, and the extracted OCT data corresponding to the extraction region is displayed in real time in the display region.

<Follow-up display>
Furthermore, for follow-up observation (follow-up) using a plurality of OCT data in which the positions of the scanning lines are the same but the imaging dates are different, the following processing may be performed.

For example, in the acquisition step, multiple OCT data may be acquired in which the scanning line positions are the same but the imaging dates are different.

In addition, in the setting step, a process of setting an extraction region for each OCT data may be performed so that the position of the extraction region with respect to the image position of the subject coincides between the multiple OCT data. In addition, in the display control step, extracted OCT extracted from each of the multiple OCT data may be displayed sequentially (switched display) in the display area. In the display area, extracted OCT data captured on different dates are switched and displayed with the positions of the tissue images approximately aligned, making it easy for the examiner to observe changes over time in the tissue of interest.

<Display of synthetic OCT data>
The OCT data in which the extraction region is set may be synthetic OCT data. The synthetic OCT data is generated by synthesizing a plurality of OCT data at different depth positions (see, for example, the following Patent Document 3 by the present applicant). The synthetic OCT data may include at least OCT data of the anterior segment and the fundus. In addition, the synthetic OCT data may further include OCT data of the equator.

JP 2012-75640 A

Since individual tissues are difficult to observe even in composite OCT data, an extraction region can be set in a desired area and the area can be enlarged and displayed in a predetermined display area.

<Reduction of data outside the extracted area>
In OCT data with deeper penetration, the data volume of the OCT data may become larger. On the other hand, in OCT data with deeper penetration, the depth area occupied by the tissue of the subject's eye may remain the same as before. Therefore, in this embodiment, an extraction area may be set, and data of areas other than the extraction area may be reduced (deleted or compressed) from the OCT. As a result, data of the extraction area (i.e., extracted OCT data) may be stored in memory instead of the original OCT data.

"Example"
An OCT system (optical coherence tomography system) shown in FIGS. 1 and 2 will be described below as an embodiment.

As shown in FIG. 1, the OCT system according to the embodiment includes at least an optical unit 10 and a control unit 50, which corresponds to the computer of the embodiment. In the embodiment, the optical unit 10 and the control unit 50 are integrated as an OCT device. The OCT system (OCT device) according to the embodiment has a basic configuration of swept-wavelength OCT (SS-OCT).

The optical unit 10 includes an OCT optical system 100 (see FIG. 2). Furthermore, the optical unit 10 in this embodiment includes an observation optical system 200. The control unit 50 is a computer in this embodiment, and includes at least an arithmetic control unit (processor) 70 that controls the entire OCT system. The arithmetic control unit (hereinafter simply referred to as the control unit) 70 is composed of, for example, a CPU and a memory. As an example, in this embodiment, the control unit 70 also serves as an image processor in the OCT system.

In addition, the OCT system may be provided with a storage unit (memory) 72, an input interface (operation unit) 75, a monitor 80, etc. Each unit is connected to the control unit 70.

Various programs, initial values, etc. for controlling the operation of the OCT device may be stored in memory 72. For example, a hard disk drive, a flash ROM, or a USB memory that is detachably attached to the OCT device may be used as memory 72. In addition, memory 72 may store various information related to imaging, in addition to OCT images generated from OCT data. Monitor 80 may display OCT data (OCT images).

<OCT optical system>
Next, the OCT optical system 100 in this embodiment will be described with reference to Fig. 2. The OCT optical system 100 guides measurement light to the test eye E by a light guide optical system 150. The OCT optical system 100 guides reference light to a reference optical system 110. The OCT optical system 100 causes a detector (light receiving element) 120 to receive interference signal light obtained by interference between the measurement light reflected by the test eye E and the reference light. The OCT optical system 100 may be mounted in a housing (apparatus main body) not shown, and alignment with the test eye may be performed by three-dimensionally moving the housing with respect to the eye E by a known alignment movement mechanism via an operating member such as a joystick.

In this embodiment, the OCT optical system 100 uses the SS-OCT method. In this case, the OCT optical system 100 has a wavelength swept light source as the OCT light source 102. In addition, the OCT optical system 100 has a point detector as the detector 120.

The wavelength of the swept light source is swept over time. The OCT light source 102 may be a VCSEL-type swept light source. The VCSEL-type swept light source includes a VCSEL that performs laser oscillation and a MEMS that realizes high-speed scanning. In this embodiment, a device capable of changing the sweep frequency is used as the VCSEL-type swept light source.

