JP2010164351A - Optical tomographic imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical tomographic imaging apparatus for observing the tomographic image of observation target matter at a high speed with high dissolving power, gradation properties and contrast. <P>SOLUTION: Low coherent laser beams 1 and 2 are split into a searching beam and a reference beam by a beam splitter 10. The observation target matter 23 is irradiated with the searching beam and scanned with a predetermined frequency by galvanomirrors 18a and 19a. The reference beam is optically delayed by an obliquely provided diffraction lattice 16 to be changed in light path length. The searching beam and reference beam reflected by the observation target matter are synthesized as a coherence beam by the beam splitter and the coherence beam is passed through a detection opening 25 to be rescanned with the same scanning frequency by a galvanomirror 28a and detected by an imaging element 30 to obtain the reflection intensity data in the observation target matter. In this constitution, the depth data of the observation target matter is obtained by the optical delay due to the diffraction lattice and coherence data is obtained by the scanning and rescanning means of the low speed corresponding to the frame rate of the imaging element. As a result, a scanning optical system is simply constituted. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical tomographic imaging apparatus, and more specifically, scans a light beam from a light source to irradiate a predetermined part of an observation target object, and utilizes reflected light from the target object using an optical interference phenomenon. The present invention relates to an optical tomographic imaging apparatus that acquires tomographic image information of a target object by performing detection processing.

  Conventionally, an imaging apparatus (Optical Coherence Tomography: OCT) of tomographic information of an observation target object using an interference phenomenon of a low-coherence light beam (partial coherent light) is non-contact and non-invasive. Since it can be observed by tomographic images, it is especially useful for observation of living organisms, and it has begun to be used in medical fields such as general ophthalmological examinations, dermatological diagnoses, and applications to endoscopes, or industrial applications. Applications are being examined as inspection equipment in the field.

  For example, in Patent Document 1 below, as an initial OCT, a means for generating a reference light in which the frequency of irradiation light is shifted and a reflected light from an object to be measured are synthesized and output with the reference light. A configuration is shown in which a reflection tomographic image of a target object is imaged by detecting a beat component.

  In the following Patent Document 2, a light source having a short coherence length characteristic and an interferometer using an optical fiber, a phase modulation means and a lateral scanning mechanism arranged in an optical path of search light toward a sample specimen, and an optical path of a reference light A configuration having an arranged ultrasonic light modulation element and movement control means for the optical path length in the optical axis direction is disclosed. This document shows a basic technique for imaging a tomographic image of a sample specimen by detecting interference light generated between search light and reference light guided through an optical fiber.

  Patent Document 3 listed below includes a semiconductor laser light source capable of optical frequency sweeping, a Michelson interferometer, and a one-dimensional or two-dimensional imaging device, and an image signal output during the optical frequency sweeping period. A configuration is disclosed in which a tomographic image is calculated by performing a Fourier transform process. This method is advantageous in that it eliminates the need for a scanning mechanism that involves mechanical movement in the direction of the optical axis, forms a stable interference optical system, and enables measurement in a short time.

  In Patent Document 4 below, a light beam is divided into a reference arm and a measurement arm, and the intensity of light that appears as a result of measurement light passing through the measurement arm interfering with the reference light passing through the reference arm is measured by a spectroscope. A configuration for detecting via the network is disclosed. The reference arm is provided with a means for changing the phase of light, and shows a configuration for optical tomography of transparent, partially transparent, and opaque objects by analyzing the signal from the spectrometer. Has been.

  In the following Patent Document 5, as an OCT device based on the principle of Non-Patent Document 1 described later (a document that has been publicly known at the time of filing), a transmissive diffraction grating is disposed in the middle of the reference optical path of the interferometer, An optical configuration of a coaxial spatial interferometer that utilizes an optical sensor array as a detector is shown. According to this configuration, there is a possibility that a tomographic image of a subject can be acquired without using mechanical light beam scanning.

  In Patent Document 6 below, in a measuring apparatus composed of an interferometer and a spectrometer (spectrometer), a light beam from a light source collects light in a line shape with respect to the measured object, and then from the measured object. A configuration is disclosed in which the observation light is detected by a two-dimensional image sensor via a spectroscope. It is shown that by performing arithmetic processing such as Fourier transform on the detection signal from the image sensor, the cross-sectional information of the measurement object can be obtained at high speed according to the calculation speed.

  In the following Patent Document 7, an OCT configuration including an interferometer, an optical modulation unit, an optical scanning unit, a rescanning unit, a two-dimensional imaging unit, and a signal processing unit that performs a predetermined calculation on a video signal from the imaging unit. is suggesting. In this configuration, it is shown that the reflection intensity information inside the target object can be acquired at high speed by processing the interference information between adjacent pixels detected according to the control of the light modulation means.

  Non-Patent Document 1 below shows a basic interferometer and a configuration of an OCT optical system in which a reflection type diffraction grating is inclined in a Littrow arrangement in a reference optical path. According to this configuration, the interference light generated by superimposing the reference light with an optical delay corresponding to the reflection position of the reference optical path from the diffraction grating and the reflected measurement light from the sample sample in the measurement optical path is converted into a two-dimensional CCD. It has been shown that a tomographic image of a sample specimen can be obtained without performing mechanical movement scanning in the depth direction by capturing with an imaging device.

