WO2015098912A1

WO2015098912A1 - Tomography device

Info

Publication number: WO2015098912A1
Application number: PCT/JP2014/084043
Authority: WO
Inventors: 伸田中
Original assignee: 興和株式会社
Priority date: 2013-12-25
Filing date: 2014-12-24
Publication date: 2015-07-02
Also published as: JP6653174B2; JPWO2015098912A1

Abstract

　In the present invention, a tomographic image (T) of a fundus captured by an OCT unit is divided into small compartments (Ts), a representative value is obtained for each divided small compartment, a representative value selected from among the obtained representative values is computed as a quality parameter indicating the quality of a tomogram, and the computed quality parameter of the tomogram is displayed in a display. Through such a configuration, it is possible to provide assistance so as to facilitate capture of a high-quality fundus tomogram.

Description

Tomography system

The present invention relates to a tomographic imaging apparatus, more specifically, a fundus imaging unit capable of observing the fundus imaging unit, and signal light from the fundus imaging fund by scanning light output from a light source connected to the fundus imaging unit. The present invention relates to a tomographic imaging apparatus including an OCT unit that captures a tomographic image of the fundus oculi based on interference light generated by superimposing a beam with reference light.

There is a tomographic imaging apparatus using optical interference called OCT (Optical Coherence Tomography), which is one of the ophthalmologic diagnosis machines and takes a tomographic image of the fundus. If general OCT imaging is performed, the obtained tomographic image is captured at a speed of, for example, 40 images / second, and 100 or more images are acquired by one inspection (imaging at a part of the retina). A completed image group is created.

When taking a tomographic image, the tomographic imaging device itself is moved up and down and left and right with respect to the eye to be examined, and the amount of push-in is adjusted to perform an alignment operation so that a tomographic image at the target position of the fundus is obtained. A focus operation is performed so that a tomographic image can be clearly captured.

An index indicating how good the alignment / focus state by this alignment / focus operation is called an image quality parameter, and is also called QI (quality index) or SSI (signal strength index). The image quality parameter indicates that if the numerical value is small, a clearer tomographic image may be taken depending on the adjustment, and if it is large, it indicates that the image can be taken by pressing the photography button soon. It is used as a judgment index for acquiring.

A technique for obtaining such image quality parameters by various methods and selectively using the image quality parameters according to shooting conditions is disclosed in Patent Document 1 below.

Further, Patent Document 2 discloses a method for obtaining an image quality parameter of a focused area instead of the entire screen, and Patent Document 3 discloses a technique for taking a tomographic image by performing image quality evaluation. .

Further, it is described in Non-Patent Document 1 that the value of what percentile of the histogram is used for calculating the image quality parameter.

JP 2013-009798 A JP 2011-218155 A JP 2009-042197 A

When photographing a tomographic image, the image quality of the tomographic image changes from moment to moment as the operator performs an alignment / focus operation. In addition, it is desirable to be able to complete alignment / focus adjustment in a short period of time because the burden on the subject is that he / she continues to fixate one point without blinking when taking a tomographic image. For these reasons, it is necessary to provide an image quality parameter as an index for determining whether the alignment / focus state is good or not, and it is required to be able to be calculated in a short time.

Each of the above-mentioned documents describes various methods for calculating image quality parameters. However, even if the entire image quality cannot be acquired in a short time or can be processed in a short time, the OCT tomographic image has a lot of noise and the image quality evaluation is not possible. There is a problem that it is easily affected by noise.

The present invention has been made in order to solve such problems, and it is possible to process tomographic images that can be processed in a short time and can perform high-quality fundus tomographic imaging by performing image quality evaluation that is not easily affected by noise. It is an object to provide an apparatus.

