Oct image processing device and oct image processing method

Abstract

The present invention achieves a technique for removing speckle appearing in an OCT image using a small number of OCT-captured images. In an OCT image processing method (S1), at least one processor executes: SCCP processing (S11) for repeatedly calculating a shift conjugate product, which is a product of complex interferogram data of an object under measurement obtained by irradiating the object under measurement with coherent incident light and a complex conjugate image of shifted image data generated by shifting the complex interferogram data in a predetermined direction by a predetermined shift amount, multiple times while varying the shift amount; averaging processing (S12) for averaging real part data of the multiple shift conjugate products; and imaging processing (S13) for imaging and outputting the averaged real part data.

Description

OCT image processing apparatus and OCT image processing method

[0001] The present invention relates to an OCT image processing apparatus and an OCT image processing method.

[0002] OCT (Optical Coherence Tomography) is a bio-imaging technique that uses optical interference and is widely used in ophthalmic clinical diagnosis and cardiovascular clinical practice. In recent years, it has also attracted attention as a three-dimensional microscopy technique in basic medical science, biology, and pharmacy. Although OCT is widely applied clinically, OCT images exhibit high-intensity granular signal patterns called "speckles." As a result, the image contrast of the actual measurement target (mainly biological tissue) is low. Furthermore, the size of the speckle granular pattern is about the same as the optically defined resolution (nominal resolution) of OCT. Therefore, in actual OCT images, it is not possible to measure fine structures of the tissue being measured at the nominal resolution, and the practical resolution deteriorates to about 10 times the nominal resolution. In other words, only structures about 10 times the size of the nominal resolution can be recognized.

[0003] To solve these problems, methods such as averaging multiple images (e.g., Non-Patent Document 1) and deep learning methods are being considered.

[0004] Szkulmowski, Maciej, and Maciej Wojtkowski. "Averaging Techniques for OCT Imaging." Optics Express 21, no. 8(August 22, 2013): 9757-73.

[0005] For example, image averaging techniques involve acquiring multiple images (e.g., several dozen to several hundred) from the same part of the sample being measured and statistically removing speckle by averaging them. This technique is widely used because of its good speckle removal performance. However, this method has the following two problems: (1) Acquiring the multiple images required by this method takes several dozen to several hundred times longer than normal OCT imaging. Therefore, this method can be used for acquiring two-dimensional tomographic images, but not for acquiring three-dimensional tomographic images. (2) Before averaging the numerous images, it is necessary to detect and correct the misalignment between all the images.

[0006] Of the above problems, (1) is particularly critical. For example, a 3D OCT scan without speckle removal can be completed in about 2 seconds. However, to obtain a 3D OCT image with speckles removed using the image averaging method described above, the scan takes about 1 minute. This is a lengthy measurement time that is practically unsuitable for clinical testing. Furthermore, in the measurement of cultured tissues in the fields of basic medicine, biology, and pharmacy, such long measurement times are unacceptable because it is necessary to repeatedly measure many samples.

[0007] One aspect of the present invention aims to realize a technique for removing speckles appearing in OCT images using fewer OCT images.

[0008] To solve the above problems, an OCT image processing method according to one aspect of the present invention includes an SCCP process in which at least one processor repeatedly calculates the shift conjugate product, which is the product of complex interference image data of a measurement target obtained by irradiating the measurement target with coherent incident light and the complex conjugate image of shifted image data generated by shifting the complex interference image data in a predetermined direction by a predetermined shift amount, by changing the shift amount multiple times; an averaging process that averages the real part data of the multiple shift conjugate products; and an imaging process that converts the averaged real part data into an image and outputs it.

[0009] To solve the above problems, an OCT image processing apparatus according to one aspect of the present invention includes: an acquisition unit that acquires complex interference image data of a measurement target obtained by irradiating the measurement target with coherent incident light; an SCCP processing unit that repeats the process of deriving a shift conjugate product, which is the product of the complex interference image data and a complex conjugate image of shifted image data generated by shifting the complex interference image data in a predetermined direction by a predetermined shift amount, multiple times with different shift amounts; an averaging unit that averages the real part data of a plurality of the shift conjugate products; and an imaging unit that converts the averaged real part data into an image and outputs it.

[0010] Each aspect of the present invention may be implemented by a computer, in which case a control program for an OCT image processing device that enables the computer to implement the OCT image processing device by operating the computer as each part (software element) of the OCT image processing device, and a computer-readable recording medium on which the program is recorded, also fall within the scope of the present invention.

[0011] According to one aspect of the present invention, a technique can be realized to remove speckles appearing in OCT images from a small number of OCT images.

[0012] This is a block diagram showing the configuration of the OCT image processing apparatus 1 according to Embodiment 1 of the present invention. This is a flowchart showing the flow of the OCT image processing method S1 according to Embodiment 1 of the present invention. This is a flowchart showing the flow of the OCT image processing method S2 when correcting complex interference image data. This is a schematic diagram illustrating an example of the spatial configuration of complex interference image data and its extraction. This is a schematic diagram showing the steps from acquiring two-dimensional complex interference image data to the image processing step. This is a schematic diagram showing training data for a machine model and the step of training the machine model using that training data. This is a diagram showing the change in speckle of the OCT image depending on the number of SCCP processed data.