  Non-Patent Document 2 below describes a modified version of the device based on the same principle as that described in Non-Patent Document 1, and a diffraction grating set in a Littrow arrangement in the reference optical path of the interferometer and a two-dimensional CMOS. A configuration of an optical system using a camera is shown. This document also shows an experimental result that a tomographic image of the surface of a living body (skin etc.) can be obtained at high speed by adopting a CMOS camera capable of ultra-high-speed imaging and simple arithmetic processing between frame images.

JP-A-4-174345 (Japanese Patent Publication No. 6-35946) Japanese National Patent Publication No. 6-511112 (Patent No. 3479069) JP-A-10-332329 (Patent No. 3332802) JP 11-325849 A JP 2006-64610 A (Patent No. 3934131) JP 2006-116028 A JP 2008-309613 A

Paper OPTIC LETTERS, Vol. 23 (1998) No. 23, pp. 1797-1799, “Nonmechanical grating-generated scanning coherence microscopy” (I. Zeylikovich, A. Gilerson, and R. R. Alfano) Paper OPTICS EXPRESS, Vol. 14 (2006) No. 12, pages 5201 to 5209, “Three-dimensional imaging by ultrahigh-speed axial-lateral parallel time domain optical coherence tomography” (Y. Watanabe, K. Yamada, and M. Sato)

  In the configurations shown in Patent Documents 1 and 2 (also referred to as “time domain method”), scanning in the depth direction (depth direction) of the observation target object is performed by movement control in the optical axis direction of the reflection mirror with respect to the reference light. Therefore, it is difficult to obtain a tomographic image of the target object at high speed. In addition, since the acquisition of tomographic image information is sequentially performed depending on the scanning in the depth direction, there is a drawback that the detection signal processing is not efficient and it is difficult to increase the sensitivity.

  The configuration disclosed in Patent Document 3 discloses an OCT method (also referred to as “swept source method”) using wavelength sweeping of a light source. While this method has the advantage that mechanical scanning in the depth direction is not required for acquiring tomographic information, the numerical calculation processing related to the detection signal is complicated. In addition, this method requires a special laser light source that can stably control the frequency of light over a desired range, so that the type and wavelength of the light source are limited and the light source itself is very expensive. was there.

  The configurations shown in Patent Documents 4 and 6 disclose an OCT method (also referred to as “spectral domain method”) using a spectroscope in the detection system. Similar to the “swept source method”, this method has the advantage that mechanical scanning in the depth direction is not necessary for acquiring tomographic information, but the numerical calculation processing related to the detection signal is complicated. In addition, this method has a drawback that the measurement range in the depth direction is limited by the characteristics of the spectroscope, and the light amount loss of the detection light is unavoidable because the spectroscope is disposed immediately before the detection element. It was.

  The configuration shown in Patent Document 5 or Non-Patent Documents 1 and 2 shows a modified version of the “time domain method”. By using a diffraction grating in the reference optical path, a cross-sectional image in the depth direction (XZ direction) Image) can be directly acquired at high speed. However, in these methods, when a strong scatterer such as a living body is observed, it is difficult to improve the gradation of the signal component having tomographic information due to the presence of strong background light superimposed as a DC component on the detector. there were.

  Patent Document 7 proposes a configuration of a new “time domain method” that can be speeded up. While this method has a characteristic advantage that a cross-sectional image in a direction perpendicular to the optical axis (XY direction) can be obtained at high speed, acquisition of a cross-sectional image in the depth direction (XZ direction) depends on image processing. For this reason, there is a difficulty in that there is a limitation in speeding up the measurement in the Z-axis direction.

  Accordingly, the present invention has been devised to solve the above-described problems, and has a simpler device configuration without using special light source components or complicated calculation methods when compared with the conventional method. Is used to obtain a tomographic image (especially a tomographic image in the depth direction) of an object to be observed (particularly a biological object such as skin or fundus having a strong scattering characteristic) at a high speed, for example, at 30 frames per second or higher. An object of the present invention is to provide a highly practical optical tomographic imaging apparatus that can be observed with gradation and contrast.

The present invention (Claim 1)
The tomographic image information of the target object is acquired by scanning the light beam from the light source and irradiating a predetermined part of the observation target object, and detecting the reflected light from the target object using an optical interference phenomenon. In an optical tomographic imaging device,
A light source that generates a low coherent light beam;
A light splitting member for splitting a light beam from the light source into search light that travels toward a target object and reference light that travels toward a predetermined reference optical path;
Optical scanning means for scanning the light beam of the search light at a predetermined frequency;
Diffractive optical means for generating a predetermined optical delay according to a spatial position in a direction orthogonal to the optical axis direction of the reference optical path with respect to the light beam of the reference light;
Interference light synthesized between the search light that has passed through the target object and the reference light that has passed through the diffractive optical means passes through a predetermined detection aperture with a gap limited in the scanning direction of the optical scanning means. A guiding optical system;
Re-scanning means for scanning the interference light via the optical system at the same scanning frequency as the optical scanning means;
Two-dimensional imaging means for detecting interference light via the rescanning means at a frame rate corresponding to the scanning frequency of the optical scanning means and the rescanning means;
Signal processing means for acquiring reflection intensity information inside the target object from the video signal output from the two-dimensional imaging means.