The present invention
Based on a fundus imaging unit capable of observing the fundus imaging unit, and interference light generated by scanning light output from a light source connected to the fundus imaging unit and superimposing signal light from the eye fundus on the reference light A tomographic imaging apparatus including an OCT unit that captures a tomographic image of the fundus,
An alignment mechanism for aligning the fundus imaging unit with the eye to be examined;
A focus adjustment mechanism for focusing the optical system of the OCT unit on the fundus;
The tomographic image of the fundus taken in the alignment state by the alignment mechanism and / or the focus state by the focus adjustment mechanism is divided into small sections, a representative value is obtained for each divided small section, and the selected representative value is selected. Image quality parameter calculating means for calculating the representative value as an image quality parameter indicating the quality of the tomographic image;
A display for displaying the value of the image quality parameter calculated by the image quality parameter calculation means;
It is provided with.

In the present invention, a tomographic image of the fundus taken by the OCT unit is divided into small sections, a representative value is obtained for each of the divided small sections, and the representative value selected from the obtained representative values is used as the quality of the tomographic image. Is calculated as an image quality parameter. Therefore, it is possible to perform image quality evaluation that can be processed in a short time and is not easily affected by noise, and when the image quality parameter is equal to or greater than a predetermined threshold value, tomographic imaging is started. A high-quality fundus tomogram can be taken.

It is a block diagram which shows the whole structure of a tomography apparatus. It is an optical diagram which shows the optical system of an OCT unit. It is an optical diagram which shows the optical system of an OCT focus adjustment mechanism. It is explanatory drawing which showed the state which scans a fundus in xy direction. It is explanatory drawing which showed the tomogram acquired. It is explanatory drawing which showed the state which divides | segments a tomographic image into small divisions. It is a diagram which shows the representative value of the calculated | required small area. It is a histogram figure of the representative value used for image quality parameter calculation. It is the flowchart figure which showed the flow which calculates an image quality parameter.

Hereinafter, the tomographic imaging apparatus of the present invention will be described in detail based on examples with reference to the drawings. Here, an example of acquiring a fundus tomographic image of an eye to be examined by a tomographic imaging apparatus for ophthalmic examination will be described.

FIG. 1 is a block diagram showing the entire tomographic image capturing apparatus for capturing a tomographic image of the fundus of the eye to be examined. What is denoted by reference numeral 1 is a fundus photographing unit 1 that observes and images the fundus (retinal) Ef of the eye E, and includes an illumination optical system 4, a photographing optical system 5, and a scanning unit 6.

The illumination optical system 4 includes an observation light source such as a halogen lamp and a photographing light source such as a xenon lamp, and light from these light sources is guided to the fundus oculi Ef via the illumination optical system 4 to illuminate the fundus oculi Ef. The photographing optical system 5 includes an optical system such as an objective lens, a photographing lens, and a focusing lens, and an imaging device such as a CCD. The photographing optical system 5 guides photographing light reflected by the fundus oculi Ef to the imaging device along the photographing optical path, and the fundus oculi Ef. Take a picture.

The focusing lens of the photographing optical system 5 can be moved in the optical axis direction by the examiner operating the fundus photographing focus adjustment mechanism 5a, and the fundus photographing unit 1 can be focused on the fundus. The imaging optical system 5 guides signal light reflected by the fundus oculi Ef, which will be described later, to the OCT unit (tomographic imaging unit) 2 via the scanning unit 6. The scanning unit 6 is a mechanism including a known galvanometer mirror for scanning the light from the low coherence light source 20 of the OCT unit 2 in the x and y directions in FIG.

The fundus imaging unit 1 is optically connected to an OCT unit 2 that captures a tomographic image of the fundus oculi Ef via a connector 7 and a connection line 8.

The OCT unit 2 is a known unit that operates, for example, in the Fourier domain method (spectral domain method), and its detailed configuration is shown in FIG. 2A. The wavelength is 700 nm to 1100 nm, and the time is about several μm to several tens μm. A low-coherence light source 20 that emits light having a specific coherence length.

The low coherence light LO generated by the low coherence light source 20 is guided to the optical coupler 22 by the optical fiber 22a, and is divided into the reference light LR and the signal light LS. The reference light LR passes through the optical fiber 22b, the collimator lens 23, the glass block 24, and the density filter 25, and reaches the reference mirror 26 that can move in the optical axis direction for adjusting the optical path length. The glass block 24 and the density filter 25 function as delay means for matching the optical path length (optical distance) of the reference light LR and the signal light LS, and as means for matching the dispersion characteristics of the reference light LR and the signal light LS. .