[0013] [Embodiment 1] (OCT Image Processing Device 1) Hereinafter, an OCT image processing device 1 according to one embodiment of the present invention will be described in detail with reference to the drawings. The OCT image processing device 1 is a device that performs speckle removal (reduction) processing in images taken using OCT (Optical Coherence Tomography) technology. In other words, the OCT image processing device 1 is not the optical coherence tomography apparatus that generates the OCT image, but a device that reduces speckle in the OCT image taken by the optical coherence tomography apparatus. The OCT image processing device 1 may be provided attached to the optical coherence tomography apparatus, but hereafter it will be described as a device independent of the optical coherence tomography apparatus. Figure 1 is a block diagram showing the configuration of the OCT image processing device 1.

[0014] As shown in Figure 1, the OCT image processing device 1 comprises a control unit 10, a processor 20, a memory 30, and an input / output interface 40. The control unit 10 comprises an acquisition unit 11, an SCCP processing unit 12, an averaging unit 13, and an imaging unit 14.

[0015] The acquisition unit 11 acquires complex interference image data of a measurement target obtained by irradiating the measurement target with coherent incident light. Complex interference image data is interference signal data acquired by an optical coherence tomography (OCT) scanner, and is hereinafter simply referred to as "OCT image data". Coherent incident light is light with aligned phase that is directed towards the measurement target. In an optical coherence tomography scanner, coherent incident light directed towards the measurement target interferes with reflected light reflected from the measurement target, and the interference light is measured by a photosensor, processed as data, and acquired as complex interference image data. The acquisition unit 11 acquires this complex interference image data and records it in the memory 30. The acquisition unit 11 may acquire this complex interference image data from the memory of any optical coherence tomography scanner, or it may acquire complex interference image data that has been pre-recorded in various databases, etc.

[0016] The SCCP processing unit 12 repeatedly calculates the product (shifted-conjugate product) of the complex interference image data and the complex conjugate image of the shifted image data generated by shifting the complex interference image data in a predetermined direction by a predetermined amount, changing the shift amount multiple times. Hereinafter, the "product of the complex interference image data and the complex conjugate image of the shifted image data generated by shifting the complex interference image data in a predetermined direction by a predetermined amount" will simply be referred to as the "shifted-conjugate product". The number of repetitions is arbitrary. SCCP (Shifted-Complex-Conjugate-Product) processing is the process of deriving the shifted-conjugate product. There may be one or several original complex interference image data from which speckles are to be removed, but the following explanation will describe the case where one complex interference image data is used. This complex interference image data is shifted in a predetermined direction by a predetermined shift amount to obtain shifted image data. The predetermined direction and shift amount can be arbitrarily set by the user. Then, the shifted-conjugate product of the original complex interference image data and the complex conjugate image of the shifted image data is derived. This process is repeated multiple times, varying the shift amount. The process can also be repeated by changing the direction of the shift. SCCP processing refers to the operation of taking the complex conjugate product of the complex interference image data, represented by a complex equation consisting of a real and imaginary part, and the complex conjugate image of the shifted image data. The details of the theoretical principles behind this process will be described later.

[0017] The averaging unit 13 performs a process to average the real part data of multiple shift conjugate products. As will be described later, in the absence of aberrations, the element of the real part of the shift conjugate product corresponding to speckle (the part (4-2) in equation (4)) is modulated by shifting. Therefore, by averaging multiple shift images, the speckle is smoothed out and becomes less noticeable. On the other hand, the non-speckle element of the real part (the part corresponding to the incoherent image of the sample under measurement, the part (4-1) in equation (4)) is not modulated even when the complex interference image data is shifted, so the image intensity does not change even when the real part data is averaged. Therefore, overall, the speckle is reduced and the resolution of the OCT image can be improved.

[0018] The imaging unit 14 converts the averaged real data into an image and outputs it externally via the input / output IF 40. The output destination may be various display devices, printing devices, memory, etc.

[0019] The processor 20 can be configured using at least one general-purpose processor such as an MPU (Micro Processing Unit) or CPU (Central Processing Unit). The processor 20 may also include a dedicated processor composed of an ASIC (Application Specific Integrated Circuit), FPGA (Field Programmable Gate Array), or PLD (Programmable Logic Device).

[0020] The memory 30 may include multiple types of memory, such as ROM (Read Only Memory) and RAM (Random Access Memory). The memory 30 may also include internal or external memory such as an HDD (Hard Disk Drive) or SSD (Solid State Drive). Furthermore, the memory 30 may be an externally located database. As an example, the processor 20 performs the functions of the acquisition unit 11, SCCP processing unit 12, averaging unit 13, and image processing unit 14 by loading various control programs recorded in the ROM of the memory 30 into the RAM and executing them.

