Correction devices, systems, methods, and programs

Abstract

To provide a correction device, a system, a method, and a program that can reduce cost for correcting artifacts due to motion in reconstruction of CT images.SOLUTION: A correction device comprises: an imaging data acquiring section; a preprocessing section; a relative motion correction value calculating section; a correction function generating section that generates a relative motion correction function; a reference center position determining section that sets a temporary reference center position correction function and determines a parameter of the temporary reference center position correction function and a reference center position correction function; and a motion correcting section. The reference center position determining section acquires a temporarily corrected projection image and determines the parameter of the temporary reference center position correction function and the reference center position correction function by calculating a degree of coincidence between the temporarily corrected projection image and the projection image at an imaging angle opposing thereto. The motion correcting section corrects main imaging data or the projection image based on the main imaging data using the reference center position correction function and the relative motion correction function.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a correction device, system, method, and program for correcting artifacts. [Background technology]

[0002] CT scanners reconstruct CT images from multiple imaging data acquired while rotating the sample or gantry. In CT scanners, movement of the sample or optical system during measurement is called motion. If imaging data affected by motion is not corrected before reconstruction, blurring and streak-like artifacts will occur in the reconstructed CT image. As a result, the reconstructed image does not accurately reflect the shape of the sample, and quantitative accuracy is lost.

[0003] To reduce such motion-induced artifacts, conventional methods have included introducing equipment other than CT scanners for imaging, devising imaging techniques, or correcting them with software.

[0004] Patent Document 1 discloses a device for correcting image shifts caused by misalignment of an imaging mechanism that irradiates a sample with radiation and captures a radiation image including transmitted radiation. The device includes: a reference image acquisition means that acquires multiple radiation images taken from multiple directions when the imaging mechanism is in a state where misalignment of the imaging mechanism may occur, corrects the radiation images in the coordinate axis direction of a predetermined coordinate system, performs a reconstruction calculation based on the corrected radiation images, and evaluates the quality of the obtained reconstruction information. This evaluation process is repeated until the evaluation is optimal, and the resulting radiation images are acquired as multiple reference images showing the radiation image of the sample when the imaging mechanism is not in a state where misalignment of the imaging mechanism may occur; a correction target image acquisition means that acquires multiple radiation images taken of the sample when the imaging mechanism is in a state where misalignment of the imaging mechanism may occur as correction target images; and a correction means that corrects the correction target images in the coordinate axis direction of a predetermined coordinate system so that the degree of agreement between corresponding images between the correction target images and the reference images is maximized.

[0005] Patent Document 2 discloses a technology for an X-ray tomography apparatus that enables the acquisition of clear tomographic images with minimal influence from inaccuracies in the relative rotation between the X-ray generator and X-ray detector pair and the object. This is achieved by projecting the tomographic image obtained by reconstruction calculation using X-ray projection data collected by an X-ray detector in each projection direction forward in the same direction as the projection direction, determining the difference between the forward projection data and the collected projection data, correcting the collected projection data based on that difference, and performing a new reconstruction calculation.

[0006] Non-Patent Document 1 discloses a technique in which the first scan is performed normally, the second scan is performed roughly and quickly, and it is assumed that there is no motion between the second quick scans. The projected image obtained in the first measurement is then corrected based on the projected image obtained in the second scan. Non-Patent Document 1 also discloses a technique in which motion is gradually estimated with increasing precision through repeated projection and back projection. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 6383707 [Patent Document 2] Japanese Patent Publication No. 2010-181153 [Non-patent literature]

[0008] [Non-Patent Document 1] Developments in X-Ray Tomography VI, edited by Stuart R. Stock, Proc. of SPIE Vol. 7078, 70781C, (2008) · 0277-786X / 08 / $18 · doi: 10.1117 / 12.793212 “Compensation of mechanical inaccuracies in micro-CT and nano-CT” [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] However, the techniques described in Patent Documents 1 and 2 both use reconstructed images for correction, which results in high computational costs. Furthermore, the technique described in Non-Patent Document 1, which involves taking two measurements, still retains some motion even with rapid measurements, and cannot correct motion based on tolerance errors originating from the rotation axis, for example. The technique described in Non-Patent Document 1, which estimates motion sequentially, requires repeated projection and back-projection calculations, which also results in high computational costs.

[0010] This invention has been made in view of these circumstances, and aims to provide a correction device, system, method, and program that can reduce the cost of correcting motion artifacts in CT image reconstruction. [Means for solving the problem]

[0011] (1) To achieve the above objective, the present invention is a correction device for correcting artifacts caused by motion during CT image measurement, comprising: an imaging data acquisition unit that acquires 360° scanned main imaging data and reference imaging data; a preprocessing unit that converts the main imaging data and the reference imaging data into a projection image; a relative motion correction value calculation unit that aligns the projection image based on the reference imaging data and the projection image based on the main imaging data corresponding to the imaging angle of the reference imaging data, and calculates a relative motion correction value for each imaging angle; and a correction function that creates a relative motion correction function that corrects the relative motion of all the main imaging data or the projection image based on the main imaging data based on the relative motion correction value. The system comprises a number creation unit, a reference center position determination unit that sets a provisional reference center position correction function and determines the parameters of the provisional reference center position correction function and the reference center position correction function, and a motion correction unit that provisionally corrects the projected image based on the actual shooting data using the provisional reference center position correction function and the relative motion correction function. The reference center position determination unit acquires the provisionally corrected projected image and calculates the degree of agreement between the provisionally corrected projected image and the projected image at the opposite shooting angle to determine the parameters of the provisional reference center position correction function and the reference center position correction function. The motion correction unit corrects the actual shooting data or the projected image based on the actual shooting data using the reference center position correction function and the relative motion correction function.

[0012] (2) Furthermore, in the correction device described in (1) above, the preprocessing unit normalizes the X-ray intensity of the actual imaging data or the reference imaging data, creates a feature extraction projection image by extracting features from the projection image based on the normalized actual imaging data or the reference imaging data, and the relative motion correction value calculation unit calculates the relative motion correction value based on the feature extraction projection image of the reference imaging data and the corresponding feature extraction projection image of the actual imaging data.

[0013] (3) Further, in the correction device described in the above (1) or (2), the preprocessing unit is characterized by performing noise removal before extraction of features.

[0014] (4) Further, in the correction device described in any one of the above (1) to (3), the motion correction unit performs provisional correction on the feature extraction projection image based on the original captured data, the reference center position determination unit acquires the provisionally corrected feature extraction projection image, and determines parameters of the provisional reference center position correction function by calculating the degree of coincidence between the provisionally corrected feature extraction projection image and the feature extraction projection image at the imaging angle facing the former.

[0015] (5) Further, in the correction device described in any one of the above (1) to (4), the relative motion correction function is a polynomial of a degree determined based on the number of reference captured data.

[0016] (6) Further, in the correction device described in any one of the above (1) to (5), the degree of the relative motion correction function is 1 / 2 or less of the number of reference captured data.

[0017] (7) Further, in the correction device described in any one of the above (1) to (6), the original captured data and the reference captured data are data obtained by a fan beam or a cone beam, the reference center position determination unit acquires conversion data obtained by performing fan parameter conversion on the provisionally corrected projection image, and determines parameters of the provisional reference center position correction function by calculating the degree of coincidence between the conversion data and the conversion data at the angle facing the former.

