Correction device, system, method, and program

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, a system, a method, and a program for correcting artifacts. [Background technology]

[0002] CT systems reconstruct CT images from multiple sets of imaging data acquired while rotating the sample or the gantry. In CT systems, the movement of the sample or optical system during measurement is called motion. If imaging data that has motion is reconstructed without correcting it, blurring or streak-like artifacts will appear in the reconstructed CT image. As a result, the reconstructed image does not accurately reflect the shape of the sample, and quantitativeness is lost.

[0003] In order to reduce such motion-induced artifacts, conventional methods have involved using devices other than CT scanners to capture images, improving imaging methods, or using software for correction.

[0004] Patent Document 1 discloses a technology for a captured image misalignment correction device that corrects misalignment of a captured image caused by misalignment of an imaging mechanism that irradiates a sample and captures a radiological image including transmitted radiation. The device includes a reference image acquisition means that acquires a plurality of radiological images obtained by capturing a sample from a plurality of directions in a state in which misalignment of the imaging mechanism may occur, corrects the radiological images in the coordinate axis directions of a predetermined coordinate system, performs a reconstruction calculation based on the corrected radiological images, and repeats an evaluation process to evaluate the quality of the obtained reconstruction information until an optimal evaluation is achieved. The evaluation is performed to acquire pre-generated radiological images as a plurality of reference images that show a radiological image of the sample in a state in which misalignment of the imaging mechanism does not occur, a correction target image acquisition means that acquires a plurality of radiological images obtained by capturing a sample in a state in which misalignment of the imaging mechanism may occur as a correction target image, and a correction means that corrects the correction target image in the coordinate axis directions of the predetermined coordinate system so as to maximize the degree of coincidence between corresponding images between the correction target image and the reference image.

[0005] Patent Document 2 discloses a technology for an X-ray tomography device that forward projects a tomographic image obtained by a reconstruction calculation using X-ray projection data in each projection direction collected by an X-ray detector in the same direction as the projection direction, determines a deviation between the forward projection data and the collected projection data, corrects the collected projection data based on the deviation, and performs a new reconstruction calculation, thereby making it possible to obtain a clear tomographic image that is less affected by inaccuracies in the relative rotation between the pair of the X-ray generator and X-ray detector and the object, regardless of the inaccuracies.

[0006] Non-Patent Document 1 discloses a technique in which the first scan is a normal scan, the second is a rough and quick scan, and it is assumed that there is no motion during the second quick scan, and the projection image obtained in the first measurement is corrected based on the projection image. Non-Patent Document 1 also discloses a technique in which the motion is gradually and precisely estimated during the repetition of projection and backprojection. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 6383707 [Patent Document 2] JP 2010-181153 A [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” Summary of the Invention [Problem to be solved by the invention]

[0009] However, the techniques described in Patent Document 1 and Patent Document 2 both use reconstructed images for correction, which requires high calculation costs. In addition, the technique described in Non-Patent Document 1 that measures twice still leaves motion even if the measurement is performed quickly, and cannot correct motion based on tolerance errors from the rotation axis, for example. The technique described in Non-Patent Document 1 that sequentially estimates motion requires repeated projection and backprojection calculations, which requires high calculation costs.

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

[0011] (1) In order to achieve the above object, a correction device of the present invention is a correction device for correcting artifacts due to motion during CT image measurement, comprising: a shooting data acquisition unit for acquiring actual shooting data and reference shooting data scanned 360°; a pre-processing unit for converting the actual shooting data and the reference shooting data into projection images; a relative motion correction value calculation unit for aligning the projection image based on the reference shooting data and the projection 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; and a correction function for creating a relative motion correction function for correcting the relative motion of all the actual shooting data or the projection image based on the actual shooting data based on the relative motion correction value. the reference center position determination unit acquires the provisionally corrected projection image and determines the parameters of the provisional reference center position correction function and the reference center position correction function by calculating a degree of coincidence between the provisionally corrected projection image and a projection image at an opposite shooting angle, and the motion correction unit corrects the actual shooting data or the projection 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 pre-processing unit normalizes the X-ray intensity of the actual shooting data or the reference shooting data, and creates a feature extraction projection image by extracting features from a projection image based on the normalized actual shooting data or the reference shooting 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 shooting data and the corresponding feature extraction projection image of the actual shooting data.

[0013] (3) In the correction device described in (1) or (2) above, the preprocessing unit is characterized in that it performs noise removal before extracting features.

[0014] (4) Furthermore, in the correction device described in any one of (1) to (3) above, the motion correction unit provisionally corrects the feature extraction projection image based on the actual shooting data, and 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 a degree of similarity between the provisionally corrected feature extraction projection image and the feature extraction projection image at an opposite shooting angle.

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

[0016] (6) In the correction device according to any one of (1) to (5) above, the degree of the relative motion correction function is equal to or less than half the number of the reference shooting data.

[0017] (7) Also, in the correction device described in any one of (1) to (6) above, the main shooting data and the reference shooting data are data obtained by a fan beam or a cone beam, and the reference center position determination unit acquires transformation data obtained by fan-parallel transformation of the provisionally corrected projection image, and determines parameters of the provisional reference center position correction function by calculating the degree of coincidence between the transformation data and the transformation data of an angle opposite thereto.

[0018] (8) Furthermore, in the correction device described in any one of (1) to (7) above, 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 a portion of the projection image or the provisionally corrected projection image.

[0019] (9) Furthermore, the correction device described in any one of (1) to (8) above is characterized in that it includes a reconstruction unit that performs reconstruction based on the actual shooting data corrected by the motion correction unit or a projection image based on the actual shooting data to generate 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 device including an X-ray source that generates X-rays, a detector that detects X-rays, and a rotation control unit that controls the rotation of the X-ray source and the detector, or a sample, and a correction device described in any one of (1) to (9) above.