In this embodiment, the detector 120 is a balanced detector that performs balanced detection using multiple (e.g., two) detectors. The control unit 70 samples the interference signal between the reference light and the return light of the measurement light in response to changes in the emission wavelength from the wavelength swept light source, and obtains OCT data of the test eye based on the interference signal at each wavelength obtained by sampling.

The coupler (splitter) 104 is used as a first optical splitter and splits the light emitted from the light source 102 into a measurement optical path and a reference optical path. The coupler 104, for example, guides the light from the light source 102 to the optical fiber 152 on the measurement optical path side and also guides the light to the reference optical system 110 on the reference optical path side.

<Light guide optical system>
The light-guiding optical system 150 is provided to guide the measurement light to the eye E. For example, the light-guiding optical system 150 may be provided with an optical fiber 152, a collimator lens 153, a focusing lens 155, an optical scanner 156, and an objective lens system 158 (objective optical system in this embodiment) in that order. In this case, the measurement light is emitted from the exit end of the optical fiber 152 and is converted into a parallel beam by the collimator lens 153. Then, the measurement light is directed to the optical scanner 156 via the focusing lens 155. The focusing lens 155 can be displaced along the optical axis by a driving unit (not shown) and is used to adjust the light-focusing state at the fundus. The light that has passed through the optical scanner 156 is irradiated to the eye E via the objective lens system 158. A first pivot point P1 is formed at a position conjugate with the optical scanner 156 with respect to the objective lens system 158. By positioning the anterior eye at this pivot point P1, the measurement light reaches the fundus without being vignetted. Furthermore, the measurement light is scanned on the fundus in response to the operation of the optical scanner 156. At this time, the measurement light is scattered and reflected by the tissue of the fundus.

The optical scanner 156 may scan the measurement light in the XY directions (transverse directions) on the eye E. The optical scanner 156 is, for example, two galvanometer mirrors, and the reflection angle is arbitrarily adjusted by a driving mechanism. The light beam emitted from the light source 102 has its reflection (traveling) direction changed and is scanned in an arbitrary direction on the fundus. As the optical scanner 156, for example, a reflection mirror (galvanometer mirror, polygon mirror, resonant scanner), or an acousto-optical element (AOM) that changes the traveling (deflection) direction of light, etc. may be used.

The scattered light (reflected light) from the eye E due to the measurement light travels back along the path taken when the light was projected, enters the optical fiber 152, and reaches the coupler 104. The coupler 104 guides the light from the optical fiber 152 to an optical path toward the detector 120.

<Reference optical system>
The reference optical system 110 generates a reference light to be combined with the fundus reflected light of the measurement light. The reference light passing through the reference optical system 110 is combined with the light from the measurement optical path by a coupler 148 and interferes with it. The reference optical system 110 may be of a Michelson type or a Mach-Zehnder type.

The reference optical system 110 shown in FIG. 2 is formed by a transmission optical system, as an example. In this case, the reference optical system 110 guides the light from the coupler 104 to the detector 120 by transmitting it without returning it. Without being limited to this, the reference optical system 110 may be formed by a reflection optical system, for example, and guide the light from the coupler 104 to the detector 120 by reflecting it with the reflection optical system. In this embodiment, an optical path length difference adjustment unit 145 and a polarization adjustment unit 147 are arranged on the optical path from the coupler 104 to the detector 120.

The optical path length difference adjustment unit 145 is used to adjust the optical path length difference between the measurement light and the reference light. In this embodiment, a mirror 145a having two orthogonal surfaces is provided on the reference light path. The optical path length of the reference light path can be increased or decreased by moving this mirror 145a in the direction of the arrow by the actuator 145b. Of course, the configuration for adjusting the optical path length difference between the measurement light and the reference light is not limited to this. For example, in the light-guiding optical system 150, the collimator lens 153 and the coupler may be moved together to adjust the optical path length of the measurement light, and as a result, the optical path length difference between the measurement light and the reference light may be adjusted.

In this embodiment, the polarization adjustment unit 147 adjusts the polarization of the reference light. The polarization adjustment unit may be disposed on the measurement light path.

<Acquisition of depth information>
The control unit 70 processes (Fourier analysis) the spectral signal detected by the detector 120 to obtain OCT data of the subject's eye.

The spectral signal (spectral data) may be rewritten as a function of wavelength λ and converted into a function I(k) that is equally spaced with respect to wavenumber k (=2π/λ). Alternatively, it may be acquired from the beginning as a function I(k) that is equally spaced with respect to wavenumber k (K-CLOCK technology). The arithmetic controller may obtain OCT data in the depth (Z) domain by performing a Fourier transform on the spectral signal in wavenumber k-space.

