EP2552295A2

EP2552295A2 - Imaging apparatus and optical interference imaging system, program, and adjustment method for imaging apparatus

Info

Publication number: EP2552295A2
Application number: EP11716073A
Authority: EP
Inventors: Makoto Sato; Yukio Sakagawa; Hirofumi Yoshida
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 2010-03-31
Filing date: 2011-03-25
Publication date: 2013-02-06
Also published as: JP5590942B2; WO2011121961A2; JP2011214967A; WO2011121961A3

Abstract

An OCT imaging apparatus includes a diffraction grating 141 that divides an incident light for each wavelength, a line sensor 139 that receives the divided light and converts it into an electric signal, a motor-driven stage 210 that adjusts a relative position between a light-receiving surface of the line sensor 139 and the light, and a display control unit 125 that displays a spectrum of the light which a sensor receives corresponding to adjustment, wherein an interference light of a measurement light and a reference light is properly aligned relative to the sensor.

Description

IMAGING APPARATUS AND OPTICAL INTERFERENCE IMAGING SYSTEM, PROGRAM, AND ADJUSTMENT METHOD FOR IMAGING APPARATUS

The present invention relates to an imaging apparatus, and an optical coherence tomography system including an adjustable member within the imaging apparatus.

In recent years, imaging apparatuses using an optical coherence tomography, to which a technique of a low-coherence interferometer or white light interferometer is applied, have become commercially practical. The method/apparatus, which is sometimes called Optical Coherence Tomography (hereinafter referred to as OCT), is used to obtain tomograms of the retina in the eye fundus in medical fields, especially in ophthalmic area.

With this method/apparatus, a measurement light and a reference light are generated by dividing a light beam from a light source, and an imaging target is irradiated with the measurement light. A return light of the measurement light with which the subject's eye is irradiated, and the reference light are combined by a beam splitter to form an interference light, which enters a diffraction grating. Then, the light is divided, and is converted into an electric signal by a sensor. A tomographic image of the imaging target can be obtained according to the signal of the interference light.

In the OCT imaging apparatus, since a light flux of the above-described interference light, and a positional relationship between a diffraction grating and a sensor exerts a significant influence on an image quality of the tomogram, a precise alignment is required. As a technique of this adjustment, Patent Document 1 discusses a technique for performing alignment of the interference light relative to a line sensor by moving the mirror and the diffraction grating by a piezoelectric element.

In addition, Patent Document 2 discusses a technique for adjusting a position of a fiber end relative to the diffraction grating based on an irradiated state of the sensor with light.

Japanese Patent Application Laid-Open (Translation of PCT Application) No. 2009-523564 Japanese Patent Application Laid-Open No. 2008-203246

However, it is not considered that how a user can check the result of the adjustment, in the prior arts. Though performance of the adjustment appears in an image as an image quality, the image quality may also vary depending on other factors. Therefore, it is difficult to exactly check whether the adjustment has been properly performed from the information of noise or brightness in the formed tomographic image.

In order to solve such an issue, an aspect of the present invention has the following arrangement. That is, an optical coherence tomographic apparatus includes an interference light generation unit configured to generate an interference light in which a measurement light routed via a imaging target and a reference light routed via a reference object are combined, a light dividing unit configured to divide a light routed via the interference light generation unit for each wavelength, an imaging unit configured to receive the divided lights and convert the divided lights into an electric signal, an image forming unit configured to form a tomographic image of the imaging target according to the electric signal, and a display control unit configured to display a spectrum of a test light incident on an optical path expended from the interference light generation unit to the imaging unit, based on the electric signal which the imaging unit outputs.

Accordingly, since a spectrum which represents an original signal for forming the tomographic image in the OCT imaging apparatus can be displayed, the user can check exactly whether an alignment between a light-receiving surface of the imaging unit and a light flux which reaches the imaging unit is properly performed.

Further features and aspects of the present invention will become apparent from the following detailed description of exemplary embodiments with reference to the attached drawings.

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments, features, and aspects of the invention and, together with the description, serve to explain the principles of the invention.

Fig. 1 is a configuration diagram of an OCT imaging apparatus according to an exemplary embodiment of the present invention. Fig. 2A illustrates a relationship between a fundus image and a scanning range by each measurement light. Fig. 2B illustrates an example of a tomographic image obtained in a first scanning range 505. Fig. 2C illustrates an example of a tomographic image obtained in a second scanning range 506. Fig. 2D illustrates an example of a tomographic image obtained in a third scanning range 507. Fig. 3A illustrates a display example indicating a light-receiving state of a line sensor 139. Fig. 3B illustrates a display example indicating a light-receiving state of the line sensor 139. Fig. 3C illustrates a display example indicating a light-receiving state of the line sensor 139. Fig. 3D illustrates a display example indicating a light-receiving state of the line sensor 139. Fig. 4A illustrates a positional relationship between a line sensor and spectra. Fig. 4B illustrates a positional relationship between a line sensor and spectra. Fig. 4C illustrates a positional relationship between a line sensor and spectra. Fig. 5 illustrates a display screen example for adjustment. Fig. 6 illustrates another display screen example for adjustment. Fig. 7 illustrates another display screen example for adjustment. Fig. 8 is a flowchart illustrating a flow of processing for adjusting the light dividing device. Fig. 9 is a flowchart illustrating a flow of automatic adjustment processing of the light dividing device. Fig. 10A illustrates a light-receiving state of the line sensor and spectra displayed on the display screen. Fig. 10B illustrates a light-receiving state of the line sensor and spectra displayed on the display screen. Fig. 10C illustrates a light-receiving state of the line sensor and spectra displayed on the display screen. Fig. 10D illustrates a light-receiving state of the line sensor and spectra displayed on the display screen. Fig. 11 illustrates a light-receiving state of another line sensor and spectra displayed on the display screen.

Various exemplary embodiments, features, and aspects of the invention will be described in detail below with reference to the drawings.

Fig. 1 is a block diagram illustrating a basic configuration of an OCT imaging apparatus (hereinafter referred to as OCT apparatus) according to an exemplary embodiment of the present invention.