[0021] (11) A method of the present invention is a method for correcting artifacts due to motion during CT image measurement, comprising the steps of acquiring 360° scanned actual shooting data and reference shooting data, converting the actual shooting data and the reference shooting data into projection images, aligning the projection images based on the reference shooting data and the projection images based on the actual shooting data corresponding to the shooting angles of the reference shooting data, and calculating a relative motion correction value for each shooting angle, and correcting the relative motion of all the actual shooting data or the projection images based on the actual shooting data based on the calculated relative motion correction value. the step of creating a relative motion correction function to correct the actual shooting data; the step of setting a provisional reference center position correction function; the step of provisionally correcting the projection image based on the actual shooting data with the provisional reference center position correction function and the relative motion correction function; the step of acquiring the provisionally corrected projection image and determining parameters of the provisional reference center position correction function and a reference center position correction function by calculating a degree of coincidence between the provisionally corrected projection image and a projection image at an opposite shooting angle thereto; and the step of correcting the actual shooting data or the projection image based on the actual shooting data using the reference center position correction function and the relative motion correction function.

[0022] (12) A program according to the present invention is a program for correcting artifacts due to motion during CT image measurement, the program including a process for acquiring actual shooting data and reference shooting data scanned 360°, a process for converting the actual shooting data and the reference shooting data into projection images, a process for aligning the projection images based on the reference shooting data and the projection images based on the actual shooting data corresponding to the shooting angles of the reference shooting data, and a process for calculating a relative motion correction value for each shooting angle, and a process for correcting the relative motion of all the actual shooting data or the projection images based on the actual shooting data based on the calculated relative motion correction value. a process for creating a relative motion correction function for correcting the actual shooting data; a process for setting a provisional reference center position correction function; a process for provisionally correcting the projection image based on the actual shooting data with the provisional reference center position correction function and the relative motion correction function; a process for determining parameters of the provisional reference center position correction function and a reference center position correction function by acquiring the provisionally corrected projection image and calculating a degree of coincidence between the provisionally corrected projection image and a projection image at an opposite shooting angle thereto; and a process for correcting the actual shooting data or the projection image based on the actual shooting data using the reference center position correction function and the relative motion correction function. [Brief description of the drawings]

[0023] [Figure 1] 13A and 13B are schematic diagrams showing a projected image based on reference shooting data at a certain shooting angle and a projected image based on the corresponding actual shooting data, respectively. [Diagram 2] 1A and 1B are schematic diagrams showing a projected image based on actual photographing data at a certain photographing angle and a projected image based on actual photographing data at an opposing photographing angle, respectively. [Diagram 3] 13A and 13B are schematic diagrams showing a sinogram of a measured projection image and a sinogram after provisional correction and fan-parallel conversion, respectively. [Figure 4] FIG. 2 is a schematic diagram showing an example of the overall system configuration. [Diagram 5] FIG. 13 is a schematic diagram showing a modified example of the overall system configuration. [Figure 6] FIG. 2 is a block diagram showing an example of the configuration of a processing device and a correction device. [Figure 7] FIG. 13 is a block diagram showing a modified example of the configuration of the processing device and the correction device. [Figure 8] FIG. 13 is a block diagram showing a modified example of the configuration of the processing device and the correction device. [Figure 9] 13A is a conceptual diagram showing an example of a UI when a user makes various settings, and FIG. 13B is a graph showing an example of a result of polynomial interpolation. [Figure 10] 10 is a flowchart showing an example of the operation of the correction device. [Figure 11] 13 is a flowchart showing a modified example of the operation of the correction device. [Figure 12] 10 is a flowchart illustrating an example of the operation of the system. [Figure 13] Graphs showing the relative motion correction function of sample 1 and the results of determining the reference center position, respectively. [Figure 14] (a)-(c) are cross-sections of CT images of sample 1 reconstructed using the actual imaging data after correction. (d)-(f) are the same cross-sections of CT images of sample 1 reconstructed using the actual imaging data without correction. [Figure 15] Graphs showing the relative motion correction function of sample 2 and the results of determining the reference center position, respectively (a) and (b). [Figure 16] (a)-(c) are cross-sections of CT images of sample 2 reconstructed using the actual imaging data after correction. (d)-(f) are the same cross-sections of CT images of sample 2 reconstructed using the actual imaging data without correction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Next, an embodiment of the present invention will be described with reference to the drawings. In order to facilitate understanding of the description, the same reference numerals are used to refer to the same components in each drawing, and duplicated description will be omitted.

[0025] [principle] CT equipment irradiates a sample with parallel, fan, or cone beam X-rays from all angles and obtains the distribution of X-ray absorption coefficients, i.e., imaging data, using a detector. In order to irradiate X-rays from all angles, CT equipment is configured to rotate the sample stage or rotate a gantry in which the X-ray source and detector are integrated, relative to a fixed X-ray source and detector.

[0026] In this way, the photographic data of the sample obtained by projecting from various angles is converted into a projection image, and the distribution of the linear absorption coefficient of the sample can be estimated from the shading of the projection image. Then, obtaining the three-dimensional linear absorption coefficient distribution from the two-dimensional projection image is called reconstruction. Reconstruction basically involves back-projecting the projection image.

[0027] Motion refers to the movement of the sample or optical system during the measurement of image data. Causes of motion include thermal drift, focal shift, tolerance errors, and improper fixation of the sample. If a projection image based on image data in which motion has occurred is reconstructed without correcting it, 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, and quantitativeness is lost. This effect is particularly problematic in CT imaging with a resolution on the order of μm.

[0028] Conventionally, in order to suppress motion artifacts, imaging methods have been devised using equipment other than CT scanners, or correction has been done using software. For example, there is a method of correction using 3D position information measured by introducing special equipment such as lasers or sensors into the CT scanner. In this case, the introduction cost is high.

