WO2011145182A1

WO2011145182A1 - Optical coherence tomography device

Info

Publication number: WO2011145182A1
Application number: PCT/JP2010/058407
Authority: WO
Inventors: 原　拓也
Original assignee: 興和株式会社
Priority date: 2010-05-19
Filing date: 2010-05-19
Publication date: 2011-11-24

Abstract

An optical coherence tomography device which has galvanometers (10, 11) as an optical scanning means for performing a two-dimensional scan of a predetermined partial scan area of a subject's eye with a signal light, wherein when performing a two-dimensional scan of a subject's eye (15), divides the whole measuring range of the eyeground of the subject's eye (15) into a plurality of partial scan areas, sequentially scans each partial scan area and panoramically synthesizes the optical coherence tomography images obtained from each partial scan area in order to obtain an optical coherence tomography image of the measuring range of the subject's eye. In measuring the partial scan areas, prescribed LEDs of an internal fixation lamp (29) arranged with LEDs in a matrix are lit to guide the line of sight of the subject's eye (15) in a direction necessary for the measurement of each partial scan area.

Description

Optical coherence tomographic image measuring device

The present invention relates to an optical coherence tomographic image measuring apparatus (OCT apparatus) that performs optical tomographic imaging, and more particularly to an optical coherent tomographic image measuring apparatus suitable for obtaining an optical coherent tomographic image of a fundus tissue of an eye to be examined.

Currently, the mainstream of OCT (Optical Coherence Tomography) is Fourier domain (frequency domain) OCT. In the conventional time domain (time domain) method, a one-dimensional tomographic image cannot be acquired unless the reference light mirror is scanned. However, according to the Fourier domain method, a one-dimensional tomographic image can be obtained with the reference light mirror fixed. Further, by performing a two-dimensional scan (raster scan) with two galvanometer mirrors, etc., it becomes substantially a three-dimensional scan (hereinafter also referred to as 3D if necessary), and a 3D image of a tomographic image is acquired at high speed. Became possible. Patent Document 1 below discloses OCT three-dimensional distribution measurement using a MEMS (Micro Electronic Mechanical System) optical scanning mirror instead of a galvanometer mirror.
JP 2009-119153 A

In Fourier domain OCT, although the processing speed of the three-dimensional scan has increased, it takes some time to obtain a wide-range or high-definition image. Normally, when one tomographic image (B scan = 2D scan) is acquired, the image is constructed by moving the A scan (1D scan in the Z axis direction) to 100 to 500 points while moving in the X axis direction. The Here, if a 3D scan is performed at the same density as the B scan, which takes 512 points for the A scan, 512 × 512 = 262144 scan, and if the camera speed is 30 k (scan / sec), the 3D scan image Acquisition will take about 8.7 seconds.

Even if a very fast 55k (scan / sec) camera is used, the processing time for image acquisition is about 4.8 seconds, which is not realistic. In the case of ophthalmic photography, accurate measurement data cannot be obtained due to fixation eye movement or blinking of the subject's eye during the measurement time of several seconds as described above, resulting in measurement failure. Therefore, the current OCT of each company reduces the spatial resolution so that the measurement is completed in about 1 to 1.5 seconds.

For example, one example of an optical coherence tomography that has already been sold is one with specifications that the camera performance is 53 k scans / second, and 3D scanning of 9 mm × 9 mm is performed in 1.6 seconds. As described above, if a 3D scan (scan in the Y-axis direction) is performed with a B scan that takes 512 points in the X-axis direction for the A scan (scan in the Z-axis direction), the time required for one B scan is About 9.7 msec. As a result, about 166 B scans can be performed in 1.6 seconds, and the resolution in the X-axis direction is calculated to be about 17.6 μm and the resolution in the Y-axis direction is calculated to be about 54.2 μm.

Usually, the resolution in the depth (Z-axis) direction is 5 to 6 μm in the Fourier domain method and about 10 μm in the time domain method, so in this example, the resolution in the Y-axis direction is particularly insufficient. In the case of displaying, image processing is performed so as to complement between lines, so that accuracy is inferior.