The present invention (Claim 3)
The tomographic image information of the target object is acquired by scanning the light beam from the light source and irradiating a predetermined part of the observation target object, and detecting the reflected light from the target object using an optical interference phenomenon. In an optical tomographic imaging device,
A light source that generates a low coherent light beam;
A light splitting member for splitting a light beam from the light source into search light that travels toward a target object and reference light that travels toward a predetermined reference optical path;
Optical scanning means for scanning the light beam of the search light at a predetermined frequency;
A light modulation means for periodically phase-shifting the light beam of the reference light at a frequency higher than the scanning frequency of the light scanning means;
Diffractive optical means for generating a predetermined optical delay according to a spatial position in a direction orthogonal to the optical axis direction of the reference optical path with respect to the light beam of the reference light via the light modulation means;
Interference light synthesized between the search light that has passed through the target object and the reference light that has passed through the light modulation means and the diffractive optical means is transmitted in a predetermined direction with a gap limited in the scanning direction of the light scanning means. An optical system guided through the detection aperture;
Re-scanning means for scanning the interference light via the optical system at the same scanning frequency as the optical scanning means;
Two-dimensional imaging means for detecting interference light via the rescanning means at a frame rate corresponding to the scanning frequency of the optical scanning means and the rescanning means;
Signal processing means for extracting interference information detected in accordance with the control of the light modulation means from the video signal output from the two-dimensional imaging means to obtain reflection intensity information inside the target object. Features.

The present invention (Claim 12)
The tomographic image information of the target object is acquired by scanning the light beam from the light source and irradiating a predetermined part of the observation target object, and detecting the reflected light from the target object using an optical interference phenomenon. In an optical tomographic imaging device,
A light source that generates a low coherent light beam;
A light splitting member for splitting a light beam from the light source into search light that travels toward a target object and reference light that travels toward a predetermined reference optical path;
First and second optical scanning means for scanning the light beam of the search light at a predetermined frequency;
A light modulation means for periodically phase-shifting the light beam of the reference light at a frequency higher than the scanning frequency of the light scanning means;
Diffractive optical means for generating a predetermined optical delay according to a spatial position in a direction orthogonal to the optical axis direction of the reference optical path with respect to the light beam of the reference light;
Limiting the gap in the scanning direction of the optical scanning unit for detecting interference light synthesized between the search light through the target object and the reference light through the light modulation unit and the diffractive optical unit A predetermined detection aperture,
Third optical scanning means for scanning the interference light that has passed through the detection aperture at the same scanning frequency as the first and second optical scanning means;
Two-dimensional imaging means for detecting the interference light that has passed through the third optical scanning means at a frame rate corresponding to the scanning frequency of the first, second, and third optical scanning means;
Signal processing means for extracting interference information detected in accordance with the control of the light modulation means from the video signal output from the two-dimensional imaging means to obtain reflection intensity information inside the target object. Features.

  According to the configuration of the present invention, a two-dimensional imaging unit is adopted as a detector, and a low-speed scanning unit and a low-speed rescanning unit corresponding to the frame rate of the imaging unit are used. It can be configured easily and electrical control is easy.

  At the same time, the tomographic image (cross-sectional image in the XZ direction or any arbitrary image related to the Z direction) having the effect of a confocal optical system and a low coherence interferometer, high resolution, low background noise, and high gradation and contrast. It is possible to acquire a cross-sectional image) at a high speed according to the frame rate of the image sensor.

  In particular, the calculation process for removing background light is easy because it is based on subtraction between pixels adjacent in the horizontal direction of the two-dimensional image sensor, and the time difference in exposure between pixels is small. Even a fast-moving target object has little blur and can always observe a tomographic image with high accuracy. By taking advantage of this characteristic and utilizing the Y-direction scanning of the optical scanning means, it is possible to continuously collect cross-sectional images in the optical axis direction (cross-sectional images in the XZ direction), and three-dimensionally inside the target object. It is also possible to acquire accurate image information (3D image).

  Furthermore, in the future, an extremely practical and economical optical tomographic imaging device that can easily upgrade the device if the two-dimensional image sensor is changed to one with higher definition, higher sensitivity, and higher speed is realized. can do.

It is a block diagram of the optical system which showed the Example of the optical tomographic imaging apparatus concerning this invention. It is explanatory drawing for demonstrating the optical principle of this invention. It is explanatory drawing for demonstrating the system of signal processing. It is explanatory drawing for demonstrating the direction etc. of the tomographic image of a to-be-examined eye.

  In the following, the present invention will be described in detail based on embodiments shown in the drawings. In the embodiment shown below, the eyeball of the human eye is illustrated as the observation target object, and an example of an optical system suitable for performing optometry is shown, but the present invention is not limited to this, The present invention can also be applied to biological tissues such as skin and biological samples having strong scattering characteristics as observation objects.

  In FIG. 1, reference numerals 1 and 2 denote high-luminance light emitting diodes (SLDs) that emit partially coherent light, and have low coherence (a small amount of light required for observing a tomographic image). It is a light source having the property of coherence. The center wavelengths are assumed to generate light in different bands of infrared (invisible), for example, 830 nm and 950 nm, respectively. The light beams from the light sources 1 and 2 are collimated by the lenses 3 and 4 and synthesized on the same optical axis via the mirror 5 and the dichroic mirror 6.

  With respect to the light sources 1 and 2, it is possible to combine the two wavelength ranges and use them as a broadband light source, or the wavelength ranges may be properly used as necessary. 1 includes one light source such as an SLD or LD (Laser Diode: semiconductor laser) that emits visible light (for example, red having a wavelength of about 670 nm), which is invisible for measurement. It can also be used as an auxiliary light source for confirming the optical path of a light beam with visible light against infrared rays.