[0018] (8) Further, in the correction device described in any one of the above (1) to (7), calculation of the relative motion correction value or determination of parameters of the provisional reference center position correction function is performed based on a part of the projection image or the provisionally corrected projection image.

[0019] (9) Furthermore, the correction device described in any of (1) to (8) above is characterized by comprising a reconstruction unit that reconstructs the actual imaging data or projection image based on the actual imaging data corrected by the motion correction unit and generates a CT image, and a display unit that displays the CT image on a display device.

[0020] (10) The system of the present invention is characterized by comprising a CT apparatus comprising an X-ray source for generating X-rays, a detector for detecting X-rays, and a rotation control unit for controlling the rotation of the X-ray source and the detector or a sample, and a correction device as described in any of (1) to (9) above.

[0021] (11) The present invention also provides a method for correcting motion artifacts during CT image measurement, comprising the steps of: acquiring 360° scanned main imaging data and reference imaging data; converting the main imaging data and the reference imaging data into projection images; aligning the projection image based on the reference imaging data with the projection image based on the main imaging data corresponding to the imaging angle of the reference imaging data, and calculating a relative motion correction value for each imaging angle; and correcting the relative motion of all the main imaging data or projection images based on the main imaging data based on the calculated relative motion correction values. The method is characterized by including the steps of: creating a relative motion correction function to correct; setting a provisional reference center position correction function; provisionally correcting the projected image based on the actual shooting data using the provisional reference center position correction function and the relative motion correction function; obtaining the provisionally corrected projected image and determining the parameters of the provisional reference center position correction function and the reference center position correction function by calculating the degree of agreement between the provisionally corrected projected image and the projected image at the opposite shooting angle; and correcting the actual shooting data or the projected image based on the actual shooting data using the reference center position correction function and the relative motion correction function.

[0022] (12) The present invention also includes a program for correcting motion artifacts during CT image measurement, comprising: a process for acquiring 360° scanned main imaging data and reference imaging data; a process for converting the main imaging data and the reference imaging data into projection images; a process for aligning the projection image based on the reference imaging data and the projection image based on the main imaging data corresponding to the shooting angle of the reference imaging data, and calculating a relative motion correction value for each shooting angle; and correcting the relative motion of all the main imaging data or the projection image based on the main imaging data based on the calculated relative motion correction value. The system is characterized by having a computer execute the following steps: creating a relative motion correction function to correct; setting a provisional reference center position correction function; provisionally correcting the projected image based on the actual shooting data using the provisional reference center position correction function and the relative motion correction function; acquiring the provisionally corrected projected image and calculating the degree of agreement between the provisionally corrected projected image and the projected image at the opposite shooting angle to determine the parameters of the provisional reference center position correction function and the reference center position correction function; and correcting the actual shooting data or the projected image based on the actual shooting data using the reference center position correction function and the relative motion correction function. [Brief explanation of the drawing]

[0023] [Figure 1] (a) and (b) are schematic diagrams showing the projected image based on reference imaging data and the corresponding projected image based on actual imaging data at a certain imaging angle, respectively. [Figure 2] (a) and (b) are schematic diagrams showing the projected image based on the actual shooting data at a certain shooting angle and the projected image based on the actual shooting data at the opposite shooting angle, respectively. [Figure 3] (a) and (b) are schematic diagrams showing the sinogram of the measured projection image and the sinogram after provisional correction and fan-parameter transformation, respectively. [Figure 4] This is a schematic diagram showing an example of the overall system configuration. [Figure 5] This is a schematic diagram showing a variation of the overall system configuration. [Figure 6] This block diagram shows an example of the configuration of a processing unit and a correction device. [Figure 7] This is a block diagram showing a modified configuration of a processing unit and a correction unit. [Figure 8] This is a block diagram showing a modified configuration of a processing unit and a correction unit. [Figure 9] (a) is a conceptual diagram showing an example of a UI when a user makes various settings, and (b) is a graph showing an example of the result of polynomial interpolation. [Figure 10] This is a flowchart illustrating an example of how the correction device works. [Figure 11] This flowchart shows a variation of the operation of the correction device. [Figure 12] This flowchart shows an example of how the system works. [Figure 13] (a) and (b) are graphs showing the relative motion correction function and the results of determining the reference center position for sample 1, respectively. [Figure 14] (a) to (c) are cross-sections of CT images of Sample 1 reconstructed using corrected original imaging data. (d) to (f) are the same cross-sections of CT images of Sample 1 reconstructed using uncorrected original imaging data. [Figure 15] (a) and (b) are graphs showing the relative motion correction function and the results of determining the reference center position for sample 2, respectively. [Figure 16] (a) to (c) are cross-sections of CT images of sample 2 reconstructed using the corrected original imaging data. (d) to (f) are the same cross-sections of CT images of sample 2 reconstructed using the uncorrected original imaging data. [Modes for carrying out the invention]

[0024] Next, embodiments of the present invention will be described with reference to the drawings. To facilitate understanding of the description, the same reference numerals are used for identical components in each drawing, and redundant descriptions are omitted.

[0025] [principle] A CT scanner irradiates a sample with parallel, fan, or cone-beam X-rays from any angle, and a detector acquires the distribution of the X-ray absorption coefficient, i.e., imaging data. To irradiate X-rays from any angle, a CT scanner is configured to rotate either the sample stage relative to a fixed X-ray source and detector, or to rotate the gantry, which is an integrated unit of the X-ray source and detector.

[0026] By projecting the sample from various angles in this way, the resulting image data is converted into a projection image, and the distribution of the sample's linear absorption coefficient can be estimated from the intensity of the projection image. The process of obtaining a three-dimensional linear absorption coefficient distribution from a two-dimensional projection image is called reconstruction. Reconstruction basically involves back-projection of the projection image.

[0027] Motion refers to the movement of a sample or optical system during the measurement of acquired data. Causes of motion include thermal drift, focus shift, tolerance errors, and improper sample fixation. If projection images based on acquired data with motion are reconstructed without correction, blurring or streak-like artifacts will appear in the reconstructed CT image. Such artifacts are called motion artifacts. When motion artifacts occur, the reconstructed image does not accurately reflect the shape of the sample, resulting in a loss of quantitative accuracy. This effect is particularly problematic in CT imaging with resolution on the order of micrometers.

[0028] Traditionally, to suppress motion artifacts, methods such as introducing equipment other than CT scanners, modifying the scanning method, or correcting with software have been employed. For example, one method involves using three-dimensional positional information measured by introducing special equipment such as lasers or sensors into the CT scanner for correction. However, this method incurs introduction costs.

[0029] Furthermore, software-based correction involves image processing. For example, one method involves correcting multiple radiation images taken from multiple directions under conditions where positional displacement may occur, along the coordinate axis of a predetermined coordinate system, performing a reconstruction calculation based on the corrected radiation image, and evaluating the quality of the reconstruction information in the reconstructed image by comparing it with multiple reference images where no positional displacement has occurred. Another method involves projecting the tomographic image obtained by a reconstruction calculation using X-ray projection data forward in the same direction as the projection direction, determining the difference between the forward projection data and the collected projection data, correcting the collected projection data based on that difference, and performing a new reconstruction calculation. However, all of these methods require reconstruction, which inevitably incurs computational costs and creates practical problems.