Furthermore, the information after the Fourier transform may be represented as a signal including real and imaginary components in Z space. The control unit 70 may obtain the OCT data by calculating the absolute values of the real and imaginary components of the signal in Z space.

When acquiring fundus OCT data, the optical path length difference between the measurement light and the reference light must be adjusted in advance.

<Software dispersion correction>
In this embodiment, the control unit 70 may perform dispersion correction processing by software on the spectrum data output from the detector 120. The control unit 70 obtains OCT data based on the spectrum data after dispersion correction. For this reason, a difference in image quality occurs between the real image and the virtual image (see FIG. 3).

In other words, in this embodiment, the difference in the amount of dispersion of the optical system between the measurement optical path and the reference optical path is corrected by signal processing. In detail, this is done by applying the correction value stored in advance in memory 72 to the processing of the above-mentioned spectrum signal.

The control unit 70 obtains the spectral intensity of the light based on the received light signal output from the detector 120 and rewrites it as a function of wavelength λ. Next, the control unit 70 converts the spectral intensity I(λ) into an equally spaced function I(k) of wavenumber k (=2π/λ).

The effect of dispersion mismatch between the measurement light and the reference light is to shift the phase of the interference component, lower the peak of the multiplexed signal of each wavelength, and make the signal broader (reduced resolution). In dispersion correction, the phase shift for each wavelength is returned to its original position to correct the reduction in resolution due to the reduction in the interference signal. In this case, the phase shift amount φ(k) as a function of the wave number k is calculated, and the phase shift is returned for each value of k by I(k)·exp-iφ(k). Here, the phase φ(k) to be subjected to dispersion correction can be calculated in advance by calibration, or the phase φ(k) corresponding to the acquired tomographic image can be calculated. Then, the memory 72 stores parameters for dispersion correction (for example, the phase φ(k)).

Then, the control unit 70 obtains OCT data by performing a Fourier transform on the dispersion-corrected spectral intensity I(k) corrected using the set dispersion correction data.

For example, a first dispersion compensation value (for normal image) is obtained from memory 72 as a dispersion compensation value for compensating for the effect of dispersion on the real image, the spectral data output from detector 120 is corrected using the first dispersion compensation value, and the corrected spectral intensity data is Fourier transformed to form OCT data. The real image R is obtained as a high-sensitivity, high-resolution image, and the virtual image M (mirror image) is obtained as a blurred image with low resolution due to differences in the dispersion compensation values.

As a result, when a real image is acquired in the first image area G1, the real image is acquired as a high-sensitivity, high-resolution image, and the virtual image (mirror image) is acquired in the second image area G2 as a low-resolution, blurred image due to differences in dispersion correction values. On the other hand, when a real image is acquired in the second image area G2, the virtual image is acquired in the first image area G1 as a low-resolution, blurred image due to differences in dispersion correction values.

Of course, this is not limited to the above, and software dispersion correction may be performed on the virtual image M. In this case, the virtual image M is acquired as a high-sensitivity, high-resolution image, and the real image R is acquired as a low-resolution, blurred image.

For details on the method of performing dispersion correction using software as described above, please refer to U.S. Patent No. 6,980,299, JP-A-2008-501118, etc. Also, please refer to JP-A-2010-29648.

When dispersion correction processing is performed by software, when obtaining OCT data at the center of the fundus, for example, the control unit 70 may extract image data of the real image and virtual image that has higher sensitivity and resolution.

<Operation description>
Next, the operation of the OCT apparatus according to the embodiment will be described with reference to a flowchart.

First, let us refer to the flowchart in Figure 4 to explain the process leading up to shooting.

<S1: Setting of shooting operation>
First, the imaging operation is set. For example, the imaging part of the subject's eye, the scan pattern, the imaging type, etc. may be set at this time. A setting screen may be displayed to set the imaging operation.

In this embodiment, image quality settings can be made on the setting screen. For example, the image quality mode can be switched between a first mode for obtaining OCT data of higher image quality and a second mode for obtaining OCT data of normal image quality. Image quality is changed by changing the sweep frequency between the first mode and the second mode. In this embodiment, the sweep frequency in the first mode is ΩA, and the sweep frequency in the second mode is ΩB (where ΩB>ΩA).

Here, the duty ratio of the light source is the same for each mode. The wavelength sweep in the light source 102 is shown in FIG. 5 when converted from wavelength space to wavenumber space.

Note that in Figure 5, ΩA = 1/Ta, ΩB = 1/Tb. Also, the wave number k = λ/2π is assumed to be swept linearly with respect to time.