[0021] The input / output IF 40 is an interface for sending and receiving data to and from the outside. Communication between the input / output IF 40 and the outside may be performed, for example, via the internet. The input / output IF 40 may be equipped with a short-range communication device such as WiFi® or Bluetooth® that can wirelessly connect to an internet connection point. Alternatively, it may be a wired connection interface such as a USB connector. For example, the acquisition unit 11 may acquire complex interferometry image data from hospitals, ophthalmology clinics, research facilities, etc., in various locations via the internet and the input / output IF 40. Then, it may return the complex interferometry image data with reduced speckle to those hospitals, ophthalmology clinics, research facilities, etc. In this case, the OCT image processing device 1 functions as an OCT image processing platform and can provide a service to remove speckle from OCT images taken at contracted facilities.

[0022] (OCT Image Processing Method S1) Next, the OCT image processing method S1 performed using the OCT image processing device 1 will be described. Figure 2 is a flowchart showing the flow of the OCT image processing method S1. As shown in Figure 2, the OCT image processing method S1 includes steps S11 to S13.

[0023] Step S11 is an SCCP processing step in which the shift conjugate product is calculated multiple times by changing the shift amount, and is the product of the complex interference image data of the object to be measured obtained by irradiating the object to be measured with coherent incident light, and the complex conjugate image of the shifted image data generated by shifting the complex interference image data in a predetermined direction by a predetermined shift amount.

[0024] SCCP processing is performed by the processor 20 of the OCT image processing device 1, specifically the acquisition unit 11 and the SCCP processing unit 12. The complex interference image data, shift image data, and their complex conjugate products are as described above. The details of the method for generating shift image data are described below.

[0025] Figure 4 is a schematic diagram illustrating an example of the spatial structure of OCT image data and its extraction. The rectangular parallelepiped shown at 401 in Figure 4 is the three-dimensional OCT image data space acquired by an optical coherence tomography (OCT) scanner. In this diagram, it is assumed that coherent incident light is irradiated from top to bottom along the z-axis toward the object to be measured. The x and y axes, which are perpendicular to the z-axis and mutually perpendicular, are set as shown in the diagram. From this OCT image data space, the acquisition unit 11 acquires one-dimensional or two-dimensional OCT image data in an arbitrary direction, and the SCCP processing unit 12 shifts it by an arbitrary specified amount in an arbitrary specified direction (one-dimensional, two-dimensional, or three-dimensional direction) to generate shifted image data. The SCCP processing unit 12 then derives the shift conjugate product of the original OCT image data and the shifted image data.

[0026] For example, the dotted line P shown in 401 is a line segment parallel to the x-axis. The acquisition unit 11 acquires one-dimensional OCT image data in a direction parallel to the dotted line P, and the SCCP processing unit 12 can shift it in a direction along the dotted line P to generate one-dimensional shifted image data. Similarly, one-dimensional OCT image data parallel to the dotted line Q parallel to the y-axis, and one-dimensional OCT image data along the dotted line R parallel to the z-axis may be shifted to generate shifted image data. The direction of shifting may be the positive or negative direction of each axis. Also, the direction in which the one-dimensional data is acquired does not need to be parallel to the dotted lines P, Q, and R, but may be any three-dimensional direction.

[0027] For example, the SCCP processing in this case may be a process that repeatedly calculates the shift conjugate product, which is the product of one-dimensional data from the complex interference image data in a direction orthogonal to the direction of incident light and the complex conjugate image of the shifted image data generated by shifting the one-dimensional data by a predetermined shift amount in a direction orthogonal to the direction of incident light, with varying shift amounts.

[0028] Furthermore, the SCCP processing in this case may also be a process of repeatedly calculating the shift conjugate product, which is the product of the one-dimensional data in the direction along the direction of the incident light from the complex interference image data and the complex conjugate image of the shifted image data generated by shifting the one-dimensional data by a predetermined shift amount in the direction along the direction of the incident light, while changing the shift amount.

[0029] Furthermore, when generating shifted image data by shifting one-dimensional OCT image data and deriving the shift conjugate product, it is necessary to shift all the one-dimensional OCT image data that constitute the desired tomographic image and derive the shift conjugate product. This method is computationally more complex than the method for deriving the shift conjugate product of the two-dimensional OCT image plane described below, but this method is also possible.

[0030] Figure 402 shows a two-dimensional OCT image plane (x-y plane) OP perpendicular to the z-axis. The acquisition unit 11 may acquire two-dimensional OCT image data on such a plane. A plane image perpendicular to the z-axis is also called an en-face image (a tomographic image facing the direction of irradiation). The acquisition unit 11 may also acquire two-dimensional OCT image data such as the OCT image plane PP parallel to the z-axis shown in 403. Alternatively, the acquisition unit 11 may acquire two-dimensional OCT image data in any direction in the OCT image space. The SCCP processing unit 12 can shift the acquired two-dimensional OCT image data by an arbitrary amount in the two-dimensional direction within that plane, or in a three-dimensional direction including the direction perpendicular to that plane, and derive the shift conjugate product.

