JP2008253492A - Tomographic image processing method, apparatus and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correct a tomographic image by accurately detecting the displacement of the center of rotation when the measuring light is rotated for scanning in the optical tomography measurement. <P>SOLUTION: Tomography information r(z) is obtained one after another from a plurality of interference signals IS obtained when a subject S for measurement is irradiated with the measuring light L1 during the rotary scan. A sheath image detecting means 53 detects a sheath image and the depth position Z<SB>S</SB>of the sheath image from each tomography information r(z). Then, the information on the displacement of the position of the center of rotation CP from the reference position of the center of rotation CPref is detected from the depth position Z<SB>S</SB>of a plurality of sheath images, and a tomographic image P with the displacement of each tomography information r(z) corrected based on the information on the displacement of the position of the center of rotation CP is produced. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a tomographic image processing method, apparatus, and program for generating an optical tomographic image by OCT (Optical Coherence Tomography) measurement.

  Conventionally, it has been proposed to use an optical tomographic image acquisition apparatus using OCT measurement when acquiring an optical tomographic image of a living tissue. For example, in addition to acquiring tomographic images of the fundus, anterior eye, and skin, various observations such as observation of the arterial blood vessel wall using an optical probe, observation of the digestive tract that inserts the optical probe from the forceps channel of the endoscope, etc. Applied to the site. In this optical tomographic image acquisition apparatus, after the low-coherent light emitted from the light source is divided into measurement light and reference light, reflected light from the measurement object when the measurement light is irradiated to the measurement object, or backscattering The light and the reference light are combined, and an optical tomographic image is acquired based on the intensity of the interference light between the reflected light and the reference light. Hereinafter, the reflected light and the backscattered light from the measurement object are collectively referred to as reflected light.

  The OCT measurement is roughly divided into two types: TD-OCT (Time domain OCT) measurement and FD (Fourier Domain) -OCT measurement. In TD-OCT (Time domain OCT) measurement, reflected light corresponding to a position in the depth direction of a measurement target (hereinafter referred to as a depth position) is measured by measuring the intensity of interference light while changing the optical path length of the reference light. This is a method for obtaining an intensity distribution.

  On the other hand, the FD (Fourier Domain) -OCT measurement measures the interference light intensity for each spectral component of the light without changing the optical path lengths of the reference light and the signal light, and uses the obtained spectral interference intensity signal as a computer. In this method, the reflected light intensity distribution corresponding to the depth position is obtained by performing frequency analysis represented by Fourier transform. In recent years, it has attracted attention as a technique that enables high-speed measurement by eliminating the need for mechanical scanning existing in TD-OCT. As typical apparatus configurations for performing FD (Fourier Domain) -OCT measurement, there are two types of apparatus, SD-OCT (Spectral Domain OCT) apparatus and SS-OCT (Swept source OCT). 3).

When observing a cross section of a tubular measurement target such as a blood vessel or esophagus by OCT measurement as described above, an optical probe is inserted into the measurement target as shown in Patent Documents 1 and 2, and the measurement light emitted from the optical probe is measured. An annular tomographic image is acquired by irradiating while rotating. Here, the optical probe includes an optical fiber that guides the measurement light to the measurement target, an irradiation optical system that irradiates the measurement target with the measurement light emitted from the optical fiber, and a sheath that covers the optical fiber and the optical system. A gap for smooth rotational movement is formed between the irradiation optical system and the sheath. The optical fiber and the optical system are integrally rotated with respect to the sheath, so that the measurement light is irradiated while rotating and scanning the measurement object.
Japanese Patent No. 3628026 Japanese Patent No. 3104984 JP 2000-262461 A

  Here, in Patent Documents 1 to 3, the rotation center of the optical system of the optical probe and the center of the sheath are set to coincide with each other. However, when the optical probe is inserted into the subject, the optical probe may be distorted according to the internal structure of the subject, and the rotation center of the irradiation optical system may be displaced from the center of the sheath due to the gap between the irradiation optical system and the sheath. is there. At this time, when the tomographic image acquisition region in the measurement target S is shifted and a plurality of tomographic images are acquired over time, the position of the sheath cross-section in the tomographic image fluctuates with time, resulting in blurring of the video. .

  On the other hand, as in Patent Document 3, it is conceivable to detect the position of the sheath image for each scanning line and correct the detected position of the sheath image so as to be positioned at a predetermined position. However, when the position of the sheath image is detected separately for each scanning line as in Patent Document 3, the robustness when an error occurs in the detection of the peak position is low, and the positioning accuracy of the sheath image is lowered and the image quality is deteriorated. There is a problem of doing.

  Accordingly, an object of the present invention is to provide a tomographic image processing method, apparatus, and program capable of accurately detecting a deviation of the rotation center when rotationally scanning measurement light in OCT measurement and correcting a tomographic image. To do.

  The tomographic image processing method of the present invention emits light, divides the emitted light into measurement light and reference light, and enters the divided measurement light into an optical probe having an optical fiber covered with a sheath. Interference light when the reflected light from the measurement object and the reference light are combined when the measurement light guided through the probe passes through the sheath and is irradiated onto the measurement object. Is detected as an interference signal, and a tomographic image processing method for generating a tomographic image using the detected interference signal is detected for each scanning line of the measurement light when the measurement light is irradiated while rotating the measurement target. Acquire a plurality of interference signals, acquire tomographic information at each depth position of the measurement target for each acquired interference signal, and determine the depth position of the sheath image and the sheath image from the tomographic information acquired for each scanning line. Detected and detected for each scan line. The position deviation of the tomographic information is calculated by using the calculated position deviation to calculate the position deviation between the rotation center position when the measurement light is rotationally scanned using the depth position of the sheath image of the sheath image and the preset reference rotation center position. A tomographic image in which the shift is corrected is generated.

