JP4414168B2 - Calcification index measuring method and X-ray CT apparatus - Google Patents

Description

  The present invention relates to a calcification index measuring method and an X-ray CT (Computer Tomography) apparatus, and more specifically, lime that can suppress the influence on the measurement due to the size of the calcified portion and the positional relationship with the slice and can improve the measurement accuracy. The present invention relates to a chemical index measurement method and an X-ray CT apparatus.

A conventional method for measuring the coronary artery calcification index (CACS), which is called the AJ method, is based on the following procedure (see Non-Patent Document 1).
(1) Twenty images are continuously captured at a slice thickness of 3 mm and a slice interval of 3 mm downward from the base of the heart of a patient to reconstruct a tomographic image.
(2) The area is determined for each portion having a CT value of 130 or more for each coronary artery in each tomographic image. When the highest CT value of each part is 130 to 199, the weight is “1”, when 200 to 299, the weight is “2”, when 300 to 399, the weight is “3”, and when it is 400 or more. Is a weight “4”. A value obtained by multiplying the weight and area of each part is defined as the calcification index of the part.
(3) A value obtained by adding the calcification indexes of all the portions of the coronary artery is used as the coronary artery calcification index of the patient.
Edited by Rikuji Morita and Makoto Takamiya, “Fundamentals and Clinics of Ultra-High-Speed CT”, Kinyoshido, February 1, 1997, p. 62-63 (IV. Coronary artery calcification by Nobuyuki Aizawa)

For example, a spherical calcified portion having a diameter of about 3 mm is assumed. When this calcified portion is included in one slice, the CT value of that portion is 130 or more on the tomographic image, and a weight of “1” to “4” is given. That is, it counts as a calcification part.
However, when this calcified portion extends over two slices, since only one half of the calcified portion is included in one slice, the CT value of that portion is less than 130 on each tomographic image of the two slices. And weighting is not possible. That is, it is not counted as a calcified portion.
Thus, in the above-described conventional calcification index measurement method, a certain calcification part is counted as a calcification part or not counted as a calcification part depending on its size or positional relationship with a slice, and the measurement accuracy There was a problem inferior to.
Accordingly, an object of the present invention is to provide a calcification index measurement method and an X-ray CT apparatus capable of suppressing the influence on the measurement due to the size of the calcification portion and the positional relationship with the slice and improving the measurement accuracy.

In the first aspect, the present invention reproduces a plurality of tomographic images Ga (a = 1, 2,...) At a tomographic image interval ds smaller than a column interval dr in a direction in which a plurality of detector rows of the multi-detector are arranged. A calcification index measuring method is provided, characterized in that the calcification index C is calculated based on the tomographic images Ga.
As described above, for example, when assuming a spherical calcified portion having a diameter close to the slice interval, the lime is divided into a case where the calcified portion is included in one slice and a case where the calcified portion extends over two slices. It may or may not be counted as a digitized part.
However, in the calcification index measurement method according to the first aspect described above, since the tomographic image interval ds is smaller than the column interval dr in the direction in which a plurality of detector columns of the multi-detector are arranged, It is possible to reduce the error of variation in the measured value depending on the position. That is, the influence of the variation on the measurement due to the size of the calcified portion and the positional relationship with the slice can be suppressed, and as a result, the measurement accuracy can be improved.

In a second aspect, the present invention provides a method for measuring a calcification index having the above-described configuration. One line on a reconstruction area P corresponding to a tomographic image G or a plurality of parallel lines L spaced apart by a plurality of pixels. , The projection data Dr is multiplied by a cone beam reconstruction load to generate projection line data Dp, and the projection line data Dp is subjected to filter processing so that each position line of the image Data Df is generated, back projection pixel data D2 of each pixel on the reconstruction part is obtained based on each position line data Df of the image, and back projection pixel data D2 of all views used for image reconstruction is associated with the pixel. There is provided a method for measuring a calcification index, characterized in that a tomographic image G is reconstructed by a three-dimensional backprojection method that adds to obtain backprojection data D3.
In the calcification index measurement method according to the second aspect, since the three-dimensional backprojection method is used, the position of the reconstruction area P is arbitrarily determined without being limited to the position of the detector row when the projection data Dr is collected. Therefore, the tomographic images G can be reconstructed, so that a plurality of tomographic images Ga can be reconstructed with a tomographic image interval ds smaller than the column interval dr in the direction in which the multiple detector rows of the multi-detector are arranged.

In a third aspect, the present invention provides a calcification index measuring method having the above-described configuration, wherein each calcification portion Rab (b = 1, b) is a region of interest in each tomographic image Ga and has a CT value range. 2,...), A weight product Cab based on the area and the CT value is obtained, and the sum of the products Cab of all the calcified portions Rab of all the tomographic images Ga is determined according to the tomographic image interval ds or the number of tomographic images. A method for measuring a calcification index is provided, which is obtained by multiplying a coefficient H to obtain a calcification index C of a region of interest of the patient.
In the calcification index measurement method according to the third aspect,
C = H × ΣCab
And By multiplying the tomographic image interval ds or the number of tomographic images by a coefficient H, the same calcification index C can be obtained even if the tomographic image interval ds or the tomographic image number is changed.