  The light beam that has passed through the mirror 5 and the dichroic mirror 6 is expanded into a light beam of a predetermined size via the lenses 7 and 8 and then enters a beam splitter (light splitting member) 10. At the position of the beam splitter 10, the optical path is divided into four directions: an optical path 9a on the light source side, a reference optical path 9b, a search optical path 9c, and a detection optical path 9d.

  The light beam traveling in the reference optical path 9 b is reflected by the mirror 12 after the light intensity is adjusted by the ND filter 11. The mirror 12 is mounted on a piezoelectric element (piezoelectric vibrator) 13, which finely mirrors the mirror 12 in a direction of 45 degrees (in the direction of the arrow 12a) with respect to the optical axis at a high frequency of, for example, several tens of kHz. It is oscillated to modulate the light beam (periodic phase shift). These reflecting mirrors and the piezoelectric vibrator constitute light modulating means in the reference optical path.

  The light beam reflected by the mirror 12 reaches the reflection type diffractive optical means (diffraction grating) 16 disposed on the end face of the optical path via the lenses 14 and 15, and the diffracted light generated there is reflected and returned. Thus, the reference optical path 9b is turned back. The optical path length of the reference optical path 9b needs to be matched so that the distance is equal to the optical path length of the search optical path 9c. For this purpose, the diffraction grating 16 is fixed on the moving stage 17 and is appropriately adjusted as necessary. As will be described later, the diffractive optical means (diffraction grating) 16 generates a predetermined optical delay with respect to the light beam of the reference light in accordance with the spatial position in the direction orthogonal to the optical axis direction of the reference optical path 9b, thereby causing the optical path length. To change. Further, the moving stage 17 constitutes an optical path length adjusting means for adjusting the optical path length.

  On the other hand, the light beam traveling on the search optical path 9 c is incident on a mirror (galvano mirror) 18 a mounted on the galvanometer 18. The light beam reflected by the galvanometer mirror 18a is reflected by the second galvanometer mirror 19a, and passes through the two galvanometer mirrors 18a or 19a in a direction orthogonal to the optical axis in a one-dimensional manner. A scan can be performed. For example, if one of the two galvanometer mirrors 18a and 19a is fixed and scanning is performed with only one, scanning in the X-axis direction or the Y-axis direction in the direction perpendicular to the optical axis (Z-axis) is possible. Alternatively, if the two galvanometer mirrors 18a and 19a are operated at the same frequency and the type, amplitude, phase, etc. of the driving waveforms are appropriately set, any line-shaped scan in the XY plane direction, Or scanning in a circle or the like becomes possible. The scanning by these galvanometer mirrors 18a and 19a is performed at the same scanning frequency as that of a normal TV camera, for example, 30 Hz (or 60 Hz, etc.). The galvanometer mirrors 18a and 19a constitute first and second optical scanning means for scanning the light beam of the search light at a predetermined frequency, respectively.

  The light beams scanned by the galvanometer mirrors 18a and 19a enter the eye 23 (the anterior eye 23a or the fundus 23b) of the object to be observed after passing through the lenses 20, 21, and 22. Here, the lenses 20 and 21 constitute a focusing optical system that can be adjusted according to the diopter (myopia, hyperopia, etc.) of the eye to be examined, 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 20 and 21 can be adjusted in the optical axis direction according to the operation of a predetermined mechanism (not shown). In addition, the lenses 20 and 21 and the lens 22 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 23 is converged in a dot shape at a predetermined position on the fundus 23b, for example, to be in a focused state. This point-focused light beam can scan the fundus 23b of the eye to be examined in a line shape or a circle shape by the action of the galvanometer mirrors 18a and 19a (light scanning means).

  The reflected light from the fundus 23b of the eye 23 to be inspected travels backward through the optical system described above, that is, reaches the beam splitter (BS) 10 via the lenses 22, 21, 20 and the galvanometer mirrors 19a, 18a. The reflected light from the eye to be inspected that travels backward through the search optical path 9c and passes through the beam splitter 10 is combined with the reference light returning from the reference optical path 9b, and interference light is generated in the detection optical path 9d. This interference light passes through the detection aperture (pinhole) 25 via the lens 24 as detection light, and further enters the galvanometer mirror 28a attached to the galvanometer 28 via the lens 26 and the cylindrical lens 27 and is reflected. The The galvanometer mirror 28a constitutes a rescanning unit (third optical scanning unit) that scans the interference light at the same scanning frequency as the galvanomirrors 18a and 19a (optical scanning unit), and the detection is performed via the galvanomirror 28a. The light is projected onto the imaging surface of a two-dimensional imaging element (two-dimensional imaging means such as a CCD camera) 30 by the lens 29.

  In this optical system, the pinhole 25 has a predetermined pinhole-shaped detection opening whose gap is limited in the scanning direction of the optical scanning means, and is detected by eliminating noise caused by unnecessary stray light and scattered light. It plays the effective role of improving the gradation of the signal component with respect to the video signal from the image sensor by improving the SN (signal-to-noise characteristics) of the interference signal and reducing the background light quantity level. . The pinhole 25 may be a minute 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.