An OCT apparatus 100 constitutes, as illustrated in Fig. 1, a Michelson interferometer as a whole, and is a Spectral Domain scheme OCT (herein after referred to as SD-OCT) or an optical coherence tomographic apparatus. Further, the OCT apparatus 100 is a multi-beam type OCT apparatus that causes a signal light emitted from a low-coherence light source to be simultaneously incident on a plurality of positions of an imaging target, and forms a tomographic image based on a return light from the imaging target of the light caused to be incident.

An emission light 104 as a low-coherence light emitted from a light source 101 is guided by a single mode fiber 110 to be incident on an optical coupler 156, and is divided by the optical coupler 156 into the emission lights 104-1 to 104-3 which pass through three optical paths consisting of a first optical path and a second optical path and a third optical path, respectively.

Moreover, these three emission lights 104-1 to 104-3 each pass through optical fibers which form the optical paths, pass through polarization controllers 153-1, and are divided into the reference lights 105-1 to 105-3 and the measurement lights 106-1 to 106-3 at the optical couplers 131-1 to 131-3 as an interference light generation unit.

Three measurement lights 106-1 to 106-3 thus divided are returned as return lights 108-1 to 108-3 reflected or scattered by respective measurement areas of a retina 127 in a subject's eye 107 as an imaging target.

Then, the returned lights 108-1 to 108-3 are mixed with the reference lights 105-1 to 105-3 which have been routed through the reference light paths by the optical couplers 131-1 to 131-3 as the interference light generation unit, and are interfered with each other depending on differences of optical path lengths between the measurement lights and the reference lights, thus generating the interference lights 142-1 to 142-3. In this way, the optical coupler 131-1 functions as the interference light generation unit which divides a low-coherence light from the light source 101 into the measurement lights and the reference lights, and combines the measurement lights routed through the imaging target and the reference lights routed through the reference object, thus generating the interference lights.

The interference lights 142-1 to 142-3 pass through the polarization controllers 153-3, and exit from an optical fiber end. The exit light is divided by a transmission type diffraction grating 141 as a light dividing unit for each wavelength, and is caused to be incident on a line sensor 139 as an imaging unit via a lens 143, and the line sensor 139 receives the light.

An optical system and the line sensor 139 of the light dividing device are arranged so that the interference lights 142-1 to 142-3 each reach different positions of an image-receiving surface of the line sensor 139. Therefore, the line sensor 139 will have thereon a region which receives the interference light 141-1, a region which receives the interference light 141-2, a region which receives the interference light 141-3, in the order from edge.

Since the light is divided by the diffraction grating for each wavelength, when focusing on each of the interference lights respectively, lights with different wavelengths will enter respective pixels in the light-receiving regions of the line sensor 139 corresponding to the interference lights. Accordingly, spectra of lights which the line sensor 139 receives can be obtained according to an electric signal which the line sensor 139 outputs.

The line sensor 139 as the imaging unit receives lights with respective wavelengths for each sensor element (pixel) and converts a light intensity into an electric signal. The computer 125 acting as an image formation unit forms a tomographic image of the subject's eye 107 according to the electric signal. Light intensity herein used is quantity of light which enters the sensor per unit time.

A motor-driven stage 210 as an adjustment unit adjusts relative positional relationship between a light-receiving surface of the line sensor 139 which receives the interference lights 142-1 to 142-3, and light fluxes of the interference lights by moving a position of the line sensor 139. Light flux herein used means a bundle of light rays.

Further, relative position between the light-receiving surface and the light fluxes means geometrical positional relationship between the light-receiving surface and the light fluxes, and means an incidence angle relative to the light-receiving surface of the light fluxes directed toward the line sensor 139, and an incidence position or range. This adjustment is implemented by the motor-driven stage 210 causing the line sensor 139 to translate or rotate. The motor-driven stage 210 is controlled by the computer 125 acting as a control unit.

In the present exemplary embodiment, the computer 125 issues a control command of the motor-driven stage 210, according to an instruction of adjustment input at an operation unit (not illustrated) of the computer 125, and the motor-driven stage 210 can change a position of the sensor according to the control command.

If relative positional relationship between the imaging unit and other optical members is deviated by vibration or heat, positions of the light fluxes of the lights which the imaging unit receives via the diffraction grating 141 and the line sensor will be deviated. Then, light quantity which should be inherently received cannot be received on some pixels of the line sensor 139.

Accordingly, signal intensity obtained by the line sensor 139 will be reduced, and as a result, there arises a problem that an image quality of obtained image is deteriorated. Hence, it is necessary to adjust positional relationship between the line sensor 139 and the light flux of the light which the line sensor 139 receives, so as to be capable of receiving the light appropriately.

Therefore, a light which is caused to be incident on the optical couplers 131-1 to 131-3, by using either of the reference light, the measurement light, and the interference light as a test light, is received by the line sensor 139. The test light reaches the line sensor 139 as three light fluxes corresponding to three emission lights.

A spectrum of the test light obtained according to an electric signal which the line sensor 139 outputs is displayed on the monitor 130 by the computer 125 acting as the control unit. Accordingly, a user or a person who performs maintenance of the apparatus can check whether the test light properly reaches the line sensor 139 due to arrangement of the optical system or the line sensor 139.

"Properly reach" herein used means a case where the test light is incident on the light-receiving surface of the line sensor 139 or a case where the test light is not incident on the light-receiving surface but within a range of the permissible value.

In this way, each of the spectra of the test light is displayed on the monitor 130. The test light is caused to be entered into the optical paths (the optical paths from the optical couplers 131-1 to 131-3 to the line sensor 139) through which a plurality of light fluxes of the measurement light (the return light) routed via the imaging target through the optical couplers 131-1 to 131-3 reach the imaging unit.

Accordingly, the light-receiving state of the test light (the measurement light, the reference light or the interference light) which the line sensor 139 receives can be changed. Then, display of the light-receiving state to be displayed on a display unit (not illustrated) will be switched by a display control of the computer 125, according to such adjustment. A display example of the light-receiving state will be described below.