We will examine the signal-to-noise ratio of OCT data in each of the modes shown above.

When the sampling period of the digitizer is the same in each mode, the relationship between the number of samples Na during a sweep in the first mode and the number of samples Nb during a sweep in the second mode is given by the following equation (1).

If the coherence length of the measurement light and the reference light is the same between the first and second modes, the quotient of the signal-to-noise ratios in each mode is given by the following equation (2):

Note that SNR(a) is the SNR in the first mode, and SNR(b) is the SNR in the second mode.

Therefore, as shown in Figure 5, when Ta>Tb, the signal-to-noise ratio is expected to improve by changing from the second mode to the first mode. Therefore, compared to the second mode, the first mode can provide OCT data with higher image quality.

However, in the above explanation, the coherence length is constant, but in reality there is a trade-off between the wavelength sweep speed and the coherence length. Therefore, a greater improvement in the S/N ratio is expected by changing from the second mode to the first mode.

In this embodiment, the sampling rate of the digitizer is changed according to the sweep frequency to suppress the change in the imaging range in the depth direction between the first and second modes. In detail, the sampling rate is increased together with the sweep frequency to suppress the change in the imaging range between the modes.

In addition, in this embodiment, the mapping information for mapping the spectral interference signals obtained by each sampling into wavelength space may be changed according to the sweep frequency. The mapping information indicates the correspondence between the sampling timing and the wavelength of the light emitted from the light source (i.e., the mapping conditions). In this embodiment, a lookup table prepared in advance for each mode is used as the mapping information. The lookup table indicates the change over time in the wavelength of the emitted light for each sweep frequency. By changing the mapping information according to the sweep frequency, appropriate OCT data is acquired at each sweep frequency based on the calculation processing of the spectral interference signal.

<S2: Alignment>
The alignment of the device is performed with respect to the subject's eye. For example, the subject is asked to gaze at a fixation target in advance, and the positional relationship between the subject's eye and the measurement optical axis is adjusted based on an anterior eye observation image captured by an anterior eye observation camera (not shown). For example, the adjustment is performed so that the pupil center of the subject's eye coincides with the measurement optical axis. The alignment may be adjusted manually or automatically. At a position where the alignment adjustment is completed, a front image of the fundus by the observation optical system 200 can be acquired as an observation image.

After the alignment is complete, the acquisition of the observation image via the observation optical system 200 and the display of the observation image on the monitor 80 are started. At the same time, the control unit 70 acquires OCT images at any time via the OCT optical system 100.

<S3 to S11: Optimization control>
Next, optimization control of the photographing conditions is performed. By performing optimization control, the fundus region desired by the examiner can be observed with high sensitivity and high resolution by the OCT optical system 100. Note that in this embodiment, as an example of optimization control in the OCT optical system 100, adjustment of the optical path length, focus adjustment, and adjustment of the polarization state (polarizer adjustment) are performed.

For example, the optimization control is started when an optimization start button (Optimize button) (not shown) is operated as a trigger.

<S3: Initialization of shooting conditions>
First, the control unit 70 executes an initialization process of the imaging conditions. In this embodiment, at least the OPL and the focus position are initialized in the initialization process. For example, the position of the focusing lens 155 and the position of the mirror 145a are each moved to a predetermined initial position (movement start position). By moving the mirror 145a to the initial position, the depth position at which OCT data is acquired is set to the initial position.

In this embodiment, when the mirror 145a is in the initial position (i.e., when the depth position is in the initial position), as shown in FIG. 6(a), the first fundus position Er1 to the second fundus position Er2 are included in a predetermined section of the OCT data (image area G1 in FIG. 6). Here, in this embodiment, the first fundus position Er1 is the fundus position assumed in a short-axis long eye. Here, as one specific example, a position 16 mm behind the cornea is used as the first fundus position Er1. Also, in this embodiment, the second fundus position Er2 is the fundus position assumed in an average subject's eye. Here, as one specific example, a position 24 mm behind the cornea is used as the second fundus position Er2.

As another example, a position corresponding to the second fundus position Er2 (corresponding to ±0D) is set as the initial position of the focusing lens 155. However, the initial position of the focusing lens 155 is not necessarily limited to this, and may be, for example, the movement limit position of the focusing lens 155 or another position.

<S4, S5: Detection process at initial position>
In this embodiment, OCT data is acquired when the depth position is the initial position. A fundus image detection process is performed on the acquired OCT data. If a fundus image is detected within a predetermined section (S5: Yes), the OPL adjustment is completed without moving the OPL.