  The galvano mirror 28a rescans the light beam that has passed through the pinhole 25 in a one-dimensional manner, and the cylindrical lens 27 extends the light beam in a direction orthogonal to the scanning direction by the galvano mirror 28a. The two-dimensional imaging of the detection light is enabled on the light receiving surface (imaging surface). In other words, the image of the pinhole 25 is formed by being stretched in the vertical direction (Y-axis direction) on the imaging surface of the imaging element 30 by the action of the lens 26, the cylindrical lens 27, and the lens 29. At the same time, the addition of a galvano mirror 28a (rescanning means) in the middle of the optical path causes a point image to be transferred in the lateral direction (X-axis direction) on the imaging surface of the imaging device 30, resulting in a pinhole. The detection light via 25 is imaged two-dimensionally.

  An output signal from the two-dimensional imaging device 30 is sent to a subsequent signal processing circuit (signal processing means) 31 to perform various signal processing relating to the video signal. The signal processing circuit 31 includes a plurality of electronic components for performing signal processing using both analog and digital techniques, such as a logarithmic amplifier circuit, a filter circuit, a delay circuit, a subtraction circuit, an A / D converter, and various digital signal processing circuits. As will be described later, a calculation process between adjacent pixels is performed on the video signal output from the image sensor 30 to remove a DC component from the video signal, and reflection intensity information inside the target object is included. To get. The output signal processed and generated by the signal processing circuit 31 is sent to a computer (Personal Computer: PC) 32.

  The PC 32 controls the overall operation of the optical system (particularly, the three galvanometers 18, 19, 28, etc.) and converts the video signal obtained through the two-dimensional image sensor 30 and the signal processing circuit 31 to a liquid crystal television monitor or the like. While outputting to the display apparatus 33 and displaying it, the control etc. which are transferred and memorize | stored in the memory | storage device 34 can be performed as needed.

  FIG. 2 is a schematic diagram for explaining that in the optical system configuration of FIG. 1, cross-sectional information in the depth direction of the observation target object (the fundus 23 b of the eye 23 to be examined) can be directly detected by the image sensor 30. It is. In FIG. 2, elements equivalent to those in FIG. 1 are denoted by common reference numerals, and portions that are not necessary for the description are drawn with the optical system partially omitted.

  The light beam from the tomographic image light source (SLD) 1 or 2 is incident on the beam splitter 10 via the lenses 3, 4, the mirror 5, the dichroic mirror 6, and the like. The light beam from the light source is split in two directions by the beam splitter 10, but in FIG. 2, the direction of the optical path is depicted differently from FIG. That is, at the position of the beam splitter 10, the relationship between the light path 9a on the light source side and the reference light path 9b and the relationship between the search light path 9c and the detection light path 9d are drawn in the straight direction in FIG. In FIG. 2, it is drawn in a perpendicular direction for convenience.

  The light beam from the light source that has traveled along the reference optical path 9b is diffracted by the reflective diffraction grating 16 disposed obliquely at the end of the reference optical path. The diffraction grating (blazed diffraction grating) 16 is set so that the angle of inclination with respect to the optical axis is in a Littrow arrangement, and the predetermined diffracted light from the diffraction grating with respect to the incident light is turned back in the reference optical path. . (See Non-Patent Documents 1 and 2 for the Littrow arrangement of the diffraction grating.)

  On the other hand, the light beam traveling on the search optical path 9c is scanned through the galvanometer mirror 19a and the like, and enters the eye 23 (the anterior eye 23a or the fundus 23b) through the lenses 20, 21, and 22. Reflected light from a predetermined part of the eye to be examined, for example, the fundus 23b, travels backward through the optical path 9c described above, is combined with the reference light via the reference optical path 9b in the beam splitter 10, and is guided to the detection optical path 9d. The interference light generated there passes through the detection aperture (pinhole) 25 via the lens 24. The detection aperture 25 has the effect of removing unnecessary optical noise and improving the SN of the interference signal, and improving the contrast and gradation of the signal.

  The interference light (detection light) that has passed through the detection aperture is guided through a lens 26 and a cylindrical lens 27 to a galvanometer mirror 28 a attached to the galvanometer 28. The detection light scanned by the galvanometer mirror 28 a (rescanning means) forms an image on the imaging surface of the imaging device 30 via the lens 29.

  Note that in FIG. 2, for convenience, the optical path passing through the galvano mirror 28 a is drawn linearly. The detection light that has passed through the pinhole 25 once converges in the Y-axis direction perpendicular to the optical axis (Z-axis) in FIG. 2 by the action of the cylindrical lens 27, and then extends at the position of the image sensor 30. So as to be optically designed. That is, the detection light that has passed through the pinhole 25 is stretched and captured in the vertical direction on the imaging surface of the imaging device 30.

  In FIG. 2, when the optical path from the diffraction grating 16 to the image sensor 30 is overviewed, the light rays (35a, 36a) that are diffracted and returned at the upper part of the diffraction grating 16 are captured corresponding to the upper side of the image pickup surface of the image sensor 30; On the other hand, light rays (35b, 36b) that are diffracted and returned by the lower part of the diffraction grating 16 are captured corresponding to the lower side of the imaging surface of the imaging element 30.

  On the other hand, the light beam reflected and returned from the illumination point of the object to be observed (the fundus 23 b of the eye 23 to be examined) passes through the pinhole 25 and then acts from the upper side of the imaging surface of the imaging device 30 by the action of the cylindrical lens 27. It is captured by spreading uniformly in the vertical direction to the lower side. As a result, the reflected light from the shallow part of the fundus interferes with the reference light (corresponding to 35a and 36a) from the upper part of the diffraction grating, and forms interference fringes on the upper part of the imaging surface. On the other hand, the reflected light from the deep part of the fundus interferes with the reference light (corresponding to 35b and 36b) from the lower part of the diffraction grating to form interference fringes at the lower part of the imaging surface.