  The tomographic image processing apparatus of the present invention emits light, divides the emitted light into measurement light and reference light, and enters the divided measurement light into an optical probe having an optical fiber covered with a sheath. When the measurement light guided through the sheath passes through the sheath and is irradiated onto the measurement target, the reflected light from the measurement target and the reference light are combined, and the interference light when the reflected light and the reference light are combined In a tomographic image processing apparatus that detects as an interference signal and generates a tomographic image using the detected interference signal, a plurality of detection lines that are detected for each scanning line of the measurement light when the measurement light is irradiated while rotating the measurement target Interference signal acquisition means for acquiring the interference signal, tomographic information acquisition means for acquiring tomographic information at each depth position of the measurement object for each interference signal acquired by the interference signal acquisition means, and scanning by the tomographic information acquisition means Per line The sheath image detection means for detecting the sheath image and the depth position of the sheath image from the acquired tomographic information, and when the measurement light is rotated and scanned from the depth positions of the plurality of sheath images detected by the sheath image detection means A positional deviation calculation means for calculating a positional deviation between the rotation center position and a preset reference rotational center position, and a tomographic image in which the positional deviation of each tomographic information is corrected using the positional deviation calculated by the positional deviation calculation means. It is characterized by the image generation means which produces | generates.

  The tomographic image processing program of the present invention emits light, divides the emitted light into measurement light and reference light, and enters the divided measurement light into an optical probe having an optical fiber covered with a sheath. When the measurement light guided through the sheath passes through the sheath and is irradiated onto the measurement target, the reflected light from the measurement target and the reference light are combined, and the interference light when the reflected light and the reference light are combined When detecting as an interference signal and generating a tomographic image using the detected interference signal, a plurality of detection lines are detected for each scanning line of the measurement light when the measurement light is irradiated onto the measurement object while rotating the computer. Acquire an interference signal, acquire tomographic information at each depth position of the measurement target for each acquired interference signal, and detect the depth position of the sheath image and the sheath image from the tomographic information acquired for each scanning line. , Detected for each scan line The position deviation of the tomographic information is calculated by using the calculated position deviation to calculate the position deviation between the rotation center position when the measurement light is rotationally scanned using the depth position of the sheath image of the sheath image and the preset reference rotation center position. Generation of a tomographic image in which the deviation is corrected is executed.

  Here, the reflected light means reflected light and backscattered light from the measurement object.

  Note that the position deviation calculation means is not limited to any method as long as it detects the depth position of the sheath image and the sheath image from the tomographic information acquired for each scanning line, for example, the depth of a plurality of sheath images. Position detection means for detecting the deepest maximum depth position and the shallowest minimum depth position, and the rotation center position and the reference rotation based on the difference between the maximum depth position and the minimum depth position detected by the position detection means A reference rotation center position from a deviation amount detecting means for detecting a deviation amount from the center position, a maximum scanning line position at which the maximum depth position is detected by the position detecting means, and a minimum scanning line position at which the minimum depth position is detected. And a deviation direction detecting means for detecting a deviation direction of the rotation center position from the rotation center.

  Alternatively, the positional deviation calculation means includes Fourier transform means for Fourier transforming the depth positions of the plurality of sheath images with respect to the scanning line, and Fourier transform means for converting the depth positions of the plurality of sheath images with respect to the scanning lines in the Fourier transform. A displacement amount detecting means for detecting a displacement amount between the reference rotation center position and the rotation center position from the value of the maximum point of the absolute value, and depth positions of the plurality of sheath images with respect to the scanning line in the Fourier transform means It may be provided with a deviation direction detecting means for detecting the deviation direction of the rotation center position from the reference rotation center position from the phase of the maximum point of the absolute value when the is subjected to Fourier transform.

  In addition, the image generation unit only needs to generate a tomographic image by acquiring a plurality of corrected tomographic information obtained by correcting the positional deviation of the tomographic information using the calculated positional deviation, and the positional deviation of each tomographic information is corrected. A tomographic image may be generated, or a plurality of tomographic information may be arranged in the rotational scanning direction to generate a tomographic image, and then the tomographic image may be corrected based on the calculated positional deviation. Good.

  The light is periodically emitted while sweeping the wavelength within a predetermined wavelength band, and the tomographic image may be acquired by so-called SS-OCT measurement. The tomographic image may be obtained by so-called SD-OCT measurement.

  According to the tomographic image processing method, apparatus, and program of the present invention, an optical probe having an optical fiber that emits light, divides the emitted light into measurement light and reference light, and covers the divided measurement light with a sheath When the measurement light that is incident on the optical probe and guided through the optical probe passes through the sheath and is irradiated onto the measurement object, the reflected light from the measurement object and the reference light are combined, and the reflected light and the reference light are combined. The tomographic information at each depth position of the measurement target from the plurality of interference signals detected for each scanning line when the measurement target is irradiated with the measurement light while being rotated and scanned. The depth position of the sheath image included in each acquired tomographic information is detected, and the rotation center position when the measurement light is rotationally scanned from the detected depth positions of the plurality of sheath images is set in advance. Reference rotation center position Compared to the case where a sheath image is detected for each tomographic information and the positional deviation is corrected by generating a tomographic image in which the positional deviation of the tomographic information is corrected using the calculated positional deviation. Thus, the robustness with respect to the detection error of the peak position in each scanning line can be improved, the shift of the rotation center when the measurement light is rotated and scanned can be detected with high accuracy, and the tomographic image can be corrected.