From the above, the current 3D scan in OCT is far from the detailed structure of the retina in 3D, and the present situation is that it only maps the thickness of each layer of the retina.

Furthermore, depending on the subject, even if the measurement time is about 1 to 1.5 seconds as described above, accurate measurement data may not be obtained due to microscopic fixation or blinking. For example, elderly people, subjects with retinal diseases, etc. have unstable fixations, so it is necessary to finish the measurement in a shorter time. For this purpose, it is necessary to reduce the scan area or reduce the spatial resolution.

As described above, when a 3D scan is performed on an eye to be examined, the clinical issue is whether to give priority to spatial resolution or measurement time.

However, high-speed cameras are expensive, and widening the scanning range is the same as increasing the angle of view in fundus cameras, and it is necessary to take measures such as increasing the objective lens and shortening the working distance. Become. However, when the objective lens is enlarged in this way, the apparatus becomes larger and consequently the apparatus becomes expensive, and when the working distance is shortened, a feeling of pressure or difficulty in opening the subject occurs. , Etc.

An object of the present invention is to provide an optical coherence tomographic image measurement apparatus capable of solving the above-described problems and performing 3D imaging of the retina of an eye to be examined without acquiring a tomographic image with a large objective lens and a wide angle of view. It is in.

In order to solve the above-described problems, according to the present invention, a light source that emits partially coherent light, a light beam emitted from the light source, a signal light that passes through a placement position of the eye to be examined, and the eye placement to be examined The signal light after passing through the position of the eye to be examined and the reference light passing through the different optical path are interfered with each other by being divided into reference light passing through a different optical path from the optical path passing through the position. An interference optical system for generating light, a diffraction grating for splitting the interference light generated by the interference optical system, a photosensor array for detecting the split interference light, and the photosensor array detected In an optical coherence tomographic image measuring apparatus having a fast Fourier transformer that performs fast Fourier transform of a signal and a control unit that images the output of the fast Fourier transformer and displays or records the optical coherent tomographic image Based on the control of the control unit, the signal light includes scanning means for two-dimensionally scanning a predetermined partial scan area of the eye to be examined at a predetermined scanning speed, and the eye to be examined is two-dimensionally scanned by the scanning means. In this case, the entire measurement range of the eye to be examined is divided into a plurality of partial scan areas, each partial scan area is sequentially scanned by the scanning means, and optical coherence tomographic images obtained from each partial scan area are panorama synthesized. A configuration for acquiring an optical coherence tomographic image of the measurement range of the eye to be examined was adopted.

According to the above configuration, each partial scan area is a minute area, and a wide range of measurement areas are covered by photographing a plurality of partial scan areas, and images obtained in each partial scan area are panorama synthesized. The image of the entire measurement area can be acquired by this, the effect of fixation movement and blinking in each partial scan area can be reduced, and the measurement time for each partial scan can be shortened. It has an excellent effect that the measurement time and resolution can be changed by variously selecting the number of measurement areas (number of acquired images), size, etc. .

It is explanatory drawing which showed the structural example of the OCT apparatus which employ | adopted this invention. It is explanatory drawing which showed the example of imaging | photography with the OCT apparatus of FIG. It is explanatory drawing which showed the example of imaging | photography with the OCT apparatus of FIG. It is explanatory drawing which showed the example of imaging | photography with the OCT apparatus of FIG. It is explanatory drawing which showed the example of a different structure of the OCT apparatus which employ | adopted this invention.

Hereinafter, as an example of the best mode for carrying out the present invention, an embodiment relating to an OCT apparatus that performs optical coherence tomographic image measurement of a fundus tissue to be examined will be described.