In a fourth aspect, the present invention provides an area Aab for each calcification portion Rab that is a region of interest in each tomographic image Ga and has a CT value equal to or greater than a threshold value in the calcification index measurement method having the above configuration. The weight Wab is determined according to the highest CT value of each calcified portion Rab, and the product Cab = Wab × Aab of the calcified portion Rab is obtained by multiplying the weight Wab of each calcified portion Rab and the area Aab. A method for measuring a calcification index characterized by the following:
Although it is possible to determine the weight Wab according to the average CT value of each calcified portion Rab, in the calcification index measuring method according to the fourth aspect, according to the highest CT value of each calcified portion Rab. By defining the weight Wab, underestimation can be avoided.

In a fifth aspect, the present invention provides the calcification index measurement method having the above-described configuration, wherein the region of interest is a coronary artery, the threshold value is 130, and the highest CT value of each calcification portion Rab is 130. When ˜199, the weight Wab = 1, when 200˜299, the weight Wab = 2, when 300˜399, the weight Wab = 3, and when 400 or more, the weight Wab = 4. A method for measuring calcification index is provided.
In the calcification index measurement method according to the fifth aspect, a weight corresponding to the weight based on the AJ method can be applied.

In a sixth aspect, the present invention provides the calcification index measurement method having the above-described configuration, wherein the coefficient H = ds / 3 when the tomographic image interval is ds [mm]. I will provide a.
In the calcification index measuring method according to the sixth aspect, the tomographic image interval ds is normalized by the tomographic image interval 3 mm based on the AJ method, so that the calcification index C corresponding to the calcification index C based on the AJ method is obtained. It will be obtained.

In a seventh aspect, the present invention provides an average tomographic image Vv (v = 1, averaged) of adjacent tomographic images of a plurality of tomographic images Ga (a = 1, 2,...) Reconstructed at a tomographic image interval ds. 2), and the calcification index C is calculated based on the original tomographic image Ga and the average tomographic image Vv, assuming that the average tomographic image Vv is located in the middle of the adjacent tomographic images. A calcification index measurement method is provided.
As described above, for example, when assuming a spherical calcified portion having a diameter close to a slice interval, the calcified portion is included in one slice and straddles two slices. It may be counted as a part or not counted, and the error becomes large.
However, in the calcification index measurement method according to the seventh aspect, in order to create the average tomographic image Vv and increase the number of tomographic images, the case where the calcification portion is included in one slice and the case where it straddles two slices. The error when it is counted or not counted as a calcified portion can be reduced. That is, the influence of variation on the measurement due to the size of the calcified portion and the positional relationship with the slice can be suppressed, and the measurement accuracy can be improved.

In an eighth aspect, the present invention provides the calcification index measurement method having the above-described configuration, wherein each calcification portion Rab that is a region of interest in each tomographic image Ga and average tomographic image Vv and whose CT value is equal to or greater than a threshold value. (B = 1, 2,...), Fvf (f = 1, 2,...), Weights products Cab and cvf based on the area and the CT value are obtained, and all tomographic images Ga and all limes of the average tomographic image Vv are obtained. The calcification index C of the region of interest of the patient is obtained by multiplying the sum of the products Cab and cvf of the normalized portions Rab and Fvf by a coefficient H corresponding to the tomographic image interval ds or the number of tomographic images. A method for measuring calcification index is provided.
In the calcification index measurement method according to the eighth aspect,
C = H × ΣCab
And By multiplying the tomographic image interval ds or the number of tomographic images by a coefficient H, the same calcification index C can be obtained even if the tomographic image interval ds or the tomographic image number is changed.

In a ninth aspect, the present invention provides the calcification index measuring method having the above-described configuration, wherein each calcification portion Rab that is a region of interest in the tomographic image Ga and the average tomographic image Vv and has a CT value equal to or greater than a threshold value. , Fvf, areas Aab, Evf are determined, weights Wab, wvf are determined according to the highest CT value of each calcified portion Rab, Fvf, weights Wab, wvf and areas Aab, Evf of each calcified portion Rab, Fvf To obtain a product Cab = Wab × Aab, cvf = wvf × Evf of the calcified portions Rab and Fvf.
Although it is possible to determine the weight Wab according to the average CT value of each calcified portion Rab, in the calcification index measuring method according to the ninth aspect, according to the highest CT value of each calcified portion Rab. By defining the weight Wab, underestimation can be avoided.

In a tenth aspect, the present invention provides the calcification index measurement method having the above-described configuration, wherein the region of interest is a coronary artery, the threshold value is 130, and the highest CT value of each calcification portion Rab is 130. When ˜199, the weight Wab = 1, when 200˜299, the weight Wab = 2, when 300˜399, the weight Wab = 3, and when 400 or more, the weight Wab = 4. A method for measuring calcification index is provided.
In the calcification index measurement method according to the tenth aspect, a weight corresponding to the weight based on the AJ method according to the above-described prior art can be applied.

In an eleventh aspect, in the calcification index measurement method having the above-described configuration, the present invention provides a coefficient H = (ds / 3) when the tomographic image interval is ds [mm] and the number of tomographic images Ga is Na. Provided is a method for measuring a calcification index, characterized in that xNa / (2xNa-1).
In the calcification index measurement method according to the eleventh aspect, the tomographic image interval ds is normalized by the tomographic image interval 3 mm based on the AJ method, and the number of tomographic images increased by adding the average tomographic image Vv is also normalized. Therefore, the calcification index C corresponding to the calcification index C based on the AJ method can be obtained.