<S6: OPL adjustment>
On the other hand, if no fundus image is detected within the predetermined section (S5: No), the mirror 145a is moved so that the OPL is changed to a predetermined second value (S6). This shifts the depth position at which the OCT data is acquired to a second position on the deeper side. As shown in FIG. 6B, in this embodiment, when the depth position is the second position, at least the third fundus position Er3 is included in the predetermined section of the OCT data. In this embodiment, as an example, a position 32 mm behind the cornea is used as the third fundus position Er3.

<S7, S8: Detection process at second position>
When the OPL is a second value, OCT data is acquired, and a fundus image detection process is performed on the acquired OCT data. When a fundus image is detected within a predetermined section, the OPL adjustment is completed. Here, the axial length values of most of the test eyes are included in the range of 16 mm to 32 mm from the cornea, which corresponds to the first fundus position Er1 to the third fundus position Er3. Therefore, at this stage (i.e., by the time the OPL is changed by at most one step), the OPL adjustment is completed for most of the test eyes.

On the other hand, if no OCT data is detected when the OPL is at the second value, the OPL may be readjusted so that the OCT data shooting range is set further back. Alternatively, it is possible that the eyelids are closed when the OCT data is acquired, and the OCT data is not acquired properly. In this case, the processing from S3 onwards may be retried. In other words, the OPL may be set again to at least one of the initial value and the second value, and then the fundus image detection processing may be executed.

In this embodiment, after the OPL adjustment, optimization control of the focus position in the OCT is performed (S9, S10). In detail, the focusing lens 155 is adjusted to a position corresponding to the fundus image detected in the detection process.

When an image of the fundus is detected within a predetermined interval in OCT data acquired when the depth position is the initial position, the focusing lens 155 is moved from the initial position, which is a position equivalent to ±0D, to the plus side (S10). That is, the focusing position of the measurement light is moved from the second fundus position to the near side. On the other hand, when an image of the fundus is detected within a predetermined interval in OCT data acquired when the depth position is the second position, the focusing lens 155 is moved from the initial position, which is a position equivalent to ±0D, to the minus side (S9). That is, the focusing position of the measurement light is moved from the second fundus position to the back side. In this way, the direction in which the focusing lens 155 is moved is appropriately set according to the position of the fundus.

In the optimization control of the focus position, focus position information of the OCT optical system 100 may be acquired based on the acquired OCT data, and the focusing lens 155 may be adjusted. In this case, the amount of movement of the focusing lens relative to the position of the fundus image in the OCT data may be determined in advance experimentally or by simulation. In addition, the position of the focusing lens 155 may be adjusted so that the focus position matches a specific layer, for example.

Optimization control of the focus position is not necessarily limited to this. For example, the optimal focus position may be detected using the observed image.

<S11: Polarizer Adjustment>
In this embodiment, the control unit 70 drives the polarizer 147 to adjust the polarization state between the measurement light and the reference light. When the polarization states of the measurement light and the reference light match, a stronger interference signal is obtained. Therefore, the polarizer 147 is driven and controlled based on the output signal output from the light receiving element 120 so that the polarization states of the measurement light and the reference light match.

More specifically, in this embodiment, the polarizer 147 is driven and controlled based on the OCT image. The control unit 70 changes the position (orientation) of the polarizer 147 and obtains the signal intensity of the OCT image acquired each time the position (orientation) is changed. For example, the signal intensity may be indicated by the above-mentioned evaluation value B. The position of the polarizer 147 where evaluation value B (peak value) is at its peak is obtained, and the polarizer adjustment is completed by adjusting to that position.

In this way, the optimization control is completed, allowing the examiner to observe the desired fundus area with high sensitivity and high resolution.

<S12: Capturing OCT images>
In this embodiment, after the optimization is completed, when the examiner presses an imaging switch (not shown), an OCT image is captured via the OCT optical system 200. The captured OCT image is stored in, for example, the memory 75. At this time, the OCT data may be captured using any one of a plurality of predetermined scan patterns.

The captured OCT data may be stored (saved) in the memory of the device in association with identification information indicating the scan position and the capture date and time. In this way, the captured OCT data is acquired by the control unit 70 as a captured image. When multiple slices are captured at one time, each slice may be acquired.

At this time, in this embodiment, a predetermined one of the first image area G1 and the second image area G2 that sandwich the zero delay position Z is extracted and acquired as a captured image. At this time, one image area acquired as the captured image contains an image of the subject's eye that is depicted with higher sensitivity and resolution as a result of the above-mentioned dispersion correction compared to the other image area.