Next, a reference light path of the reference light 105 will be described. Each of three reference lights 105-1 to 105-3 divided by the optical couplers 131-1 to 131-3 passes through the polarization controllers 153-2, and is rendered to be substantially parallel by the lens 135 and exits therefrom.

Next, the reference lights 105-1 to 105-3 pass through a dispersion compensation glass 115, and are collected on mirrors 114-1 to 114-3 as an example of a reference object, by the lenses 135-2. Next, the reference lights 105-1 to 105-3 are changed in their directions by the mirrors 114-1 to 114-3 as the example of the reference object, and are again directed toward the optical couplers 131-1 to 131-3.

Then, the reference lights 105-1 to 105-3 pass through the optical couplers 131-1 to 131-3, and are guided to the line sensor 139. The dispersion compensation glass 115 is used to compensate for dispersion generated when the measurement light 106 has travelled between the subject's eye 107 and a scanning optical system, to the reference light 105.

Moreover, an optical path length of the reference light 105 can be changed by moving motor-driven stages 117-1 to 117-3 in a direction indicated by an arrow. The motor-driven stages 117-1 to 117-3 are controlled by the computer 125, and the optical path lengths of the reference lights 105-1 to 105-3 can be changed each independently, or simultaneously.

Next, the measurement light path of the measurement light 106 will be described. Each of the measurement lights 106-1 to 106-3 divided by the optical couplers 131-1 to -3 passes through the polarization controllers 153-4 is made to be substantially parallel light by the lens 120-3 and go out therefrom, and is caused to be incident on a mirror of an XY scanner 119 which constitutes the scanning optical system.

Here, for simplicity, the XY scanner 119 is described as one mirror, but in practice, two mirrors including a mirror for X scanning and a mirror for Y scanning are arranged in proximity to each other, and perform raster scanning in a direction normal to an optical axis on the retina 127.

Further, the lenses 120-1 and 120-3 are adjusted so that a center of each of the measurement lights 106-1 to 106-3 substantially agrees with a center of rotation of a mirror of the XY scanner 119.

The lenses 120-1 and 120-2 are an optical system for scanning the retina 127 with the measurement lights 106-1 to 106-3, and is used to scan the retina 127 with the measurement light 106 by causing an area near a cornea 126 to serve as a fulcrum or pivot point. The measurement lights 106-1 to 106-3 each form an image on an arbitrary position on the retina 127.

The motor-driven stage 117-4 can move in a direction indicated by an arrow, and can adjust and control a position of the lens 120-2 attached thereto. By adjusting the position of the lens 120-2, each of the measurement lights 106-1 to 106-3 can be collected onto a desired layer of the retina 127 of the subject's eye 107 and can be observed.

When the measurement lights 106-1 to 106-3 are incident on the subject's eye 107, they become the return lights 108-1 to 108-3 due to reflection or scatter from the retina 127, and the return lights 108-1 to 108-3 pass through the optical couplers 131-1 to 131-3, and are guided to the line sensor 139. The motor-driven stage 117-4 is controlled by the computer 125. Through the above-described configuration, three measurement lights can scan the target object simultaneously.

Next, a configuration of a detection system will be described. The return lights 108-1 to 108-3 reflected or scattered at the retina 127 as the imaging target are mixed with the reference lights 105-1 to 105-3 by the optical coupler 131-1 to 131-3, and the mixed interference lights 142-1 to 141-3 are incident on the light dividing device, and then the spectra are obtained.

The computer 125 acting as the image formation unit performs formation processing of tomograms on these spectra, and thereby the tomograms can be obtained. As reconfiguration processing, a generation process of general OCT images can be employed, and the tomograms can be generated by performing fixed pattern noise removal, wavelength-to-wave number conversion, Fourier transformation.

Fig. 2A illustrates an example of regions on the retina in the fundus and tomograms captured by the above-described OCT apparatus. In a fundus 501, as illustrated in a fundus image in Fig. 2A and a tomographic image in Fig. 2B, a macula flava 502, an optic disk 503 and blood vessels 504 and the like exist.

Three measurement lights 106-1 to 106-3 scan a first scanning range 505, a second scanning range 506, and a third scanning range 507, respectively, and examples of tomographic images obtained by respective scanning operations are given in Figs. 2B, 2C, 2D, respectively.

Respective regions are overlapped by about 20%, as illustrated in Fig. 2A as an overlap 508 between the first scanning range and the second scanning range, and an overlap 509 between the second scanning range and the third scanning range. Coordinate axes are set as illustrated in Figs. 2B to 2D, and scanning in an x-direction is called fast-scan, scanning in a y-direction is called slow-scan, and a z-direction extends from back surface side to front surface side to the drawing surface of Figs. 2A to 2D.

In this case, it is assumed to scan, e.g., 1024 lines in the x-direction, and e.g., 1024 lines in the y-direction per one measurement light. However, 512 lines when excluding overlapped portion in the y-direction are scanned by three measurement lights. Ultimately, rectangular region surrounded by alternate long and short dash line illustrated in Fig. 2A becomes an imaging range on the fundus, and tomograms will be acquired in this region.

On the other hand, a near-infrared light 190 emitted from a near-infrared light source 180 is irradiated onto the fundus 127 via a half mirror 200, an illumination optical system 150, and a dichroic mirror 220 that is inserted within the measurement light path. The near-infrared light reflected at the fundus returns again through the same optical path, forms an image on two-dimensional area sensor 170 via the half mirror 200, and an image-formation optical system 160.

Two-dimensional image of the fundus which has been captured in this way is input into the computer 125. This two-dimensional image is used to observe the region of OCT imaging.

A shutter 230 arranged in the measurement light path can block incidences of the measurement lights 106-1 to -3 on the fundus 127 by a driving device (not illustrated) under control of the computer 125.

Hereinbelow, relationship between a display screen and a light-receiving state of the line sensor will be described with reference to Figs. 3A to 3D and Figs. 4A to 4C. The reference light is used as the test light. Figs. 3A to 3D illustrate display examples of spectra of respective reference lights projected on the line sensor 139.