[0029] In addition, in the case of correction by software, image processing is performed to perform the correction. For example, there is a method in which multiple radiation images captured from multiple directions in a state where positional deviation may occur are corrected in the coordinate axis direction of a predetermined coordinate system, a reconstruction calculation is performed based on the corrected radiation images, and the quality of the reconstruction information of the reconstructed image is evaluated by comparing it with multiple reference images without positional deviation. There is also a method in which a tomographic image obtained by a reconstruction calculation using X-ray projection data is forward projected in the same direction as the projection direction, a deviation between the forward projection data and the collected projection data is obtained, and the collected projection data is corrected based on the deviation to perform a new reconstruction calculation. However, in either case, reconstruction is required, which inevitably requires calculation costs and causes practical problems.

[0030] In addition, as a method that combines the ingenuity of the imaging method and correction by software, there is a method in which the first measurement is performed precisely, the second measurement is performed quickly, and the projection image measured in the second measurement is used as a reference to correct the projection image measured in the first measurement (reference scan measurement). However, since the rotation axis may move regardless of the measurement time, when using this method, it is not possible to correct the motion caused by the tolerance error from the rotation axis. In addition, the method of correcting the projection image without using the reconstructed image has insufficient correction accuracy for samples with high-contrast and low-contrast structures, because the calculation accuracy of the motion depends on the structure and contrast of the sample.

[0031] In the present invention, the actual shooting data is corrected in the following procedure. First, the actual shooting data and the reference shooting data scanned 360° are acquired and converted into a projected image. Next, 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 are aligned, and a relative motion correction value is calculated for each shooting angle. Next, a relative motion correction function for correcting the relative motion is created based on the calculated relative motion correction value. Next, a temporary reference center position correction function is set, and the projected image based on the actual shooting data is temporarily corrected using the temporary reference center position correction function and the relative motion correction function. Next, a projected image based on the temporarily corrected actual shooting data is acquired, and the degree of coincidence between the temporarily corrected projected image at a certain shooting angle and the projected image at the opposite shooting angle is calculated to determine the parameters of the temporary reference center position correction function and the reference center position correction function. Then, the actual shooting data or the projected image based on the actual shooting data is corrected using the reference center position correction function and the relative motion correction function.

[0032] FIG. 1 is a schematic diagram showing a projection image based on reference imaging data and a projection image based on actual imaging data at a certain imaging angle. The position of the sample rotation axis is not actually displayed, but is described for the purpose of explanation. By comparing these, a 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 in the CU direction (x-axis direction) and CV direction (y-axis direction) of the actual imaging data at which the degree of agreement between the projection image based on the reference imaging data at the imaging angle and the corresponding projection image based on the actual imaging data is the largest. 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, the 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 the relative motion can be obtained.

[0033] In this specification, the relative motion compensation function is a function calculated based on a plurality of relative motion compensation values, and is a function for compensating the relative motion of all the main shooting data or the projection image based on the main shooting data. Any function may be used as the relative motion compensation function as long as it can appropriately compensate the relative motion.

[0034] When the specimen rotation axis and the central axis in the detector plane are aligned, a relative motion correction function is created and used to correct the actual data or the projection image based on the actual data, thereby correcting the motion artifacts in the CT image. However, when the specimen rotation axis and the central axis in the detector plane are not aligned, the motion artifacts in the CT image cannot be corrected by correction using the relative motion correction function alone. In addition, the deviation of the specimen rotation axis cannot be determined by the relative motion correction function created by comparing the actual data with the reference data. In CT imaging with a resolution on the order of μm, even a deviation of a few pixels can be a problem. In such cases, for example, the deviation of the specimen rotation axis can be determined by sequential calculation of slice reconstruction, but reconstruction is required, which takes time for calculation.

[0035] FIG. 2 is a schematic diagram showing a projection image based on actual imaging data at a certain imaging angle and a projection image based on actual imaging data at an opposing imaging angle. By comparing these after correction (provisional correction) 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 deviation of the sample rotation axis relative 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. In the correction method of the present invention, the reference center position correction function is determined so that the degree of agreement between the projection image corrected by the relative motion correction function and the projection image at the opposing angle is increased, so that reconstruction is not necessary, and the calculation time can be sufficiently reduced. In this specification, the 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 devices such as lasers and sensors, thereby reducing the introduction costs. In addition, since the correction is performed on the shooting data or the projection image, it is not necessary to repeat reconstruction, thereby reducing the calculation costs. In addition, while the data used to create the relative motion correction function that corrects the relative motion are the reference shooting data and the actual shooting data, the data used to determine the reference center position correction function are the actual shooting data opposite to the actual shooting data in which the relative motion has been corrected, so that not only the relative motion but also the motion derived from the rotation axis can be corrected.

[0037] The correction performed in the present invention targets the translational motion of the captured image caused by thermal drift of the sample during CT imaging, poor fixation, and focal spot movement. The correction method of the present invention can perform high-precision absolute motion correction without the need for reconstruction, reducing calculation costs, and without the effect of the structure or contrast of the sample on calculation accuracy.

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

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

[0040] For normalization of the X-ray intensity, it is preferable to rescale the X-ray intensity using the maximum and minimum values ​​of the X-ray intensity of the actual imaging data or the reference imaging data. By normalizing using both the minimum and maximum values ​​of the X-ray intensity, the intensity difference between low contrast and high contrast in the feature extraction projection image is reduced. Therefore, low contrast structures are more likely to be reflected in the coincidence calculation. For example, the X-ray intensity can be normalized using the following formula (1). In the following formula (1), I(x, y, θ) represents the X-ray intensity of a pixel at the imaging angle θ. The following formula (1) indicates that the X-ray intensity of all pixels at the imaging angle θ is converted into the value of the equation on the right side. I max (θ) and I min (θ) represents the maximum and minimum values ​​of the histogram of X-ray intensity obtained for each imaging angle θ. max (θ) and I min (θ) may be the maximum and minimum values ​​of the histogram of the X-ray intensity of the entire main imaging data or the entire reference imaging data, respectively. The normalization of the X-ray intensity is not limited to the formula (1).