In FIG. 1, what is indicated by reference numeral 1 is a high-intensity light emitting diode (Super Luminescent Diode: SLD) that emits partially coherent light, and has low coherence (coherence is necessary) for observing a tomographic image. This is a light source having a small number of properties. The center wavelength is assumed to generate light in the infrared (invisible) band of 840 nm, for example. The light beam from the light source 1 is collimated by the lens 2, and the light beam passing through the mirror 3 is expanded into a light beam of a predetermined size via the

lenses

4 and 5, and then a beam splitter (BS: light The light is incident on the dividing member 7. At the position of the beam splitter 7, the optical path is divided into four directions: an optical path 6a on the light source side, a reference optical path 6b, a search optical path 6c, and a detection optical path 6d.

Further, another light source (not shown), for example, an SLD or LD (Laser Diode: semiconductor laser) that emits visible light (for example, red having a wavelength of about 670 nm) is provided, and this is used as a light source 1 using a dichroic mirror or the like. By matching with the optical axis, it can be used as an auxiliary light source for confirming the optical path of the light beam with visible light against invisible infrared rays for measurement.

The light beam traveling in the reference light path 6 b is reflected by the reference light mirror 9, and the light beam reflected by the reference light mirror 9 returns through the lens 8 to the reference light path 6 b.

On the other hand, the light beam traveling along the search optical path 6c is incident on the galvanometer mirror 10a attached to the galvanometer 10. The light beam reflected by the galvanometer mirror 10a is reflected by the galvanometer mirror 11a of the second galvanometer 11, and the light beam is passed through these two

galvanometer mirrors

10a or 11a in a direction perpendicular to the optical axis. Each can be scanned one-dimensionally.

For example, if one of the two

galvanometer mirrors

10a and 11a is fixed and scanning is performed with only one, scanning in the X-axis direction or Y-axis direction perpendicular to the optical axis (Z-axis) is possible. In the case of FIG. 1, for example, the galvanometer 11 can perform scanning in the X-axis direction, and the galvanometer 10 can perform scanning in the Y-axis direction.

Alternatively, by operating the two

galvanometer mirrors

10a and 11a at the same frequency and appropriately setting the type, amplitude, phase, and the like of the waveforms for driving the

galvanometer mirrors

10a and 11a, Or scanning in a circle or the like becomes possible. These galvanometer mirrors 10a and 11a constitute first and second optical scanning means for scanning the light beam of the search light at the same frequency as the line sensor array constituting the spectrometer 21, respectively.

The light beams scanned by the

galvanometer mirrors

10a and 11a enter the eye 15 (the anterior eye portion 15a or the fundus 15b) of the object to be observed after passing through the

lenses

12, 13, and 14. Here, the

lenses

12 and 13 constitute a focusing optical system that can be adjusted according to the diopter of the eye to be examined (myopia, hyperopia, etc.), and change the focal position of the light beam according to the optical characteristics of the target object. It is a focus adjustment means. The positions of the

lenses

12 and 13 can be adjusted in the optical axis direction according to the operation of a predetermined mechanism (not shown). Further, the

lenses

12 and 13 and the lens 14 constitute a telecentric optical system so that the conjugate relationship between the galvanometer mirror and the eye to be examined is kept substantially constant.

The light beam incident on the eye 15 is converged in a dot shape at a predetermined position on the fundus 15b, for example, to be in a focused state. This point-focused light beam can scan the fundus 15b of the eye to be examined in a line shape or a circle shape by scanning with

galvanometer mirrors

10a and 11a (light scanning means). In the example, as shown in FIGS. 2A to 2C, which will be described later, a rectangular small area is two-dimensionally scanned, and a similar rectangular area is scanned in a grid pattern while shifting the position. Panorama image.

Reflected light from the fundus 15b of the eye 15 to be inspected travels backward through the optical system described above, that is, reaches the beam splitter (BS) 7 via the

lenses

12, 13, and 14 and the galvanometer mirrors 10a and 11a. The reflected light from the eye 15 to be inspected that travels backward in the search optical path 6c and passes through the beam splitter 7 is combined with the reference light that returns from the reference optical path 6b, thereby generating interference light in the detection optical path 6d.

This interference light passes through the detection aperture (pinhole) 17 through the lens 16 as detection light, and further enters the diffraction grating 19 disposed at an inclination with respect to the optical axis through the lens 18. The detection light passing through the diffraction grating 19 is detected by a spectrometer 21 including a line sensor array through a lens 20.