  The position deviation calculating means is detected by a position detecting means for detecting a maximum depth position where the depth position of the sheath image is the deepest and a shallowest minimum depth position among the plurality of sheath images, and the position detection means. Deviation amount detection means for detecting the deviation amount between the rotation center position and the reference rotation center position from the difference between the maximum depth position and the minimum depth position, and the maximum scanning line position where the maximum depth position is detected by the position detection means And a deviation direction detecting means for detecting a deviation direction of the rotation center position from the reference rotation center position from the minimum scanning line position where the minimum depth position is detected, and there is an error in detection of the sheath image. Even in this case, it is possible to minimize the influence of the error and improve the detection accuracy of the positional deviation of the rotation center position.

  In addition, the position shift calculation means includes a Fourier transform means for Fourier transforming the depth positions of the plurality of sheath images with respect to the scanning line, and a Fourier transform means for when the depth positions of the plurality of sheath images with respect to the scan line are Fourier transformed. A deviation amount detecting means for detecting a deviation amount between the reference rotation center position and the rotation center position from the value of the absolute maximum point, and when the depth position of a plurality of sheath images with respect to the scanning line is Fourier transformed in the Fourier transform means If there is a deviation direction detecting means for detecting the deviation direction of the rotation center position from the reference rotation center position from the phase of the maximum point of the absolute value, even if there is an error in the detection of the sheath image It is possible to minimize the influence of the error and improve the detection accuracy of the displacement of the rotation center position.

  Embodiments of a tomographic image processing apparatus according to the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic diagram showing a preferred embodiment of an optical tomographic imaging system using the tomographic image processing apparatus of the present invention. The optical tomographic imaging system 1 acquires a tomographic image P to be measured such as a living tissue or a cell in a body cavity by SS-OCT (Spectral Domain OCT) measurement, and a light source unit 310 that emits light L. And the light splitting means 3 for splitting the light L emitted from the light source unit 310 into the measurement light L1 and the reference light L2, and the measurement light L1 split by the light splitting means is reflected at each depth position of the measuring object S. The combined light 4 that combines the reflected light (backscattered light) and the reference light L2, and the interference light L4 between the reflected light L3 combined by the combining means 4 and the reference light L2 is an interference signal IS. And a tomographic image processing apparatus 50 for generating a tomographic image from the interference signal IS detected by the interference signal detecting means 40.

  The light source unit 310 emits the laser light L while sweeping the wavelength at a constant period T within the wavelength band Δλ as shown in FIG. Specifically, the light source unit 310 includes a semiconductor optical amplifier (semiconductor gain medium) 311 and an optical fiber FB10, and the optical fiber FB10 is connected to both ends of the semiconductor optical amplifier 311. The semiconductor optical amplifier 311 has a function of emitting weak emission light to one end side of the optical fiber FB10 by injecting drive current and amplifying light incident from the other end side of the optical fiber FB10. When a driving current is supplied to the semiconductor optical amplifier 311, a pulsed laser beam L is emitted to the optical fiber FB 1 by an optical resonator formed by the semiconductor optical amplifier 311 and the optical fiber FB 10. .

  Further, an optical branching device 312 is coupled to the optical fiber FB10, and a part of the light guided in the optical fiber FB10 is emitted from the optical branching device 312 to the optical fiber FB11 side. Light emitted from the optical fiber FB11 is reflected by a rotating polygon mirror (polygon mirror) 316 via a collimator lens 313, a diffraction grating element 314, and an optical system 315. Then, the reflected light is incident on the optical fiber FB11 again via the optical system 315, the diffraction grating element 314, and the collimator lens 313.

  Here, the rotary polygon mirror 316 rotates in the direction of the arrow R1, and the angle of each reflecting surface changes with respect to the optical axis of the optical system 315. As a result, only light having a specific wavelength out of the light dispersed in the diffraction grating element 314 returns to the optical fiber FB11 again. The wavelength of the light returning to the optical fiber FB11 is determined by the angle between the optical axis of the optical system 315 and the reflecting surface. The light having a specific wavelength incident on the optical fiber FB11 is incident on the optical fiber FB10 from the optical splitter 312. As a result, the laser light L having a specific wavelength is emitted to the optical fiber FB1 side.

  Therefore, when the rotary polygon mirror 316 rotates at a constant speed in the direction of the arrow R1, the wavelength λ of light incident on the optical fiber FB11 again changes with a constant period as time passes. In this way, the light source unit 310 sweeps the wavelength with a constant period T as shown in FIG. 2, and the laser light L is emitted to the optical fiber FB1 side.

  The light splitting means 3 is composed of, for example, a 2 × 2 optical coupler, and splits the light L guided from the light source unit 310 through the optical fiber FB1 into the measurement light L1 and the reference light L2. The light splitting means 3 is optically connected to the two optical fibers FB2 and FB3, respectively, the measuring light L1 is guided by the optical fiber FB2, and the reference light L2 is guided by the optical fiber FB3. The light dividing means 3 in this embodiment also functions as the multiplexing means 4.

  An optical probe 30 is optically connected to the optical fiber FB2, and the measurement light L1 is guided from the optical fiber FB2 to the optical probe 30. FIG. 3 is a schematic diagram showing an example of the tip portion of the optical probe 30 of FIG. The optical probe 30 is inserted into a body cavity from a forceps port through a forceps channel, for example, and is detachably attached to the optical fiber FB2 by an optical connector 30A. A sheath 31, an optical fiber FB20, an optical lens 32, and the like are included. The sheath 31 is made of a cylindrical member having flexibility, and is made of a material that transmits the measurement light L1 and the reflected light L3. The sheath 31 has a structure in which the tip is closed by a cap.

  The optical fiber FB20 guides the measuring light L1 to the measuring object S and guides the reflected light (backscattered light) L3 from the measuring object S when the measuring light L1 is irradiated to the measuring object S to the optical fiber FB2. And is accommodated in the sheath 31. The optical fiber FB20 is rotated in the direction of the arrow θ with respect to the sheath 31 by the optical connector 30A.