  Since the diffraction grating 16 is optically arranged obliquely, the optical delay of the reference light is continuously generated within a predetermined range corresponding to the blazed angle and optical setting of the diffraction grating 16. . Thereby, information in the depth direction (Z-axis direction) of the fundus 23b can be directly transferred and captured as interference fringe information in the vertical direction (Y-axis direction) of the imaging surface of the imaging element 30.

  In the optical system as shown in FIG. 2, the diffraction grating 16 is arranged in the reference optical path as an optical component in which the light loss is the largest. On the other hand, in the optical path between the observation target object (eye to be inspected) 23 and the image sensor 30, there are few optical components that cause light loss, so that the efficiency of the detection system is high and the SN of the detection signal is advantageous. There is a feature.

  FIG. 3 is a schematic diagram for explaining the principle when the video signal obtained from the two-dimensional image sensor 30 is processed through the signal processing circuit 31 in the configuration of FIGS. 1 and 2.

  In FIG. 3A, the horizontal axis (X axis) corresponds to the horizontal direction of the imaging surface of the two-dimensional image sensor 30, and the vertical axis (Y axis) corresponds to the vertical direction of the imaging surface. On the imaging surface of the imaging device 30, a stretched image 37 by a pinhole cylindrical lens is reflected in a dark background 38 by a function of the optical system described above at a predetermined moment. This longitudinally stretched image 37 is cyclic in the X-axis direction (the direction of the arrow 37a) in FIG. 3 (a) over time according to the scanning of the rescanning means (galvano mirror 28a in FIGS. 1 and 2). Will be moved to.

  On the other hand, the light beam in the reference optical path is subjected to fine vibration (periodic phase shift) in the optical axis direction by the action of the light modulation means (mirror 12 and piezoelectric element 13 in FIG. 1). ) Is schematically depicted as a vibration waveform 39. In FIG. 3B, the scanning period of the rescanning means (galvanomirror 28a) is schematically drawn as a waveform 40. As shown in this figure, the fine vibration 39 by the light modulation means is generated by the galvanomirror. It is controlled at a higher frequency than the scanning frequency (waveform 40, corresponding to the frame rate of the image sensor). As one embodiment, if the image pickup device 30 picks up images at 60 frames per second, the scanning frequency of the rescanning means 28a (at the same time, the optical scanning means 18a or 19a) is 60 Hz. Is set to about 30 kHz to 50 kHz, for example. This modulation frequency can be easily realized by controlling the piezoelectric element 13.

  According to the OCT interference optical system, the optical path lengths of the reference optical path and the search optical path coincide with each other, and the reflection component from the inside of the target object (fundus, etc.) (that is, the reflection component from the boundary surface with different reflectivity). When there is, a predetermined pattern of interference fringes is detected from the image sensor. An example of a detected waveform obtained by performing various signal processing on the detected interference fringe signal is schematically shown as a waveform 41 in FIG. Since the reference light undergoes phase modulation by the fine vibration 39 of the light modulation means, the detection waveform (interference signal) 41 is an AC signal having the same frequency as the phase modulation. The detection waveform 41 is further processed, and then converted into a signal component indicating reflection intensity information inside the target object.

  In general, when a highly diffusive object such as a human biological tissue or biological sample is observed by OCT, the contrast of the detected interference fringes is low due to the influence of the direct current component (DC component) superimposed as background light, The signal component (AC component) of the tomographic image is often orders of magnitude smaller than the DC component. The influence of the DC component can be removed by performing an operation between adjacent pixels on the video signal from the two-dimensional image sensor 30. That is, if subtraction is performed between pixels adjacent in the horizontal direction (X-axis direction), unnecessary DC components are removed, and reflection intensity information from the inside of the target object is extracted as AC components.

  The above concept will be described below using simple mathematical expressions that are easier to understand. For example, in the two-dimensional image sensor 30, interference fringe signals detected by pixels adjacent to the horizontal direction (three pixels as an example) can be simply described as follows.

I _n-1 = I _D + I _A (−sin α)
_{I n = I D + I A} (cosα)
I _{n + 1} = I _D + I _A (sin α)
Here, I _n−1 , I _n , and I _{n + 1} are signal intensities at adjacent pixels, I _D is a DC component, I _A is an AC component (signal component of a tomographic image), and α is a phase of interference fringes. . In the above formula, it is assumed that the phase difference of interference fringes between adjacent pixels is 90 degrees with each other, and such a condition is that the drive frequency and amplitude of the light modulation means are controlled by the optical scanning means. It can be realized by setting appropriately according to the.

In the actual measuring system, _typically, I _D »I _A, ie DC component, because it is often far greater than the signal component to Find, as an example, performs the following calculation.

(I _n −I _n−1 ) ² = I _A ² (1 + ² cos α × sin α)
^{_{(I n + 1 - I n}} ) 2 = I A 2 (1-2cosα × sinα)
Therefore,
(I _n −I _n−1 ) ² + (I _{n + 1} −In _n ) ² = 2I _A ²
That is, by performing subtraction between adjacent pixels, unnecessary DC components can be reliably removed. Further, if simple calculations including addition / subtraction and multiplication are performed on the detection signals of three adjacent pixels, the accompanying DC component can be obtained. The phase term to be eliminated can also be eliminated. By such arithmetic processing, a necessary AC component (signal component) can be easily extracted.