[0030] Another method, combining refined imaging techniques with software correction, involves performing a precise measurement the first time, a quick measurement the second time, and then correcting the projection image from the first measurement using the second measurement as a reference (reference scan measurement). However, since the rotation axis can move regardless of the measurement time, this method cannot correct motion caused by tolerance errors originating from the rotation axis. Furthermore, methods that correct the projection image without using reconstructed images have insufficient accuracy for samples with high-contrast and low-contrast structures, as the accuracy of motion calculations depends on the structure and contrast of the sample.

[0031] The present invention corrects the actual image data using the following procedure. First, the actual image data and reference image data scanned in 360° are acquired and converted into projected images. Next, the projected image based on the reference image data and the projected image based on the actual image data corresponding to the shooting angle of the reference image data are aligned, and relative motion correction values ​​are calculated for each shooting angle. Next, a relative motion correction function is created to correct the relative motion based on the calculated relative motion correction values. Next, a provisional reference center position correction function is set, and the projected image based on the actual image data is provisionally corrected using the provisional reference center position correction function and the relative motion correction function. Next, the projected image based on the provisionally corrected actual image data is acquired, and the parameters of the provisional reference center position correction function and the reference center position correction function are determined by calculating the degree of agreement between the projected image at a certain shooting angle and the projected image at the opposite shooting angle. Finally, the actual image data or the projected image based on the actual image data is corrected using the reference center position correction function and the relative motion correction function.

[0032] Figure 1 is a schematic diagram showing the projected image based on reference imaging data and the projected image based on the actual imaging data at a certain imaging angle. The position of the sample rotation axis is not actually shown, but is included for illustrative purposes. By comparing these, the relative motion correction value at a certain imaging angle can be calculated. The relative motion correction value at a certain imaging angle is the amount of movement of the actual imaging data in the CU direction (x-axis direction) and CV direction (y-axis direction) that maximizes the degree of agreement between the projected image based on the reference imaging data and the corresponding projected image based on the actual imaging data at that imaging angle. In other words, the relative motion correction value is the deviation of the actual imaging data from the reference imaging data at a certain imaging angle. In this specification, relative motion is the deviation of the actual imaging data from the reference imaging data estimated from the relative motion correction value. In this way, by calculating the relative motion correction value, information for correcting relative motion can be obtained.

[0033] In this specification, a relative motion correction function is a function calculated based on multiple relative motion correction values, and is a function that corrects the relative motion of all actual shooting data or projected images based on actual shooting data. Any function may be used as the relative motion correction function, as long as it can appropriately correct the relative motion.

[0034] When the sample rotation axis and the central axis within the detector plane coincide, a relative motion correction function can be created and used to correct the actual acquisition data or the projected image based on that data, thereby correcting motion artifacts in the CT image. However, when the sample rotation axis and the central axis within the detector plane do not coincide, correction using only the relative motion correction function is insufficient to correct motion artifacts in the CT image. Furthermore, a relative motion correction function created by comparing the actual acquisition data with reference acquisition data cannot determine the displacement of the sample rotation axis. In CT imaging with resolution on the order of micrometers, even a displacement of a few pixels can be problematic. In such cases, for example, the displacement of the sample rotation axis can be determined from sequential calculations of slice reconstruction, but this requires reconstruction, which is computationally intensive.

[0035] Figure 2 is a schematic diagram showing the projected image based on the actual imaging data at a certain imaging angle and the projected image based on the actual imaging data at the opposite imaging angle. By comparing these after correcting (provisional correction) them with a provisional reference center position correction function and a relative motion correction function, the parameters of the provisional reference center position correction function can be determined. This is referred to as the reference center position correction function. In this specification, the reference center position correction function is a function that represents the displacement of the sample rotation axis with respect to the central axis in the detector plane. The provisional reference center position correction function and the reference center position correction function may be constants. The correction method of the present invention significantly reduces computation time because it eliminates the need for reconstruction by determining the reference center position correction function so that the degree of agreement between the projected image after correction by the relative motion correction function and the projected image at the opposite angle is large. In this specification, absolute motion is the sum of the reference center position correction function and the relative motion correction function.

[0036] This correction method eliminates the need to introduce special equipment such as lasers and sensors, thus reducing implementation costs. Furthermore, since the correction is performed on the captured data or projected image, there is no need to repeatedly reconstruct the image, thus reducing computational costs. In addition, while the data used to create the relative motion correction function that corrects relative motion consists of reference and actual captured data, the data used to determine the reference center position correction function consists of actual captured data with corrected relative motion and the actual captured data opposite it. Therefore, it is possible to correct not only relative motion but also motion originating from the rotation axis.

[0037] The correction performed in this invention targets thermal drift, poor fixation, and translational motion of the captured image resulting from focus shift of the sample during CT scanning. The correction method of this invention does not require reconstruction, reduces computational costs, and can perform highly accurate absolute motion correction without being affected by the calculation accuracy due to the sample's structure or contrast.

[0038] [Embodiment] The correction method of the present invention will be described in detail below. First, the main image data and reference image data obtained by scanning 360° are acquired. Preferably, the main image data consists of 600 to 2400 images taken at intervals of 0.15° to 0.6°. Preferably, the reference image data consists of 8 to 36 images taken at intervals of 10° to 45° before or after the main image data is taken. The number of reference image data images is a divisor of the number of main image data images taken.

[0039] Next, the source image data and reference image data are converted into projection images. The source image data and reference image data can be converted into projection images by logarithmic transformation. Before converting the source image data or reference image data into projection images, it is preferable to normalize the X-ray intensity of the source image data or reference image data and create a feature-extracted projection image by extracting features from the projection image based on the normalized source image data and reference image data.

[0040] X-ray intensity normalization is preferably performed by rescaling the X-ray intensity using the maximum and minimum values ​​of the X-ray intensity of the actual imaging data or reference imaging data. Normalization using both the minimum and maximum values ​​of the X-ray intensity reduces the intensity difference between low-contrast and high-contrast areas in the feature extraction projection image. Therefore, low-contrast structures are more easily reflected in the agreement calculation. X-ray intensity normalization can be performed, for example, using the following formula (1). In the following formula (1), I(x,y,θ) represents the X-ray intensity of a certain pixel at imaging angle θ. The following formula (1) shows that the X-ray intensity of all pixels at imaging angle θ is converted to the value of the formula on the right side. max (θ) and I min (θ) represents the maximum and minimum values ​​of the X-ray intensity histogram obtained for each imaging angle θ. max (θ) and I min (θ) may be the maximum and minimum values ​​of the X-ray intensity histogram for the entire present imaging data or reference imaging data, respectively. The normalization of X-ray intensity is not limited to formula (1).

[0041]

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[0042] Feature extraction of a projected image is preferably performed by detecting the edges of the projected image. Edge detection can be performed, for example, using a Sobel filter. It is also preferable to denoise the projected image before feature extraction. Denoise reduction can be performed, for example, using a median filter or a Gaussian filter. Denoise reduction and edge detection can be performed on the projected image by applying, for example, a median filter, a Gaussian filter, and a Sobel filter in sequence. Feature extraction and denoise reduction of a projected image are not limited to median filters, Gaussian filters, or Sobel filters.

