JP2007127425A - Correction method in optical tomographic imaging method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a method for correcting the strains of a three-dimensional image due to the movement of matter to be measured using only three-dimensional measuring data, without having to use a complex added systems, such as compensation optics or a motion track. <P>SOLUTION: In this optical tomographic imaging method, based on optical coherence tomography 1 for acquiring a plurality of the two-dimensional tomographic images parallel to the axis in the depth direction of the matter 8 to be measured to constitute a three-dimensional image by using the optical coherence tomography 1, while positionally shifting them in the direction vertical to the two-dimensional tomographic images, the positional shift of a plurality of the respective acquired two-dimensional tomographic images, due to the movement of the matter 8 to be measured is detected using digital correlation and the correction of the positional shift of the two-dimensional tomographic images, is performed on the basis of the detection result. Then, by reconstructing the three-dimensional image, the strains of the three-dimensional image of the optical tomographic image of the optical coherent tomography are corrected, based on the movement of the matter 8 to be measured. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a motion artifact correction method in optical tomography of optical coherence tomography. Here, “motion artifact” is usually used in the technical field of optical coherence tomography as a term meaning “image distortion due to movement of an object to be measured”.

  As one of non-destructive tomographic measurement techniques used in the medical field or the like, there is an optical tomographic imaging method “optical coherence tomography” (OCT) using temporally low coherence light as a probe (probe) (Patent Document 1). reference). Since OCT uses light as a measurement probe, it has the advantage that it can measure the refractive index distribution, spectral information, polarization information (birefringence distribution), etc. of the measured object.

  The basic OCT 43 is based on a Michelson interferometer, and its principle will be described with reference to FIG. The light emitted from the light source 44 is collimated by the collimator lens 45 and then divided into reference light and object light by the beam splitter 46. The object light is condensed on the measurement object 48 by the objective lens 47 in the object arm, scattered and reflected there, and then returns to the objective lens 47 and the beam splitter 46 again.

  On the other hand, the reference light passes through the objective lens 49 in the reference arm, is reflected by the reference mirror 50, and returns to the beam splitter 46 through the objective lens 49 again. The object light and the reference light that have returned to the beam splitter 46 in this way are incident on the condensing lens 51 together with the object light and are collected on the photodetector 52 (photodiode or the like).

  The light source 44 of the OCT uses a light source of light having low temporal coherence (light emitted from the light source at different times is extremely difficult to interfere with each other). In a Michelson interferometer using temporally low coherence light as a light source, an interference signal appears only when the distance between the reference arm and the object arm is approximately equal. As a result, when the intensity of the interference signal is measured by the photodetector 52 while changing the optical path length difference (τ) between the reference arm and the object arm, an interference signal (interferogram) for the optical path length difference is obtained.

  The shape of the interferogram shows the reflectance distribution in the depth direction of the measurement object 48, and the structure in the depth direction of the measurement object 48 can be obtained by one-dimensional axial scanning. Thus, in the OCT 43, the structure in the depth direction of the measurement object 48 can be measured by optical path length scanning.

  In addition to the scanning in the axial direction, a two-dimensional cross-sectional image of the object to be measured can be obtained by performing a two-dimensional scanning by adding a horizontal mechanical scanning. The scanning device that performs the horizontal scanning includes a configuration in which the object to be measured is directly moved, a configuration in which the objective lens is shifted while the object is fixed, and a pupil of the objective lens while the object to be measured and the objective lens are fixed. The structure etc. which rotate the angle of the galvanometer mirror in the surface vicinity are used.

  As a development of the above basic OCT, a wavelength scanning OCT (Swept Source OCT, abbreviated as “SS-OCT” for short) that scans the wavelength of a light source to obtain a spectrum interference signal, and a spectroscope are used. There is a spectral domain OCT for obtaining a spectral signal. The latter includes Fourier domain OCT (Fourier Domain OCT, abbreviated as “FD-OCT”; see Patent Document 2), and polarization-sensitive OCT (Polarization-Sensitive OCT, abbreviated as “PS”. -OCT "(see Patent Document 3).