[0041]

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[0042] The feature extraction of the projection image is preferably performed by detecting edges of the projection image. The edge detection can be performed, for example, by using a Sobel filter. In addition, it is preferable to perform noise removal of the projection image before the feature extraction of the projection image. The noise removal can be performed, for example, by using a median filter or a Gaussian filter. The noise removal and edge detection can be performed by applying, for example, a median filter, a Gaussian filter, and a Sobel filter to the projection image in this order. The feature extraction and noise removal of the projection image are not limited to the median filter, the Gaussian filter, or the Sobel filter.

[0043] These processes improve the calculation accuracy in calculating the relative motion correction value and determining the reference center position. This is particularly effective for samples with high-contrast and low-contrast structures. Therefore, when the tolerance error of the sample rotation axis is zero or very small, one embodiment of the present invention may include the steps of normalizing the X-ray intensity, extracting features of the projection image, creating a relative motion correction function, and correcting the imaging data using the relative motion correction function. In this case, better results can be obtained than with conventional techniques that correct the relative motion without normalizing the X-ray intensity or extracting features of the projection image.

[0044] Next, 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 are aligned, and a relative motion correction value is calculated for each imaging angle. Note that, when normalization of X-ray intensity, noise removal from the projection image, and feature extraction are performed as described above, the projection image in the following steps is preferably a projection image (feature-extracted projection image) that has been normalized for X-ray intensity, noise removal from the projection image, and feature extraction.

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

[0046]

number

[0047]

number

[0048]

number

[0049] Next, a relative motion correction function is created that corrects the relative motion of all the actual imaging data or the projection images based on the actual imaging 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. Any function may be used as the relative motion correction function as long as it can appropriately correct the relative motion. For example, a finite-order polynomial, Fourier series, spline function, etc., with the rotation angle θ of the sample rotation axis as a variable, can be used. It is simple to use a polynomial as the relative motion correction function. When a polynomial is used, the relative motion correction function can be obtained by polynomial interpolation based on the relative motion correction value. In the following, 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 called x shift (θ), y shift Let (θ).

[0050] The relative motion compensation function is preferably a polynomial whose degree is determined based on the number of reference shooting data. In addition, when the relative motion compensation function is a polynomial, the degree of the relative motion compensation function is preferably equal to or less than half the number of reference shooting data. This allows the degree of the relative motion compensation function to be reduced within an appropriate range, thereby reducing the cost required for processing.

[0051] Next, a provisional reference center position correction function is set, and the projection image based on the actual imaging data is corrected using the provisional reference center position correction function and the relative motion correction function. Correcting the projection image based on the actual imaging 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 may have angle dependency. For example, if the rotation axis projected on the detector is expected to move like a sine wave, a model with amplitude and phase as parameters can be considered. Such a provisional reference center position correction function center(θ) is expressed, for example, as in the following formula (5). a, δ, and b are parameters. The projection image based on the actual imaging data provisionally corrected using the provisional reference center position correction function and the relative motion correction function is defined as P1. P1 is expressed as the following formula (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 degree of coincidence between a certain provisionally corrected projection image and a projection image at an opposite shooting angle is calculated to determine the parameters of the provisional reference center position correction function. The provisionally corrected projection image based on the actual shooting data at the shooting angle opposite to P1 is flipped in the x direction with respect to the provisional reference center position to obtain a projection image P2. P2 is expressed by the following formula (7). The negative x coordinate indicates that it has been flipped.

[0055]

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[0056] The provisional reference center position correction function and the reference center position correction function based on the calculation of the degree of coincidence between a provisionally corrected projection image and a projection image at an opposing imaging angle can be determined, for example, by using the following formula (8). P1 and P2 in formula (8) are the above P1 and P2, respectively. That is, in the set provisional reference center position correction function center(θ), the MSE is calculated for the provisionally corrected projection image based on the actual imaging data and the projection image at the opposing imaging angle. Then, the parameters of the provisional reference center position correction function center(θ) that minimizes the MSE are found, and the result is used as the reference center position correction function.

[0057]

number

[0058] In the sigma calculation on the right side of the formula (8), (x, y) used to determine the parameters of the provisional reference center position correction function may be all points on the projection image, or may be limited to points within a frame set on the projection image. In addition, the projection image (i.e., the value of θ) used to determine the parameters of the provisional reference center position correction function may be calculated from a part of the projection image based on the actual shooting data and its opposing projection image, rather than from the projection image based on all the actual shooting data. This reduces the calculation cost required to determine the reference center position correction function. The function used to calculate the degree of coincidence is not limited to MSE, and for example, mutual information, correlation function, etc. may be used.

[0059] Then, the actual radiography data or a projection image based on the actual radiography 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 radiography data can be corrected without reconstruction.

[0060] The above explanation is for the method when the imaging data is captured with a parallel beam, but when the imaging data is captured with a fan beam or a cone beam, the reference center position correction function cannot be determined as it is. Therefore, the following explains the correction points when the imaging data is captured with a fan beam.

[0061] When the optical system of a CT scanner is a fan beam optical system, the projection images of the projection data taken do not strictly correspond to the projection images at the opposing shooting angles due to the magnification ratio. Therefore, fan-parallel conversion is performed to convert the projection images obtained by the fan beam method to those by the parallel beam method. In addition, fan-parallel conversion for projection images with motion must be performed after the motion is corrected. Therefore, fan-parallel conversion is performed at the following times.

[0062] The process can be performed in the same manner as above up to the step of creating a relative motion correction function and setting a provisional reference center position correction function. This is because the creation of the relative motion correction function is performed by comparing a projection image based on reference imaging data at the same imaging angle with a projection image based on actual imaging data. When the imaging data is data captured with a fan beam or cone beam and the X-ray intensity is normalized, the maximum and minimum values ​​are preferably the maximum and minimum values ​​of the histogram of the X-ray intensity of the entire actual imaging data or reference imaging data.