  The optical lens 32 condenses the measurement light L1 emitted from the optical fiber FB20 onto the measurement target S, collects the reflected light L3 from the measurement target S, and enters the optical fiber FB20. The optical lens 32 is fixed to the light emitting end of the optical fiber FB20, and when the optical fiber FB20 rotates in the arrow θ direction, the optical lens 32 also rotates integrally in the arrow R1 direction. Therefore, the optical probe 30 irradiates the measuring object S with the measuring light L1 emitted from the optical lens 32 while scanning in the arrow θ direction.

  On the other hand, the optical path length adjusting means 20 is disposed on the reference light L2 exit side of the optical fiber FB3 in FIG. The optical path length adjusting unit 20 changes the optical path length of the reference light L2 in order to adjust the measurement start position with respect to the measurement target S, and includes a collimator lens 21 and a reflection mirror 22. Then, the reference light L2 emitted from the optical fiber FB3 passes through the collimator lens 21, is reflected by the reflection mirror 22, and enters the optical fiber FB3 again through the collimator lens 21.

  Here, the reflection mirror 22 is disposed on the movable stage 23, and the movable stage 23 is provided so as to be movable in the direction of arrow A by the mirror driving means 24. When the movable stage 23 moves in the arrow A direction, the optical path length of the reference light L2 is changed.

  The combining means 4 is composed of a 2 × 2 optical coupler, and combines the reference light L2 whose optical path length has been changed by the optical path length adjusting means 20 and the reflected light L3 from the measuring object S and bisects it. The optical fiber FB1 and the optical fiber FB4 are emitted to the interference signal detecting means 40 side.

  The interference signal detection means 40 is composed of, for example, a photodiode or the like, and detects the interference light L4 between the reflected light L3 and the reference light L2 combined by the multiplexing means 4 and outputs it as an interference signal IS. The apparatus of this example has a mechanism for performing balance detection by guiding the interference light L4 obtained by dividing the interference light L4 into two by the multiplexing means 4 (optical fiber coupler) 4 to the photodetectors 40a and 40b, respectively.

  Next, an operation example of the above-described optical tomographic imaging system 1 will be described. First, when the movable stage 23 moves in the direction of arrow A, the optical path length is adjusted so that the measuring object S is positioned in the measurable region. Thereafter, the light L is emitted from the light source unit 310, and the light L is split into the measurement light L1 and the reference light L2 by the light splitting means 3. The measurement light L1 is guided into the body cavity by the optical probe 30 and irradiated to the measurement object S. Then, the reflected light L3 from the measuring object S is combined with the reference light L2 reflected by the reflecting mirror 22 by the combining means 4, and the interference light L4 between the reflected light L3 and the reference light L2 is detected as an interference signal IS as an interference signal IS. Detected by means 40.

  Then, by rotating the optical fiber in the optical probe 30 in the direction of the arrow θ, the measurement light L1 is scanned in the direction of the arrow θ with respect to the measurement target S. Then, information on the depth direction of the measurement object S (the optical axis direction z of the measurement light L1) is obtained at each portion along the scanning direction θ. Therefore, in the tomographic image processing apparatus 50, the tomographic image P is acquired from the plurality of interference signals IS. Note that the measurement light S1 is scanned with respect to the measurement object S in a second direction (longitudinal direction of the optical probe 30) perpendicular to the scanning direction, so that the tomographic plane including the second direction is measured. It is also possible to acquire a tomographic image P.

  FIG. 4 is a block diagram showing a preferred embodiment of the tomographic image processing apparatus of the present invention. The tomographic image processing apparatus 50 will be described with reference to FIG. The configuration of the tomographic image processing apparatus 50 as shown in FIG. 4 is realized by executing a tomographic image processing program read into the auxiliary storage device on a computer (for example, a personal computer). At this time, the tomographic image processing program is stored in an information storage medium such as a CD-ROM or distributed via a network such as the Internet and installed in a computer.

  The tomographic image processing apparatus 50 includes an interference signal acquisition unit 51, a tomographic information acquisition unit 52, a sheath image detection unit 53, a positional deviation calculation unit 54, an image generation unit 55, and an image output unit 56. The interference signal acquisition means 51 acquires the interference signal IS detected by the interference signal detection means 40. Since the interference signal IS is detected in the interference signal detection means 40 under the influence of the spectral intensity of the light, the interference signal acquisition means 51 removes the influence of the spectral shape of the light L as preprocessing. It may be. Further, the interference signal IS is acquired as the interference intensity with respect to the time axis (wavelength axis). On the other hand, the tomographic information acquisition means 52 described later requires an interference signal IS that is equally spaced along the wavenumber k-axis. Therefore, the interference signal acquisition means 51 may measure the time-wavelength sweep characteristic of the light source unit 310 in advance and perform preprocessing for converting the interference signal so as to be equally spaced on the wavenumber k axis. . Details of this signal conversion technique are disclosed in US Pat. No. 5,956,355.

  The tomographic information acquisition unit 52 acquires the tomographic information r (z) at each depth position of the measurement target S from the interference signal IS acquired by the interference signal acquisition unit 51. Here, the tomographic information acquisition means 52 acquires the tomographic information (reflectance) in the depth direction z by using a known spectral analysis technique such as Fourier transform processing, maximum entropy method (MEM), Yule-Walker method, or the like. To do. Further, the tomographic information acquisition unit 52 acquires the tomographic information r (z) for one scanning line each time the interference signal detection unit 40 detects the interference signal IS for one scanning line. That is, the tomographic information acquisition means 52 acquires the tomographic information r (z) obtained from the interference signal IS for one period of wavelength sweep in the light source unit 310 as the tomographic information r (z) for one line. Furthermore, when the measurement light L1 is irradiated while being scanned onto the measurement object S by the optical probe 30, the tomographic information acquisition unit 52 stores a plurality of pieces of tomographic information r (z) acquired sequentially. For example, when the wavelength sweep frequency of the light source unit 310 is 20 kHz and the optical probe 30 scans the measurement light L1 in the arrow θ direction at 20 Hz, as shown in FIG. 5, the tomographic information r for n = 1024 scan lines (Z) is stored.