  The wavelength scanning type OCT obtains a three-dimensional optical tomographic image by changing the wavelength of a light source with a high-speed wavelength scanning laser, rearranging interference signals using a light source scanning signal acquired in synchronization with a spectrum signal, and applying signal processing Is. As a means for changing the wavelength of the light source, a device using a monochromator can be used as the wavelength scanning OCT.

  In the Fourier domain OCT, the wavelength spectrum of the reflected light from the object to be measured is acquired with a spectrometer (spectrum spectrometer), and Fourier transform is performed on this spectrum intensity distribution, so that the real space (OCT signal space) is obtained. This Fourier domain OCT does not need to scan in the depth direction, and can measure the cross-sectional structure of the object to be measured by scanning in the x-axis direction.

Like the Fourier domain OCT, the polarization-sensitive OCT acquires the wavelength spectrum of the reflected light from the object to be measured with a spectrum spectrometer. For example, horizontal linearly polarized light, vertical linearly polarized light, 45 ° linearly polarized light, and circularly polarized light passed through a four-wavelength plate, etc. Only the horizontally polarized component is incident on the spectrum spectrometer to cause interference, and only the component having a specific polarization state of the object light is extracted and subjected to Fourier transform. This polarization sensitive OCT also does not need to scan in the depth direction.
JP 2002-310897 A JP 11-325849 A JP 2004-028970 A

  By the way, in the three-dimensional measurement of the shape of a living body, if the object to be measured moves and the relative positional relationship between the object to be measured and the measuring instrument moves within the measurement time, the image is distorted due to the movement of the object to be measured itself. Has occurred.

  Conventionally, as a means for solving the problem, correction of a measurement position is mainly performed in real time using an adaptive optical system, a motion track (means for sequentially measuring movement), or the like. However, the compensation optical system and the motion track are extremely complicated means, and it is expensive and troublesome to attach these means.

  That is, the conventionally used adaptive optics system uses a variable-shape mirror (the surface shape of the mirror is deformed by computer control etc.) to monitor the reflected image and the like so that its shape and position do not change during measurement. The optical system is changed so as to compensate for the movement of the object to be measured, and a deformable mirror, a liquid crystal optical element, a prism, or the like is used.

  Measured object monitoring measurement system, optical system compensation amount calculation, optical system deformation, post-deformation monitor object measurement, optical system compensation amount calculation, optical system deformation feedback loop The system is complicated and the optical system is expensive. There is no guarantee of stability.

  A motion track is a simplified version of the above-mentioned adaptive optics system that monitors a specific point of the object to be measured and monitors the movement of the object to be measured from its movement, which also requires a separate optical system and processing system. It is.

  The object of the present invention is to solve the above-described conventional problems, and as a means for solving this problem, an object to be measured is used by using only three-dimensional measurement data without using a complicated additional system such as adaptive optics or a motion track. In particular, the initial relative position and distortion between two-dimensional tomographic images composed of a plurality of one-dimensional images measured at the same time can be determined between the images. The means for correcting by the movement of the correlation peak position is realized.

  In order to solve the above problems, the present invention acquires a plurality of two-dimensional tomographic images parallel to the depth direction axis of the object to be measured while shifting the position in the vertical direction with respect to the two-dimensional tomographic image using coherence tomography. In an optical tomographic imaging method using optical coherence tomography constituting a three-dimensional image, a positional shift of each of the plurality of two-dimensional acquired two-dimensional tomographic images caused by movement blur of the measurement object is detected using digital correlation, and the detection is performed. The distortion of the three-dimensional image due to the movement of the object to be measured in the optical tomography method of optical coherence tomography, wherein the positional deviation of the two-dimensional tomographic image is corrected based on the result and the three-dimensional image is reconstructed. A method for correcting the above is provided.

  In the method of correcting the distortion of the three-dimensional image due to the movement of the object to be measured in the optical tomographic imaging method of optical coherence tomography, a histogram of the peak of the digital correlation is taken, and the deviation is larger than the average value and relatively small. A peak having the above may be extracted as an effective correlation peak.

  In the method of correcting the distortion of the three-dimensional image due to the movement of the object to be measured in the optical tomographic imaging method of optical coherence tomography, the effective correlation peak position is complemented with a polynomial, and the zero-order or linear function is used. Image distortion due to movement of the object to be measured may be corrected by mapping.