As illustrated in Figs. 3A to 3D, three spectra 144-1 to -3 are projected on the line sensor 139, and signals read out from the line sensor 139 are subjected to reconstruction processing for each of the regions illustrated in SR1 to SR3, thus generating the tomograms. Then, image data for display is generated by the computer 125 as a display control unit based on the tomographic images, and is displayed on a display unit (not illustrated).

Further, Fig. 4 illustrates positional a relationship between light fluxes which the line sensor 139 receives and the light-receiving surface of the line sensor 139. In Figs. 4A to 4C, the light-receiving surface of the line sensor 139 is illustrated, and spectra of lights, which are incident on the light-receiving surface in a direction extended from front surface side to back surface side to the drawing surface of Fig. 4A to 4C are indicated by oblique lines.

Fig. 3A is an example of display, which is an example in which values of electric signals according to light quantity which the line sensor 139 receives on the light-receiving surface are directly displayed as they are. In Fig. 3A, horizontal axis is a position of the line sensor and at the same time corresponds to wavelength, and vertical axis corresponds to signal intensity for each wavelength. Alternatively, the horizontal axis may represent frequency to display intensity with respect to the frequency.

Light-receiving state corresponding to the state illustrated in Fig. 3A is illustrated in Fig. 4A. In Fig. 4A, spectra 144-1 to 144-3 corresponding to respective measurement lights are properly incident on the light-receiving surface of the line sensor 139.

For this reason, peaks of the spectra illustrated in Fig. 3A are large, and variation between the spectra is small. In this way, a light-receiving state of the line sensor can be presented in a visually easy-to-understand manner to the user, by displaying shapes of the spectra.

Fig. 3B is another display example, and is a display in the case where positional relationship between the line sensor 139 and the light flux of the reference light is deviated. In Fig. 3B, the spectrum 144-1 and the spectrum 144-2 are smaller than the spectrum 144-3. This is a phenomenon that occurs since lights received at the portions corresponding to the regions SR1 and SR2 of the line sensor 139 become weak.

In such a case, it is considered that the light flux of the reference light and the light-receiving surface of the line sensor 139 have been rotated relative to each other. Alternatively, it is also considered that the positions of the optical components which guide the reference lights corresponding to the spectrum 144-1 and the spectrum 144-2 may have been shifted.

This light-receiving state corresponding to the state illustrated in Fig. 3B is illustrated in Fig. 4B. In Fig. 4B, the line sensor 139 has been inclined relative to the light fluxes of the respective measurement lights. Then, especially the spectrum 144-1 is not properly incident on the line sensor 139. Accordingly, a peak of the spectrum 144-1 is small in Fig. 3B.

In this way, if the positions the line sensor 139 and the light are shifted, shape of the spectrum is changed, and the light-receiving state of the line sensor 139 can be presented visually to the user.

The effect described for the above-described displays in Fig. 3A and Fig. 3B, is not limited to especially multi-beam type OCT apparatus, but similar effect is obtained for single beam type OCT apparatus as well. In the case of the multi-beam type apparatus, since a plurality of spectra are displayed, the light-receiving state can be displayed in an easy-to-understand manner, and the shift of relative position between the line sensor and the light can be presented to the user, by displaying so that shapes of the respective spectra can be compared with one another.

In the single beam type OCT apparatus, the light-receiving state will be determined based on a shape of one spectrum. Compared to this, in multi-beam type, since a plurality of shapes can be compared, the effect of the display according to the present exemplary embodiment can be expected.

In addition, in the OCT imaging apparatus using a plurality of the measurement lights of multi-beam, the respective interference lights need to be properly aligned relative to the line sensor, so that image quality may not vary for each of the measurement regions by the respective measurement lights.

For this reason, the need to adjust the spectra corresponding to the respective measurement lights according to displays illustrated by an example in Fig. 3A to 3D is higher in comparison to the single beam, and the displays illustrated by the example in Fig. 3 are of great significance from this viewpoint as well.

Fig. 3C illustrates another display example, and magnitudes of the respective spectra are smaller, in comparison with those in Fig. 3A. The reason is considered that because, although the line sensor 139 and the light flux of the reference light are not rotated relative to each other, they are translated relative to each other, and the lights which respective areas of the line sensor 139 receive have become weak as a whole.

The light-receiving state corresponding to the state illustrated in Fig. 3C is illustrated in Fig. 4C. In Fig. 4C, the line sensor 139 is shifted in a direction orthogonal to the longitudinal direction relative to the light flux. As a result, it can be seen that the light-receiving states of the respective spectra are uniformly worsened.

Fig. 3D is yet another display example, and is an example in which magnitudes of peaks of spectra of the test lights are displayed as numerical values corresponding to the respective spectra 144-1 to 144-3.

The magnitudes of peaks are used as feature quantity indicating light quantity or light intensity of each reference light. In this way, there is an advantage that quantities to be adjusted can be presented to the user as not only shapes of spectra, but also numerical values of the peaks, by displaying the magnitudes of peaks as numerical values.

In the case where spectra are uniformly small like in Fig. 3C, it may be uncertain in some cases whether there is a problem with the light-receiving state, by just viewing shapes of the spectra. However, even in such a case, abnormality of the light-receiving state can be presented in an easy-to-understand manner to the user, by displaying the numerical values.

In the above-described exemplary embodiment, examples of displaying spectra of the lights have been illustrated as a display of the light-receiving state of lights by the line sensor. However, it is not limited thereto, and peak values or areas of the spectra may be also displayed as values indicating light quantities. Further, a display indicating whether each of the regions SR1 to SR3 of the line sensor which receive the reference lights or the interference lights corresponding to the respective measurement lights is illuminated with a light equal or greater than a threshold value may be performed

In the above-described exemplary embodiment, as a multi-beam type optical coherence tomographic apparatus having a plurality of measurement lights, an example of dividing a light emitted from one light source by the optical coupler is illustrated. However, it is not limited thereto, and the optical coherence tomographic apparatus may have a plurality of light sources. In this case, a plurality of light sources with relatively small light intensity can be also used, without using a single light source with a high light intensity.