In a twelfth aspect, the present invention provides an X-ray tube, a multi-detector having a plurality of detector rows, and projection data while rotating at least one of the X-ray tube or the multi-detector around an object to be imaged. For reconstructing a plurality of tomographic images Ga (a = 1, 2,...) With a tomographic image interval ds smaller than a column interval dr in a direction in which a plurality of detector columns of the multi-detector are arranged. Provided is an X-ray CT apparatus comprising: a reconstruction unit; and a calcification index calculation unit that calculates a calcification index C based on the tomographic image Ga.
In the X-ray CT apparatus according to the twelfth aspect, the calcification index measurement method according to the first aspect can be suitably implemented.

In a thirteenth aspect, the present invention provides the X-ray CT apparatus having the above-described configuration, wherein the image reconstruction means includes one line on the reconstruction area P corresponding to a certain tomographic image G or a plurality of pixels spaced by a plurality of pixels. Projection data Dr corresponding to the parallel line L of the book is extracted, the projection data Dr is multiplied by a cone beam reconstruction load to create projection line data Dp, and the projection line data Dp is filtered. Image position line data Df is generated, back projection pixel data D2 of each pixel on the reconstruction portion is obtained based on the image position line data Df, and back projection pixels of all views used for image reconstruction Provided is an X-ray CT apparatus characterized by reconstructing a tomographic image G by a three-dimensional backprojection method that adds back data D2 in correspondence with pixels to obtain backprojection data D3.
In the X-ray CT apparatus according to the thirteenth aspect, the calcification index measuring method according to the second aspect can be suitably implemented.

In a fourteenth aspect, the present invention provides the X-ray CT apparatus having the above-described configuration, wherein the calcification index calculating means is a calcification that is a region of interest in each of the tomographic images Ga and has a CT value equal to or greater than a threshold value. A product Cab of weights based on the area and CT value is obtained for the portion Rab (b = 1, 2,...), And the product Cab of all the calcified portions Rab of all the tomographic images Ga is summed to obtain a value obtained by adding the product Cab. There is provided an X-ray CT apparatus characterized by multiplying a corresponding coefficient H to obtain a calcification index C of a region of interest of the patient.
In the X-ray CT apparatus according to the fourteenth aspect, the calcification index measurement method according to the third aspect can be suitably implemented.

In a fifteenth aspect, the present invention provides the X-ray CT apparatus configured as described above, wherein the calcification index calculation means is a calcification that is a region of interest in each of the tomographic images Ga and has a CT value equal to or greater than a threshold value. The area Aab is obtained for each portion Rab, the weight Wab is determined according to the highest CT value of each calcified portion Rab, the weight Wab of each calcified portion Rab is multiplied by the area Aab, and the product Cab of the calcified portion Rab is calculated. An X-ray CT apparatus characterized by obtaining = Wab × Aab is provided.
In the X-ray CT apparatus according to the fifteenth aspect, the calcification index measurement method according to the fourth aspect can be suitably implemented.

In a sixteenth aspect, the present invention provides the X-ray CT apparatus having the above-described configuration, wherein the region of interest is a coronary artery, the threshold is 130, and the highest CT value of each calcified portion Rab is 130 to The weight Wab = 1 when 199, the weight Wab = 2 when 200-299, the weight Wab = 3 when 300-399, and the weight Wab = 4 when 400 or more. An X-ray CT apparatus is provided.
In the X-ray CT apparatus according to the sixteenth aspect, the calcification index measurement method based on the AJ method according to the fifth aspect can be suitably implemented.

According to a seventeenth aspect, the present invention provides the X-ray CT apparatus having the above-described configuration, wherein the calcification index calculating means sets a coefficient H = ds / 3 when the tomographic image interval is ds [mm]. An X-ray CT apparatus is provided.
In the X-ray CT apparatus according to the seventeenth aspect, the calcification index measurement method based on the AJ method according to the sixth aspect can be suitably implemented.

In an eighteenth aspect, the present invention provides an X-ray tube, a multi-detector having a plurality of detector rows, and projection data while rotating at least one of the X-ray tube or the multi-detector around an imaging target. Scanning means for collecting image data, image reconstruction means for reconstructing a plurality of tomographic images Ga (a = 1, 2,...) At a tomographic image interval ds, and a plurality of tomographic images Ga reconstructed at a tomographic image interval ds. Average tomographic image creation means for creating an average tomographic image Vv (v = 1, 2,...) Obtained by averaging adjacent tomographic images (a = 1, 2,...), And the average between the adjacent tomographic images. There is provided an X-ray CT apparatus comprising a calcification index calculating means for calculating a calcification index C based on an original tomographic image Ga and an average tomographic image Vv as the tomographic image Vv is located.
In the X-ray CT apparatus according to the eighteenth aspect, the calcification index measurement method according to the seventh aspect can be suitably implemented.