  In the method of correcting the distortion of the three-dimensional image due to the movement of the object to be measured in the optical tomographic imaging method of the optical coherence tomography, all of the two-dimensional tomographic image, data of a portion with less noise or a portion of interest is obtained. It is also possible to correct distortion of the two-dimensional tomographic image and apply the correction data to all or part of the image of the three-dimensional image to reconstruct the three-dimensional image.

  In the method of correcting the distortion of the three-dimensional image due to the movement of the object to be measured in the optical tomography method of optical coherence tomography, the same movement as the object to be measured is performed, not the correlation of the entire image of the two-dimensional tomographic image. A reference surface may be monitored, and the movement of the object to be measured may be compensated with reference to the position.

  Since the method of the present invention is as described above, the movement of the object to be measured is performed using only the three-dimensional measurement data without using a complicated, expensive, and cumbersome additional system such as adaptive optics and a motion track. It is possible to correct the distortion of the derived image.

  The best mode of the motion artifact correction method in the optical tomographic imaging method of optical coherence tomography according to the present invention will be described below with reference to the drawings based on the embodiments.

  FIG. 1 is a diagram illustrating an overall configuration of the FD-OCT 1. A broadband light source 2, a low coherence interferometer 3, and a spectrometer 4 (spectrometer) are provided. Since the FD-OCT 1 obtains resolution in the depth direction using the principle of low coherence interference, a broadband light source 2 such as an SLD (super luminescent diode) or an ultrashort pulse laser is used as a light source.

  The light emitted from the broadband light source 2 is first split into object light and reference light by the beam splitter 5. Of these, the object light is reflected by the galvanometer mirror 7 through the lens 6 and irradiates the measurement object 8 (biological sample such as the fundus), and is reflected and scattered there and then guided to the spectrometer 4. On the other hand, the reference light is reflected by the reference mirror 10 (plane mirror) through the lens 9 and then guided to the spectroscope 4 in parallel with the object light. These two lights are simultaneously dispersed by the diffraction grating 11 of the spectroscope 4 and interfere in the spectral region. As a result, the spectral interference fringes are measured by the CCD 12.

  By performing appropriate signal processing on the spectral interference fringes, it is possible to obtain a differential of the one-dimensional refractive index distribution in the depth direction at a certain point of the measured object 8, that is, a reflectance distribution. Furthermore, a two-dimensional tomographic image (FD-OCT image) can be obtained by driving the galvanometer mirror 7 and one-dimensionally scanning a measurement point on the measurement object 8.

  In normal OCT, in order to obtain a two-dimensional tomographic image, scanning in the depth (optical axis) direction (this scanning is referred to as “A-scan”, and this direction is also referred to as “A-direction”), and vertical. FD-OCT1 does not require an A-scan, whereas two-dimensional mechanical scanning of a direction operation (this scan is referred to as a “B-scan” and this direction is also referred to as a “B-direction”) is required. Therefore, only one-dimensional mechanical scanning of B-scan is required because the backscattering data in the depth direction can be acquired by one measurement. In short, in FD-OCT1, by performing two-dimensional scanning (B-scan and C-scan) in a plane, high-speed tomographic measurement is possible, and three-dimensional information inside the measurement object 8 can be obtained.

  In the FD-OCT 1 as described above, the present invention acquires the three-dimensional data of the measured object 8 and reconstructs the three-dimensional stereoscopic image in the computer. In order to correct the distortion, a plurality of two-dimensional tomographic images of the measurement object 8 are acquired while shifting the position in the horizontal direction (this scanning is called “C-scan”, and this direction is also called “C-direction”). This is a method that detects and corrects the positional deviation of each two-dimensional slice using digital correlation, and corrects the positional relationship using information of the measurement data itself. This will be described in more detail below.

  In FD-OCT1, as shown in FIG. 2A, a two-dimensional cross-sectional image C1 (en-face image) obtained by B-scan at the first position in the lateral direction is used, and a minute distance from the first position. A two-dimensional cross-sectional image C2 obtained by B-scan at the second position moved laterally by s. Since these two images C1 and C2 are measured at different times, there is a possibility that their relative positions are shifted due to the movement of the measured object 8 (living body) in the A direction. Further, the object to be measured 8 may move in the A direction when scanning in the B direction.