The signal light LS is guided to the fundus imaging unit 1 through the optical fiber 22c, the OCT focus adjustment mechanism 27 for focusing the optical system of the OCT unit and the fundus to be examined, and the optical fiber 22c inserted into the connection line 8. Then, it reaches the fundus oculi Ef via the scanning unit 6 and the photographing optical system 5 in FIG. 1, and scans the fundus in the x and y directions. The signal light LS that has reached the fundus oculi Ef is reflected by the fundus oculi Ef and returns to the optical coupler 22 by following the above path in reverse.

The reference light LR reflected by the reference mirror 26 and the signal light LS reflected by the fundus oculi Ef are superimposed by the optical coupler 22 to become interference light LC. The interference light LC is guided to the OCT signal detection device 21 by the optical fiber 22d. The interference light LC is converted into a parallel light beam by the collimator lens 21a in the OCT signal detection device 21, and then is incident on the diffraction grating 21b and dispersed, and is imaged on the CCD 21d by the imaging lens 21c. The OCT signal detection device 21 generates an OCT signal indicating information in the depth direction (z direction) of the fundus oculi based on the dispersed interference light.

Also, an OCT focus adjustment mechanism 27 for focusing the optical system of the OCT unit and the fundus of the eye to be examined is provided. As shown in FIG. 2b, the OCT focus adjustment mechanism 27 includes

lenses

27a, 27b, and 27c, and the inner lens 27b can be moved in the optical axis direction by the examiner operating the OCT focus adjustment mechanism 27. The optical system of unit 2 is focused on the fundus.

Returning to FIG. 1, the fundus imaging unit 1 can be moved in the x, y, and z directions with respect to the eye E by an alignment mechanism 33 such as a joystick or an adjustment knob, and alignment (positioning) is performed.

In the tomographic imaging apparatus, for example, an image processing apparatus 3 constituted by a microcomputer built in the fundus imaging unit 1 or a personal computer connected to the fundus imaging unit 1 is provided. The image processing apparatus 3 is provided with a control calculation unit 30 including a CPU, a RAM, a ROM, and the like. The control calculation unit 30 controls the entire image processing by executing an image processing program. In addition, the control calculation unit 30 includes image quality parameter calculation means 34 that calculates the image quality parameter of the tomographic image.

The display unit 31 is configured by, for example, a display device such as an LCD, and displays an image generated or processed by the image processing device 3 and accompanying information such as information on the subject. Further, the value of the image quality parameter calculated by the image quality parameter calculation means 34 is displayed on the display 31a of the display 31.

The operation unit 32 includes, for example, a mouse, a keyboard, an operation panel, and the like, and is used by an operator to give an instruction to the image processing apparatus 3 and the like.

The image processing apparatus 3 forms a tomographic image of the fundus oculi Ef based on the OCT signal detected by the OCT signal detection apparatus 21 by executing a known analysis method such as a Fourier domain method (spectral domain method). The formed tomographic image is stored in a storage unit 35 constituted by, for example, a semiconductor memory, a hard disk device or the like.

When photographing a fundus tomographic image with such a configuration, the alignment mechanism 33 aligns the eye E with the fundus photographing unit 1 (alignment), and the fundus photographing focus adjustment mechanism 5a focuses on the fundus. Matched to some degree accurately. In this state, the low-coherence light source 20 is turned on, the signal light from the OCT unit 2 is swept in the x and y directions by the scanning unit 6, and the fundus oculi Ef is scanned. This state is shown in FIG. 3a, and the region R where the macular portion of the retina is present is scanned with n scanning lines y1, y2,..., Yn in the direction parallel to the x axis.

The signal light LS reflected by the fundus oculi Ef is superimposed on the reference light LR reflected by the reference mirror 26 in the OCT unit 2. As a result, interference light LC is generated, and an OCT signal is generated from the OCT signal detector 21. The image processing device 3 generates a tomographic image of the fundus oculi Ef based on the OCT signal when the OCT focus adjustment mechanism 27 brings the optical system of the OCT unit and the eye to be inspected more accurately than the previous state. The obtained tomographic image is stored in the storage unit 35.