In a nineteenth aspect, the present invention provides the X-ray CT apparatus configured as described above, wherein the calcification index calculation means is a region of interest in each of the tomographic images Ga and the average tomographic image Vv, and the CT value is a threshold value. For each of the above calcified portions Rab (b = 1, 2,...), Fvf (f = 1, 2,...), The products of weights Cab and cvf based on the area and the CT value are obtained. The sum of the products Cab and cvf of all the calcified portions Rab and Fvf of the tomographic image Vv is multiplied by the coefficient H corresponding to the tomographic image interval ds or the number of tomographic images, and the calcification index C of the region of interest of the patient. An X-ray CT apparatus characterized by obtaining the above is provided.
In the X-ray CT apparatus according to the nineteenth aspect, the calcification index measurement method according to the eighth aspect can be suitably implemented.

In a twentieth aspect, the present invention provides the X-ray CT apparatus configured as described above, wherein the calcification index calculation means is a region of interest in each of the tomographic images Ga and the average tomographic image Vv, and the CT value is a threshold value. The areas Aab and Evf are obtained for each of the above calcified portions Rab and Fvf, the weights Wab and wvf are determined according to the highest CT values of the calcified portions Rab and Fvf, and the weights Wab, Provided is an X-ray CT apparatus characterized by multiplying wvf and areas Aab and Evf to obtain a product Cab = Wab × Aab, cvf = wvf × Evf of the calcified portions Rab and Fvf.
In the X-ray CT apparatus according to the twentieth aspect, the calcification index measurement method according to the ninth aspect can be suitably implemented.

In a twenty-first aspect, the present invention provides the X-ray CT apparatus configured as described above, wherein the region of interest is a coronary artery, the threshold is 130, and the highest CT value of each calcified portion Rab is 130 to The weight Wab = 1 when 199, the weight Wab = 2 when 200-299, the weight Wab = 3 when 300-399, and the weight Wab = 4 when 400 or more. An X-ray CT apparatus is provided.
In the X-ray CT apparatus according to the twenty-first aspect, the calcification index measurement method based on the AJ method according to the tenth aspect can be suitably implemented.

In a twenty-second aspect, the present invention provides the X-ray CT apparatus having the above-described configuration, wherein the calcification index calculating means has a coefficient when the tomographic image interval is ds [mm] and the number of tomographic images Ga is Na. Provided is an X-ray CT apparatus characterized by H = (ds / 3) × Na / (2 × Na−1).
In the X-ray CT apparatus according to the twenty-second aspect, the calcification index measurement method based on the AJ method according to the eleventh aspect can be suitably implemented.

  According to the calcification index measuring method and the X-ray CT apparatus of the present invention, it is possible to suppress the influence of variation on the measurement due to the size of the calcified portion and the positional relationship with the slice, and improve the measurement accuracy.

  Hereinafter, the present invention will be described in more detail with reference to embodiments shown in the drawings. Note that the present invention is not limited thereby.

FIG. 1 is a configuration block diagram illustrating an X-ray CT apparatus 100 according to the first embodiment.
The X-ray CT apparatus 100 includes an operation console 1, an imaging table 10, and a scanning gantry 20.

  The operation console 1 includes an input device 2 that receives input from an operator, a central processing unit 3 that executes image reconstruction processing, a data collection buffer 5 that collects projection data acquired by the scanning gantry 20, and a projection data. A CRT 6 that displays a tomographic image reconstructed in a three-dimensional image, and a storage device 7 that stores programs, data, and X-ray tomographic images are provided.

  The table device 10 includes a cradle 12 that puts a subject and puts it in and out of a bore (cavity) of the scanning gantry 20. The cradle 12 is moved up and down and linearly moved by a motor built in the table apparatus 10.

  The scanning gantry 20 rotates to control the X-ray tube 21, X-ray controller 22, collimator 23, multi-detector 24, DAS (Data Acquisition System) 25, X-ray controller 22, collimator 23, and DAS 25. A side controller 26 and a control controller 29 for exchanging control signals and the like with the operation console 1 and the imaging table 10 are provided.

2 and 3 are explanatory diagrams of the X-ray tube 21 and the multi-detector 24. FIG.
The X-ray tube 21 and the multi-detector 24 rotate around the rotation center IC. When the vertical direction is the y direction, the horizontal direction is the x direction, and the direction perpendicular thereto is the z direction, the rotation plane of the X-ray tube 21 and the multi-detector 24 is the xy plane. The moving direction of the cradle 12 is the z direction.
The X-ray tube 21 generates an X-ray beam called a cone beam CB.
The multi-detector 24 has, for example, 256 detector rows. The detector row interval dr of the multi-detector 24 becomes the projection data interval in the direction in which the detector rows of the multi-detector 24 are arranged. Each detector row has, for example, 1024 channels.

FIG. 4 is a flowchart showing an outline of the operation of the X-ray CT apparatus 100.
In step S1, the X-ray tube 21 and the multi-detector 24 are rotated around the object to be imaged, and are represented by the z-direction position z of the multi-detector 24, the view angle view, the detector row number j, and the channel number i. Projection data D0 (z, view, j, i) is collected. For example, when measuring the coronary artery calcification index, projection data D0 (z, view, j, i) is collected in an imaging range including a range of 60 mm below the base of the heart of the patient.

In step S2, preprocessing (offset correction, logarithmic correction, X-ray dose correction, sensitivity correction) is performed on the projection data D0 (z, view, j, i).
In step S3, filter processing is performed on the preprocessed projection data D0 (z, view, j, i). That is, Fourier transform is performed, a filter (reconstruction function) is applied, and inverse Fourier transform is performed.