[0063] Next, a projection image based on the actual shooting data provisionally corrected by the provisional reference center position correction function and the relative motion correction function is obtained, and the provisionally corrected projection image is subjected to fan-parallel conversion. Figures 3(a) and (b) are schematic diagrams showing a sinogram of an actually measured projection image and a sinogram after provisional correction and fan-parallel conversion, respectively. Figure 3(a) shows a sinogram seen on the CU-θ plane before fan-parallel conversion, and Figure 3(b) shows a sinogram seen on the CU-θ plane after provisional correction and fan-parallel conversion. In Figure 3(b), the coordinates after fan-parallel conversion are replaced with the coordinates of a virtual detection plane. Each pixel of the projection image at angle θ in Figure 3(a) corresponds to a pixel on a cross section represented by a straight line near angle θ of the sinogram in Figure 3(b). The opposing positions of each pixel of the projection image after fan-parallel conversion are on a 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 Projected image P based on the actual photographic data provisionally corrected by (θ) main The converted data obtained by fan-parallel conversion is P p (x p ,y p ,θ p ;center(θ)). P p (x p ,y p ,θ p ;center(θ)) is expressed as the following formula (9). FanPara is a function that performs FanPara transformation, and (x p ,y p ,θ p ) indicate the coordinates on the virtual detection surface after Fan-Para transformation.

[0065]

number

[0066] The parameters of the provisional reference center position correction function and the reference center position correction function based on the calculation of the degree of coincidence between a certain transformation data after the fan-parallel transformation and the transformation data of the opposite angle can be determined, for example, by using the following formula (10). p is P in formula (9). p The x-coordinate of the second term on the right hand side is x p The minus sign in indicates that the function is inverted with respect to the center of the virtual detection surface after fan-parallel conversion. In other words, for the set temporary reference center position correction function center(θ), the projected image based on the temporarily corrected actual shooting data is converted into fan-parallel conversion, and the MSE is calculated for converted data at an angle opposite to a certain converted data after fan-parallel conversion. Then, the parameters of the temporary reference center position correction function center(θ) that minimizes the MSE are found, and this is used as the reference center position correction function.

[0067]

number

[0068] In this way, by using the projection image that has been provisionally corrected with the provisional reference center position correction function and the relative motion correction function and then fan-parallel converted, the reference center position correction function can be determined even when the imaging data is data obtained by a fan beam. Therefore, even when there is a motion derived from the rotation axis, the motion artifact can be corrected. That is, the present invention can also be applied when the X-ray is a fan beam. Note that the present invention can also be applied when the X-ray is a cone beam, since the cone beam can be regarded as a fan beam by setting a frame near the central cross section in the CV direction of the projection image.

[0069] [Entire system] FIG. 4 is a schematic diagram showing the configuration of the entire system 100 including a CT device 200 and a processing device 300, a correction device 400, an input device 510, and a display device 520 connected thereto. Here, the CT device 200 shown in FIG. 4 is configured to rotate a sample relative to an X-ray source 260 and a detector 270, but is not limited to this, and may be configured to rotate a gantry in which an X-ray source and a detector are integrated. In addition, the CT device 200 can be used with any device that uses a parallel beam, a fan beam, or a cone beam. However, regardless of the beam, 360° scanning is required when determining a reference center position correction function.

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

[0071] In Fig. 4, the processing device 300 and the correction device 400 are shown as separate components in order to emphasize the correction function of the correction device 400, but as shown in Fig. 5, the correction device 400 may be configured as a part of the function included in the processing device 300, or the correction device 400 and the processing device 300 may be configured as an integrated device. Fig. 5 is a schematic diagram showing a modified example of the overall system configuration. By using such a system, it is possible to reduce the cost of correcting motion-induced artifacts in CT image reconstruction.

[0072] [CT device] 4, the CT device 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. Note that the X-ray source 260 and the detector 270 may be installed on a gantry (not shown), and the gantry may be rotated relative to the sample fixed to the sample stage 250.

[0073] The CT device 200 drives the sample stage 250 at a timing instructed by the processing device 300 to obtain imaging data of the sample. The imaging data is transmitted to the processing device 300. The CT device 200 is suitable for use in precision industrial products such as semiconductor devices, but can also be applied to veterinary devices as well as industrial devices.

[0074] The X-ray source 260 irradiates X-rays toward the detector 270. The detector 270 has a light receiving surface that receives X-rays, and can measure the intensity distribution of the X-rays that have passed 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 driving unit 280.

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

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

[0077] The imaging data storage unit 310 stores imaging data acquired from the CT device 200. The imaging data includes main imaging data and reference imaging data. The main imaging data and the reference imaging data include rotation angle information and X-ray intensity detected at each pixel of the detector at the rotation angle. The device information storage unit 320 stores device information acquired from the CT device 200. The device information includes the device name, beam shape, geometry at the time of measurement, scan 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 extraction projection image on the display device 520. This allows the user to check the CT image based on the corrected imaging data, the imaging data and projection images before and after correction, or the feature extraction projection image. In addition, the user can give instructions and designations to the processing device 300, the correction device 400, etc. based on the CT image, the imaging data and projection images before and after correction, or the feature extraction projection image.

[0079] [Correction device] The correction device 400 is configured by a computer having a CPU, a ROM, a RAM, and a memory connected to a bus. The correction device 400 may be directly connected to the CT device 200, or may be connected to the CT device 200 via the processing device 300. The correction device 400 may receive information from the CT device 200 or may receive information from the processing device 300. As shown in FIG. 7, the correction device 400 may be configured as a part of the functions included in the processing device 300, or as shown in FIG. 8, the correction device 400 and the processing device 300 may be configured as an integrated device. The correction device 400 may also have a part of the functions of the processing device 300.

[0080] The correction device 400 includes an imaging 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 transmit and receive information via a control bus L. When the correction device 400 and the processing device 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 device 300.