[0043] These processes improve calculation accuracy in determining relative motion correction values ​​and the reference center position. This is particularly effective for samples containing high-contrast and low-contrast structures. Therefore, in cases where there is no or very small tolerance error in the sample rotation axis, one aspect of the present invention may include the steps of normalizing the X-ray intensity, extracting features from the projection image, creating a relative motion correction function, and correcting the imaging data using the relative motion correction function. In this case, superior results can be obtained compared to conventional techniques that correct relative motion without normalizing the X-ray intensity or extracting features from the projection image.

[0044] Next, the projection image based on the reference imaging data and the projection image based on the actual imaging data corresponding to the imaging angle of the reference imaging data are aligned, and relative motion correction values ​​are calculated for each imaging angle. If, as described above, X-ray intensity normalization, noise reduction of the projection image, and feature extraction have been performed, it is preferable that the projection image in the following steps is a projection image that has undergone X-ray intensity normalization, noise reduction of the projection image, and feature extraction (feature-extracted projection image).

[0045] Alignment of the projected image based on reference imaging data and the projected image based on this imaging data corresponding to the imaging angle of the reference imaging data can be performed, for example, using the following formula (2). In the following formula (2), min represents the minimum value, and arg represents the argument that gives that value. P in formula (2) main , P ref These represent the projected image based on the actual shooting data and the projected image based on the reference shooting data at the shooting angle θ, respectively, and are defined by the following equations (3) and (4). That is, the Mean Squared Error (MSE) is calculated for the projected image based on the reference shooting data and the projected image based on the actual shooting data at each shooting angle θ, and the shift amount in the x-axis and y-axis directions of the projected image based on the actual shooting data that minimizes the MSE is (x shift ,y shiftFind and use it as the relative motion correction value. In the sigma calculation on the right side of Equation (2), (x, y) may be all points on the projection image, or may be limited to points within the frame set in the projection image. The function used for alignment is not limited to MSE. For example, mutual information, correlation function, etc. may be used.

[0046]

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[0047]

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[0048] > [[ID=2"]

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[0049] Next, create a relative motion correction function that corrects the relative motion of all the main shooting data or the projection image based on the main shooting data, based on the calculated multiple relative motion correction values. It is preferable to create the relative motion correction function for each of the x-axis direction and the y-axis direction based on the calculated relative motion correction values. The relative motion correction function may use any function as long as it can appropriately correct the relative motion. For example, a finite-order polynomial, a Fourier series, a spline function, etc. with the rotation angle θ of the sample rotation axis as a variable can be used. It is convenient to use a polynomial for the relative motion correction function. When using a polynomial, the relative motion correction function can be obtained by performing polynomial interpolation based on the relative motion correction value. Hereinafter, the relative motion correction functions in the x-axis direction and the y-axis direction with the rotation angle θ of the sample rotation axis as a variable are respectively x shift (θ), y shift (θ).

[0050] The relative motion correction function is preferably a polynomial of degree determined based on the number of reference images. Furthermore, if the relative motion correction function is a polynomial, its degree is preferably less than or equal to half the number of reference images. This allows the degree of the relative motion correction function to be reduced within an appropriate range, thereby reducing the processing cost.

[0051] Next, a provisional reference center position correction function is set, and the projected image based on the actual captured data is corrected using the provisional reference center position correction function and the relative motion correction function. The correction of the projected image based on the actual captured data using the provisional reference center position correction function and the relative motion correction function is referred to as provisional correction. The provisional reference center position correction function center(θ) may be a constant or it may have an angle dependence. For example, if the rotation axis projected onto the detector is expected to move like a sine wave, a model can be considered in which amplitude and phase are parameters. Such a provisional reference center position correction function center(θ) can be expressed, for example, as shown in the following equation (5), where a, δ, and b are parameters. Let P1 be the projected image based on the actual captured data that has been provisionally corrected using the provisional reference center position correction function and the relative motion correction function. P1 can be expressed as shown in the following equation (6).

[0052]

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[0053]

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[0054] Next, a projection image based on the provisionally corrected actual shooting data is obtained, and the parameters of the provisional reference center position correction function are determined by calculating the degree of agreement between a provisionally corrected projection image and the projection image at the opposite shooting angle. Let P2 be the projection image obtained by inverting the provisionally corrected projection image based on the actual shooting data at the opposite shooting angle to P1 in the x direction with respect to the provisional reference center position. P2 is expressed as shown in equation (7) below. The minus sign in the x coordinate indicates inversion.

[0055]

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[0056] The determination of a provisional reference center position correction function and a reference center position correction function based on the calculation of the degree of agreement between a provisionally corrected projection image and the projection image at the opposite shooting angle can be performed, for example, using the following equation (8). P1 and P2 in equation (8) are the same as P1 and P2 above. That is, the MSE is calculated for the projection image based on the provisionally corrected actual shooting data and the projection image at the opposite shooting angle, using the set provisional reference center position correction function center(θ). Then, the parameters of the provisional reference center position correction function center(θ) that minimize the MSE are found and used as the reference center position correction function.

[0057]

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[0058] In the sigma calculation on the right-hand side of equation (8), the (x,y) used to determine the parameters of the provisional reference center position correction function may be any point on the projected image, or it may be limited to points within the frame set on the projected image. Furthermore, the projected image (i.e., the value of θ) used to determine the parameters of the provisional reference center position correction function may be calculated not from all the projected images based on the actual imaging data, but from a portion of the projected images based on the actual imaging data and the corresponding projected image. These measures can reduce the computational cost required to determine the reference center position correction function. The function used to calculate the degree of agreement is not limited to MSE; for example, mutual information, correlation functions, etc., may also be used.

[0059] Then, the actual captured data or the projected image based on the actual captured data is corrected using the determined reference center position correction function and relative motion correction function. In this way, the absolute motion of the actual captured data can be corrected without reconstruction.

[0060] The above explanation describes the method when the image data is captured using a parallel beam. However, if the image data is captured using a fan beam or cone beam, the reference center position correction function cannot be determined directly. Therefore, the following explains the corrections needed when the image data is captured using a fan beam.

[0061] When a CT scanner uses a fan-beam optical system, the projected images obtained from the acquired data do not precisely correspond to images at opposing scanning angles due to the magnification. Therefore, a fan-parallel conversion is performed to convert the projection image obtained by the fan-beam method to a projection image obtained by the parallel-beam method. Furthermore, for projection images with motion, the fan-parallel conversion must be performed after correcting for the motion. For this reason, the fan-parallel conversion is performed at the following timings.

[0062] The process up to the step of creating a relative motion correction function and setting a provisional reference center position correction function can be carried out in the same manner as described above. This is because the relative motion correction function is created by comparing the projected image based on reference imaging data at the same imaging angle with the projected image based on the actual imaging data. Furthermore, if the imaging data is acquired with a fan beam or cone beam and X-ray intensity normalization is performed, it is preferable that the maximum and minimum values ​​are the maximum and minimum values ​​of the X-ray intensity histogram of the entire actual imaging data or reference imaging data.