<OCT image display control>
Next, an ophthalmologic image processing method executed by the OCT system of the embodiment will be described with reference to the flowchart shown in Fig. 8. Each process of the flowchart may be executed by the control unit 70 based on an ophthalmologic image processing program. In this embodiment, by executing each process of the flowchart, at least the extracted OCT data is displayed in the manner shown in Figs. 9 to 11.

For convenience, the screens shown in Figures 9 to 11 are referred to as viewer screens, and it is assumed that OCT data is displayed after imaging is completed. Furthermore, for convenience, all OCT data in the following explanation is B-scan data. In addition, OCT data corresponding to a scan line is also referred to as a slice.

<S52: Selection of display target>
In this embodiment, OCT data is acquired by the process of S12 that has been performed in advance. At this time, if multiple slices have been acquired, the slice that is displayed first on the screens shown in Figures 9 and 10 is selected. The slice that is displayed first may be determined in advance for each scan pattern.

As an example, the examples in Figures 9 and 10 show a display example of slices captured using the "multi" scan pattern. In this case, each slice is acquired based on a horizontal scan. The scan lines 231 to 233 corresponding to each slice are set to be different from each other in the vertical direction. In this case, as shown in Figures 9 and 10, it may be predetermined that the slice corresponding to the scan line 231 that passes through the fovea is selected as the slice to be displayed first.

<S53: Automatic Setting of Extraction Region (Setting Step of the Present Embodiment)>
Next, an extraction region in the slice selected as the display target is set (S53). In this embodiment, the fundus image included in the slice may be detected by image processing, and the extraction region may be set based on the detection position of the fundus image.

The fundus image may be detected, for example, based on the signal intensity distribution in the depth direction of the OCT data, based on image features, or by other detection methods.

The size of the extraction region set in step S52 may be determined in advance. In this case, the distance between the zero delay position and the extraction region is adjusted so that the detected image position is included between the upper and lower ends of the extraction region.

<S54: Display of extracted OCT data>
After the extraction region is set, the extracted OCT data is displayed. For example, the data is displayed in the manner shown in FIGS.

As shown in Figures 9 and 10, the extracted OCT data is displayed in a predetermined first display area 210 on the viewer screen.

In the viewer screen shown in Figs. 9 and 10, a second display area 220 is provided at a position different from the first display area 210. The second display area 220 is also called a thumbnail table area. The entire slice from which the extracted OCT data was extracted is displayed as a thumbnail in the second display area 220. That is, in this embodiment, the extracted OCT data and the OCT data from which the extracted OCT data was extracted are displayed simultaneously in different display areas. At this time, the extracted OCT data is displayed enlarged relative to the thumbnail.

In the second display area 220, a selection frame 221 is displayed together with the thumbnail. The selection frame 221 graphically indicates the extraction position of the extracted OCT data. In this embodiment, the selection frame 221 indicates the positional relationship of the extraction area to the OCT data from which it was extracted.

Text information indicating the depth position of the extraction region may also be displayed on the viewer screen. The text information may indicate the position of the extraction region relative to the origin position (zero delay position), and may be, for example, the Z coordinate of the extraction region or the optical path length from the origin position to the extraction region.

Additionally, a frontal image of the fundus may be displayed in a third display area 230 on the viewer screen. Scan lines may be superimposed on the frontal image. In Figs. 9 and 10, a scan line 231 corresponding to the slice being displayed, and scan lines 232 and 233 corresponding to other slices that can be switched from the displayed slice and displayed are each displayed on the frontal image.

<S55: Receiving various operation inputs>
With the viewer screen displayed, the control unit 70 can accept various instructions based on operational input to the input interface 75 (S55). For example, various widgets can be selected by moving the pointer C via the input interface 75. Various operational inputs are input via the various widgets.

<Change of extraction area>
In this embodiment, while the viewer screen is displayed, the control unit 70 may receive a change instruction to change the extraction area while maintaining the slice to be displayed. The change instruction to the extraction area may be received based on an operation input via the above-mentioned selection frame 221 (an example of a widget). If the change instruction to the extraction area is received (S56: Yes), the extraction area is updated (reset) in accordance with the instruction (S57).

For example, the position of the extraction region may be changeable based on an instruction. In this case, the selection frame 221 may be moveable in the vertical direction on the screen based on an operation via an input interface. By inputting an operation to move the selection frame 221, the position of the extraction region in the OCT data may be changed while maintaining the size and shape of the selection frame 221.

In addition, for example, the size of the extraction region may be changeable based on an instruction. In this case, the size of the selection frame 221 may be changeable based on an operation input on the screen for each control point of the selection frame 221.