Alternatively, a line sensor may be provided independently for each of the measurement lights. In this case, the need to independently adjust each sensor arises, but positional relationship between light fluxes of lights which the respective sensors receive, and the sensors can be adjusted more precisely.

Moreover, in the above-described exemplary embodiment, an example of adjusting a position of the line sensor has been illustrated. However, it is not limited thereto, and it is only necessary that a positional relationship between the light fluxes of lights which the line sensor receives and the line sensor can be adjusted.

For example, a position of a fiber end of an optical fiber or orientation of a light exiting from the fiber end may be adjusted, a position of a lens disposed between the fiber end and a light dividing unit may be adjusted, a position of a diffraction grating may be adjusted, or a position of the lens disposed between the diffraction grating and the line sensor may be adjusted.

In a case where the line sensor can be precisely positioned in advance, adjustment of the light-receiving state becomes possible by adjusting positions of optical system members.

In the present exemplary embodiment, a display of spectra illustrated in a display example according to the first exemplary embodiment, and "A" scan image or a profile of "A" scan and "B" scan image and the like are displayed. Further, the display screen where adjustment and its confirmation are possible by scanning icons on the display screen is provided.

The computer 125 acquires outputs of the line sensor 139, and generates spectrum information and "A" scan image, "B" scan image to be used for the display screen. Setting information such as images of icons and arrangement of the display is stored in the computer 125 in advance. Image data of the display screen is generated according to the acquired information and the setting information, and the computer 125 executes processing of performing display control.

In the display screen, the user can click buttons and other icons using a mouse or keyboard (not illustrated) connected to the computer 125. The computer 125 acquires the operation information, and executes a control of the motor-driven stage 210 according to the operation information.

The computer 125 generates image data of a new display screen based on newly acquired outputs from the line sensor 139, and performs display control for causing the display unit to display the image data. Through this control, the display screen will be switched.

Fig. 5 is an example of the display screen for adjustment. In a spectrum display region 600, three spectra are displayed as illustrated in the exemplary embodiment previously described referring to Figs. 3A to 3D. The display of the spectra is updated sequentially by continuously processing outputs of the line sensor 139, and performing display control by the computer 125.

Signals obtained by subjecting three spectra 144-1 to 144-3 to reconstruction processing are displayed in tomogram signal display regions 603-1 to 603-3. In the present exemplary embodiment, they are to be called "A" scan image or a profile of "A" scan line.

On the other hand, a tomogram display region 605 is a region where a plurality of "A" scans obtained by driving a mirror for X scanning are displayed as two-dimensional images by well-known interpolation processing. In the subsequent explanation, a tomogram composed of the plurality of "A" scans is called "B" scan image.

In the display example illustrated in Fig. 5, because of a state in which the reference lights are displayed, the "A" scan image or the "B" scan image are not displayed in the tomogram signal display regions 603-1 to 603-3, and the tomogram display region 605.

Region select buttons 606-1 to 606-3 are icons for selecting a display of any one of the tomograms by three measurement lights. A tomographic image corresponding to A-A' cross-section illustrated in Fig. 2A is displayed in the tomogram display region 605 by an operator of the apparatus by pressing a switch displayed as a region "A". B-B' cross-section will be displayed by pressing a display of a region "B", and C-C' cross-section will be displayed by pressing a display of a region "C".

In the present exemplary embodiment, since the reference light is displayed as a spectrum display, displays of the spectrum display region 600 or the tomogram signal display regions 603-1 to 603-3 will not be changed.

Next, a slider 604-1 and a slider 604-2 in Fig. 5 are sliders for adjusting the position of the line sensor 139 relative to the spectra by driving the motor-driven stage 210. The height and rotation of each line sensor can be adjusted relative to the spectrum by operating these sliders by an operator.

"Height" herein used refers to a displacement or an amount of movement in a direction orthogonal to a longitudinal direction of the line sensor. "Rotation" refers to a rotation around an axis which passes through a center point with respect to the longitudinal direction of the line sensor 139, and is orthogonal to a plane including the light-receiving surface. The center of rotation is not limited to a midpoint with respect to the longitudinal direction of the line sensor 139.

Further, the line sensor may be configured to be able to perform translational or rotational movement out of the plane including the light-receiving surface. For example, the line sensor may be movable in three axes directions using a motor and a feed screw. Since the display of the spectrum display region 600 will be switched by operation of these sliders, the user can adjust a position of the line sensor by the operation on the screen, and check a result of the adjustment on the display screen.

Light source buttons 607-1 and 607-2 are used to turn ON or OFF the power source of the light source 101, thereby emission of the low-coherence light from the light source 101 is stopped, and the spectra cease to be displayed in the spectrum display region 600.

Upon operating shutter buttons 608-1 and 608-2 by the operator, the optical paths of the measurement lights 106-1 to 106-3 can be blocked or opened by driving a shutter 230. When the optical path is opened by the shutter 230, the interference light containing tomogram information of the retina will be obtained, and spectra of the interference light will be displayed in the spectrum display region 600, in a case where an objective lens is arranged ahead of the subject's eye.

In the above-described display example, the light-dividing device is adjusted using only the reference light in a state where the measurement light is blocked by operating the shutter 230. However, this is not essential for the present exemplary embodiment, and the light-dividing device may be adjusted using a stable standard object such as a model eye. In this case, adjustment is performed in a state where the shutter button 608-1 is pressed by the operator, and the shutter 230 is opened.

In the present exemplary embodiment, when the model eye as an object in which multilayer film is formed is set on the OCT imaging apparatus, and the shutter is opened by the shutter button 608-1, an adjustment screen becomes the one as illustrated by an example in Fig. 6. That is, a tomogram of the model eye is displayed in the tomogram display region 605, and tomogram signals ("A" scan profiles) generated from the respective spectra are displayed in the tomogram signal display regions 603-1 to 603-3.