[0063] Next, a projection image is obtained based on the actual captured data that has been provisionally corrected using a provisional reference center position correction function and a relative motion correction function, and the provisionally corrected projection image is subjected to fan-parameter transformation. Figures 3(a) and (b) are schematic diagrams showing the sinogram of the measured projection image and the sinogram after provisional correction and fan-parameter transformation, respectively. Figure 3(a) is the sinogram viewed in the CU-θ plane before fan-parameter transformation, and Figure 3(b) is the sinogram viewed in the CU-θ plane after provisional correction and fan-parameter transformation. In Figure 3(b), the coordinates after fan-parameter transformation are replaced with the coordinates of a virtual detection surface. Each pixel of the projection image at angle θ in Figure 3(a) corresponds to a pixel on the cross-section represented by a straight line near angle θ in the sinogram of Figure 3(b). The opposing position of each pixel of the projection image after fan-parameter transformation lies on the cross-section represented by a dotted line near angle θ+π in Figure 3(b).

[0064] Because the coordinates are replaced in this way, the provisional reference center position correction function center(θ) and the relative motion correction function x shift (θ), y shift Projection image P based on the actual shooting data provisionally corrected by (θ). main The transformed data obtained by performing a fan parametric transformation is P p (x p ,y p ,θ p Let P be center(θ). p (x p ,y p ,θ p ;center(θ)) is expressed as shown in the following equation (9). FanPara indicates a function that performs fanparameter transformation, and (x p ,y p ,θ p ) indicates the coordinates on the virtual detection surface after fan-parameter transformation.

[0065]

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[0066] The parameters of the provisional reference center position correction function and the reference center position correction function can be determined, for example, using the following equation (10). P on the right-hand side of equation (10) p P in equation (9) p The x-coordinate of the second term on the right-hand side is x. p The minus sign indicates that the image has been inverted with respect to the center of the virtual detection surface after fan-parameter transformation. In other words, the projection image based on the pre-corrected actual imaging data is transformed using the set provisional reference center position correction function center(θ), and the MSE is calculated for the transformed data at an angle opposite to a certain transformed data after fan-parameter transformation. Then, the parameters of the provisional reference center position correction function center(θ) that minimize the MSE are found, and these are used as the reference center position correction function.

[0067]

number

[0068] Thus, by using a projected image that has been provisionally corrected with a provisional reference center position correction function and a relative motion correction function, and then transformed using a fan-parameter transformation, the reference center position correction function can be determined even when the imaging data is obtained from a fan beam. Therefore, even when there is motion originating from the rotation axis, motion artifacts can be corrected. In other words, the present invention can also be applied when the X-ray is a fan beam. Furthermore, even when the X-ray is a cone beam, the present invention can be applied because the cone beam can be treated as a fan beam by setting a frame near the central cross-section in the CV direction of the projected image.

[0069] [Overall System] Figure 4 is a schematic diagram showing the configuration of the entire system 100, which includes the CT apparatus 200 and the connected processing unit 300, correction device 400, input device 510, and display device 520. Here, the CT apparatus 200 shown in Figure 4 is configured to rotate the sample relative to the X-ray source 260 and detector 270, but it is not limited to this configuration, and a configuration in which a gantry with the X-ray source and detector integrated is rotated is also possible. Furthermore, the CT apparatus 200 can be used with any apparatus that uses a parallel beam, fan beam, or cone beam. However, regardless of the beam, a 360° scan is required to determine the reference center position correction function.

[0070] The processing unit 300 is connected to the CT scanner 200 and controls the CT scanner 200 and processes the acquired data. The correction device 400 corrects the imaging data or projection image. The processing unit 300 and the correction device 400 may be PC terminals or servers on the cloud. The input device 510 is, for example, a keyboard or mouse and provides input to the processing unit 300 and the correction device 400. The display device 520 is, for example, a display and shows imaging data, projection images, etc.

[0071] In Figure 4, the processing unit 300 and the correction device 400 are shown as separate components to emphasize the correction function of the correction device 400. However, as shown in Figure 5, the correction device 400 may be configured as a part of the processing unit 300, or the correction device 400 and the processing unit 300 may be configured as an integrated unit. Figure 5 is a schematic diagram showing a modified configuration of the overall system. By using such a system, the cost of correcting motion artifacts in CT image reconstruction can be reduced.

[0072] [CT device] As shown in Figure 4, the CT apparatus 200 includes a rotation control unit 210, a sample stage 250, an X-ray source 260, a detector 270, and a drive unit 280. X-ray CT imaging is performed by rotating the sample stage 250, which is installed between the X-ray source 260 and the detector 270. Alternatively, the X-ray source 260 and the detector 270 may be installed in a gantry (not shown), and the gantry may be rotated relative to a sample fixed to the sample stage 250.

[0073] The CT scanner 200 drives the sample stage 250 at the timing instructed by the processing unit 300 and acquires imaging data of the sample. The imaging data is transmitted to the processing unit 300. The CT scanner 200 is suitable for use with precision industrial products such as semiconductor devices, but it can be applied not only to industrial equipment but also to animal equipment.

[0074] The X-ray source 260 directs X-rays towards the detector 270. The detector 270 has a light-receiving surface that receives X-rays and can measure the intensity distribution of X-rays transmitted through the sample using a large number of pixels. The rotation control unit 210 rotates the sample stage 250 at a speed set during CT imaging using the drive unit 280.

[0075] [Processing device] Figure 6 is a block diagram showing the configuration of the processing unit 300 and the correction unit 400. The processing unit 300 is composed of a computer consisting of a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), and memory connected to a bus. The processing unit 300 is connected to the CT device 200 to receive information.

[0076] The processing unit 300 comprises an image capture data storage unit 310, a device information storage unit 320, a reconstruction unit 330, and a display unit 340. Each unit can send and receive information via a control bus L. The input device 510 and the display device 520 are connected to the CPU via appropriate interfaces.

[0077] The imaging data storage unit 310 stores imaging data acquired from the CT scanner 200. The imaging data includes the main imaging data and reference imaging data. The main imaging data and reference imaging data include rotation angle information and the X-ray intensity detected at each pixel of the detector at that rotation angle. The device information storage unit 320 stores device information acquired from the CT scanner 200. The device information includes the device name, beam shape, measurement geometry, scanning method, etc.

[0078] The reconstruction unit 330 reconstructs a CT image from the target imaging data. The display unit 340 displays the reconstructed CT image, the imaging data and projection images before and after correction, or the feature-extracted projection image on the display device 520. This allows the user to confirm the CT image based on the corrected imaging data, the imaging data and projection images before and after correction, or the feature-extracted projection image. The user can also give instructions and specifications to the processing unit 300, the correction device 400, etc., based on the CT image, the imaging data and projection images before and after correction, or the feature-extracted projection image.

[0079] [Correction device] The correction device 400 is composed of a computer with a CPU, ROM, RAM, and memory connected to a bus. The correction device 400 may be directly connected to the CT device 200, or it may be connected to the CT device 200 via the processing device 300. The correction device 400 may also receive information from the CT device 200 or from the processing device 300. As shown in Figure 7, the correction device 400 may be configured as a part of the processing device 300, or as shown in Figure 8, the correction device 400 and the processing device 300 may be configured as an integrated unit. Furthermore, the correction device 400 may also possess some of the functions of the processing device 300.