The output signal of the spectrometer 21 is converted into a spectrum distribution signal by a fast Fourier transformer (FFT) 22 and input to a PC (personal computer) 23.

The PC 23 can measure the three-dimensional distribution of the biological components of the eye to be examined by performing image processing on the detection light information input from the fast Fourier transformer 22.

The PC 23 controls the overall operation of the optical system (particularly, the two galvanometers 10 and 11), and the measurement result of the three-dimensional distribution of the measurement target tissue in the eye to be examined is displayed on a display device 24 such as a liquid crystal television monitor. Control is performed such as outputting and displaying, and transferring the measurement result to the storage device 25 and storing it as necessary. The PC 23 has a keyboard and a pointing device (such as a mouse), and can perform settings for measurement control via these user interface means.

The pinhole 17 provided in the optical system has a predetermined pinhole-shaped detection aperture with a gap limited in the scanning direction of the optical scanning means, and detects noise caused by unnecessary stray light and scattered light. In addition to improving the SN (signal-to-noise characteristics) of the interference signal to be generated, the background light amount level is reduced, thereby improving the gradation of the signal component with respect to the video signal from the image sensor. The pinhole 17 may be a small square-shaped opening, and this opening can also be configured by stacking two pieces of slit-shaped parts formed in a thin plate at right angles.

In the above configuration, the light beam incident on the eye 15 to be examined is focused and focused in a dot shape at a predetermined position of the fundus 15b, for example, and the fundus 15b of the eye to be examined is made into a line shape or a circle shape by the galvanometer mirrors 10a and 11a. In this embodiment, as shown in FIGS. 2A to 2C, a small rectangular area is two-dimensionally scanned, and a similar rectangular area is scanned in a grid pattern while shifting the position. Then, panorama synthesis is performed on images obtained from these areas.

In this way, by dividing the actual 3D scan range into smaller areas and then panorama synthesizing, the measurement time in each area can be shortened, and the effects of eye movement and blinking can be reduced. It is possible to obtain a more accurate measurement result by panoramicly combining images obtained in each area later.

The following shows the specific scanning procedure. Here, the imaging speed by the spectrometer 21 (line sensor array), the fast Fourier transformer 22 and the PC 23 of this apparatus is 40 k (scan / sec).

FIG. 2A shows the entire measurement range 101 divided by four partial scan areas 102 each having a rectangular shape (square).

In FIG. 2A, the scan range of the two

galvanometers

10 and 11 is controlled by the PC 23 so that the scan size of one partial scan area 102 is 6 mm × 6 mm, and the image acquisition point is 200 pt × 200 pt (that is, the resolution is 30 μm). ). The entire measurement range 101 is 11 × 11 mm, and adjacent partial scan areas 102 have 1 mm overlap portions O that overlap each other.

In this case, the scan of one partial scan area 102 can be processed in one second, so that no burden is imposed on the subject. If the

galvanometers

10 and 11 are controlled at a short interval each time one scan is completed and the adjacent

partial scan areas

102, 102... Are sequentially photographed, four scan images are obtained as shown in the figure. It is done.

Then, an image of the entire measurement range 101 is formed by performing a process of overlapping adjacent 1 mm edges of the four scan images by a known panorama synthesis process. The overlap portion O of the partial scan area 102 can be used for alignment by pattern matching in the panorama synthesis process, and a known complement or blend process is performed so that the image connection is good in the overlapped portion. Can do. Since the overlap portions O of 1 mm are overlapped with each other in the adjacent partial scan areas 102, the image of the entire measurement range 101 finally obtained has a size of 11 mm × 11 mm.

By performing such measurement control, a relatively wide range of scanning is possible, and the entire examination time exceeds 4 seconds. During that time, the subject's line of sight is not changed so as not to change. The fixation eye is gazed, and the line of sight of the eye to be examined is guided and fixed in a fixed direction (the same applies to the examples of FIGS. 2B and 2C. The example of the internal fixation lamp is shown in FIG. 3).