The operation input for changing the position of the extraction area and the operation input for changing the size of the extraction area may be different. In this case, the extraction area (in other words, the area inside the selection frame 221) and the selection frame 221 itself may be set as widgets that can be individually selected (specified) as operation targets, so that the above two types of operation inputs may be input separately.

When the extraction region is updated (reset) in response to an instruction to change the extraction region (S57), the extracted OCT data corresponding to the updated extraction region is newly displayed in the first display region 210 (S54). As a result, even from OCT data that is long in the depth direction, the examiner can enlarge and observe a desired portion in the first display region 210.

As an example, by changing the depth position of the extraction region in the OCT data to a deeper position compared to Figure 9, a new screen like the one shown in Figure 10 will be displayed.

When the size of the extraction area is changed, the layout of the first display area 210 on the screen may be adjusted to match the changed size. For example, the range that the first display area 210 occupies on the screen may be adjusted. Also, the range that the first display area 210 occupies on the screen may be constant, and the vertical and horizontal scales of the extracted OCT data may be changed individually to match the shape of the first display area 210.

When the position of the extraction area is changed, the amount of displacement between the extracted area after the change and the extracted area set in the processing of S53 may be stored in memory 72. Furthermore, when the size of the extraction area is changed, information specifying the size after the change may be stored in memory 72.

<Changing the OCT data to be displayed>
In this embodiment, while the viewer screen is displayed, the control unit 70 may receive a change instruction for selecting a new slice as a display target. In this embodiment, the control unit 70 may receive a change instruction for the OCT data based on an operation input for selecting a scan line corresponding to a new slice on the front image and an operation input to the forward buttons 211 to 214.

If an instruction to change the slice is received (S58: Yes), a new slice corresponding to the instruction is selected as the slice to be displayed (S59).

Next, an extraction region is set for the new slice (OCT data). In this embodiment, the method for setting the extraction region differs depending on whether the Auto button 219, which is shown in advance as a checkbox in Figures 9 and 10, is On/Off.

If the Auto button 219 has been turned on beforehand (S60: Yes), the extraction area setting process for the new slice is performed so that the position of the extraction area relative to the fundus image position is consistent between the slices before and after the change (S53).

In detail, if the Auto button 219 has been turned on beforehand (S60: Yes), the extraction area is automatically set based on the image position of the fundus in the new OCT data.

At this time, in this embodiment, it is possible that the extraction region in the immediately preceding (displayed) OCT data has been changed from its initial set position based on an instruction to change the extraction region. In this case, the position of the extraction region for the new OCT data may be set taking into consideration the amount of displacement of the extraction region before and after the change, which is stored in memory in step S57. For example, the extraction region may be set at a position offset from the image position of the fundus image in the new OCT data according to the amount of displacement stored in the processing of S57.

In addition, a matching process may be performed between the immediately preceding OCT data and the new OCT data to determine the amount of displacement, and an extraction region for the new OCT data may be set based on this amount of displacement.

This allows the area that is magnified and observed using the extracted OCT data to be maintained before and after the OCT data to be displayed is changed, making it easier to focus on observing a specific area.

On the other hand, if the Auto button 219 has been turned off beforehand (S60: No), an extraction region setting process is performed for the new slice so that the depth position of the extraction region is consistent between the slices before and after the change (S61). The depth position of the extraction region in the previous (displayed) OCT data (e.g., the Z coordinate of the extraction region, or the optical path length from the origin position to the extraction region) is carried over as the depth position of the extraction region in the new OCT data. As a result, the appearance position of the fundus image in the extraction OCT data may change depending on the actual fundus shape before and after the slice change. This makes it easier for the examiner to grasp the three-dimensional shape of the fundus tissue from the appearance position of the fundus image in the extraction OCT data.

<End of display>
Also, for example, in this embodiment, an instruction to end the display of the viewer screen may be accepted. When the instruction is accepted (S62: Yes), the control unit 70 ends the display of the viewer screen.

"Example of transformation"
While the present disclosure has been described above based on the embodiment and examples, it is not necessarily limited to these and various modifications are permissible.

For example, in the above embodiment, a case has been described in which the extracted OCT data is displayed when the OCT data is displayed after the image capture is completed. However, this is not necessarily limited to this. For example, the display of the extracted OCT data may be performed based on the OCT data acquired in real time while the OCT data is being captured or while the OCT optical system 100 is being adjusted during the image capture.

In the above embodiment, the OCT data of the fundus is captured via the OCT optical system 100. However, this is not necessarily limited to this. In the OCT with high penetration depth (wide imaging range in the depth direction) shown in the embodiment, it is possible that the anterior segment and the fundus are captured by a single device, either alternately or simultaneously.