[0031] For example, the SCCP processing in this case may involve generating shifted image data by shifting the complex interference image data at a predetermined depth in at least one of the following directions: the Z direction, which is the depth direction along the direction of the incident light; the X direction, which is perpendicular to the Z direction; and the Y direction, which is perpendicular to both the Z and X directions. The process of calculating the shift conjugate product, which is the product of the original image and the complex conjugate image of these shifted image data, may be repeated multiple times with varying amounts of shift.

[0032] Furthermore, the SCCP processing in this case may involve generating shifted image data by shifting complex interference image data on the XY plane at a predetermined depth in a one-dimensional or two-dimensional direction, and then repeating the process of calculating the shifted conjugate product, which is the product of the original image and the complex conjugate image of these shifted image data, multiple times with varying shift amounts.

[0033] In the above embodiment, the shift conjugate product of complex interference image data (original image data) in any direction of one or two dimensions and its shifted image data was derived. However, it is also possible to generate shifted image data shifted in a certain direction from the original image data, and counter-shifted image data shifted by an arbitrary amount in the opposite direction to that direction, and then derive the shift conjugate product of these shifted image data and counter-shifted image data. In other words, the SCCP process may be a process that generates counter-shifted image data by shifting the complex interference image data by an arbitrary amount in the direction opposite to the predetermined direction in which the shifted image data was generated, and then calculates the shift conjugate product of the complex conjugate image of the counter-shifted image data and the complex conjugate image of the shifted image data, repeating this process multiple times with different shift amounts. Alternatively, it may be a process that derives the shift conjugate product of shifted image data shifted in a certain direction and counter-shifted data shifted in a different direction, repeating this process multiple times with different shift amounts.

[0034] The acquired OCT image data contains various measurement errors. Therefore, a correction process may be performed to correct these measurement errors before performing SCCP processing. This correction process will be described later.

[0035] Returning to Figure 2, step S12 is an averaging process step in which the real part data of multiple shift conjugate products are averaged. Step S13 is an imaging process step in which the averaged real part data is converted into an image and output.

[0036] The steps from acquiring the OCT image data to the imaging process described above will be explained with reference to FIG. 5. FIG. 5 is a schematic diagram showing the steps from acquiring two-dimensional OCT image data to the imaging process. This schematic diagram shows a case where shift image data and inverse shift image data are generated from the original image data, and a shift conjugate product is derived from these.

[0037] A-0 at the upper left of FIG. 5 is the three-dimensional OCT image space described in FIG. 4. Next, A-1 is a schematic diagram of an acquisition step for acquiring two-dimensional OCT image data S (hereinafter referred to as "original image S") orthogonal to the z-axis from the three-dimensional OCT image space. Note that focusing correction and / or variance correction described later may be performed on the original image S. Next, shift image data of the original image S is generated. In the illustrated example, two shift image data S1 and S2 are generated. The shift image data S1 shown in A-2 is shift image data obtained by shifting the original image S by Δx / 2 in the negative direction of the x-axis and by Δy / 2 in the negative direction of the y-axis. On the other hand, the shift image data S2 shown in A-3 is shift image data obtained by shifting the original image S by Δx / 2 in the positive direction of the x-axis and by Δy / 2 in the positive direction of the y-axis.

[0038] Next, the complex conjugate S2 of the shift image data S2 ＊ , ＊ , ＊ , ＊ , ＊ is generated (A-4). Next, the product (S1S2 ＊ ) of the shift image data S1 and the complex conjugate S2 ＊ is generated (B-1). The process until the shift image is generated and this shift conjugate product S1S2 ＊ is derived, or the shift conjugate product is abbreviated as SCCP. Next, the real part of the shift conjugate product S1S2 ＊ is acquired. Such steps are repeated while changing the shift amount. The shift direction may also be changed. The real parts of the plurality of shift conjugate products thus acquired are averaged and imaged (D-1). By such processing, a corrected image with reduced speckle of the original image S is obtained.

[0039] (SCCP Theory) Next, we will explain the theoretical aspects of the SCCP processing described above. Optical coherence tomography (OCT) images are composed of complex signals with real and imaginary parts. In image observation, the absolute square intensity of the complex signal is frequently calculated and displayed on a dB scale. On the other hand, the phase of the complex signal is used in phase-sensitive OCT measurements such as Doppler OCT and high-sensitivity displacement measurements. In other words, in such conventional OCT image formation processes, the complex signal is decomposed into amplitude and phase.

[0040] Tomita et al. (K. Tomita et.al., Biomed. Opt. Express 14, 3100 (2023)) demonstrated a novel formulation of OCT, which describes the OCT signal as the sum of two mathematical entities: a "meaningful OCT image" and "speckles." Furthermore, they used this formulation to design a novel complex image processing method for volume difference imaging, which utilizes the "imaginary part" of the manipulated complex OCT signal.