  Since the two images C1 and C2 are different position information in the measurement object 8 (living body), they do not completely coincide with each other, but are very close to each other (a minute distance s). , C2 is expected to have a strong correlation. By utilizing this correlation, the positional information shift due to the movement of the measurement object 8 is corrected by the deformation of the image C2, and the connection to the image C1 makes it possible to connect the three-dimensional information.

  In order to obtain a correlation between the images C1 and C2, as shown in FIG. 2B, the B-scan data in the first B1 of the image C1 is set to B11. As shown in FIG. 2C, the B-scan data in B2 corresponding to the image C2 is B21. These are line data in the A direction (the depth direction of the measured object 8) in B1 and B2, respectively.

  In order to obtain the positional relationship between these two line data, these cross-correlations are taken. Specifically, correlation data can be obtained by taking the product of the complex conjugate data of B11 Fourier transform and B21 Fourier transform, and inverse Fourier transforming the result. This correlation peak represents the amount of lateral deviation between data. This procedure is performed for all the B-scan data of the images C1 and C2, and the peak position is obtained.

(The purpose of taking an effective correlation)
Since the biological data in the case of the object to be measured 8 contains a large amount of noise, a large number of correlation peak ghosts may appear. In living body measurement, there is a lot of noise, and it seems that there is a part where the structure changes rapidly. Therefore, the detected peak does not necessarily correspond to the movement of the living body. Even if this correction is performed in a place where nothing is shown, there is no point.

  That is, the C-scan image (C1 or C2) includes a tomographic image of the object to be measured, but there are portions where nothing is captured and portions where there is a lot of noise. Even if it is applied to such a part, it is difficult to obtain a correlation peak and an error occurs.

(Means to take effective correlation)
For this reason, as a method of extracting effective correlation peaks, a method of taking a histogram of correlation peak values and making peaks larger than a threshold value (average value) effective. As a method of extracting effective correlation peaks, a method of taking a histogram of correlation peaks and making a peak larger than the average value effective is adopted.

  Specifically, when the correlation between B11 and B21 is taken, the integral is obtained by shifting one data sideways. In the following formula 1, when N is the number of data such as B11 and B21, x is the value of B11 data (image density), and y is the value of B21 data, R (k) is the correlation value (magnitude). )become.

  Here, k is a shift amount and is a “correlation distance”. The value of k at which R is maximized in Equation 1 is the “correlation peak position”, and is the shift amount at which the correlation between B11 and B21 is maximized. When the correlation value is schematically expressed as a function of k, the jagged wavy line shown in FIG. Among the k values, a value that is larger than the threshold and whose correlation peak position (k value) is not far apart is selected.

  Here, the “threshold value” is, for example, an average value in which R in Equation 1 is the correlation peak value of R as a whole. Smaller correlation peaks are considered noise. In short, when the correlation between B11 and B21 is calculated and the correlation peak is detected, “the value of the correlation peak is small” (see FIG. 3B), that is, a specific value (usually an average value is often used). Smaller ones are excluded from the data as noise.

Since the position of the correlation peak indicates the movement of the object to be measured, the movement amount is empirically known (such as within 1 mm / second). Therefore, with respect to the “correlation peak position”, the average represented by the following Equation 2 and the variance represented by the following Equation 3 are calculated. Here, k _i is the “correlation peak position”, i is the B-scan position, and FIG. 3B shows the position of the correlation peak with respect to this B-scan position on the horizontal axis. It is the figure typically shown as a vertical axis | shaft.

The above-mentioned “select the one whose correlation peak position (value of k) is not far apart” means to exclude “the peak position is greatly shifted” as shown in FIG. . Here, “the peak position is greatly deviated” means that k _i satisfying the following formula 4 (coefficient 3 is an example and varies depending on the case), and i is in the B scan direction. Since it is a parameter, k _i is obtained while changing _i , whether or not Expression 4 is satisfied is confirmed, and if it is satisfied, it is excluded as “the peak position is greatly deviated”. In other words, “k _i as shown in Equation 4 below is excluded as the peak position is greatly shifted”.