4 detects the sheath image and the depth position z _s of the sheath image from the plurality of tomographic information r (z) for each scanning line acquired by the tomographic information acquiring unit 52. It is. Specifically, as shown in FIG. 6, when the tomographic information r (z) is acquired from the measurement target S such as a biological tissue, the tomographic information from the inner surface 31a and the outer surface 31b of the sheath 31 is the tomographic information of the measurement target S. It is extremely large compared to. Therefore, the sheath image detection means 53 determines that the one having the maximum value in the tomographic information r (z) for one scanning line is a sheath image, and detects the depth position z _s .

  In addition, although the reflection from the sheath inner surface 31a and the reflection from the sheath outer surface 31b can be obtained as the sheath image, only one of them may be detected as the sheath image, or one of them may be detected as the sheath image. Also good. Alternatively, there may be one peak depending on the resolution, the thickness of the sheath 31, and the like. In this case, one peak may be detected as a sheath image. In addition, the sheath image detection means 53 may detect the sheath image after suppressing fine fluctuations by smoothing the tomographic information before detecting the sheath image.

  4 is set in advance as a rotation center position CP when the measurement light L1 is rotationally scanned from a plurality of sheath images detected for each tomographic information r (z) by the sheath image detection means 53. The positional deviation from the reference rotation center position CPref is detected. For example, as shown in FIG. 7, the reference rotation center position CPref is set at the center of the sheath 31 formed in a substantially circular cross section of the sheath 31, and the rotation center position CP is shifted from the reference rotation center position CPref. Suppose that When the measurement light L1 scans around the reference rotation center position CPref, a tomographic image P with no positional deviation is obtained (see FIG. 5). On the other hand, when the measurement light L1 scans around the rotation center position CP, the sheath image becomes a distorted tomographic image P as shown in FIG.

FIG. 9 is a schematic diagram showing the displacement of the sheath image when the tomographic information r (z) for each scanning line is arranged linearly along the scanning direction θ. When the measurement light L1 scans around the reference rotation center position CPref, the sheath image is substantially linear as shown by the wavy line in FIG. 9, but when the measurement light L1 scans around the rotation center position CP, it is shown in FIG. As shown by the solid line, the sheath image is periodically displaced. Here, when the depth position of the sheath image with respect to the scanning direction θ is r _S (θ), the radius of the sheath inner surface 31a is R, and the displacement amount is d, the following equation (1) is established.

R ² = r _S ² (θ) + d ² −2r _S (θ) d cos θ (1)
Solving Equation (1) for the sheath image r _S (θ) yields Equation (2) below.

r _S (θ) = d cos θ + ((d cos θ) ² + R ² −d ² ) ^1/2 (2)
Considering that the radius R of the sheath inner surface 31a is sufficiently larger than the positional deviation amount d, the equation (2) may be approximated as the following equation (3).

r _S (θ) ≈dcos θ + R (3)
Here, when the rotational scanning of the measuring light L1 is performed at a constant speed, the rotational angle θ (t) of the measuring light L1 is θ (t) = αt + β (α is the rotational speed, and β is the direction of displacement. Phase). Therefore, when Expressions (3) and (4) are replaced with a periodic function having the rotation angle θ as a variable and a periodic function having the time t as a variable, the following Expressions (4) and (5) are obtained.

r _S (t) = dcos (αt + β) + ((dcos (αt + β)) ² + R ² −d ² ) ^1/2 (4)
r _S (t) ≈dcos (αt + β) + R (5)
Equation (4), Equation (5) is a sheath image r sheath image r _S in the depth position z = R from the reference rotation center position CPref _(t) is actually observed when misaligned _S ( t). Accordingly, the positional deviation amount of the tomographic information in each scanning line is obtained by subtracting the radius R from the equations (4) and (5). For example, in the equation (5), the positional deviation amount P (t) ≈dcos (αt + β). That is, in the tomographic information r (z) (= r (t)) acquired when the measuring light L1 is irradiated on the measuring object S at time t, the positional deviation amount P (t) ≈dcos (αt + β) Therefore, it is only necessary to perform correction for shifting the position of the tomographic information.

  Here, the positional deviation calculating means 54 has a function of detecting the positional deviation amount d and the phase β indicating the positional deviation direction in the equation (4) or the equation (5). Specifically, as shown in FIG. 4, a position detection unit 54a, a deviation amount detection unit 54b, and a deviation direction detection unit 54c are provided.

As shown in FIG. 10, the position detection unit 54a has a maximum depth position z _{MAX at} which the depth position z of the sheath image r _S (t) is maximum and a minimum depth at which the depth is minimum among the tomographic information of each scanning line. The position z _MIN is detected. The deviation amount detection means 54b is based on the displacement width between the maximum depth position z _MAX and the minimum depth position z _MIN detected by the position detection means 54a, and the deviation amount between the reference rotation center position CPref and the rotation center position CP. d is calculated. That is, the shift amount d can be calculated from the maximum depth position z _{MAX -the} minimum depth position z _MIN = 2d.