In step S4, three-dimensional backprojection processing is performed on the filtered projection data D0 (z, view, j, i), and a plurality of detector rows of the multi-detector 24 are arranged as shown in FIG. Back projection data D3 (x, y) are obtained for a plurality of reconstruction areas Pa (a = 1, 2,...) Arranged at a tomographic image interval ds smaller than the column interval dr.
The three-dimensional backprojection process will be described later with reference to FIG.

  For example, when measuring the coronary artery calcification index, in the above-described prior art, 20 tomographic images were reconstructed continuously at a slice thickness of 3 mm and a slice interval of 3 mm downward from the base of the heart. In order to maintain compatibility with this, n (= 20 [sheets] × 3 [mm] ÷ ds [mm]) reconstructions in succession at reconstruction region intervals ds downward from the base of the patient's heart. The back projection data D3 (x, y) for the areas P1 to Pn are respectively obtained. For example, if ds = 0.75 mm, n = 80.

  In step S5, post-processing is performed on the backprojection data D3 (x, y) of the reconstruction areas P1 to Pn, respectively, and tomographic images G1 to Gn are obtained.

  In step S7, a calcified portion Rab (b = 1, 2,...) That is a region of interest on each tomographic image Ga and has a CT value equal to or greater than a threshold value is automatically or manually extracted.

  In step S8, an area Aab is obtained for each calcified portion Rab, a weight Wab is determined according to the highest CT value of each calcified portion Rab, and the weight Wab of each calcified portion Rab is multiplied by the area Aab. The partial product Cab = Wab × Aab is calculated.

  In step S9, the product Cab of all parts of all the tomographic images G1 to Gn is summed and multiplied by a coefficient H according to the tomographic image interval ds or the number of tomographic images to obtain the calcification index C of the region of interest of the patient. The coefficient H = ds [mm] / 3 for maintaining compatibility with the above-described conventional technique for measuring the coronary artery calcification index CACS, and if ds = 0.75 mm, H = 0.25.

  Steps S7 to S9 will be described in detail later with reference to FIGS.

FIG. 6 is a flowchart showing details of the three-dimensional backprojection process (step S4 in FIG. 4).
In step R1, attention is paid to one view in all views (that is, a view of 360 ° or a view of “180 ° + fan angle”) necessary for reconstruction of one tomographic image Ga.

  In step R2, projection data Dr corresponding to a plurality of parallel lines spaced by a plurality of pixels on the reconstruction area is extracted from the projection data D0 (z, view, j, i) of the view of interest.

FIG. 7 illustrates a plurality of parallel lines L0 to L8 on one reconstruction area P.
The number of lines is 1/64 to 1/2 of the maximum number of pixels in the reconstruction area in the direction orthogonal to the lines. For example, when the number of pixels in the reconstruction area P is 512 × 512, the number of lines is nine.
In the case of −45 ° ≦ view <45 ° (or a view angle range including and surrounding the subject) and 135 ° ≦ view <225 ° (or a view angle range including and surrounding the subject), the x direction Is the line direction. In addition, in the case of 45 ° ≦ view <135 ° (or a view angle range including the periphery and including the periphery) and 225 ° ≦ view <315 ° (or a view angle range including the periphery and including the periphery), the y direction is set. Line direction.
A projection plane pp that passes through the rotation center IC and is parallel to the lines L0 to L8 is assumed.

FIG. 8 shows lines T0 to T8 obtained by projecting the lines L0 to L8 onto the detector surface dp in the X-ray transmission direction.
The X-ray transmission direction is the geometric position of the X-ray tube 21, the multi-detector 24, and the lines L0 to L8 (the z-axis direction from the xy plane passing through the center of the multi-detector 24 in the z-axis direction to the reconstruction region P. And the positions of the lines L0 to L8, which are a set of pixel points on the reconstruction area P).
If the row data of the detector row j and the channel i corresponding to the lines T0 to T8 projected on the detector plane dp is extracted, these are the projection data Dr corresponding to the lines L0 to L8.

  Then, as shown in FIG. 9, assuming the lines L0 ′ to L8 ′ obtained by projecting the lines T0 to T8 on the projection plane pp in the X-ray transmission direction, the projection data Dr is developed on these lines L0 ′ to L8 ′. Keep it. The projection plane pp is an xz plane that passes through the rotation center IC. Further, when the central axis direction of the cone beam CB is parallel to the y direction, view = 0 °.

Returning to FIG. 6, in step R3, the projection data Dr of each line L0 ′ to L8 ′ is multiplied by the cone beam reconstruction load to create projection line data Dp as shown in FIG.
Here, the cone beam reconstruction load is projected from the focus of the X-ray tube 21 with the distance from the focus of the X-ray tube 21 to the detector row j and the channel i of the multi-detector 24 corresponding to the projection data Dr being r0. When the distance to a point on the reconstruction area P corresponding to the data Dr is r1, (r1 / r0) ² .

  In step R4, filter processing is performed on the projection line data Dp. That is, FFT is applied to the projection line data Dp, a filter function (reconstruction function) is applied, and inverse FFT is performed to obtain image position line data Df as shown in FIG.