FIG. 2B shows measurement control when a higher resolution scan is desired. FIG. 2B shows the entire measurement range 101 divided by nine rectangular (square) partial scan areas 102.

In FIG. 2B, by the same control as described above, one scan size is set to 4 mm × 4 mm, and the image acquisition point is set to 200 pt × 200 pt (that is, the resolution is 20 μm). Adjacent partial scan areas 102 have 1 mm overlap portions O that overlap each other.

In this case as well, one partial scan area 102 can be scanned in one second. In order to compensate for the narrowing of the scan area with high resolution, a wide range of measurement results are obtained by obtaining nine images. In this case, an image of the entire measurement range 101 of 10 mm × 10 mm is finally obtained by panoramic synthesis processing of nine images.

Also, FIG. 2C shows measurement control when it is desired to perform a shorter scan. FIG. 2C shows the entire measurement range 101 divided by four partial scan areas 102 each having a rectangular shape (square).

The method shown in FIGS. 2A and 2B does not give any burden to normal subjects because each scan is performed in one second, but it is difficult for elderly and infant subjects. There is a case. Therefore, in the case of FIG. 2C, the size of one partial scan area 102 is 4 mm × 4 mm, and adjacent partial scan areas 102 have 1 mm overlapping portions O that overlap each other.

If the image acquisition point is 133 pt × 133 pt in order to keep the resolution at 30 μm, one scan can be completed in 0.44 seconds. However, in this case, even if four images are acquired, the finally obtained scan image range is 7 mm × 7 mm. However, since one scan can be completed in a short time, the probability of failure in each measurement is reduced, so that reliable measurement is possible although the measurement range is narrow.

As described above, the scan speed of the galvanometer mirrors 10a and 11a is set to a predetermined value, the scan size and the acquisition point (element for determining resolution) are determined, and the measurement region is further divided into several images. Measurement control parameters for controlling measurement conditions such as whether to capture and combine in panorama processing can be selected in various ways using user interface means of the PC 23 including a keyboard and pointing device (such as a mouse). In particular, various panoramic patterns similar to those shown in FIGS. 2A to 2C can be set by the PC 23 controlling the operation of the two

galvanometers

10 and 11 of the optical system, and the command can be set via the user interface means of the PC 23. Can be set.

As described above, the scan range can be changed, each partial scan area is made into a minute area, and a wide range of measurement areas are covered by photographing a plurality of partial scan areas, and obtained in each partial scan area. The entire measurement area can be acquired by panoramic synthesis of the image, the effects of fixation micromotion and blinking in each partial scan area can be reduced, and the measurement time for each partial scan can be shortened. Therefore, there is an excellent effect of being able to cope with the subject (the elderly or a patient with a disease).

Also, since the measurement time and resolution can be changed by variously selecting the number of partial scan areas (number of acquired images) and size, a measurement effect different from panoramic photography of the fundus camera can be expected. The above-described panoramic pattern shown in FIGS. 2A to 2C is an example, and various measurement demands can be met by changing the number of overlapping and the overlapping distance.

Further, since it is not necessary to acquire a tomographic image with a wide angle of view when photographing one partial scan area, the objective lens (14) does not have to be large. Therefore, there are excellent effects that the configuration of the apparatus is simple and inexpensive, and the panoramic function enables a three-dimensional scan of the optical coherence tomographic image with a wide range and an arbitrary resolution.

Further, as shown in FIG. 3, by providing an internal fixation lamp 29 and controlling the direction of gaze guidance for each measurement area, the gaze of the eye to be examined is reliably guided in the measurement of each partial scan area constituting a wider measurement range. In the measurement of each area, it is possible to reduce the effect of fixation micromotion and blink, and an accurate image can be acquired.

FIG. 3 shows an example in which an internal fixation lamp 29 having a plurality of lighting parts as a fixation target is arranged in the main body.