[0041] In this embodiment, a complex image processing method designed based on the formulation by Tomita et al. is used. The image processing method combines the formation of a new complex image with the acquisition of its real and imaginary parts. In real part imaging in this embodiment, speckle reduction is possible using only one original image.

[0042] In the theoretical framework formulated by Tomita et al., the object being measured is modeled as a spatially slowly changing refractive index distribution, and the scatterers are spatially randomly dispersed. This representation of the object being measured is expressed as the "dispersive scatterer model" (DSM). Let (x, y, z) be the position within the object being measured, x and y be the lateral positions, and z be the depth position in the direction of irradiation. The spatially slowly changing refractive index is represented by n(x, y, z), and it is assumed that small scatterers are dispersed (i.e., embedded), and that the size of the scatterers is significantly smaller than the spatial variation of n(x, y, z). The position of the i-th scatterer is (xi, yi, zi), and the refractive index of all scatterers is assumed to be the same, ns. The irradiation light is incident from above the object being measured, and the measurement surface (depth z ０Consider an en face (front) image in which only the scattering from N scatterers within a coherence gate (in the xy plane) contributes to imaging.

[0043] Based on the above assumptions, for a depth z ０ the complex OCT image signal s within a coherence gate is represented by the following equation (1). This corresponds to the two-dimensional OCT image data S(A-1) in FIG. 5. In the following equations and explanations, variables representing vectors are described in boldface, and variables representing scalars are described in italics.

[0044] x and z represent positions in the measurement target space, and x' and z' represent positions in the image space. Φi is the phase offset caused by the depth position of the i-th scatterer with respect to the center depth of the coherence gate z ０ φ is the phase of the complex point response function. Pa is the amplitude of the point response function.

[0045] Assume that Pa included in this complex OCT image signal s is a Gaussian-type point response function represented by the following equation (2).

[0046] Based on such a premise, the product (B-1 in FIG. 5) of the shifted image data obtained by shifting the image data S by -Δx / 2 in the x-axis direction and -Δy / 2 in the y-axis direction, and the complex conjugate of the shifted image data obtained by shifting the image data S by +Δx / 2 in the x-axis direction and +Δy / 2 in the y-axis direction, as described in FIG. 5, is represented by the following equation (3).

[0047] In equation (3), D and D' are non-binary scatterer density maps in two-dimensional and four-dimensional spaces, respectively. k ０ is the wave number of the irradiation light, and n is the refractive index of the sample surrounding the scatterer. w is the radius of the irradiation light, and w ０ is the beam radius at the depth of focus, that is, the beam waist radius (corresponding to the resolution). R is the phase curvature radius of the wavefront caused by defocus. R.H.S. means "right side".

[0048] Next, when the real part data in equation (3) is taken out, it becomes the following equation (4).

[0049] Here, Φ ｐｑ is a substantially random phase defined by the depth position of the scatterer. In this equation, w = w ０ In this case, we consider the image at the point of focus. In this case, R approaches infinity, so the cosine term in equation (4-1) (the actual image portion, not speckle) becomes approximately 1. Also, the other terms become constant terms. Changing this does not change the shape of the image. On the other hand, part (4-2) of equation (the speckle part is Modulation occurs by changing [something]. Therefore, Speckle is reduced by averaging the real-part images of multiple SCCPs with different characteristics.

[0050] (Correction of OCT Image Data) OCT image data contains data such as focus shift. For example, the focal point of incident coherent light is fixed at a predetermined depth. Therefore, focus shift occurs at depths before and after this point. In the case of a frontal image at a depth shifted from the focal point, focus correction processing can be performed before SCCP processing. For example, the acquisition unit 11 may further perform data correction processing to remove at least a portion of at least one of the low-order aberrations and higher-order aberrations included in the complex interference image data. Low-order aberrations are so-called focus shift aberrations. Higher-order aberrations are, for example, astigmatism and spherical aberration. Data correction processing can be performed, for example, by computational defocusing, and specifically, data correction processing can be performed by phase filtering, complex filtering, data point resampling (ISAM, Interferometric Synthetic Aperture Microscopy), or a combination thereof.

[0051] Furthermore, the acquisition unit 11 may further perform dispersion correction processing to pre-correct the wavelength dispersion included in the complex interference image data. Dispersion correction processing is effective when acquiring shift image data in the Z-axis (depth) direction. Dispersion correction processing can be performed by signal processing methods, hardware methods, or a combination thereof. Specifically, signal processing methods include, for example, a method of multiplying the spectral interference signal by a phase function and then reconstructing the OCT signal (FFT). Hardware methods include, for example, a method of designing the optical system so that the wavelength dispersion of the two arms of the interferometer is equal.