[0080] The correction device 400 comprises a shooting data acquisition unit 410, a preprocessing unit 420, a relative motion correction value calculation unit 430, a correction function creation unit 440, a reference center position determination unit 450, and a motion correction unit 460. Each unit can send and receive information via the control bus L. If the correction device 400 and the processing unit 300 have different configurations, the input device 510 and the display device 520 are also connected to the CPU of the correction device 400 via an appropriate interface. In this case, the input device 510 and the display device 520 may be different from those connected to the processing unit 300.

[0081] The imaging data acquisition unit 410 acquires the actual imaging data and reference imaging data from the CT device 200 or the processing device 300. The actual imaging data and reference imaging data may be data obtained using a parallel beam, fan beam, or cone beam.

[0082] The preprocessing unit 420 converts the main image data and the reference image data into projected images.

[0083] The preprocessing unit 420 preferably normalizes the X-ray intensity of the actual imaging data or reference imaging data and creates a feature-extracted projection image by extracting features from the projection image based on the normalized actual imaging data or reference imaging data. Furthermore, it is preferable that the preprocessing unit 420 performs noise reduction before extracting features.

[0084] The relative motion correction value calculation unit 430 aligns the projected image based on the reference shooting data and the projected image based on the actual shooting data corresponding to the shooting angle of the reference shooting data, and calculates a relative motion correction value for each shooting angle.

[0085] When the preprocessing unit 420 creates a feature extraction projection image, it is preferable that the relative motion correction value calculation unit 430 calculates a relative motion correction value based on the feature extraction projection image of the reference shooting data and the corresponding feature extraction projection image of the actual shooting data.

[0086] The correction function creation unit 440 creates a relative motion correction function that corrects the relative motion of all actual shooting data or projection images based on actual shooting data, based on the relative motion correction value calculated by the relative motion correction value calculation unit 430.

[0087] The relative motion correction function is preferably a polynomial of degree determined based on the number of reference images. Furthermore, if the relative motion correction function is a polynomial, its degree is preferably 1 / 2 or less of the number of reference images. The function form and degree of the relative motion correction function may be set by the user, or automatically by the computer based on the number of reference images. Alternatively, these may be predetermined.

[0088] The reference center position determination unit 450 sets a provisional reference center position correction function. The reference center position determination unit 450 also determines the parameters of the provisional reference center position correction function and the reference center position correction function. The reference center position determination unit 450 acquires the provisionally corrected projection image and calculates the degree of agreement between the provisionally corrected projection image and the projection image at the opposite shooting angle to determine the parameters of the provisional reference center position correction function and the reference center position correction function.

[0089] The actual imaging data and reference imaging data may be data obtained by a cone beam or a fan beam. In this case, the preprocessing unit 420 or other components of the correction device 400 may have a function to perform fan-parameter conversion. Alternatively, a separate fan-parameter conversion unit may be provided. Preferably, the reference center position determination unit 450 acquires conversion data obtained by fan-parameter conversion of the provisionally corrected projection image, and determines the parameters of the provisional reference center position correction function by calculating the degree of agreement between the conversion data and the conversion data of the opposite angle.

[0090] The motion correction unit 460 provisionally corrects the actual imaging data or the projected image based on the actual imaging data using a provisional reference center position correction function and a relative motion correction function. The motion correction unit 460 also corrects the actual imaging data or the projected image based on the actual imaging data using the reference center position correction function and the relative motion correction function. This allows for absolute motion correction using the reference center position correction function and the relative motion correction function. The corrected actual imaging data or projected image is finally output to the reconstruction unit 330 and converted into a CT image.

[0091] When the preprocessing unit 420 creates a feature extraction projection image, it is preferable that the motion correction unit 460 provisionally corrects the feature extraction projection image based on the actual shooting data using a provisional reference center position correction function and a relative motion correction function. Furthermore, it is preferable that the reference center position determination unit 450 acquires the provisionally corrected feature extraction projection image and calculates the degree of agreement between the provisionally corrected feature extraction projection image and the feature extraction projection image at the opposite shooting angle to determine the parameters of the provisional reference center position correction function.

[0092] It is preferable that the calculation of relative motion correction values ​​be based on a portion of the projected image. Furthermore, it is preferable that the parameters of the provisional reference center position correction function be determined based on a portion of the provisionally corrected projected image. This reduces computational costs. The setting of a portion of the projected image may be performed by the user. For example, the area can be set by specifying the width in the x-axis and y-axis directions and the center position of the frame. Alternatively, the computer may automatically set the area based on its characteristic structure. It may also be predetermined.

[0093] When the above settings are specified by the user, it is preferable to use a UI function that allows various settings to be made using, for example, mouse or keyboard operations. Figure 9(a) is a conceptual diagram showing an example of a UI when the user makes various settings. Figure 9(b) is a graph showing an example of the results of polynomial interpolation. In Figure 9(a), for example, a certain is displayed on the right side of the screen. ReferenceA frame can be set on the display screen of the captured data or projected image to calculate the degree of agreement with the corresponding image of the captured data or projected image. Additionally, a frame can be set on the display screen of a given captured data or projected image, displayed on the right side of the screen, to calculate the degree of agreement with the image of the opposing captured data or projected image.

[0094] In the example in Figure 9, the (x,y) calculation range can be set to the image range used for calculating relative motion correction values ​​or determining the reference center position. The (x,y) calculation range corresponds to the frame of the image view. The (x,y) search range can be set to the maximum amount to move the captured data or projected image up, down, left, and right. The order can be set to the order of the polynomial interpolation of the relative motion correction function. The reference center position search range can be set to the search range for the x-direction alignment of the data at opposing angles. The UI function may also have a calculation result display function. The calculation result display function can be set to visually display the results of the alignment calculation or polynomial interpolation, for example, as shown in Figure 9(b). Note that the settings shown in Figure 9(a) are just examples, and even when the user sets these, only some of them may be set, or all of them may be set. Also, there may be settings that are not shown in Figure 9.

[0095] [Measurement method] The CT scanner 200 is used to place a sample, and by repeatedly moving the rotation axis and projecting X-rays under predetermined conditions, the scanner irradiates the sample with X-rays while acquiring the main imaging data or reference imaging data. The CT scanner 200 transmits device information such as the scanning method and the acquired main imaging data or reference imaging data as imaging data to the processing unit 300 or correction unit 400.

[0096] [Correction Method] (Explanation of the flow in the case of parallel beams) Figure 10 is a flowchart illustrating an example of the operation of the correction device 400. First, the correction device 400 acquires the shooting data (step S1). Next, it performs preprocessing (step S2). Next, it calculates the relative motion correction value (step S3). For each shooting angle of the reference shooting data, the relative motion correction value is defined as the amount of movement in the x-axis and y-axis directions that maximizes the degree of agreement between the projected image based on the reference shooting data and the projected image based on the actual shooting data at the same shooting angle. If a frame is set for the projected image, the degree of agreement is calculated only within the area of ​​the frame. Next, it creates the relative motion correction function (step S4). Relative motion correction function Degree It is preferable to set this to less than or equal to half the number of reference data pages.