In FIG. 3b, the tomographic image Ti (i = i = N) at different times ti (i = 1 to N) of the xz tomographic image (B-scan image) obtained with the scanning line yj passing through the approximate center of the macular portion of the retina. 1 to N) are illustrated. The time interval between ti and ti + 1 corresponds to the time required for scanning in the x direction on the scanning line yj. These tomographic images Ti (i = 1 to N) are formed every time ti (i = 1 to N) and are sequentially stored in the storage unit 35.

With such a configuration, when capturing a tomographic image of the fundus of the subject's eye, if the alignment between the fundus imaging unit and the eye to be examined and / or the focus state between the optical system of the OCT unit and the eye to be examined are poor, the ideal state Only a weak interference signal can be obtained, and the tomographic image becomes unclear.

Therefore, in the present invention, the image quality parameter is calculated according to the flow shown in FIG. 5, and when the value exceeds a predetermined threshold value, it is determined that a high-quality tomogram is obtained, and the tomogram is taken. Do. The processing shown in FIG. 5 is performed by executing an image processing program in the control calculation unit 30 and calculating image quality parameters.

In step S1, the fundus photographing unit 1 is aligned with the eye to be examined by the alignment mechanism 33, and the fundus photographing focus adjusting mechanism 5a and the OCT focus adjusting mechanism 27 are focused on the fundus.

Temporarily, a tomographic image is taken and one tomographic image is acquired from the plurality of tomographic images Ti (step S2).

Subsequently, as shown in FIG. 4a, the entire frame of the acquired tomographic image T is divided into small sections Ts (step S3), and a representative value is obtained for each small section Ts (step S4). Each small section Ts is, for example, a shape having a width and a height of n × n pixels (pixels) and is set to a section where the respective sides are adjacent to each other without overlapping each other.

FIGS. 4a and 4b show an example in which n = 4 and the width and height are each divided into small pixels Ts each having a width of 16 pixels and an area of 16 pixels. The luminance value of the pixel having the Nth (for example, N = 4) highest luminance value is calculated as the representative value of the small section. The processing that uses the fourth highest luminance value in 16 pixels as a representative value instead of the median or average value in a small section focuses on the high luminance (= strong signal) in the tomographic image, and the influence of noise. It is assumed that it is expected that a value corresponding to the brightness of the area is likely to be obtained. Therefore, in order for the examiner to acquire a high-quality tomographic image, the value of N is changed at any time according to the size of the small section Ts, the medical condition of the eye to be examined, or the imaging environment state, instead of setting the value of N as a fixed value. It is preferable to be able to. Therefore, in the above-described example, N = 4 can be set to before and after that and 3, 5.

Thus, representative values obtained for each small section Ts of one frame of the tomographic image are shown in FIG. 4b. Among the representative values obtained in each of the small sections, a value at a certain position from the top is obtained, and this is used as the value of the image quality parameter for the entire frame (step S5). Specifically, as shown in FIG. 4c, a representative value for each small section and a histogram indicating the number thereof are obtained, and values located in the order determined by the M percentile from the top (for example, M = 0.5, that is, a small value). If there are 1000 sections, the fifth largest value) is set as the value of the image quality parameter of the frame.

From the viewpoint of focusing on the signal strength, the highest value in the frame should be the image quality parameter value. However, the alignment and / or focus state is not sufficient, but a tomographic image in which high-luminance points have partially appeared has a low score, and the high-luminance portion has no area to some extent. In order to avoid a high score, for example, the value of M is set to 0.5. However, instead of setting the value of M as a fixed value, the value of M is set based on the calculated histogram as shown in FIG. 4c in order to obtain a good tomographic image.