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

[0082] The pre-processing unit 420 converts the main shooting data and the reference shooting data into a projection image.

[0083] The pre-processing unit 420 preferably normalizes the X-ray intensity of the actual photographing data or the reference photographing data, and creates a feature-extracted projection image by extracting features from the projection image based on the normalized actual photographing data or the reference photographing data. In this case, the pre-processing unit 420 preferably performs noise removal before extracting the features.

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

[0085] When the pre-processing unit 420 creates a feature extraction projection image, it is preferable that the relative motion compensation value calculation unit 430 calculates a relative motion compensation 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 generating section 440 generates a relative motion correction function for correcting the relative motion of all the main photographing data or the projected image based on the main photographing data, based on the relative motion correction value calculated by the relative motion correction value calculating section 430 .

[0087] The relative motion compensation function is preferably a polynomial of an order determined based on the number of reference shooting data. When the relative motion compensation function is a polynomial, the order of the relative motion compensation function is preferably equal to or less than half the number of reference shooting data. The function form and order of the relative motion compensation function may be set by a user. Alternatively, the function form and order may be automatically set by a computer based on the number of reference shooting data. Alternatively, the function form and order may be determined in advance.

[0088] The reference center position determination unit 450 sets a provisional reference center position correction function. Also, the reference center position determination unit 450 determines parameters of the provisional reference center position correction function and the reference center position correction function. The reference center position determination unit 450 acquires a provisionally corrected projection image, and determines the parameters of the provisional reference center position correction function and the reference center position correction function by calculating the degree of coincidence between the provisionally corrected projection image and a projection image at an imaging angle opposite thereto.

[0089] The main imaging data and the 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 of performing fan-parallel conversion. Also, a fan-parallel conversion unit may be provided separately. It is preferable that the reference center position determination unit 450 obtains conversion data obtained by performing fan-parallel conversion of 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 of the angle opposite thereto.

[0090] The motion correction unit 460 provisionally corrects the actual imaging data or the projection image based on the actual imaging data using the provisional reference center position correction function and the relative motion correction function. The motion correction unit 460 also corrects the actual imaging data or the projection image based on the actual imaging data using the reference center position correction function and the relative motion correction function. This allows absolute motion correction to be performed using the reference center position correction function and the relative motion correction function. The corrected actual imaging data or projection 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, the motion correction unit 460 preferably temporarily corrects the feature extraction projection image based on the actual shooting data with a temporary reference center position correction function and a relative motion correction function. At this time, the reference center position determination unit 450 preferably acquires the temporarily corrected feature extraction projection image and determines the parameters of the temporary reference center position correction function by calculating the degree of coincidence between the temporarily corrected feature extraction projection image and a feature extraction projection image at an opposite shooting angle.

[0092] It is preferable that the calculation of the relative motion correction value is performed based on a partial area of ​​the projected image. It is also preferable that the parameters of the provisional reference center position correction function are determined based on a partial area of ​​the provisionally corrected projected image. This can reduce calculation costs. The partial area of ​​the projected image may be set by a user. For example, the area can be set by specifying the width in the x-axis direction and the y-axis direction and the center position of the frame. It may also be configured so that the computer automatically sets it based on a characteristic structure. It may also be determined in advance.

[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 by, for example, mouse operation or keyboard operation. FIG. 9(a) is a conceptual diagram showing an example of a UI when the user makes various settings. FIG. 9(b) is a graph showing an example of a result of polynomial interpolation. In FIG. 9(a), for example, a frame can be set on a display screen of certain reference shooting data or a projection image displayed on the right side of the screen to calculate the degree of matching with the corresponding main shooting data or projection image. Also, a frame can be set on a display screen of certain shooting data or a projection image displayed on the right side of the screen to calculate the degree of matching with the opposing shooting data or projection image.

[0094] In the example of FIG. 9, the (x,y) calculation range can set the image range used to calculate the relative motion correction value or determine the reference center position. The (x,y) calculation range corresponds to the frame of the image View. The (x,y) search range can set the maximum amount to move the shooting data or the projected image up, down, left, and right. The degree can set the degree of the polynomial interpolation of the relative motion correction function. The search range of the reference center position can set the search range of the x-direction alignment of the data of the opposing angles. The UI function may have a function to display the calculation results. 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 FIG. 9(b). Note that the setting items displayed in FIG. 9(a) are just an example, and even if the user sets these, only some of them may be set, or all of them may be set. In addition, there may be setting items not displayed in FIG. 9.

[0095] [Measurement method] A sample is placed in the CT device 200, and the rotation axis is moved and X-rays are projected repeatedly under predetermined conditions to obtain actual or reference imaging data while irradiating the sample with X-rays. The CT device 200 transmits device information such as the scan method and the obtained actual or reference imaging data as imaging data to the processing device 300 or the correction device 400.

[0096] [Correction method] (Explanation of flow in case of parallel beam) FIG. 10 is a flowchart showing an example of the operation of the correction device 400. First, the correction device 400 acquires shooting data (step S1). Next, preprocessing is performed (step S2). Next, a relative motion correction value is calculated (step S3). At each shooting angle of the reference shooting data, the amount of movement in the x-axis direction and the y-axis direction at which the degree of coincidence between the projection image based on the reference shooting data and the projection image based on the main shooting data at the same shooting angle is maximized is set as the relative motion correction value. If a frame is set for the projection image, the degree of coincidence is calculated only for the area within the frame. Next, a relative motion correction function is created (step S4). It is preferable to set the relative motion correction function to 1 / 2 or less of the number of reference data.

[0097] Next, a provisional reference center position correction function is set (step S5). Next, a projection image based on the actual shooting data is provisionally corrected using a relative motion correction function and a provisional reference center position correction function (step S6). Next, the degree of coincidence between a provisionally corrected projection image and a projection image at an opposing angle is calculated (step S7).