[0097] Next, a provisional reference center position correction function is set (Step S5). Then, the projected image based on the actual captured data is provisionally corrected using the relative motion correction function and the provisional reference center position correction function (Step S6). Next, the degree of agreement between a provisionally corrected projected image and a projected image at an opposite angle is calculated (Step S7).

[0098] If the set conditions are not met (step S8-NO), the process returns to step S5, a different provisional reference center position correction function is set, and the process up to step S7 is repeated. On the other hand, if the set conditions are met (step S8-YES), the parameters of the provisional reference center position correction function and the reference center position correction function are determined (step S9). Then, the actual captured data or the projected image based on the actual captured data is corrected using the relative motion correction function and the determined reference center position correction function (step S10). In this way, the actual captured data or the projected image can be corrected. The conditions in step S8 can include whether the parameters of the provisional reference center position correction function cover all of the set ranges, whether the sum of the degree of agreement calculated for a certain provisional reference center position satisfies a predetermined threshold, or whether the sum of the degree of agreement calculated for a certain provisional reference center position is an extreme value. In addition, for the relative motion correction function, for example, multiple orders can be set, steps 4 to 9 can be executed, and the order that yields the best degree of agreement in step S8 can be adopted. This allows for a more advanced estimation of absolute motion.

[0099] (Flow description for fan beam or cone beam) Figure 11 is a flowchart showing a modified operation of the correction device 400. Figure 11 is an example of operation when correcting imaging data obtained by a fan beam or cone beam. First, the correction device 400 acquires imaging data (step T1). Next, it performs preprocessing (step T2). Next, it calculates the relative motion correction value (step T3). Next, it creates the relative motion correction function (step T4).

[0100] Next, a provisional reference center position correction function is set (Step T5). Next, the projected image based on the actual captured data is provisionally corrected using the relative motion correction function and the provisional reference center position correction function (Step T6). Next, the provisionally corrected projected image is subjected to fan-parameter transformation (Step T7). Next, the degree of agreement between a certain transformed data after fan-parameter transformation and the transformed data of the opposite angle is calculated (Step T8).

[0101] If the set conditions are not met (step T9-NO), the process returns to step T5, a different provisional reference center position correction function is set, and the process up to step T7 is repeated. On the other hand, if the set conditions are met (step T9-YES), the parameters of the provisional reference center position correction function and the reference center position correction function are determined (step T10). Then, the actual captured data or the projected image based on the actual captured data is corrected using the relative motion correction function and the determined reference center position correction function (step T11). In this way, the actual captured data or the projected image can be corrected. The conditions in step T9 can include whether the parameters of the provisional reference center position correction function cover all of the set ranges, whether the sum of the degree of agreement calculated for a certain provisional reference center position satisfies a predetermined threshold, or whether the sum of the degree of agreement calculated for a certain provisional reference center position is an extreme value.

[0102] [Correction and reconstruction methods] The flowcharts in Figures 10 and 11 show the operation of the correction device 400 only. This is sufficient for correcting the actual captured data or projected image, but in order to clarify the difference from conventional technology, the operation including the capture and reconstruction of the actual captured data will also be explained.

[0103] Figure 12 is a flowchart illustrating an example of the operation of system 100. First, the CT scanner 200 performs a CT scan (step U1). The CT scan involves repeated movement of the rotation axis and projection of X-rays. Next, the system corrects the acquired image data or the projected image based on the acquired image data. (Step U2). The flow for correcting the actual imaging data or the projection image based on the actual imaging data may be one of the flows shown in Figure 10 or Figure 11, depending on the type of optical system of the acquired projection image. Alternatively, the optical system may be identified from the device information and a suitable flow may be selected. The processing device 300 or correction device 400 then reconstructs the CT image using the corrected actual imaging data or the projection image based on the actual imaging data (Step U3). In this way, a CT image reconstructed using the corrected actual imaging data or the projection image based on the actual imaging data can be obtained.

[0104] Conventional techniques involved repeatedly reconstructing CT images and correcting them to reduce artifacts. In contrast, the present invention applies artifact reduction correction to the projection image before reconstruction. This reduces the cost of correction. Furthermore, it can correct not only relative motion but also motion originating from the rotation axis.

[0105] [Example 1] The nonwoven fabric (sample 1) was observed using the system 100 configured as described above. The CT scanner 200 used a Rigaku nano3DX (pseudo-parallel beam optical system) for the measurements. Figures 13(a) and (b) are graphs showing the relative motion correction function and the determination of the reference center position of sample 1 obtained by the method of the present invention, respectively. Figure 13(a) shows the relative motion correction values ​​and relative motion correction function in the x and y directions. Figure 13(b) shows the set provisional reference center position and the MSE value at that time, and the position where the MSE value is smallest is the determined reference center position. Figures 14(a) to (f) are cross-sections of the CT image of sample 1 reconstructed using the corrected main imaging data and the same cross-section of the CT image of sample 1 reconstructed using the uncorrected main imaging data, respectively. Figures 14(a) to (c) show the corrected image, and Figures 14(d) to (f) show the uncorrected image. Reconstruction was performed using the FDK method.

[0106] The reference center position determined by the method of the present invention was -16 pixels, which is the same value as the reference value (center position obtained from sequential calculation of slice reconstruction). In other words, it was confirmed that the method of the present invention can accurately determine the reference center position in a short time without using reconstruction. Furthermore, by comparing Figures 14(a) to (c) and (d) to (f), it was found that artifacts were reduced by the correction of the method of the present invention.

[0107] [Example 2] Next, the capacitor (sample 2) was observed. Measurements were taken using a Rigaku cone-beam optical system CT scanner 200. Figures 15(a) and (b) are graphs showing the relative motion correction function and the determination of the reference center position for sample 2, respectively, obtained by the method of the present invention. Figure 15(a) shows the relative motion correction values ​​and relative motion correction function in the x and y directions. Figure 15(b) shows the set provisional reference center position and the MSE value at that time; the position where the MSE value is smallest is the determined reference center position. Figures 16(a) to (f) show a cross-section of the CT image of sample 2 reconstructed using the corrected main imaging data and the same cross-section of the CT image of sample 2 reconstructed using the uncorrected main imaging data, respectively. Figures 16(a) to (c) show the corrected image, and Figures 16(d) to (f) show the uncorrected image. Reconstruction was performed using the FDK method, similar to sample 1.

[0108] The reference center position determined by the method of the present invention was -6 pixels, which was the same value as the reference value (center position obtained from sequential calculation of slice reconstruction). In other words, it was confirmed that the method of the present invention can accurately determine the reference center position in a short time, even with imaging data obtained from a cone beam, without using reconstruction. Furthermore, by comparing Figures 16(a) to (c) and (d) to (f), it was found that artifacts were reduced by the correction of the method of the present invention. It was confirmed that the correction method of the present invention can also be applied to imaging data measured with a cone beam or fan beam.