Shift direction detecting means 54c, based on the maximum depth position _{z MAX} Maximum scanning line position is detected _{S MAX} and the minimum depth position _{z MIN} is detected scan line position _{S MIN} in the position detection unit 54a, the reference A shift direction of the rotation center position CP from the rotation center position CPref is detected as a phase β. Specifically, the rotation center position CP and the reference rotation center position CPref exist on the straight line L connecting the maximum scanning line position S _MAX and the minimum scanning line position S _MIN , and the angle between the reference line CL and the straight line L. β can be detected as a phase.

  In this manner, the displacement amount detection means 54b and the displacement direction detection means 54c detect the amount and direction of the positional displacement, thereby detecting the parameters d and β in the above equation (4) or (5), and each tomographic information. It is possible to correct the displacement of r (z).

  The image generation unit 55 in FIG. 4 uses the positional deviation (the positional deviation amount d and the phase β) detected by the positional deviation calculation unit 54 to correct the positional deviation of each tomographic information r (z). P is generated. The image generating unit 55 includes a misalignment correcting unit 55a and an imaging unit 55b.

  The positional deviation correction means 55a corrects the positional deviation of each tomographic information r (z) using the deviation amount d and the phase β detected by the positional deviation calculation means 54. The imaging unit 55b generates the tomographic image P as shown in FIG. 5 by arranging the tomographic information corrected by the positional deviation correcting unit 55a along the rotational scanning direction θ. Then, the image output means 56 displays the tomographic image P on the display device 60 of FIG.

  Note that not only when the tomographic image P is generated after the positional deviation is corrected, but also after the imaging unit 55b generates the tomographic image P as shown in FIG. The tomographic image P may be corrected by shifting (translating) the entire tomographic image P based on the positional deviation direction β.

  As described above, the sheath image 31a is not detected for each tomographic information r (z) and the positional deviation is corrected, but rotation is performed from the entire plurality of tomographic information r (z) constituting one tomographic image P. By detecting the position shift of the center position CP and correcting each tomographic information r (z) based on the detected position shift, the robustness with respect to the detection error of the peak position in each line is improved, and the measurement light L1 is used. It is possible to accurately detect a shift of the rotation center when the rotational scanning is performed and correct the tomographic image.

  In addition, when a plurality of tomographic images P are acquired over time by repeating the rotational scanning of the measuring light L1 a plurality of times, the position of the cross section of the sheath 31 in the tomographic image P varies with time, resulting in an image. It is possible to prevent blurring.

  Furthermore, in addition to scanning of the measurement light L1 in the direction of the arrow θ, the measurement light L1 is further scanned in the longitudinal direction of the optical probe 30, and the tomographic image P is acquired along the longitudinal direction of the optical probe 30 to obtain a three-dimensional view. There are cases where a tomographic image is acquired. At this time, even if the rotation center positions are different in each tomographic image P, a plurality of tomographic images P obtained from the same rotation center position CP are obtained by correcting the positional deviation for each tomographic image P. It is possible to achieve consistency between the tomographic images P in the three-dimensional tomographic image.

  In addition, when the positional deviation calculation unit 54 of FIG. 4 detects the positional deviation of the rotation center position CP, the positional deviation amount d and the direction β are statistically detected from a plurality of sheath images acquired from each scanning line. Therefore, even when there is an error in the detection of the sheath image, the influence of the error can be suppressed to the minimum, and the detection accuracy of the positional deviation of the rotation center position CP can be improved.

  FIG. 11 is a flowchart showing a preferred embodiment of the tomographic image processing method of the present invention. The tomographic image processing method will be described with reference to FIGS. First, the interference signal acquisition means 51 acquires the interference signal IS when the measurement probe S is transmitted through the sheath 31 from the optical probe 30 (step ST1). Then, the tomographic information acquisition means 52 sequentially acquires the tomographic information r (z) from the plurality of interference signals IS acquired when the measurement light L1 is irradiated while rotating and scanning the measurement object S (step ST2). .

Next, the sheath image detection means 53 detects a sheath image from each tomographic information r (z) constituting one piece of tomographic image P (step ST3). Thereafter, the positional deviation (deviation amount d and phase β) of the rotational center position CP with respect to the reference rotational center position CPref is detected by the positional deviation calculation means 54 (step ST4). Then, the tomographic image P is generated using the plurality of tomographic information r (z) in which the positional deviation of each tomographic information r (z) is corrected based on the positional deviation information of the rotation center position CP in the image generating unit 55. (Step ST5). Alternatively, after the tomographic image P is generated using a plurality of tomographic information r (z), the positional deviation of each tomographic information r (z) is corrected. The corrected tomographic image P is displayed on the display device 60 (step ST6).
Thereby, the robustness with respect to the detection error of the peak position in each scanning line can be improved as compared with the conventional case where the sheath image is detected for each tomographic information r (z) and the positional deviation is corrected. .

FIG. 12 is a block diagram showing another embodiment of the misregistration calculation means. The misregistration calculation means 154 will be described with reference to FIG. The positional deviation calculation unit 154 includes a Fourier transform unit 154a, a deviation amount detection unit 154b, and a deviation direction detection unit 154c. The Fourier transform unit 154a performs Fourier transform on the depth position r _S (t) of the sheath image of each scanning line. The deviation amount detection means 154b determines the reference rotation center position CPref and the rotation center position CP based on the value of the maximum point of the absolute value when the depth position r _S (t) of the sheath image of each scanning line is Fourier transformed. The shift amount d is detected. On the other hand, the deviation direction detecting means 154c is based on the phase of the maximum point of the absolute value when the depth position r _S (t) of the sheath image of each scanning line is Fourier transformed, and the rotation center position from the reference rotation center position CPref. The direction of CP deviation (phase β) is detected. Even in this case, since the amount of displacement d and the direction β are statistically detected from a plurality of sheath images acquired from each scanning line, even if there is an error in the detection of the sheath image, the error is detected. Thus, the detection accuracy of the displacement of the rotation center position CP can be improved.