By referring to, for example, both of light-receiving state and "A" scan profile of the respective measurement lights, based on such display, information can be presented, so that the user can check magnitude of signal components with regard to a certain "A" scan profile, and determine based thereon whether adjustment is necessary.

By referring to "B" scan image as well as "A" scan profile, information for checking whether there is abnormality in a region with a large noise, for example, in the "B" scan image, in the spectra of the interference lights, and for identifying the cause, can be presented.

In a state where the "A" scan image and "B" scan image are displayed, the reference light can be displayed by shielding the optical path by pressing the shutter button 608-2.

The display of the tomogram display region 605 can be switched by the region select buttons 606-1 to 606-3 provided above the display region 605. Fig. 6 illustrates a state where the region "A" in the middle is selected, and B scanned image by the measurement light of the region "A" is displayed in the tomogram display region 605.

When a region to be selected is switched, "B" scan image of the selected position is displayed in the tomogram display region 605. In parallel, the spectrum of the interference light corresponding to the selected region is displayed in the spectrum display region 600, and "A" scan profiles will be displayed in the tomogram signal display regions 603-1 to 603-3. In such a way, the display will be switched according to the selection of the region select buttons 606-1 to 606-3.

The interference light acquired based on the measurement light, which is irradiated on a certain position of the imaging target is to be displayed is determined in advance according to the selection of a region. For example, the interference light at central position may be used, or the interference light at edge may be used, for the respective measurement lights. Further, averaging of the spectra of the interference lights corresponding to a plurality of "A" scan positions may be displayed.

In this way, the display of spectrum and "A" scan image and "B" scan image is switched according to the selection of a region, thereby intensity of signal in an image can be checked for each region.

The optical interference imaging apparatus according to the present exemplary embodiment has a mode for automatically executing adjustment of the light dividing device, in addition to a mode in which the user manually adjusts the light dividing device.

An example of the display screen which is display-controlled by the computer 125 is illustrated in Fig. 7. On the display screen, automatic adjustment will be executed by displaying a button 602 for instructing an execution of the automatic adjustment as an icon, and by pressing the button on the screen via the operation unit (not illustrated) by the user.

Next, in the above-described OCT imaging apparatus, an adjustment method of the light dividing device to be performed before the imaging of the subject's eye will be described referring to Fig. 8. The processing described below is realized by causing the computer 125 illustrated in Fig. 1 to execute a control program to control operation of each unit.

In step S100, the computer 125 displays a screen for adjustment of the light dividing device on the monitor 130. The display screen is similar to that in the previously described second exemplary embodiment, except that an automatic adjustment button 602 is arranged. Therefore, description thereof will not be repeated.

In step S200, the computer 125 detects whether the automatic adjustment button 602 has been pressed by the operator. If not pressed (NO in step S200), the computer 125 shifts the mode to a manual mode in step S300. If pressed (YES in step S200), the computer 125 shifts the mode to an automatic mode in step S400.

In step S300, the computer 125 monitors whether each operation button illustrated in Fig. 7 is pressed, and shifts the mode to the manual mode in which adjustment is performed under the operation of the operator. The manual mode is a mode in which a position of the line sensor 139 is manually adjusted under the operation of the operator.

In this mode, while adjusting the height of the line sensor 139 with the slider 604-1, the rotation with the slider 604-2, adjustment is performed so that the heights of the spectra of the respective test lights displayed in the spectrum display region 600 are uniform or fall within a predetermined range of difference, and are as high as possible.

First, in the present exemplary embodiment, adjustment is assumed to be performed in a state where the shutter 230 blocks the measurement lights 106-1 to 106-3. More specifically, the shutter button 608-2 is pressed by the operator, thereby the shutter 230 blocks the measurement light, and as a result, only the spectra of the reference lights 105-1 to 105-3 are assumed to be incident on the line sensor 139.

Therefore, although tomograms cannot be generated, even when the detected signals are subjected to reconstruction processing, an interference component itself which depends on an object is unnecessary signal to monitor a balance of respective spectra. For this reason, it is preferable.

In the present exemplary embodiment, since the measurement lights are blocked, as described above, nothing is displayed in the tomogram signal display regions 603-1 to 603-3 and the tomogram display region 605. Next, position adjustment of the line sensor in the manual mode will be specifically described.

For example, shapes of the spectra displayed in the spectrum display region 600 immediately after start of adjustment may be in a state as illustrated in Fig. 3B. In such a case, when the operator operates the slider 604-2, the computer 125 drives the motor-driven stage 210 to rotate the line sensor 139.

By further operating the slider 604-1, the operator, while monitoring the shapes of the spectra 144-1 to 144-3 displayed in the spectrum display region 600, adjusts a position of the line sensor 139 so that these heights are uniform, and become highest.

If a positional relationship between the line sensor and the spectra is as illustrated in Fig. 4C, the spectra detected by the line sensor correspond to the state in Fig. 3C. Here, when the slider 604-2 is operated, the computer 125 drives and rotates the line sensor 139, which becomes the state in Fig. 4B.

Next, when the slider 604-1 is operated, the computer 125 causes the line sensor 139 to perform translational movement, and finally the line sensor 139 becomes the state in Fig. 4A. Thus, the line sensor is properly aligned relative to the respective spectra.

As described above, when the operator performs alignment of the line sensor, the computer 125 computes areas or peak values of respective spectra which are input sequentially, and the computed numerical values may be displayed near the spectra within the spectrum display region 600. In this way, it is favorable since to the user can check the heights and balance of the respective spectra more easily.

Fig. 3D is an example of a form of the display, where peak values which the computer 125 has computed on the respective spectra are displayed together with arrows. Although peak values of the spectra are displayed in this example, as a matter of course, areas or other numerical values may be displayed, and a position of the display may be anywhere on the display screen illustrated in Fig. 7.

In step S400, when an automatic adjustment button 602 is pressed by the operator in step S200, the computer 125 shifts to the automatic mode. In this mode, adjustment described in step S300 is automatically performed.