[0109] Based on the above results, it has been confirmed that the correction device, system, method, and program of the present invention can effectively correct motion-induced artifacts in CT image reconstruction and reduce computational costs. [Explanation of symbols]

[0110] 100 Systems 200 CT equipment 210 Rotation Control Unit 250 sample stage 260 X-ray source 270 detectors 280 Drive unit 300 Processing Units 310 Shooting data storage unit 320 Device information storage unit 330 Reconstruction part 340 Display section 400 Correction device 410 Image Data Acquisition Unit 420 Pre-processing 430 Relative motion correction value calculation unit 440 Correction Function Creation Section 450 Reference center position determination section 460 Motion Correction Unit 510 Input device 520 Display device

Claims

1. A correction device for correcting artifacts caused by motion during CT image measurement, A shooting data acquisition unit that acquires the main shooting data and reference shooting data scanned in 360°, A preprocessing unit that converts the aforementioned actual shooting data and the aforementioned reference shooting data into a projected image, A relative motion correction value calculation unit aligns the projected image based on the reference shooting data and the projected image based on the actual shooting data corresponding to the shooting angle of the reference shooting data, and calculates a relative motion correction value for each shooting angle. A correction function creation unit creates a relative motion correction function that corrects the relative motion of all the actual shooting data or the projected image based on the actual shooting data based on the relative motion correction value, A reference center position determination unit sets a provisional reference center position correction function and determines the parameters of the provisional reference center position correction function and the reference center position correction function, The system includes a motion correction unit that provisionally corrects the projected image based on the actual shooting data using the provisional reference center position correction function and the relative motion correction function, The reference center position determination unit acquires the provisionally corrected projection image, calculates the degree of agreement between the provisionally corrected projection image and the projection image at the opposite shooting angle, inverted across the central axis in the detector plane of the actual shooting data, and determines the reference center position correction function by determining the parameters of the provisional reference center position correction function that improve the degree of agreement. The motion correction unit corrects the actual shooting data or the projected image based on the actual shooting data using the reference center position correction function and the relative motion correction function. The aforementioned provisional reference center position correction function is a function that expresses the displacement of the sample rotation axis with respect to the central axis in the detector plane using the aforementioned parameters. The correction device is characterized in that the aforementioned reference center position correction function is a function that represents the displacement of the sample rotation axis with respect to the central axis in the detector plane.

2. The preprocessing unit normalizes the X-ray intensity of the actual imaging data or the reference imaging data, and creates a feature-extracted projection image by extracting features from the projection image based on the normalized actual imaging data or the reference imaging data. The correction device according to claim 1, characterized in that the relative motion correction value calculation unit calculates the relative motion correction value based on the feature extraction projection image of the reference shooting data and the corresponding feature extraction projection image of the actual shooting data.

3. The correction device according to claim 2, characterized in that the preprocessing unit performs noise reduction before feature extraction.

4. The motion correction unit performs the provisional correction on the feature extraction projection image based on the actual shooting data. The correction device according to claim 2, wherein the reference center position determination unit, when determining the reference center position correction function, acquires the provisionally corrected feature extraction projection image, calculates the degree of agreement between the provisionally corrected feature extraction projection image and the feature extraction projection image at the opposite shooting angle, inverted across the central axis in the detector plane of the actual shooting data, and determines the parameters of the provisional reference center position correction function that improve the degree of agreement.

5. The correction device according to claim 1, characterized in that the relative motion correction function is a polynomial of degree determined based on the number of reference shooting data.

6. The correction device according to claim 5, characterized in that the order of the relative motion correction function is 1 / 2 or less of the number of reference shooting data.

7. The aforementioned imaging data and reference imaging data are data obtained using a fan beam or cone beam. The correction device according to claim 1, characterized in that, when determining the reference center position determination function, the reference center position determination unit acquires conversion data obtained by fan-parameter transformation of the provisionally corrected projection image, calculates the degree of agreement between the conversion data and the conversion data at the opposite angle, inverted across the central axis in the virtual detector surface after fan-parameter transformation, and determines the parameters of the provisional reference center position correction function that improve the degree of agreement.

8. The correction device according to claim 1, characterized in that the calculation of the relative motion correction value or the determination of the parameters of the provisional reference center position correction function is performed based on the projected image or a portion of the provisionally corrected projected image.

9. A reconstruction unit that reconstructs the image based on the actual shooting data or the projection image based on the actual shooting data corrected by the motion correction unit and generates a CT image, The correction device according to claim 1, further comprising a display unit for displaying the CT image on a display device.

10. A CT apparatus comprising an X-ray source for generating X-rays, a detector for detecting X-rays, and a rotation control unit for controlling the rotation of the X-ray source and the detector, or the sample. A system comprising a correction device according to any one of claims 1 to 9.

11. A method for correcting artifacts caused by motion during CT image measurement, The steps include acquiring the main image data and reference image data obtained by scanning 360°, The steps include converting the aforementioned actual shooting data and the aforementioned reference shooting data into a projected image, The steps include aligning the projected image based on the reference shooting data and the projected image based on the actual shooting data corresponding to the shooting angle of the reference shooting data, and calculating a relative motion correction value for each shooting angle, The steps include creating a relative motion correction function that corrects the relative motion of all the actual shooting data or the projected image based on the actual shooting data based on the calculated relative motion correction value, The steps include setting a provisional reference center position correction function, The steps include: provisionally correcting the projected image based on the actual shooting data using the provisional reference center position correction function and the relative motion correction function; The steps include: obtaining the provisionally corrected projection image; calculating the degree of agreement between the provisionally corrected projection image and the projection image at the opposite shooting angle, inverted across the central axis in the detector plane of the actual shooting data; and determining the parameters of the provisional reference center position correction function that improve the degree of agreement, thereby determining the reference center position correction function; The step includes correcting the actual shooting data or the projected image based on the actual shooting data using the aforementioned reference center position correction function and the aforementioned relative motion correction function, The aforementioned provisional reference center position correction function is a function that expresses the displacement of the sample rotation axis with respect to the central axis in the detector plane using the aforementioned parameters. The method is characterized in that the reference center position correction function is a function that represents the displacement of the sample rotation axis with respect to the central axis in the detector plane.

12. A program for correcting artifacts caused by motion during CT image measurement, The process involves acquiring the main image data and reference image data obtained from a 360° scan, A process to convert the aforementioned actual shooting data and the aforementioned reference shooting data into a projected image, A process to align the projected image based on the reference shooting data and the projected image based on the actual shooting data corresponding to the shooting angle of the reference shooting data, and to calculate a relative motion correction value for each shooting angle, A process to create a relative motion correction function that corrects the relative motion of all the actual shooting data or the projected image based on the actual shooting data based on the calculated relative motion correction value, The process of setting a provisional reference center position correction function, A process to provisionally correct the projected image based on the actual shooting data using the provisional reference center position correction function and the relative motion correction function, The process involves acquiring the provisionally corrected projection image, calculating the degree of agreement between the provisionally corrected projection image and the projection image at the opposite shooting angle, inverted across the central axis within the detector surface of the actual shooting data, and determining the parameters of the provisional reference center position correction function that improve the degree of agreement, thereby determining the reference center position correction function. The computer is instructed to perform a process of correcting the actual shooting data or the projected image based on the actual shooting data using the aforementioned reference center position correction function and the aforementioned relative motion correction function. The aforementioned provisional reference center position correction function is a function that expresses the displacement of the sample rotation axis with respect to the central axis in the detector plane using the aforementioned parameters. The program is characterized in that the aforementioned reference center position correction function is a function that represents the displacement of the sample rotation axis with respect to the central axis within the detector surface.

Images