[0052] (Subpixel Shift) Next, we will explain subpixel shift. Subpixel shift refers to shifting the original image data by an amount smaller than the size of one pixel when generating shifted image data. In OCT images, one sensor element of the photosensor corresponds to one pixel. Therefore, the shift is usually performed in units of the size of a pixel, but the amount of shift may be smaller than the size of one pixel in complex interferometry image data.

[0053] When shifting by a size smaller than one pixel, it is preferable to create some kind of interpolation data when shifting complex interferometric image data. For example, the pixel density of the image may be improved by linear and / or nonlinear interpolation methods for the complex interferometric image data. For example, the pixel density of the image may be improved by a Fourier domain zero-filling method for the complex interferometric image data before shifting. This makes it possible to reduce speckle with high accuracy even when subpixel shifting is performed.

[0054] As described above, the OCT image processing method S2 for correcting complex interference image data will now be explained. Figure 3 is a flowchart showing the flow of the OCT image processing method S2. As shown in Figure 3, the OCT image processing method S2 includes steps S21 to S27. The OCT image processing method S2 can be executed by each part of the control unit 10 of the OCT image processing device 1.

[0055] Step S21 is an acquisition step in which complex interference image data of the object to be measured is obtained by irradiating the object with coherent incident light. This acquisition step is as described in the function of the acquisition unit 11.

[0056] Step S22 is a step to remove at least a portion of at least one of the low-order aberrations and higher-order aberrations that may be included in the complex interference image data. Step S23 is a step to correct image blurring due to wavelength dispersion that may be included in the complex interference image data. Note that the order in which steps S22 and S23 are performed does not matter, and only a portion of them may be performed.

[0057] Step S24 is a step in which the process of deriving the shift conjugate product of complex interference image data and shifted image data generated by shifting the complex interference image data in a predetermined direction by a predetermined shift amount is repeated multiple times, with the shift amount being changed each time. The specific method is as described above.

[0058] Step S25 is a step in which, when shifting the complex interference image data in step S24, the pixel density of the image is improved with respect to the complex interference image data by linear and / or nonlinear interpolation methods. These specific methods are as described above.

[0059] Steps S26 and S27 are the same as steps S12 and S3 of the OCT image processing method S1 described above.

[0060] According to the OCT image processing device 1 or OCT image processing methods S1 and S2 described above, speckles appearing in OCT images can be removed using fewer OCT images (basically just one).

[0061] (Training Data for Machine Models and Trained Machine Models) Next, we will describe the training data for machine models and the OCT image recognition machine model trained using that training data. Figure 6 is a schematic diagram showing the training data 61 for machine models and the steps of training an untrained machine model 62 using that training data 61. The training data 61 includes multiple datasets, each consisting of a set of speckle-reduced OCT image data and a label attached to that OCT image data. The speckle-reduced OCT image data is OCT image data obtained by the OCT image processing device or OCT image processing method described above. The label is a so-called ground truth label that indicates what features the OCT image data has. The label may be, for example, the name of a disease related to the eye or other organs. Alternatively, the label may be the name of a cell indicating what type of cell it is. The machine model can be any model using any program, such as a convolutional neural network (CNN) model suitable for image recognition.

[0062] By training an untrained machine model 62 using such training data 61, a trained OCT image recognition machine model 63 capable of accurately identifying and determining the features described in the labels can be generated. Furthermore, by using images with reduced speckle, a machine model capable of recognizing OCT images with even greater accuracy can be generated.

[0063] [Example of implementation by software] The functions of the OCT image processing device 1 (hereinafter referred to as "device") can be realized by a program that causes a computer to function as the device, and by a program that causes a computer to function as each control block of the device (particularly each part included in the control unit 10).

[0064] In this case, the device includes a computer having at least one control device (e.g., a processor 20) and at least one storage device (e.g., a memory 30) as hardware for executing the program. By executing the program using this control device and storage device, each of the functions described in the above embodiment is realized.

[0065] The above program may be recorded on one or more computer-readable recording media, not temporary ones. These recording media may or may not be provided by the above device. In the latter case, the program may be supplied to the above device via any wired or wireless transmission medium.

[0066] Furthermore, some or all of the functions of each of the above control blocks can also be realized by logic circuits. For example, an integrated circuit in which logic circuits functioning as each of the above control blocks are formed is also included in the scope of the present invention. In addition, it is also possible to realize the functions of each of the above control blocks by, for example, a quantum computer.

[0067] The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0068] Next, an embodiment of the present invention (an embodiment in which the speckle of an actual OCT image is reduced) will be described below. Figure 7 is a diagram showing the change in speckle of an OCT image depending on the number of SCCP-processed data. 701 in Figure 7 is the original OCT image (original image) acquired by an optical coherence tomography (OCT) system. 702 is an averaged image obtained by averaging the real part data of a total of 7 × 7 = 49 shift conjugate products of images shifted by 1 pixel in the x direction from -3 pixels to +3 pixels (including zero pixels) and images shifted by 1 pixel in the y direction from -3 pixels to +3 pixels (including zero pixels).