In this case, as shown in FIG. 11, extracted OCT data relating to the anterior segment may be displayed. The depth range (vertical width) of the extraction region set for the anterior segment OCT data from which the data is extracted may be different from the extraction region set for the fundus OCT data. In addition, the extracted OCT data relating to the anterior segment may be displayed in the first display region 210 at a scale different from that of the fundus. In this way, the extraction region is automatically set according to the part of the subject's eye included in the OCT data, making it easier to observe each part well.

In addition, the operation input does not necessarily require moving the pointer C. For example, the setting position of the extraction region for the OCT data or the slice to be displayed may be changed by scrolling the mouse wheel.

In the above embodiment, the positional relationship of the extraction region to the OCT data from which it was extracted is shown via a thumbnail (image displayed in the second display area 220) of the OCT data from which it was extracted. However, this is not necessarily limited to this, and the positional relationship of the extraction region to the OCT data from which it was extracted may be shown on the screen without using a thumbnail. As an example, as shown in FIG. 12, the positional relationship of the extraction region to the OCT data from which it was extracted may be shown by a graphic 240 displayed in the first display area 210. In FIG. 12, when the OCT data from which it was extracted includes images of the anterior segment and the fundus, the extraction region is set between the anterior segment and the fundus. In this case, the arrows and text displayed as the graphic 240 indicate tissues present above and below the extraction region. In this case, even if the image of the tissue is not included in the extraction region, the examiner can grasp the position of the extraction region. As a result, it becomes easier for the examiner to adjust the position of the extraction region so that the desired tissue is displayed in the first display area 210.

In this embodiment, an ophthalmologic imaging device for capturing OCT data of the subject's eye E has been described as an example, but the present invention is not limited to this. For example, this embodiment may be applied to a device for capturing OCT data of a subject. For example, the subject may be a living body such as an eye, skin, or blood vessel, or may be a non-living sample such as a resin body.

Reference Signs List 1 OCT device 10 Imaging unit 50 Control unit 70 Control unit 80 Monitor 102 Light source 100 OCT optical system 120 Detector 145 Optical path length difference adjustment unit

Claims (6)

an OCT optical system that detects a spectral interference signal between a measurement light and a reference light guided to a tissue of a test eye, the OCT optical system being capable of acquiring OCT data in a photographing range of 10 mm or more in a depth direction;
an image processor that acquires the OCT data for the subject's eye based on the spectral interference signal output from the OCT optical system;
an optical path length difference adjustment unit that changes an optical path length difference between a measurement light and a reference light in order to adjust a depth position at which the OCT data is acquired;
a control unit that executes an adjustment process for at least adjusting the depth position and a capture process for capturing the OCT data;
By the control means,
As an initial position of the depth position in the adjustment process, a position is set such that a first fundus position, which is an assumed fundus position in a short-axis long eye or a long-axis long eye, to a second fundus position, which is an assumed fundus position in an average long-axis long eye, is included in a predetermined section in the OCT data;
An OCT device in which, when an image of the fundus is located within the specified section when the depth position is the initial position, adjustment of the depth position is skipped and the capture process is performed regardless of the position of the image of the fundus. The OCT device of claim 1, wherein in the adjustment process, when the depth position is the initial position and the image of the fundus is not included within the specified section, the depth position is changed from the initial position. The other of the fundus position assumed in the short-axis long eye and the fundus position assumed in the long-axis long eye is referred to as a third fundus position,
The OCT device of claim 2, wherein in the adjustment process, if the image of the fundus is not included within the specified interval when the depth position is the initial position, the depth position is changed to a second position such that the third fundus position is included within the specified interval. The OCT device of claim 3, wherein the overlap amount of the predetermined section between the initial position and the second position is less than half of the predetermined section. In the adjustment process,
At the initial position, the second fundus position is disposed at the center of the predetermined section,
An OCT device as described in claim 1 or 2, wherein if the image of the fundus is not included within the specified interval when the depth position is the initial position, the depth position is sequentially changed to a third position closer to the initial position and a fourth position farther from the initial position, and when the image of the fundus is located within the specified interval at either the third position or the fourth position, the capture process is executed regardless of the position of the image of the fundus. The control means further
a setting process of setting a depth region including an image position of the fundus as an extraction region for the OCT data acquired by the capture process;
The OCT device according to any one of claims 1 to 5, further comprising: a display control process for extracting extracted OCT data corresponding to the extraction region from the OCT data and displaying the extracted OCT data in a predetermined display region on a monitor.

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