The “shift amount” shown in FIG. 3B is the amount of movement of the C2 image with the C1 image as 0 (reference). The dotted line in FIG. 3B is the position of the previous image (C1 image). Since the C2 image is shifted laterally or deformed into a parallelogram and connected, the shift amount (correlation peak position) is called a shift amount. The solid line is obtained result of fitting a straight line for valid k _i.

(Means for correcting from correlation peaks)
An effective peak is extracted in this way, and fitting is performed using a polynomial for the position of an effective correlation peak. Since the movement of the living body during measurement is not so large, a median shift or a linear function is effective. Therefore, the relative positional relationship can be maintained if the C2 image is laterally shifted in the A-direction or deformed into a parallelogram with respect to the C1 image.

  This will be described in more detail. Since the movement of the living body is smooth, the position of the correlation peak is approximated by a low-order polynomial (0th order or linear function), and all A-scan images are moved (mapped) by one function. Here, “one function” means that all the BX1 images are moved and deformed (mapped) by the same function regardless of the position. This is because there is a premise that the movement of the object to be measured is smooth within the measurement time.

  That is, in order to connect the C1 image and the C2 image, when the same shift amount is given to BX1 in order to determine the relationship between the B11 image and B21, the C2 image is shifted by the shift amount and connected to the C1 image. In this case, the approximation (fitting) is performed with a zero-order function, and the shift amount between the C1 image and the C2 image fitted with this zero-order function (lateral shift) is referred to as “shift amount” as described above. If they are shifted laterally by the amount of “shift amount”, the motion artifact of the three-dimensional image is corrected.

  In this way, when a C2 image is connected on the basis of the C1 image to create a three-dimensional image, there is movement during B-scan and C-scan, so C2 is moved in the A-scan direction with respect to C1. Need to connect. If there is no movement of the measured object 8 during the B-scan, the connection between the C1 image and the C2 image may be simply shifted laterally (lateral movement), but the measured object is being acquired during the C2 image acquisition, that is, during the B-scan. If there is movement in 8, the C2 image is transformed into a parallelogram and connected to the C1 image. When fitting with a linear function, it becomes a straight line that goes up or down to the right.

  A three-dimensional image can be constructed by stacking the C-scan images corrected as described above. If such correction is not performed, an image wavy in the C-scan direction is obtained.

(Another correction method)
A correction method using a method different from the above will be described below. In this method, it is possible to set a plurality of reference planes by providing a plurality of reference mirrors 10 in OCT. For example, in the case of an eyeball, it is possible to measure an anterior segment (cornea or the like) with one reference plane and measure a retina or the like with a second reference plane.

  These two measurements can be recorded simultaneously on one A-B-scan image (specific C-scan image). If the shape of the cornea is known, a three-dimensional image can be constructed by connecting a plurality of C-scan images based on the shape of the cornea. In this case, motion artifacts of the retina can be corrected.

  In this correction method, instead of the correlation of the whole two-dimensional tomographic image (correlation of the object recorded as an image), the reference surface that moves in the same manner as the object to be measured is monitored, and the object to be measured is based on the position. In the above example, the cornea and retina are integrated in the eyeball, so it is expected to move the same, and the shape of the cornea is known in advance, so its surface is monitored and images included in multiple images In this method, correlation peaks are taken so as to connect smoothly, and the position (or shape) of the cornea is shifted by that position.

  FIG. 4 is a diagram illustrating an overall configuration of PS-FD-OCT13 (polarization-sensitive spectral interference tomography apparatus) according to the second embodiment. As in the first embodiment, a broadband light source 2, a low coherence interferometer 3 (Michelson interferometer), and a spectrometer 4 (spectrometer) are provided. A specific configuration will be described below together with the operation.

  The light emitted from the broadband light source 2 is reduced in power by the optical wedge 14 and then becomes horizontal linearly polarized light (hereinafter referred to as “H”) by the polarizer 15. Then, the polarization state of the incident light is converted into horizontal linearly polarized light (H), vertical linearly polarized light (hereinafter referred to as “V”), 45 ° linearly polarized light (hereinafter referred to as “P”) by the ½ wavelength plate 16 and the ¼ wavelength plate 17. ”) And right-handed circularly polarized light (hereinafter referred to as“ R ”), and selectively adjusts the beam into reference light and light incident on the object to be measured 8 by the beam splitter 5.