[0069] Similarly, 703 is an averaged image obtained by averaging the real part data of the shift conjugate product of a total of 11 × 11 = 121 images, which are shifted in the x-direction by 1 pixel increments from -5 pixels to +5 pixels (including zero pixels) and in the y-direction by 1 pixel increments from -5 pixels to +5 pixels (including zero pixels).

[0070] Image 704 is an averaged image obtained by averaging the real part data of the shift conjugate product of a total of 15 × 15 = 225 images, which are shifted in the x-direction by 1 pixel increments from -7 pixels to +7 pixels (including zero pixels) and in the y-direction by 1 pixel increments from -7 pixels to +7 pixels (including zero pixels).

[0071] Focusing on the elliptical areas shown in each figure, we can see that as the number of averaged shift conjugation products increases, the tiny black spots (speckles) within the ellipse disappear, and the outlines of the cells (dark shadow areas) gradually become clearer. Furthermore, the arrows in figures 703 and 704 indicate regions where cell loss can be observed. Thus, averaging multiple shift conjugation products can reduce speckles, resulting in a clearer image of real cells.

[0072] [Summary] (Aspect 1) An OCT image processing method comprising: an SCCP process in which at least one processor repeatedly calculates the shift conjugate product, which is the product of complex interference image data of a measurement target obtained by irradiating the measurement target with coherent incident light and the complex conjugate image of shifted image data generated by shifting the complex interference image data in a predetermined direction by a predetermined shift amount, by changing the shift amount multiple times; an averaging process in which the real part data of the multiple shift conjugate products are averaged; and an imaging process in which the averaged real part data is converted into an image and output.

[0073] (Aspect 2) The OCT image processing method according to aspect 1, wherein the SCCP processing is a process of generating shifted image data by shifting the complex interference image data at a predetermined depth in at least one of the following directions: the Z direction, which is the depth direction along the direction of the incident light; the X direction, which is the direction perpendicular to the Z direction; and the Y direction, which is the direction perpendicular to both the Z direction and the X direction; and calculating the shift conjugate product, and repeating this process multiple times with a different shift amount.

[0074] (Aspect 3) The OCT image processing method according to aspect 2, wherein the SCCP processing is a process of generating shifted image data obtained by shifting the complex interference image data on the XY plane at a predetermined depth in a one-dimensional or two-dimensional direction, and calculating the shift conjugate product, and repeating this process multiple times with a different shift amount.

[0075] (Aspect 4) The OCT image processing method according to aspect 2, wherein the SCCP processing is a process of generating one-dimensional data in a direction orthogonal to the direction of the incident light and shifted image data generated by shifting the one-dimensional data by a predetermined shift amount in a direction orthogonal to the direction of the incident light, and calculating the shift conjugate product, and repeating this process multiple times with a different shift amount.

[0076] (Aspect 5) The OCT image processing method according to aspect 2, wherein the SCCP processing is a process of generating one-dimensional data in the direction along the direction of the incident light and shifted image data generated by shifting the one-dimensional data by a predetermined shift amount in the direction along the direction of the incident light, and calculating the shift conjugate product, and repeating the process multiple times with a different shift amount.

[0077] (Aspect 6) The OCT image processing method according to aspect 2, wherein the SCCP processing is a process of generating counter-shifted image data by shifting the complex interference image data by an arbitrary shift amount in the direction opposite to or different from the predetermined direction in which the shifted image data was generated, and deriving the shift conjugate product of the counter-shifted image data and the shifted image data, and repeating this process multiple times with different shift amounts.

[0078] (Aspect 7) The OCT image processing method according to any one of aspects 1 to 6, wherein the processor further performs a data correction process to remove at least a portion of at least one of the lower-order aberrations and higher-order aberrations included in the complex interference image data.

[0079] (Aspect 8) The OCT image processing method according to any one of aspects 1 to 7, wherein the processor further performs dispersion correction processing to pre-correct the wavelength dispersion included in the complex interference image data.

[0080] (Aspect 9) The OCT image processing method according to any one of aspects 1 to 8, wherein the shift amount is smaller than one pixel of the complex interference image data or smaller than the resolution.

[0081] (Aspect 10) The OCT image processing method according to any one of aspects 1 to 9, wherein when shifting the complex interference image data, the processor further performs a process to improve the pixel density of the image by a linear and / or nonlinear interpolation method on the complex interference image data.

[0082] (Aspect 11) Training data for training a machine model that performs OCT image judgment, comprising an OCT image obtained using the OCT image processing method described in any one of aspects 1 to 10, and a label indicating what features the OCT image has.

[0083] (Aspect 12) An OCT image recognition machine model trained using the training data described in Aspect 11.

[0084] (Aspect 13) An OCT image processing apparatus comprising: an acquisition unit that acquires complex interference image data of a measurement target obtained by irradiating the measurement target with coherent incident light; an SCCP processing unit that repeats the process of deriving a shift conjugate product, which is the product of the complex interference image data and a complex conjugate image of shifted image data generated by shifting the complex interference image data in a predetermined direction by a predetermined shift amount, multiple times with different shift amounts; an averaging unit that averages the real part data of a plurality of the shift conjugate products; and an imaging unit that converts the averaged real part data into an image and outputs it.