Hereinbelow, a flow of the processing of automatic mode will be described referring to a flowchart described below with reference to Fig. 9.

In step S410, the computer 125 turns ON the power source of the light source 101, and causes the shutter 230 to be operated, thus the measurement lights 106-1 to 106-3 are blocked. Accordingly, only the spectra of the reference light 105-1 to 105-3 will be incident on the line sensor 139.

In step S420, the computer 125 moves the position of the line sensor 139 to a state where any of three spectra is not incident. Fig. 10A illustrates a positional relationship at this time between the line sensor and the spectra and intensities of the spectra detected by the line sensor, and no spectra are detected in this step.

At this time, if the line sensor 139 has been rotated by a predetermined angle in advance, it is preferable since adjustment of rotational direction only needs to be performed basically on the basis of one direction in subsequent steps. Relative deviation amount that could occur due to assembly errors of the apparatus or the like between the line sensor and the spectra is estimated in advance. This angle only needs to take a value which sufficiently exceeds an angle determined therefrom.

In step S430, the computer 125 inputs sequentially the detection results of the spectra from the line sensor 139, while causing the line sensor 139 to perform parallel movement in a direction indicated by an upward arrow in Fig. 10A. In this case, the computer 125 monitors a height of the spectrum 144-2 positioned in the middle, and stops the movement at a position where it becomes maximal. The state at this time is illustrated in Fig. 10B.

In step S440, the computer 125 checks whether a difference of heights of spectra detected by the line sensor 139 falls within a permissible range. If within a permissible range (YES in step S440), the computer 125 advances the processing to step S460. On the other hand, If not (NO in step S440), the computer 125 advances the processing to step S450.

This permissible range may be determined based on difference between image qualities due to the difference between the spectra. More specifically, heights of the spectra affect sensitivity for extracting a structure of the object, and sensitivity is lowered as a whole, when the heights of the spectra are low, and as a result, the tomogram obtained by reconstructing become dark.

Therefore, if it is determined by subjective evaluation or the like that to what extent of difference among respective scanning ranges 505 to 507 illustrated in Fig. 2A is permissible, then regarding the heights of the spectra, their permissible range can be decided.

In step S450, the computer 125 inputs sequentially the detection results of the spectra from the line sensor 139, while rotating the line sensor 139 toward the direction indicated by an arrow in Fig. 10B. In this step, heights of the three spectra 144-1 to 144-3 are all monitored, and rotation is stopped at an angle at which three heights become substantially the same. The state at this time is illustrated in Fig. 10C.

In step S460, the computer 125 checks whether heights of three spectra and their differences fall within a specified range. If within a specified range (YES in step S460), the computer 125 terminates adjustment. If not (NO in step S460), the computer 125 advances the processing again to step S430. If the processing proceeds to step S430, the line sensor 139 is moved as illustrated in Fig. 10C, and similar processing will be repeated again.

In this case, it is only necessary to have determined in advance a specified range relating to the height of spectrum based on image qualities in respective scanning ranges and their differences as described in step S440.

As described above, according to the present exemplary embodiment, in an adjustment of the light dividing device in the tomographic imaging apparatus having a plurality of measurement lights, positions of the sensor and the interference light can be properly adjusted. In the present exemplary embodiment, their heights are used as an index representing characteristics of the spectra detected by the line sensor 139, but the present invention is not limited to this and, for example, areas of spectra may be used.

Not only adjustment based on the reference light, adjustment of the light dividing device may be performed using the spectra including interference signals. A flow of the processing is basically similar to that in the first exemplary embodiment. However, since interference signals are included in the spectra detected by the line sensor 139, when heights of the spectra are evaluated, in step S440, and step S460, adjustment is performed using heights including the interference signals.

Alternatively, in step S410, when initial setting is performed, first, the computer 125 acquires three spectra 144-1 to 144-3 while the shutter 230 is closed, and stores them in a memory inside the computer 125. Next, subtraction is made from the spectra acquired while the shutter 230 is opened, to obtain only interference signals, and amplitudes of these signals may be used as the index.

Thus, it becomes possible to adjust the light dividing device to keep the same level of image quality with respect to a standard object.

In the exemplary embodiments described above, although the line sensor 139 is composed of one row of detection elements, a two-dimensional sensor or a line sensor having a plurality of rows of elements can be used in the present exemplary embodiment. Fig. 11 illustrates an example of a spectrum in a case where such a sensor is used.

In the line sensor 139, two rows of detection elements 139-1 and 139-2 are arrayed, and the output signals thereof are input into the computer 125.

At this time, two detected spectra exist for respective rows of detection elements, and a spectrum by a detection element row 139-1 is illustrated by a dashed line, and a spectrum by a detection element row 139-2 is illustrated by a solid line.

In such a case, in adjusting a position of the line sensor 139, adjustment is performed so that the light-receiving state by each of these rows, that is, values of two obtained spectra are the same or fall within a predetermined difference range.

Amounts indicating the light-receiving state include the height of spectrum, average position, variation (standard deviation), and area in wavelength-intensity graph. Adjustment is made so that one or all of these indexes are equal to or greater than a certain value, and a difference between respective rows falls within a predetermined range.

Therefore, in the above-described exemplary embodiments, these two types of spectra are displayed in an identifiable manner in the spectrum display region 600 as illustrated in Fig. 11. Since the light-receiving surface becomes larger in size, by using a two-dimensional sensor or a sensor having a plurality of rows, adjustment becomes easier, and time and work for adjustment can be reduced.

Alternatively, as another example, in the above-described exemplary embodiments, the exemplary embodiments in which circuits corresponding to respective functional blocks within the optical coherence tomography system or the image processing apparatus realize the present invention, have been described, but the exemplary embodiments of the present invention are not limited to this.

For example, the processing performed in the image processing apparatus may be distributed among a plurality of apparatuses and implemented as a system, or the processing configured as one functional block may be distributed among a plurality of circuits or apparatuses and implemented. By incorporating the functions of the image processing apparatus and display apparatus in the above-described exemplary embodiments to the optical coherence tomographic apparatus, the present invention may be realized by the optical coherence tomographic apparatus.