[0098] If the set condition is not satisfied (step S8-NO), the process returns to step S5, another temporary reference center position correction function is set, and the process up to step S7 is performed again. On the other hand, if the set condition is satisfied (step S8-YES), the parameters of the temporary reference center position correction function and the reference center position correction function are then determined (step S9). Then, the actual shooting data or the projected image based on the actual shooting data is corrected using the relative motion correction function and the determined reference center position correction function (step S10). In this way, the actual shooting data or the projected image can be corrected. The condition in step S8 can be whether the parameters of the temporary reference center position correction function cover the entire set range, whether the total value of the degree of agreement calculated for a certain temporary reference center position meets a predetermined threshold, whether the total value of the degree of agreement calculated for a certain temporary reference center position is an extreme value, or the like. In addition, for example, the relative motion correction function can be set to multiple orders, steps 4 to 9 can be performed, and the order that provides the best degree of agreement in step S8 can be adopted. This allows for a more advanced estimation of the absolute motion.

[0099] (Explanation of the flow for fan beam or cone beam) Fig. 11 is a flowchart showing a modified example of the operation of the correction device 400. Fig. 11 shows an example of the operation when correcting imaging data obtained by a fan beam or a cone beam. First, the correction device 400 acquires imaging data (step T1). Next, preprocessing is performed (step T2). Next, a relative motion correction value is calculated (step T3). Next, a relative motion correction function is created (step T4).

[0100] Next, a provisional reference center position correction function is set (step T5). Next, a projection image based on actual shooting data is provisionally corrected using a relative motion correction function and a provisional reference center position correction function (step T6). Next, the provisionally corrected projection image is subjected to fan-parallel conversion (step T7). Next, the degree of agreement between a certain conversion data after fan-parallel conversion and conversion data of an opposing angle is calculated (step T8).

[0101] If the set condition is not satisfied (step T9-NO), the process returns to step T5, another temporary reference center position correction function is set, and the process up to step T7 is performed again. On the other hand, if the set condition is satisfied (step T9-YES), the parameters of the temporary reference center position correction function and the reference center position correction function are then determined (step T10). Then, the actual photographing data or the projected image based on the actual photographing data are corrected using the relative motion correction function and the determined reference center position correction function (step T11). In this way, the actual photographing data or the projected image can be corrected. The condition in step T9 can be, for example, whether the parameters of the temporary reference center position correction function cover the entire set range, whether the total value of the degree of agreement calculated for a certain temporary reference center position satisfies a predetermined threshold, whether the total value of the degree of agreement calculated for a certain temporary reference center position is an extreme value, or the like.

[0102] [Correction and reconstruction methods] 10 and 11 show the operation of only the correction device 400. This is sufficient for correcting the actual photographed data or the projected image, but to clarify the difference from the conventional technology, the operation including the photographing and reconstruction of the actual photographed data will also be described.

[0103] FIG. 12 is a flow chart showing an example of the operation of the system 100. First, the CT device 200 performs CT imaging (step U1). CT imaging includes repetition of moving the rotation axis and projecting X-rays. Next, the main imaging data or the projection image based on the main imaging data is corrected (step U2). The flow for correcting the main imaging data or the projection image based on the main imaging data may adopt, for example, one of the flows in FIG. 10 or FIG. 11 according to the type of optical system of the acquired projection image. In addition, the optical system may be identified from the device information to select an appropriate flow. Then, the processing device 300 or the correction device 400 reconstructs a CT image using the corrected main imaging data or the projection image based on the main imaging data (step U3). In this way, a CT image reconstructed using the corrected main imaging data or the projection image based on the main imaging data can be obtained.

[0104] In the conventional technology, the reconstruction of CT images and the correction for artifact reduction are repeated. In contrast, in the present invention, the correction for artifact reduction is performed on the projection image before reconstruction. In this way, the cost for correction can be reduced. In addition to the relative motion, the motion derived from the rotation axis can be corrected.

[0105] [Example 1] Using the system 100 configured as described above, a nonwoven fabric (sample 1) was observed. Measurements were performed using a Rigaku nano3DX (quasi-parallel beam optical system) CT device 200. Figures 13(a) and (b) are graphs showing the relative motion correction function of sample 1 obtained by the method of the present invention, and the result of determining the reference center position. Figure 13(a) shows the relative motion correction value and the relative motion correction function in the x and y directions. Figure 13(b) shows the set tentative reference center position and the MSE value at that time, and the position where the MSE value is the smallest is the determined reference center position. Figures 14(a) to (f) show a cross section of a CT image of sample 1 reconstructed using corrected actual imaging data and the same cross section of a CT image of sample 1 reconstructed using uncorrected actual imaging data, respectively. Figures 14(a) to (c) show correction, and Figures 14(d) to (f) show no correction. The FDK method was used for reconstruction.

[0106] The reference center position determined by the method of the present invention was -16 pixels, which was the same as the reference value (the center position obtained by 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. In addition, by comparing Figures 14(a) to (c) and (d) to (f), it was found that the correction by the method of the present invention reduced artifacts.

[0107] [Example 2] Next, the capacitor (sample 2) was observed. The CT device 200 was a Rigaku CT device with a cone beam optical system for measurement. Figures 15(a) and (b) are graphs showing the relative motion correction function of sample 2 obtained by the method of the present invention, and the result of determining the reference center position. Figure 15(a) shows the relative motion correction value and the relative motion correction function in the x and y directions. Figure 15(b) shows the set tentative reference center position and the MSE value at that time, and the position where the MSE value is the smallest is the determined reference center position. Figures 16(a) to (f) show a cross section of a CT image of sample 2 reconstructed using corrected actual imaging data and the same cross section of a CT image of sample 2 reconstructed using uncorrected actual imaging data, respectively. Figures 16(a) to (c) show correction, and Figures 16(d) to (f) show no correction. The FDK method was used for reconstruction, as with sample 1.