  Practically, the operations including the subtraction between the pixels in the horizontal direction described above can be executed easily and quickly by an analog delay circuit and subtraction circuit, etc., and with high accuracy without depending on digital gradation. It is. After such analog processing, it is possible to execute more complicated operations with further consideration of noise reduction and image quality improvement through an A / D conversion circuit and a digital operation circuit, which is relatively easy. The reflection intensity information inside the target object can be extracted.

  Further, according to the method of the present invention, as the optical principle, since the difference in exposure time between adjacent pixels is extremely small, it is assumed that the target object is a living body (such as the fundus of the eye to be examined) with movement. However, it is possible to obtain a high-accuracy image with little blur at the time of imaging and excellent in resolving power, gradation, and contrast.

  FIG. 4 is an explanatory diagram when a human eyeball is assumed as the observation target object, and FIG. 4A shows a coordinate system that can be assumed for the eyeball. As shown in FIG. 4A, in the human eye measurement system, the XY image 42 in a direction orthogonal to the optical axis (eyeball axis) of the eye 23 to be examined and the optical axis of the eye to be examined are shown. A directional X-Z image 43 (or a Y-Z image not shown in FIG. 4A) is conceivable. In the optical system of the present invention, the video signal obtained via the image sensor 30 and the signal processing circuit 31 is an XZ image (or other cross section including a coordinate system of the Z axis) in which a cross section in the optical axis direction is detected. Information). Therefore, if a plurality of these X-Z images 43 are sampled in the Y-axis direction in accordance with the scanning of the optical scanning means (19a in FIG. 1) as shown in FIG. 4B, It is possible to collect three-dimensional information inside the eye to be examined.

  FIG. 4 (c) is an exemplary diagram showing that, for example, cross-sectional information (XZ image) of the fundus, for example, inside the eye to be examined is collected at high speed and displayed in real time on the monitor screen of the display device 33. . In FIG. 4D, various image processing by software is performed on the image data collected in the manner shown in FIG. 4B by the PC 32 (see FIG. 1), and the three-dimensional structural information of the fundus is displayed. However, FIG. Such a cross-sectional image of the fundus is one of the important applications in clinical medicine of OCT and is effectively used for precise diagnosis of various ophthalmic diseases such as retinal degeneration and retinal detachment and surgical planning. be able to.

1, 2 Light source 10 Beam splitter 13 Piezoelectric element 16 Diffraction grating 18a, 19a Scanning means (galvano mirror)
23 Object to be observed (eye to be examined)
25 Detection aperture (pinhole)
27 Cylindrical lens 28a Re-scanning means (galvano mirror)
30 Two-dimensional image sensor 33 Display device

Claims (18)