In step R5, interpolation processing is performed in the line direction for each position line data Df of the image, and high density image position line data Dh as shown in FIG. 12 is created.
The data density of each position line data Dh in the high-density image is 8 to 32 times the maximum number of pixels in the reconstruction area in the line direction. For example, when the number of pixels of the reconstruction area P is 512 × 512 with 16 times, the data density is 8192 points / line.

  In step R6, each position line data Dh of the high-density image is sampled and subjected to interpolation / extrapolation processing as necessary to obtain the back projection data D2 of the pixels on the lines L0 to L8 as shown in FIG. .

  In step R7, each position line data Dh of the high-density image is sampled and subjected to interpolation / extrapolation processing to obtain back projection data D2 of pixels between the lines L0 to L8 as shown in FIG.

  9 to 14 are views of −45 ° ≦ view <45 ° (or a view angle range including and including the periphery) and 135 ° ≦ view <225 ° (or a view including and including the periphery mainly). Angle range), but 45 ° ≦ view <135 ° (or a view angle range including and surrounding the subject) and 225 ° ≦ view <315 ° (or a view including and surrounding the subject) In the angle range), it becomes as shown in FIGS.

Returning to FIG. 6, in step R8, as shown in FIG. 21, the backprojection data D2 shown in FIG.
In step R9, steps R1 to R8 are repeated for all the views necessary for reconstruction of the tomographic image (that is, the view of 360 ° or the view of “180 ° + fan angle”), and the backprojection data D3 (x , y).

  Three-dimensional image reconstruction methods are disclosed in Japanese Patent Application No. 2002-066420, Japanese Patent Application No. 2002-147061, Japanese Patent Application No. 2002-147231, Japanese Patent Application No. 2002-235561, Japanese Patent Application No. 2002-235661, and Japanese Patent Application No. 2002-267833. The three-dimensional image reconstruction method proposed in Japanese Patent Application No. 2002-322756 and Japanese Patent Application No. 2002-338947 may be used.

Next, the processing contents of the above-described steps S7 to S9 will be described with reference to schematic examples.
As shown in FIG. 22, it is assumed that there is only one calcified portion Q having an area = A and a CT value = 190 penetrating through slices corresponding to all tomographic images.

  FIG. 23 corresponds to the AJ method of the prior art, and the tomographic images g1 and g2 are reconstructed with a slice thickness of 3 mm and a tomographic image interval ds = 3 mm. The area covered by the tomographic images g1 and g2 is an area having a width of 6 mm centered on the position α (tomographic image interval ds = 3 mm) × (the number of tomographic images n = 2) = 6 mm. In this case, the CT values of the calcified portions R11 and R21 in the tomographic images g1 and g2 are all “190”. Therefore, in the AJ method, the weights W11 = 1 and W21 = 1 and the area is A, so the calcification index C = 2A.

  In FIG. 24, the first embodiment of the present invention is applied to the same region as FIG. 23, and the tomographic images G1 to G8 are reconstructed with a slice thickness of 3 mm and a tomographic image interval ds = 0.75 mm. The area covered by the tomographic images G1 to G8 is an area having a width of (mm tomographic image interval ds = 0.75 mm) × (the number of tomographic images n = 8) = 6 mm centering on the position α, and corresponds to FIG. is doing. In this case, the CT values of the calcified portions R11 to R81 in the tomographic images G1 to G8 are all “190”.

  In step S7, when the threshold value is set to “130”, for example, calcified portions R11,..., R81 are extracted from the tomographic images G1,.

  Next, in step S8, the area A11 =... A81 = A of each calcified portion R11,. For example, when the highest CT value of each calcified portion is 130 to 199, the weight is “1”, when 200 to 299, the weight is “2”, when 300 to 399, the weight is “3”, 400 In this case, when the weight is set to “4”, the weights W11 =... R81 of R11,. Therefore, the product C11 = ... = C81 = A of the area A of each calcified portion R11,..., R81 and the weights W11,.

  Next, in step S9, the products C11 to C81 of all the calcified portions R11 to R81 of all the tomographic images G1 to G8 are summed and multiplied by a coefficient H corresponding to the tomographic image interval ds or the number of tomographic images, The site of interest calcification index C. Here, since the tomographic image interval ds = 0.75 mm and the coefficient H = 0.75 / 3 = 0.25, the patient's region of interest calcification index C = 8A × 0.25 = 2A.

  That is, for the calcified portion Q that penetrates through all slices, the region-of-interest calcification index C obtained by the above-described prior art and the present invention is compatible.

Next, as shown in FIG. 25, it is assumed that there is only one calcified portion Q having an area = A, a length = 3.75 mm, and a CT value = 190 across the tomographic images g1, g2.
Then, the CT value of the portion R11 corresponding to the calcified portion Q in the tomographic image g1 is “119”, and the CT value of the portion R21 corresponding to the calcified portion Q in the tomographic image g2 is “119”. Therefore, in the AJ method, the weights W11 = 0, W21 = 0, and the calcification index C = 0.

  In FIG. 26, the present invention is applied to the same area as FIG. 25, and tomographic images G1 to G8 are reconstructed with a slice thickness of 3 mm and a tomographic image interval ds = 0.75 mm. In this case, the CT value of the calcified portion R11 in the tomographic image G1 is “48”, the CT value of the calcified portion R21 in the tomographic image G2 is “95”, and the CT value of the calcified portion R31 in the tomographic image G3 is “143”. The CT value of the calcified portion R41 in the tomographic image G4 is “190”, the CT value of the calcified portion R51 in the tomographic image G5 is “190”, and the CT value of the calcified portion R61 in the tomographic image G6 is “143”. In the image G7, the CT value of the calcified portion R71 is “95”, and in the tomographic image G8, the CT value of the calcified portion R81 is “48”.