  The reference light divided by the beam splitter 5 is adjusted by the reference mirror 10 of the reference light optical system and the two quarter-wave plates 18 and 19 so that the polarization state becomes H, V, P, and R. It is incident again on the splitter 5. On the other hand, the light incident on the measurement object 8 is collected by the lens 6 at one point on the measurement object 8 and reflected to the beam splitter 5 as object light. The beam splitter 5 transmits the incident reference light and reflects the object light by 45 °, and superimposes them.

  The reference light adjusted in such a manner that the polarization state emitted from the beam splitter 5 is superimposed as H, V, P, and R and the object light reflected from the measured object 8 are mirror 20. Then, the polarization state is changed to H through the quarter-wave plate 21 and the half-wave plate 22 and enters the spectroscope 4 including the diffraction grating 11, the lens 23, and the CCD 12.

  In this way, by causing the reference light of specific polarization (reference light in any polarization state of H, V, P, or R) to interfere with the object light, only the specific polarization component of the object light causes spectral interference fringes on the CCD 12. As a result, only the component having the same polarization state as the reference light in the object light can be extracted as a signal. Then, this spectral interference fringe is taken into a computer (not shown), one horizontal line is extracted from one point on the y-axis of the image, and a space is obtained by discrete Fourier transform (DFT: Fast Fourier transform). Compute a general Fourier transform.

  Thereby, a one-dimensional correlation signal between the reference beam and the object beam is obtained. Further, by obtaining a Mueller matrix by combining these signal intensities, polarization information inside the object to be measured 8 can be captured.

  In the second embodiment, as in the first embodiment, in order to correct the distortion of the image resulting from the movement of the measured object 8 itself, the horizontal position of the two-dimensional tomographic image of the measured object 8 is shifted. (This scan is referred to as “C-scan”, and this direction is also referred to as “C-direction.”), And the positional deviation of each two-dimensional slice is detected using digital correlation and corrected. In this method, the positional relationship is corrected using information of the measurement data itself, and the details thereof are exactly the same as those in the first embodiment, and thus the description thereof is omitted.

  FIG. 5 is a diagram illustrating an overall configuration of a wavelength scanning OCT 24 to which the correction method according to the third embodiment of the present invention is applied. The output light emitted from the wavelength scanning light source 25 is sent to the fiber coupler 27 through the fiber 26. In the fiber coupler 27, the output light is divided into object light that is irradiated onto the measurement object 29 through the fiber 28 and reference light that is irradiated onto the fixed reference mirror 31 through the fiber 30.

  The object light is irradiated and reflected on the measurement object 29 through the fiber 28, the lens 32, the scanning mirror 33 and the lens 34 having variable angles, and returns to the fiber coupler 27 through the same route. The reference light is irradiated and reflected on the fixed reference mirror 31 through the fiber 30, the lens 35, and the lens 36, and returns to the fiber coupler 27 through the same route.

  Then, the object light and the reference light are overlapped by the fiber coupler 27 and sent to the optical detector 38 (a point sensor such as a PD (photodiode) is used) through the fiber 37 and detected as a spectrum interference signal. Is taken into the computer 39. Based on the detection output of the photodetector 38, cross-sectional images of the measured object 29 in the depth direction (A direction) and the scanning direction of the scanning mirror (B direction) are formed. A display 40 is connected to the computer 39.

  Here, the wavelength scanning light source 25 is a light source that scans while changing the wavelength with time, that is, a light source having a wavelength-dependent wavelength. This makes it possible to obtain the reflectance distribution in the depth direction of the object 29 to be measured and to obtain the structure in the depth direction without scanning (moving, A-scan) the fixed reference mirror 31. Scanning in the primary direction A two-dimensional tomographic image can be formed simply by performing (B-scan).

  In the third embodiment, as in the first embodiment, in order to correct the distortion of the image resulting from the movement of the measured object 29 itself, the horizontal position of the two-dimensional tomographic image of the measured object 29 is shifted. In this method, a plurality of images are acquired, and the positional deviation of each two-dimensional slice is detected using digital correlation, and correction is performed, and the positional relationship is corrected using information of measurement data itself. The details are the same as those of the first embodiment, and the description thereof is omitted.