[0108] The reference center position determined by the method of the present invention was -6 pixels, and the same value as the reference value (the center position obtained by sequential calculation of slice reconstruction) was calculated. That is, it was confirmed that the method of the present invention can accurately determine the reference center position in a short time even for imaging data obtained by a cone beam without using reconstruction. In addition, by comparing Figures 16(a) to (c) and (d) to (f), it was found that artifacts were reduced by the correction by 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 by a cone beam or a fan beam.

[0109] The above results confirm that the correction device, system, method, and program of the present invention can effectively correct motion-induced artifacts in CT image reconstruction and reduce calculation costs. [Explanation of symbols]

[0110] 100 Systems 200 CT equipment 210 Rotation control unit 250 Sample stage 260 X-ray source 270 Detector 280 Drive Unit 300 Processing Equipment 310 Shooting data storage unit 320 Device information storage unit 330 Reconstruction part 340 Display section 400 Correction Device 410 Shooting data acquisition unit 420 Pretreatment section 430 Relative motion correction value calculation unit 440 Correction function creation section 450 Reference center position determination section 460 Motion Compensation Unit 510 Input Device 520 Display device

Claims

1. A correction device for correcting motion artifacts during CT image measurement, comprising: A photographing data acquisition unit that acquires the main photographing data and the reference photographing data scanned 360°; a pre-processing unit for converting the main photographing data and the reference photographing data into a projected image; a relative motion compensation value calculation unit that aligns the projection image based on the reference shooting data and the projection image based on the main shooting data corresponding to a shooting angle of the reference shooting data, and calculates a relative motion compensation value for each shooting angle; a correction function creating unit that creates a relative motion correction function for correcting the relative motion of all of the main photography data or the projection image based on the main photography data based on the relative motion correction value; a reference center position determination unit that sets a temporary reference center position correction function and determines parameters of the temporary reference center position correction function and the reference center position correction function; a motion correction unit that provisionally corrects the projection image based on the actual photography 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, and determines a parameter of the provisional reference center position correction function and the reference center position correction function by calculating a degree of coincidence between the provisionally corrected projection image and a projection image at an opposite shooting angle; The correction device, wherein the motion correction unit corrects the main shooting data or the projected image based on the main shooting data by using the reference center position correction function and the relative motion correction function.

2. the preprocessing unit normalizes X-ray intensities of the main imaging data or the reference imaging data, and creates a feature-extracted projection image by extracting features from a projection image based on the normalized main imaging data or the reference imaging data; The correction device according to claim 1 , wherein 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. 3. The correction device according to claim 2, wherein the preprocessing unit performs noise removal before extracting features.

4. the motion correction unit provisionally corrects the feature extraction projection image based on the actual photographing data; The correction device according to claim 2, wherein 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 a degree of coincidence between the provisionally corrected feature extraction projection image and the feature extraction projection image at an opposite shooting angle.

5. 2. The correction device according to claim 1, wherein the relative motion correction function is a polynomial of an order determined based on the number of frames of the reference shooting data.

6. 6. The correction device according to claim 5, wherein the order of the relative motion correction function is equal to or smaller than half the number of the reference photographic data.

7. the main imaging data and the reference imaging data are data obtained by a fan beam or a cone beam, The correction device described in claim 1, characterized in that the reference center position determination unit obtains transformation data obtained by fan-parallel transformation of the provisionally corrected projection image, and determines parameters of the provisional reference center position correction function by calculating the degree of coincidence between the transformation data and the transformation data of an angle opposite thereto.

8. 2. The correction device according to claim 1, wherein 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 a partial area of ​​the projected image or the provisionally corrected projected image.

9. a reconstruction unit that performs reconstruction based on the main photographing data corrected by the motion correction unit or a projection image based on the main photographing data to generate a CT image; 2. 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 including an X-ray source that generates X-rays, a detector that detects X-rays, and a rotation control unit that controls the rotation of the X-ray source and the detector, or a sample; A system comprising: a correction device according to any one of claims 1 to 9.

11. 1. A method for correcting motion artifacts during CT imaging, comprising: A step of acquiring main shooting data and reference shooting data scanned 360 degrees; converting the main photography data and the reference photography data into a projected image; aligning the projection image based on the reference shooting data and the projection image based on the main shooting data corresponding to a shooting angle of the reference shooting data, and calculating a relative motion correction value for each shooting angle; creating a relative motion compensation function for compensating for the relative motion of all of the main shooting data or the projection image based on the main shooting data based on the calculated relative motion compensation value; A step of setting a temporary reference center position correction function; provisionally correcting the projection image based on the actual photographing data using the provisional reference center position correction function and the relative motion correction function; acquiring the provisionally corrected projection image, and calculating a degree of coincidence between the provisionally corrected projection image and a projection image at an opposite shooting angle to the provisionally corrected projection image, thereby determining parameters of the provisional reference center position correction function and a reference center position correction function; and correcting the main shooting data or the projected image based on the main shooting data using the reference center position correction function and the relative motion correction function.

12. A program for correcting motion artifacts during CT image measurement, comprising: A process of acquiring the main shooting data and the reference shooting data scanned 360°; A process of converting the main photography data and the reference photography data into a projected image; A process of aligning the projection image based on the reference shooting data and the projection image based on the main shooting data corresponding to a shooting angle of the reference shooting data, and calculating a relative motion correction value for each shooting angle; A process of creating a relative motion compensation function for compensating for the relative motion of all of the main photography data or the projection image based on the main photography data based on the calculated relative motion compensation value; A process of setting a temporary reference center position correction function; a process of provisionally correcting the projection image based on the actual photographing data using the provisional reference center position correction function and the relative motion correction function; a process of acquiring the provisionally corrected projection image, and calculating a degree of coincidence between the provisionally corrected projection image and a projection image at an opposite shooting angle to the provisionally corrected projection image, thereby determining parameters of the provisional reference center position correction function and a reference center position correction function; and correcting the main shooting data or the projected image based on the main shooting data using the reference center position correction function and the relative motion correction function.

Images