In addition to the above-described Fourier transform, for example, the equation (4) in which the depth position of the sheath image of each scanning line actually measured using, for example, the least square method and appropriate initial values d and β are set. Alternatively, the positional deviation amount d and the phase β may be calculated so that the error from the function r _S (t) shown in (5) is minimized.

  According to the above embodiment, the tomographic information r (z) at each depth position z of the measurement target S is acquired from each interference signal IS, and the depth position z of the sheath image included in each acquired tomographic information is obtained. Each is detected, and a positional deviation (deviation d and phase β) between the rotation center position CP and the reference rotation center position CPref when the measurement light L1 is rotationally scanned from the depth positions z of the detected plurality of sheath images is calculated. When the tomographic image P is generated by correcting the positional deviation of the tomographic information r (z) using the calculated positional deviation, the sheath image is detected for each tomographic information r (z) and the positional deviation is corrected. Compared to the above, the robustness with respect to the detection error of the peak position in each scanning line can be improved, and the displacement of the rotation center when the measurement light L1 is rotationally scanned can be detected with high accuracy and the tomographic image can be corrected.

Further, as shown in FIG. 4, the positional deviation calculation means 54 detects the maximum depth position z _MAX where the depth position of the sheath image is the deepest and the shallowest minimum depth position z _MIN among the plurality of sheath images. A deviation amount for detecting a deviation amount between the rotation center position CP and the reference rotation center position CPref from the position detection means 54a and the difference between the maximum depth position z _MAX and the minimum depth position z _MIN detected by the position detection means 54a. The reference rotation center position CPref from the detection means 54b and the maximum scanning line position S _MAX where the maximum depth position z _MAX is detected by the position detection means 54a and the minimum scanning line position S _MIN where the minimum depth position z _MIN is detected. And a deviation direction detecting means 54c for detecting a deviation direction of the rotation center position CP from the rotation center position CP. The influence of the error minimized, thereby improving the detection accuracy of the displacement of the rotation center position CP.

  Further, as shown in FIG. 12, the position deviation calculation unit 154 performs Fourier transform on the depth position of the plurality of sheath images with respect to the scanning line, and Fourier transform unit 154b. Deviation amount detection means 154b for detecting the deviation amount between the reference rotation center position CPref and the rotation center position CP from the value of the maximum absolute value when the depth position is Fourier transformed, and the Fourier transformation means 154a with respect to the scanning line Displacement direction detecting means 154c for detecting the displacement direction of the rotation center position CP from the reference rotation center position CPref from the phase of the maximum point of the absolute value when the depth positions of the plurality of sheath images are Fourier transformed. Therefore, even if there is an error in the detection of the sheath image, the influence of the error is minimized. It is possible to improve the detection accuracy of the displacement of the rotation center position CP.

  The embodiment of the present invention is not limited to the above embodiment. For example, FIG. 1 illustrates the case where the tomographic image processing apparatus 50 is applied to so-called SS-OCT measurement, but the same applies to an optical tomographic imaging system using SD-OCT measurement as shown in FIG. be able to. In FIG. 13, the light source unit 110 emits broadband low-coherence light. In the interference signal detection unit 140, the interference light L4 is incident on the diffraction grating element 42 via the lens 41, and the diffraction grating element After being split for each wavelength band at 42, the light detection unit 44 in which a plurality of light detection elements (photodiodes and the like) are arranged through the lens 43 is detected as an interference signal IS. Even in this case, the robustness with respect to the detection error of the peak position in each scanning line is improved and the measurement light L1 is used compared with the case where the sheath image is detected for each tomographic information r (z) and the positional deviation is corrected. It is possible to accurately detect a shift of the rotation center when the rotational scanning is performed and correct the tomographic image.

  Furthermore, the present invention can be applied to the optical tomographic imaging system for TD-OCT measurement and the above-described tomographic image processing apparatus 50. In this case, when the reflection mirror 22 moves in the direction of arrow A, the tomographic information acquisition unit 53 acquires the tomographic information r (z) at each depth position z.

1 is a schematic configuration diagram showing an example of an optical tomographic imaging system to which a tomographic image processing apparatus of the present invention is applied. The graph which shows a mode that the wavelength of the light inject | emitted from the light source unit of FIG. 3 is swept Schematic diagram showing an example of an optical probe used in the optical tomographic imaging system of FIG. The block diagram which shows preferable embodiment of the tomographic image processing apparatus of this invention The schematic diagram which shows a mode that an interference signal is acquired for every scanning line in the interference signal acquisition means of FIG. The graph which shows an example of the tomographic information for 1 scanning line acquired in the tomographic information acquisition means of FIG. FIG. 3 is a schematic diagram illustrating a state in which the rotation center position of the measurement light L1 is displaced from the reference rotation center position in the optical probe of FIG. FIG. 7 is a schematic diagram showing an example of a tomographic image acquired when the rotation center position is displaced from the reference rotation center position as shown in FIG. FIG. 8 is a schematic diagram showing an example of a tomographic image when the tomographic information acquired for each scanning line in the tomographic image of FIG. 8 is linearly arranged. FIG. 4 is a schematic diagram showing how a misalignment is detected by the misalignment calculating means in FIG. The flowchart which shows preferable embodiment of the tomographic image processing method of this invention. The block diagram which shows another embodiment of the position shift calculation means in the tomographic image processing apparatus of this invention. Schematic diagram illustrating another embodiment of an optical tomographic imaging system