The tomographic image information of the target object is acquired by scanning the light beam from the light source and irradiating a predetermined part of the observation target object, and detecting the reflected light from the target object using an optical interference phenomenon. In an optical tomographic imaging device,
A light source that generates a low coherent light beam;
A light splitting member for splitting a light beam from the light source into search light that travels toward a target object and reference light that travels toward a predetermined reference optical path;
Optical scanning means for scanning the light beam of the search light at a predetermined frequency;
Diffractive optical means for generating a predetermined optical delay according to a spatial position in a direction orthogonal to the optical axis direction of the reference optical path with respect to the light beam of the reference light;
Interference light synthesized between the search light that has passed through the target object and the reference light that has passed through the diffractive optical means passes through a predetermined detection aperture with a gap limited in the scanning direction of the optical scanning means. A guiding optical system;
Re-scanning means for scanning the interference light via the optical system at the same scanning frequency as the optical scanning means;
Two-dimensional imaging means for detecting interference light via the rescanning means at a frame rate corresponding to the scanning frequency of the optical scanning means and the rescanning means;
Signal processing means for obtaining reflection intensity information inside the target object from the video signal output from the two-dimensional imaging means;
An optical tomographic imaging apparatus comprising:   The signal processing means removes a direct current component from the video signal by arithmetic processing between adjacent pixels of the video signal output from the two-dimensional imaging means, and acquires reflection intensity information inside the target object. The optical tomographic imaging apparatus according to claim 1. The tomographic image information of the target object is acquired by scanning the light beam from the light source and irradiating a predetermined part of the observation target object, and detecting the reflected light from the target object using an optical interference phenomenon. In an optical tomographic imaging device,
A light source that generates a low coherent light beam;
A light splitting member for splitting a light beam from the light source into search light that travels toward a target object and reference light that travels toward a predetermined reference optical path;
Optical scanning means for scanning the light beam of the search light at a predetermined frequency;
A light modulation means for periodically phase-shifting the light beam of the reference light at a frequency higher than the scanning frequency of the light scanning means;
Diffractive optical means for generating a predetermined optical delay according to a spatial position in a direction orthogonal to the optical axis direction of the reference optical path with respect to the light beam of the reference light via the light modulation means;
Interference light synthesized between the search light that has passed through the target object and the reference light that has passed through the light modulation means and the diffractive optical means is transmitted in a predetermined direction with a gap limited in the scanning direction of the light scanning means. An optical system guided through the detection aperture;
Re-scanning means for scanning the interference light via the optical system at the same scanning frequency as the optical scanning means;
Two-dimensional imaging means for detecting interference light via the rescanning means at a frame rate corresponding to the scanning frequency of the optical scanning means and the rescanning means;
Signal processing means for extracting interference information detected in accordance with control of the light modulation means from the video signal output from the two-dimensional imaging means to obtain reflection intensity information inside the target object;
An optical tomographic imaging apparatus comprising:   The signal processing means extracts interference information by removing a direct current component from the video signal through arithmetic processing between adjacent pixels of the video signal output from the two-dimensional imaging means, and obtains reflection intensity information inside the target object. The optical tomographic imaging apparatus according to claim 3, wherein the optical tomographic imaging apparatus is obtained.   A focus adjusting means for changing the focal position of the light beam according to the optical characteristics of the target object is added to the optical path of the search light, and the optical path length can be adjusted to the optical path of the reference light 5. The optical tomographic imaging apparatus according to claim 1, further comprising an optical path length adjusting unit.   6. The diffractive optical means is constituted by a reflective diffraction grating disposed obliquely with respect to a direction orthogonal to the optical axis direction of the reference optical path. An optical tomographic imaging apparatus according to 1.   The said light beam illuminates an observation object as a point-like light beam, and the said detection opening is square shape or a pinhole-shaped opening, The any one of Claim 1 to 6 characterized by the above-mentioned. Optical tomographic imaging device.   A cylindrical lens is disposed in the optical system that guides through the detection aperture, and the interference light to be detected is stretched in a direction perpendicular to the light receiving surface of the two-dimensional imaging unit by the action of the cylindrical lens, and then to the imaging unit. The optical tomographic imaging apparatus according to claim 1, wherein the optical tomographic imaging apparatus is guided.   The optical scanning means is constituted by reflection mirrors mounted on two orthogonal galvanometers, and the scanning direction by the scanning means can be scanned in a direction perpendicular to the optical axis direction of the search optical path. The optical tomographic imaging apparatus according to any one of claims 1 to 8.   The rescanning means uses a third galvanometer different from the two sets of galvanometers of the optical scanning means, and the interference light to the two-dimensional imaging means is reflected by a reflection mirror mounted on the third galvanometer. The optical tomographic imaging apparatus according to any one of claims 1 to 9, wherein scanning is performed.   The repetition frequency of the phase shift by the light modulation means is set at least two digits higher than the scanning frequency of the light scanning means and the rescanning means and the frame rate of the two-dimensional imaging means. The optical tomographic imaging apparatus according to any one of 1 to 10. The tomographic image information of the target object is acquired by scanning the light beam from the light source and irradiating a predetermined part of the observation target object, and detecting the reflected light from the target object using an optical interference phenomenon. In an optical tomographic imaging device,
A light source that generates a low coherent light beam;
A light splitting member for splitting a light beam from the light source into search light that travels toward a target object and reference light that travels toward a predetermined reference optical path;
First and second optical scanning means for scanning the light beam of the search light at a predetermined frequency;
A light modulation means for periodically phase-shifting the light beam of the reference light at a frequency higher than the scanning frequency of the light scanning means;
Diffractive optical means for generating a predetermined optical delay according to a spatial position in a direction orthogonal to the optical axis direction of the reference optical path with respect to the light beam of the reference light;
Limiting the gap in the scanning direction of the optical scanning unit for detecting interference light synthesized between the search light through the target object and the reference light through the light modulation unit and the diffractive optical unit A predetermined detection aperture,
Third optical scanning means for scanning the interference light that has passed through the detection aperture at the same scanning frequency as the first and second optical scanning means;
Two-dimensional imaging means for detecting the interference light that has passed through the third optical scanning means at a frame rate corresponding to the scanning frequency of the first, second, and third optical scanning means;
Signal processing means for extracting interference information detected in accordance with control of the light modulation means from the video signal output from the two-dimensional imaging means to obtain reflection intensity information inside the target object;
An optical tomographic imaging apparatus comprising:   The signal processing means extracts interference information by removing a direct current component from the video signal through arithmetic processing between adjacent pixels of the video signal output from the two-dimensional imaging means, and obtains reflection intensity information inside the target object. The optical tomographic imaging apparatus according to claim 12, wherein the optical tomographic imaging apparatus is obtained.   A focus adjusting means for changing the focal position of the light beam according to the optical characteristics of the target object is added to the optical path of the search light, and the optical path length can be adjusted to the optical path of the reference light 14. The optical tomographic imaging apparatus according to claim 12, further comprising an optical path length adjusting unit.   15. The diffractive optical means is constituted by a reflection type diffraction grating disposed obliquely with respect to a direction orthogonal to the optical axis direction of the reference optical path. An optical tomographic imaging apparatus according to 1.   16. The light beam according to claim 12, wherein the light beam illuminates an object to be observed as a point light beam, and the detection aperture is a square-shaped or pinhole-shaped aperture. Optical tomographic imaging device.   A cylindrical lens is disposed in the optical system that guides through the detection aperture, and the interference light to be detected is stretched in a direction perpendicular to the light receiving surface of the two-dimensional imaging unit by the action of the cylindrical lens, and then to the imaging unit. The optical tomographic imaging apparatus according to claim 12, wherein the optical tomographic imaging apparatus is guided.   The repetition frequency of the phase shift by the light modulation means is set at least two digits higher than the scanning frequency of the first, second and third light scanning means and the frame rate of the two-dimensional imaging means. The optical tomographic imaging apparatus according to claim 12, wherein the optical tomographic imaging apparatus is characterized in that

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