  In step S7, when the threshold value is set to “130”, for example, calcified portions R31 to R61 of the tomographic images G3 to G6 are extracted.

  Next, in step S8, the area A of the calcified portions R31 to R61 is obtained. For example, when the highest CT value of each part is 130 to 199, the weight is “1”, when 200 to 299, the weight is “2”, when 300 to 399, the weight is “3”, and 400 or more. When the weight is “4”, the weights W31 = W41 = W51 = W61 = 1 of the calcified portions R31 to R61 are obtained, so the product C31 = C41 = C51 = C61 = 1 of the calcified portions R31 to R61. XA is obtained.

  Next, in step S9, the products of all the parts of all the tomographic images are summed and multiplied by a coefficient H corresponding to the tomographic image interval ds or the number of tomographic images to obtain a calcification index C of the region of interest of the patient. Here, since the tomographic image interval ds = 0.75 mm and the coefficient H = 0.75 / 3 = 0.25, the patient's region of interest calcification index C = 4A × 0.25 = A.

  That is, in the conventional technique, as shown in FIG. 25, the region of interest calcification index C = 0 even when the calcified portion Q exists, but in the present invention, as shown in FIG. The calcification index C = A, and the presence of the calcification portion Q can be detected.

FIG. 27 is a configuration block diagram illustrating an X-ray CT apparatus 200 according to the second embodiment.
The X-ray CT apparatus 200 is basically the same as the X-ray CT apparatus 100 according to the first embodiment, but includes a dual detector 24 ′ having two detector rows instead of the multi-detector 24. ing.

FIG. 28 is a flowchart showing an outline of the operation of the X-ray CT apparatus 200.
In step S1 ′, the z-direction position z, the view angle view, the detector row number j, the channel number i of the dual detector 24 ′ are rotated while the X-ray tube 21 and the dual detector 24 ′ are rotated around the object to be imaged. The projection data D0 (z, view, j, i) represented by This is repeated by moving the cradle 12 twice the slice thickness. For example, when measuring the coronary artery calcification index, the slice thickness is 3 mm, and the imaging is repeated by moving 6 mm downward from the heart base of the patient's heart so that the range is 60 mm below the heart base of the patient's heart. Projection data D0 (z, view, j, i) is collected.

In step S2, preprocessing (offset correction, logarithmic correction, X-ray dose correction, sensitivity correction) is performed on the projection data D0 (z, view, j, i).
In step S3 ′, a tomographic image is reconstructed by a conventionally known two-dimensional image reconstruction method. In the above numerical example, 20 tomographic images are reconstructed.
In step S5, post-processing is performed on each tomographic image.

  In step S6, an average tomographic image Vv (v = 1, 2,...) Is created by averaging adjacent tomographic images of the reconstructed tomographic image Ga (a = 1, 2,...). In the above numerical example, 19 average tomographic images V1,..., V19 are reconstructed between 20 tomographic images G1,.

  In step S7 ′, calcified portions Rab (b = 1, 2,...), Fvf (f = 1, 2,...) That are portions of interest on the tomographic images Ga and Vv and have a CT value equal to or greater than a threshold value. Are extracted automatically or manually.

  In step S8 ′, areas Aab and Evf are obtained for the calcified portions Rab and Fvf, weights Wab and wvf are determined according to the highest CT values of the calcified portions Rab and Fvf, and the calcified portions Rab and Fvf are determined. The weights Wab, wvf and the areas Aab, Evf are multiplied to calculate the product of the part, Cab = Wab × Aab, cvf = wvf × Evf.

In step S9 ', the products Cab and cvf of all the tomographic images Ga and Vv are summed and multiplied by a coefficient H corresponding to the tomographic image interval ds to obtain the calcification index C of the region of interest of the patient.
For example, the coefficient H for maintaining compatibility with the prior art for measuring the coronary artery calcification index CACS described above is H = (ds [mm] / 3) × Na / when the number of tomographic images Ga is Na. If (2 × Na−1), ds = 3 mm, and Na = 20, H = 20/39.

Next, the processing contents of the above-described steps S6, S7 ′ to S9 ′ will be described with a schematic example.
As shown in FIG. 22, it is assumed that there is only one calcified portion Q having an area = A and a CT value = 190 penetrating through slices corresponding to all tomographic images.

  As shown in FIG. 23, the calcification index C = 2A is obtained in the case corresponding to the conventional AJ method.

  FIG. 29 applies the second embodiment of the present invention, and creates an average tomographic image V1 between the tomographic images g1 and g2. Then, the CT values of the calcified portions R11, F11, and R21 in the tomographic images g1, V1, and g2 are all “190”.

  In step S7 ', when the threshold value is set to "130", for example, calcified portions R11, F11, and R21 are extracted from the tomographic images G1, V1, and G2, respectively.