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical tomographic imaging system 30 Optical probe 31 Sheath 40 Interference signal detection means 50 Tomography image processing device 51 Interference signal acquisition means 52 Tomography information acquisition means 53 Sheath image detection means 54 Position shift calculation means 54a Position detection means 54b Deviation amount detection means 54c Deviation direction detection means 55 Image generation means 55a Position deviation correction means 55b Imaging means 56 Image output means 60 Display device 110, 310 Light source unit CP Rotation center position CPref Reference rotation center position d Deviation amount β Phase (deviation direction)
IS interference signal L light L1 measurement light L2 reference light L3 reflected light L4 interference light P tomographic image r (z) tomographic information S measurement object S _MAX maximum scanning line position S _MIN minimum scanning line position

Claims (7)

The light is emitted, the emitted light is divided into measurement light and reference light, and the divided measurement light is incident on an optical probe having the optical fiber covered with a sheath and guided in the optical probe. When the measurement light passes through the sheath and is irradiated on the measurement object, the reflected light from the measurement object and the reference light are combined, and interference when the reflected light and the reference light are combined In a tomographic image processing method for detecting light as an interference signal and generating a tomographic image using the detected interference signal,
Obtaining a plurality of the interference signals detected for each scanning line of the measurement light when the measurement light is irradiated while rotating and scanning the measurement object;
Obtaining tomographic information at each depth position of the measurement object for each acquired interference signal,
Detecting a sheath image and a depth position of the sheath image from the tomographic information acquired for each scanning line;
Calculating a positional deviation between the rotation center position when the measurement light is rotationally scanned using the depth positions of the plurality of sheath images detected for each scanning line and a preset reference rotation center position;
The tomographic image processing method, wherein the tomographic image in which the positional deviation of each piece of tomographic information is corrected is generated using the calculated positional deviation. The light is emitted, the emitted light is divided into measurement light and reference light, and the divided measurement light is incident on an optical probe having the optical fiber covered with a sheath, and is guided in the optical probe. When measurement light passes through the sheath and is irradiated onto the measurement object, the reflected light from the measurement object and the reference light are combined, and interference light when the reflected light and the reference light are combined In a tomographic image processing apparatus for generating a tomographic image using the detected interference signal,
Interference signal acquisition means for acquiring a plurality of interference signals detected for each scanning line of the measurement light when the measurement light is irradiated to the measurement object while being rotationally scanned;
Tomographic information acquisition means for acquiring tomographic information at each depth position of the measurement target for each interference signal acquired by the interference signal acquisition means;
A sheath image detecting means for detecting a sheath image and a depth position of the sheath image from the tomographic information acquired for each scanning line in the tomographic information acquiring means;
A positional deviation calculation for calculating a positional deviation between a rotation center position when the measurement light is rotationally scanned from a depth position of the plurality of sheath images detected by the sheath image detection means and a preset reference rotation center position. Means,
A tomographic image processing apparatus comprising: an image generating unit configured to generate the tomographic image in which the positional shift of each piece of tomographic information is corrected using the positional shift calculated by the positional shift calculating unit. The positional deviation calculating means is
Position detecting means for detecting a maximum depth position and a shallowest minimum depth position where the depth position is the deepest among the plurality of sheath images;
A deviation amount detection means for detecting a deviation amount between the rotation center position and the reference rotation center position from a difference between the maximum depth position and the minimum depth position detected by the position detection means;
A shift direction of the rotation center position from the reference rotation center position is detected from the maximum scanning line position where the maximum depth position is detected and the minimum scanning line position where the minimum depth position is detected by the position detection means. The tomographic image processing apparatus according to claim 2, further comprising: The positional deviation calculating means is
Fourier transform means for Fourier transforming the depth position of the plurality of sheath images with respect to the scanning line;
In the Fourier transform means, a shift amount between the reference rotation center position and the rotation center position is detected from the value of the maximum point of the absolute value when the depth positions of the plurality of sheath images with respect to the scanning line are Fourier transformed. Deviation amount detection means;
In the Fourier transform means, the shift direction of the rotation center position from the reference rotation center position is detected from the phase of the maximum point of the absolute value when the depth position of the plurality of sheath images with respect to the scanning line is Fourier transformed. The tomographic image processing apparatus according to claim 2, further comprising: a deviation direction detecting unit.   The image generation means corrects the positional deviation calculated by the positional deviation calculation means for each tomographic information, and a plurality of tomographic information corrected by the positional deviation correction means in the rotational scanning direction. The tomographic image processing apparatus according to claim 2, further comprising an imaging unit configured to generate the tomographic image by arranging the tomographic images.   The image generation means generates the tomographic image by arranging the plurality of tomographic information in the rotational scanning direction, and the positional deviation amount calculation means converts the tomographic image generated by the imaging means. The tomographic image processing apparatus according to claim 2, further comprising a positional deviation correction unit that corrects based on the calculated positional deviation. The light is emitted, the emitted light is divided into measurement light and reference light, and the divided measurement light is incident on an optical probe having the optical fiber covered with a sheath, and is guided in the optical probe. When measurement light passes through the sheath and is irradiated onto the measurement object, the reflected light from the measurement object and the reference light are combined, and interference light when the reflected light and the reference light are combined In a tomographic image processing program for generating a tomographic image using the detected interference signal,
On the computer,
Obtaining a plurality of the interference signals detected for each scanning line of the measurement light when the measurement light is irradiated while rotating and scanning the measurement object;
Obtaining tomographic information at each depth position of the measurement object for each acquired interference signal,
Detecting a sheath image and a depth position of the sheath image from the tomographic information acquired for each scanning line;
Calculating a positional deviation between the rotation center position when the measurement light is rotationally scanned using the depth positions of the plurality of sheath images detected for each scanning line and a preset reference rotation center position;
A tomographic image processing program for executing generation of the tomographic image in which the positional deviation of each piece of tomographic information is corrected using the calculated positional deviation.

Images