  The best mode for carrying out the present invention has been described above based on the embodiments. However, the present invention is not limited to such embodiments, and the technical matters described in the claims are not limited. It goes without saying that there are various embodiments within the scope.

  The correction method of the present invention is simple in configuration without using a complicated additional system such as adaptive optics or a motion track, and corrects the movement of the object to be measured using only three-dimensional measurement data to reduce image distortion. Therefore, it is particularly effective when applied as a correction method for an optical tomographic imaging apparatus in a medical field such as ophthalmology in which an accurate examination cannot be performed when an image is distorted due to movement or shaking of a biological sample such as a fundus examination.

It is a figure which shows the whole structure of FD-OCT to which Example 1 of this invention is applied. FIG. 3 is a schematic explanatory diagram for explaining the principle and operation of the first embodiment. (A) is a diagram schematically showing a correlation value (magnitude) as a function of a correlation distance k, and (b) is a diagram showing a correlation peak position with respect to a B-scan. It is a figure which shows the whole structure of PS-FD-OCT to which Example 2 of this invention is applied. It is a figure which shows the whole structure of SS-OCT to which Example 3 of this invention is applied. It is a figure explaining the conventional OCT.

Explanation of symbols

1 FD-OCT
2 Broadband light source
3 Low coherence interferometer
4 Spectrometer
5 Beam splitter
6, 9, 23, 32, 34, 35, 36 Lens
7 Galvano mirror
8 Object to be measured
10 Reference mirror
11 Diffraction grating
12 CCD
13 PS-FD-OCT
14 Light wedge
15 Polarizer
16, 22 1/2 wavelength plate
17, 18, 19, 21 1/4 wave plate
20 mirror
24 wavelength scanning OCT
25 wavelength scanning light source
26, 28, 37 fiber
27 Fiber coupler
29, 48 Object to be measured
30 fiber
31 Fixed reference mirror
33 Scanning mirror
38 Light detector
39 computers
40 display
43 OCT
44 Light source
45 Collimating lens
46 Beam splitter
47 Objective lens in the object arm
49 Objective lens in the reference arm
50 reference mirror
51 condenser lens
52 (Photodiode etc.) Photodetector

Claims (5)

Using optical coherence tomography, a plurality of two-dimensional tomographic images parallel to the depth axis of the object to be measured are acquired while shifting the position in the vertical direction with respect to the two-dimensional tomographic image to form a three-dimensional image. In optical tomography,
Detecting a positional shift of each of the plurality of two-dimensional tomographic images acquired due to the movement of the measurement object using digital correlation;
Based on the detection result, the displacement of the two-dimensional tomographic image is corrected, and the three-dimensional image is reconstructed, and the three-dimensional image is generated by the movement of the object to be measured in the optical tomography method of optical coherence tomography. To correct distortion.   A histogram of the peak of the digital correlation is taken, and a peak that is larger than the average value and has a relatively small deviation is extracted as an effective correlation peak. A method for correcting distortion of a three-dimensional image due to movement of a measurement object.   In the optical tomographic imaging method of optical coherence tomography, the effective correlation peak position is supplemented with a polynomial, and distortion of the image due to movement of the object to be measured is corrected by mapping with a zero-order or linear function. A method for correcting distortion of a three-dimensional image due to movement of an object to be measured.   The distortion of the two-dimensional tomographic image is corrected using data of the entire two-dimensional tomographic image, a part with less noise or a part of interest, and the correction data is applied to all or a part of the image of the three-dimensional image. A method for correcting distortion of a three-dimensional image due to movement of an object to be measured in an optical tomographic imaging method of optical coherence tomography, which is applied and reconstructs the three-dimensional image.   Optical coherence is characterized by monitoring a reference surface that moves in the same manner as the object to be measured instead of the correlation of the whole image of the two-dimensional tomographic image, and compensating for the movement of the object to be measured based on the position. A method of correcting distortion of a three-dimensional image due to movement of an object to be measured in tomographic optical tomography.

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