[0085] (Aspect 14) An OCT image processing program for causing a computer to function as an OCT image processing apparatus as described in Aspect 13, wherein the computer functions as the acquisition unit, the SCCP processing unit, the averaging unit, and the imaging unit.

[0086] (Aspect 15) A computer-readable non-temporary recording medium on which the OCT image processing program described in Aspect 14 is recorded.

[0087] 1...OCT image processing device 10...Control unit 11...Acquisition unit 12...SCCP processing unit 13...Averaging unit 14...Image processing unit 20...Processor 30...Memory 40...Input / Output IF 61...Training data 62...Untrained machine model 63...Trained machine model

Claims

1. An OCT image processing method comprising: an SCCP process in which at least one processor repeatedly calculates a shift conjugate product, which is the product of complex interference image data of a measurement target obtained by irradiating the measurement target with coherent incident light, and a complex conjugate image of shifted image data generated by shifting the complex interference image data in a predetermined direction by a predetermined shift amount, by changing the shift amount multiple times; an averaging process in which the real part data of the multiple shift conjugate products are averaged; and an imaging process in which the averaged real part data is converted into an image and output.

2. The OCT image processing method according to claim 1, wherein the SCCP processing is a process of generating shifted image data by shifting the complex interference image data at a predetermined depth in at least one of the following directions: the Z direction, which is the depth direction along the direction of the incident light; the X direction, which is the direction perpendicular to the Z direction; and the Y direction, which is the direction perpendicular to both the Z direction and the X direction; and calculating the shift conjugate product, and repeating this process multiple times with a different shift amount.

3. The OCT image processing method according to claim 2, wherein the SCCP processing is a process of generating shifted image data obtained by shifting the complex interference image data on the XY plane at a predetermined depth in a one-dimensional or two-dimensional direction, and calculating the shift conjugate product, and repeating this process multiple times with a different shift amount.

4. The OCT image processing method according to claim 2, wherein the SCCP processing is a process of generating one-dimensional data from the complex interference image data in a direction orthogonal to the direction of the incident light, and shifted image data generated by shifting the one-dimensional data by a predetermined shift amount in a direction orthogonal to the direction of the incident light, and calculating the shift conjugate product, and repeating this process multiple times with different shift amounts.

5. The OCT image processing method according to claim 2, wherein the SCCP processing is a process of generating one-dimensional data in the direction along the direction of the incident light and shifted image data generated by shifting the one-dimensional data by a predetermined shift amount in the direction along the direction of the incident light from the complex interference image data, and calculating the shift conjugate product, and repeating the process multiple times with a different shift amount.

6. The OCT image processing method according to claim 2, wherein the SCCP processing is a process of generating counter-shifted image data by shifting the complex interference image data by an arbitrary shift amount in the direction opposite to or different from the predetermined direction in which the shifted image data was generated, and deriving the shift conjugate product of the counter-shifted image data and the shifted image data, and repeating this process multiple times with different shift amounts.

7. The OCT image processing method according to any one of claims 1 to 6, wherein the processor further performs data correction processing to remove at least a portion of at least one of the lower-order aberrations and higher-order aberrations included in the complex interference image data.

8. The OCT image processing method according to any one of claims 1 to 6, wherein the processor further performs dispersion correction processing to pre-correct the wavelength dispersion included in the complex interference image data.

9. The OCT image processing method according to any one of claims 1 to 6, wherein the shift amount is smaller than one pixel of the complex interference image data or smaller than the resolution.

10. The OCT image processing method according to claim 9, wherein when shifting the complex interference image data, the processor further performs a process to improve the pixel density of the image by linear and / or nonlinear interpolation methods for the complex interference image data.

11. Training data for training a machine model that performs OCT image judgment, comprising an OCT image obtained using the OCT image processing method described in any one of claims 1 to 6, and a label indicating the characteristics of the OCT image.

12. An OCT image judgment machine model trained using the training data described in claim 11.

13. An OCT image processing apparatus comprising: an acquisition unit that acquires complex interference image data of a measurement target obtained by irradiating the measurement target with coherent incident light; an SCCP processing unit that derives a shift conjugate product which is the product of the complex interference image data and a complex conjugate image of shifted image data generated by shifting the complex interference image data in a predetermined direction by a predetermined shift amount, repeating the process multiple times with different shift amounts; an averaging unit that averages the real part data of multiple shift conjugate products; and an imaging unit that converts the averaged real part data into an image and outputs it.

14. An OCT image processing program for causing a computer to function as an OCT image processing apparatus according to claim 13, wherein the computer functions as the acquisition unit, the SCCP processing unit, the averaging unit, and the imaging unit.

15. A computer-readable non-temporary recording medium on which the OCT image processing program described in claim 14 is recorded.

Images