It is determined whether or not the calculated image quality parameter value has reached a predetermined threshold value (step S6). If the threshold value is not reached, a clearer tomographic image may be taken depending on the adjustment. Therefore, the process returns to step S1 to perform alignment and / or focus operation. On the other hand, if the image quality parameter is equal to or greater than the threshold value, it indicates that a high-quality tomographic image can be obtained, so that shooting is automatically started or the operator presses a shooting button (not shown) To start. At this time, in order to support photographing, it is preferable to change the display of the image quality parameter displayed on the display 31a when the image quality parameter becomes equal to or higher than a predetermined threshold value. For example, change the color, shape, size, and font of characters to be displayed, or change the blinking state (flash the display in advance and stop blinking when it exceeds the threshold, conversely above the threshold It is possible to cause the display to blink when it becomes, or to change the blinking speed.

It should be noted that the threshold value for determining the quality of the image quality parameter is not a fixed value, but can be changed according to the medical condition of the subject and the imaging environment. For example, when there is opacity due to cataract and a strong signal cannot be obtained, the image quality parameter does not rise above a certain value even if the alignment and / or focus state is ideal. The threshold for determining the threshold value can be set to a predetermined value according to the medical condition of the subject and the imaging environment.

Thus, according to the present invention, the tomographic image of the fundus is divided into small sections, a representative value is obtained for each of the divided small sections, and the representative value selected from the obtained representative values is used as the quality of the tomographic image. Therefore, it is possible to perform image quality evaluation that can be processed in a short time and is not easily affected by noise.

DESCRIPTION OF SYMBOLS 1 Fundus imaging unit 2 OCT unit 3 Image processing device 4 Illumination optical system 5 Imaging optical system 5a Focus adjustment mechanism for fundus imaging 6 Scan unit 7 Connector 21 OCT signal detector 21a Diffraction grating 21d CCD
22 Optical Coupler 26 Reference Mirror 27 OCT Focus Adjustment Mechanism 30 Control Calculation Unit 31 Display Unit 32 Operation Unit 33 Alignment Mechanism 34 Image Quality Parameter Calculation Unit 35 Storage Unit

Claims

Based on a fundus imaging unit capable of observing the fundus imaging unit, and interference light generated by superimposing signal light from the fundus imaging unit and reference light by scanning light output from a light source connected to the fundus imaging unit A tomographic imaging apparatus including an OCT unit that captures a tomographic image of the fundus,
An alignment mechanism for aligning the fundus imaging unit with the eye to be examined;
A focus adjustment mechanism for focusing the optical system of the OCT unit on the fundus;
The tomographic image of the fundus taken in the alignment state by the alignment mechanism and / or the focus state by the focus adjustment mechanism is divided into small sections, a representative value is obtained for each divided small section, and the selected representative value is selected. Image quality parameter calculating means for calculating the representative value as an image quality parameter indicating the quality of the tomographic image;
A display for displaying the value of the image quality parameter calculated by the image quality parameter calculation means;
A tomographic imaging apparatus comprising:
2. The tomographic imaging apparatus according to claim 1, wherein the tomographic imaging is automatically started when the image quality parameter exceeds a predetermined threshold value.
When the image quality parameter exceeds a predetermined threshold value, the display color, display shape, display size, or display character font of the image quality parameter displayed on the display is changed, or the display blinking state is changed. The tomographic imaging apparatus according to claim 1, wherein the tomographic imaging apparatus is changed.
4. The image quality parameter calculating means uses a luminance value of a pixel having the Nth largest luminance value among luminance values of pixels constituting a small block as a representative value of the small block. The tomography apparatus of any one of Claims.
5. The image quality parameter calculation means selects one of the representative values based on a histogram of representative values for each subsection and uses it as an image quality parameter for a tomographic image. 6. The tomographic imaging apparatus described.
The tomographic imaging apparatus according to any one of claims 1 to 5, wherein the small section has a size of 4x4 pixels and N is 4.
7. The image quality parameter calculating means uses, as an image quality parameter, a representative value that is determined based on a histogram of representative values for each subsection and that is in the order of the M percentile from the top. The tomographic imaging apparatus according to item 1.
The tomography apparatus according to claim 7, wherein the M is 0.5.