The internal fixation lamp 29 is composed of LEDs arranged in a matrix. When a specific LED of the internal fixation lamp 29 is turned on according to the control of the PC 23, the emitted light is converted into a lens 30, a total reflection mirror 28, The line of sight of the subject eye 15 can be guided and fixed in the direction of the LED that is incident on the eye 15 by the perforated total reflection mirror 26 via the lens 27 and the internal fixation lamp 29 is lit. 3 is the same as that of FIG. Alternatively, a liquid crystal display (LCD) and a backlight unit are arranged instead of the position of the internal fixation lamp 29, and a specific portion is brightly displayed to guide and fix the line of sight of the eye 15 to be examined. It may be.

Therefore, when measuring each partial scan area of FIGS. 2A to 2C to be panorama combined later, the internal fixation lamp 29 corresponding to each partial scan area is switched on and turned on in a direction suitable for the measurement of the partial scan area. By guiding the line of sight to the lighted spot, the line of sight is reliably guided for a short time during measurement of each partial scan area, and each area can be measured accurately, resulting in panorama synthesis. It is possible to accurately measure a fundus image in a wider range by performing. The lighting position of the internal fixation lamp 29 can be recorded in the storage device 25 by the PC 23 in correspondence with information indicating which part of the fundus is currently being measured.

As described above, the optical coherence tomographic image measurement can be performed in a wider measurement range by switching on and lighting a plurality of predetermined fixation targets and guiding the line of sight in a direction suitable for the measurement of each partial scan area. .

The optical coherence tomographic image measurement apparatus of the present invention can be used for three-dimensional measurement of the tissue of the fundus of the eye to be examined.

DESCRIPTION OF SYMBOLS 1 Light source 2

Lens 3 Mirror

4, 5 Lens 7 Beam splitter 8

Lens

10, 11

Galvanometer

10a,

11a Galvanometer mirror

12, 13, 14 Lens 15 Eye to be examined 16, 18, 20 Lens 19 Diffraction grating 21 Spectrometer (line sensor array) )
22 Fast Fourier Transform (FFT)
23 PC (personal computer)
25 Storage device 28 Total reflection mirror 29 Internal fixation lamp 30 Lens 101 Measurement range 102 Partial scan area

Claims

A light source that emits partially coherent light;
The light beam emitted from the light source is divided into a signal light passing through the placement position of the eye to be examined and a reference light passing through a light path different from the optical path going through the eye placement position, and the eye placement An interference optical system that generates interference light by superimposing the signal light after passing through the position and the reference light passing through the different optical paths;
A diffraction grating for dispersing the interference light generated by the interference optical system;
An optical sensor array for detecting the split interference light;
A fast Fourier transformer that fast Fourier transforms signals detected by the photosensor array;
In an optical coherence tomographic image measurement apparatus having a control unit that images the output of the fast Fourier transform and displays or records it as an optical coherence tomographic image,
Based on the control of the control unit, it has an optical scanning means for two-dimensionally scanning a predetermined partial scan area of the eye to be examined with the signal light at a predetermined scan speed,
When the eye to be examined is two-dimensionally scanned by the optical scanning means, the entire measurement range of the eye to be examined is divided into a plurality of partial scan areas, and each partial scan area is sequentially scanned by the optical scanning means, and each partial scan area An optical coherence tomographic image measurement apparatus for acquiring an optical coherence tomographic image of the measurement range of the eye to be inspected by panoramic synthesizing optical coherence tomographic images obtained from the above.
2. The optical coherence tomographic image measurement apparatus according to claim 1, wherein each partial scan area overlaps a predetermined amount with an adjacent partial scan area within the measurement range. apparatus.
3. The optical coherence tomographic image measurement apparatus according to claim 1, wherein a plurality of fixation targets that can be visually recognized by the eye to be examined are provided, and when scanning the specific partial scan area, a predetermined corresponding to the partial scan area is provided. An optical coherence tomographic image measuring apparatus that guides the line of sight of the eye to be scanned in a direction corresponding to a partial scan area to be scanned by switching and fixing the fixation target and scanning the partial scan area.