Further, the present invention is realized by supplying a recording medium which has recorded a program code of software that implements the functions of the above-described exemplary embodiments to system or apparatus, and by executing the program code stored in the recording medium by a CPU in the system or apparatus.

Further, a case where operating system (OS) running on the computer performs a part or whole of actual processing, by executing a program code which the computer has read out, and the functions of the above-described exemplary embodiments are implemented by the processing is also included in the present invention. The functions may be distributed to a plurality of CPUs to realize the present invention.

In this case, the program code itself read out from the recording medium will implement the functions of the above-described exemplary embodiments, and the recording medium that has recorded the program or program code will constitute the present invention.

Moreover, a case where the program code read out from the recording medium is written into a memory within a function expansion card or a function expansion unit attached to the computer, and the arithmetic device within the expansion card or the expansion unit performs a part or whole of the processing, and the functions of the above-described exemplary embodiments are implemented, is also included in the present invention. In this case, the present invention is realized by circuits mounted by hardware and the functions implemented by the cooperation of software and hardware.

Descriptions in the above-described exemplary embodiments are an example of a control apparatus of suitable fundus tomographic imaging apparatus according to the present invention, and the present invention is not limited to this.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications, equivalent structures, and functions.

This application claims priority from Japanese Patent Application No. 2010-082810 filed March 31, 2010, which is hereby incorporated by reference herein in its entirety.

100 OCT imaging apparatus
125 computer
139 line sensor
141 diffraction grating
210 motor-driven stage
600 spectrum display region
602 automatic adjustment button
604-1 line sensor height adjustment slider
604-2 line sensor rotation adjustment slider

Claims

An optical coherence tomographic apparatus comprising:
an interference light generation unit configured to generate an interference light in which a measurement light routed via a imaging target and a reference light routed via a reference object are combined;
a light dividing unit configured to divide a light routed via the interference light generation unit for each wavelength;
an imaging unit configured to receive the divided lights and convert the divided lights into an electric signal;
an image forming unit configured to form a tomographic image of the imaging target according to the electric signal, and
a display control unit configured to display a spectrum of a test light incident on an optical path expended from the interference light generation unit to the imaging unit, based on the electric signal which the imaging unit outputs.
The optical coherence tomographic apparatus according to claim 1, wherein the display control unit displays a peak value of the spectrum of the test light.
The optical coherence tomographic apparatus according to claim 1 or claim 2, wherein the display control unit displays a values indicating light quantity of the test light which the imaging unit receives.
The optical coherence tomographic apparatus according to claim 1, wherein the optical coherence tomographic apparatus causes a measurement light emitted from a low-coherence light source to be simultaneously incident on a plurality of positions of the imaging target, and forms a tomographic image based on a return light of the incident light from the imaging target,
wherein the display control unit displays spectra of a plurality of test lights incident on each of optical paths extended from the interference light generation unit to the imaging unit, through which a plurality of light fluxes of the return light pass.
The optical coherence tomographic apparatus according to claim 4, further comprising an optical system configured to cause each of interference lights corresponding to each of measurement lights simultaneously incident on a plurality of positions on a surface of the imaging target to reach different positions on a light-receiving surface of the imaging unit.
The optical coherence tomographic apparatus according to claim 4, wherein the display control unit displays peak values of spectra of the test lights each corresponding to a plurality of light fluxes of the return light.
The optical coherence tomographic apparatus according to claim 4, wherein the display control unit displays differences of peak values between spectra of the test lights each corresponding to a plurality of light fluxes of the return light .
The optical coherence tomographic apparatus according to claim 5, further comprising an adjustment unit configured to adjust relative position of a light-receiving surface of the imaging unit to the light fluxes of lights which the imaging unit receives,
wherein the display control unit displays a light-receiving state of light which the imaging unit receives according to the adjustment.
The optical coherence tomographic apparatus according to claim 8, further comprising a control unit configured to control the adjustment unit so that a difference of light quantities of the test lights each corresponding to a plurality of light fluxes of the return light fall within a predetermined range.
The optical coherence tomographic apparatus according to claim 8, further comprising a control unit configured to control the adjustment unit so that a difference of light-receiving states in each row of the two-dimensional sensor falls within a predetermined range.
The optical coherence tomographic apparatus according to claim 8, wherein the adjustment unit adjusts a position of the imaging unit.
The optical coherence tomographic apparatus according to any one of claims 1 to 11, wherein the test light is any one of the signal light, the reference light, or the interference light.
The optical coherence tomographic apparatus according to any one of claims 1 to 12, wherein the imaging unit is two-dimensional sensor,
wherein the display control unit displays a light-receiving state in each row of the two-dimensional sensor.
An optical coherence tomographic apparatus that causes a signal light emitted from a low-coherence light source to be simultaneously incident on a plurality of positions of a imaging target, and forms a tomographic image based on a return light from the imaging target of the incident light, the optical coherence tomographic apparatus comprising:
an interference light generation unit configured to combine the return light and a reference light routed via a reference object to obtain an interference light;
a light dividing unit configured to divide a light routed via the interference light generation unit for each wavelength;
an imaging unit configured to receive the divided light and convert it into an electric signal; and
an adjustment unit configured to adjust relative position of a light-receiving surface of the imaging unit to the light flux of light which the imaging unit receives.
An optical coherence tomographic system comprising:
a light source configured to emit a low-coherence light;
an interference light generation unit configured to divide the low-coherence light into a measurement light and a reference light, and combine the measurement light routed via a imaging target and the reference light routed via a reference object to generate the interference light;
a light dividing unit configured to divide a light routed via the interference light generation unit for each wavelength;
an imaging unit configured to receive the divided light and converts the received divided light into an electric signal;
an image forming unit configured to form a tomographic image of the imaging target based the electric signal; and
a display unit configured to display a spectrum of a test light incident on an optical path extended from the interference light generation unit to the imaging unit, based on the electric signal which the imaging unit outputs.