  Next, in step S8 ', the area A11 = E11 = A21 = A of each calcified portion R11, F11, R21 is obtained. For example, when the highest CT value of each calcified portion is 130 to 199, the weight is “1”, when 200 to 299, the weight is “2”, when 300 to 399, the weight is “3”, 400 In this case, when the weight is “4”, the weights of R11, F11, and R21 are W11 = w11 = W21 = 1. Therefore, the weight C11 = 1 of the calcified portion R11 is multiplied by the area A11 = A to obtain the product C11 = 1 × A. Similarly, the product c11 = 1 × A of the calcified portion F11 and the product C21 = 1 × A of the calcified portion R21 are obtained.

  Next, in step S9 ', the products C11, c11, C21 of all the calcified portions R11, F11, R21 of all the tomographic images G1, V1, G2 are summed, and the tomographic image interval ds and the number of tomographic images Na are determined. Is multiplied by the coefficient H to obtain the calcification index C of the region of interest of the patient. In FIG. 29, since the tomographic image interval ds = 3 mm and the number of tomographic images Na = 2, the coefficient H = (3/3) × 2 / (2 × 2-1) = 2/3. Therefore, the region of interest calcification index C = 2A of the patient is obtained.

  That is, for the calcified portion Q that penetrates through all slices, the region-of-interest calcification index C obtained by the above-described prior art and the present invention is compatible.

Next, as shown in FIG. 30, it is assumed that a calcified portion Q having an area = A, a length = 4.5 mm, and a CT value = 190 passes through the tomographic image g1 and is only half in the tomographic image g2.
Then, the CT value of the portion R11 corresponding to the calcified portion Q in the tomographic image g1 is “190”, and the CT value of the portion R21 corresponding to the calcified portion Q in the tomographic image g2 is “85”. Therefore, in the AJ method, the weights W11 = 1 and W21 = 0, and the calcification index C = A.

  FIG. 31 applies the second embodiment of the present invention, and creates an average tomographic image V1 between tomographic images g1 and g2. Then, the CT value of the calcified portion R11 of the tomographic image g1 is “190”, the CT value of the calcified portion F11 of the average tomographic image V1 is “138”, and the CT value of the calcified portion R21 of the tomographic image g2 is “85”. It becomes.

  In step S7 ', when the threshold value is set to "130", for example, the calcified portion R11 is extracted from the tomographic image G1, and the calcified portion F11 is extracted from the average tomographic image V1.

  Next, in step S8 ', the area A of the calcified portions R11 and F11 is obtained. For example, when the highest CT value of each calcified portion is 130 to 199, the weight is “1”, when 200 to 299, the weight is “2”, and when 300 to 399, the weight is “3”. When the weight is “4”, the weight W11 = 1 of the calcified portion R11 and the weight w11 = 1 of the calcified portion F11 are obtained, so that the product C11 = 1 × A of the calcified portion R11, the calcified portion F11. To obtain the product c11 = 1 × A.

  Next, in step S9 ′, the products of all the calcification portions of all the tomographic images are summed, and multiplied by a coefficient H corresponding to the tomographic image interval ds and the number of tomographic images Na, thereby calculating the calcification index of the region of interest of the patient. C. Here, the tomographic image interval ds = 3 mm, the number of tomographic images Na = 2, and the coefficient H = 2/3. Therefore, the region of interest calcification of the patient is C = 4A / 3.

  As can be seen from a comparison between FIG. 30 and FIG. 31, in FIG. 30, the calcified portion Q that is only half in the tomographic image g2 is ignored, but in FIG. Some calcified portion Q is also detected. That is, the error is small.

  The calcification index measuring method and X-ray CT apparatus of the present invention can be used for quantitatively grasping the calcification index of a coronary artery, for example.

1 is a block diagram illustrating an X-ray CT apparatus according to Embodiment 1. FIG. It is explanatory drawing which shows rotation of a X-ray tube and a multi-detector. It is explanatory drawing which shows a cone beam. FIG. 3 is a flowchart illustrating the operation of the X-ray CT apparatus according to the first embodiment. It is explanatory drawing which shows a reconstruction area space | interval. It is a flowchart which shows the detail of a three-dimensional image reconstruction process. It is a conceptual diagram which shows the state which projects the line on a reconstruction area | region to a X-ray transmissive direction. It is a conceptual diagram which shows the line projected on the detector surface. It is a conceptual diagram which shows the state which projected the projection data Dr of each line in view = 0 degree on the projection surface. It is a conceptual diagram which shows the state which projected the projection line data Dp of each line in view = 0 degree on the projection surface. It is a conceptual diagram which shows the state which projected the image each position line data Df of each line in view = 0 degree on the projection surface. It is a conceptual diagram which shows the state which projected the high-density image of each line in view = 0 degree each position line data Dh on a projection surface. It is a conceptual diagram which shows the backprojection pixel data D2 of each line on a reconstruction area | region in view = 0 degree. It is a conceptual diagram which shows the backprojection pixel data D2 of each pixel on a reconstruction area | region in view = 0 degree. It is a conceptual diagram which shows the state which projected the projection data Dr of each line in view = 90 degrees on the projection surface. It is a conceptual diagram which shows the state which projected the projection line data Dp of each line in view = 90 degrees on the projection surface. It is a conceptual diagram which shows the state which projected the image each position line data Df of each line in view = 90 degree on the projection surface. It is a conceptual diagram which shows the state which projected the high-density image each position line data Dh of each line in view = 90 degrees on the projection surface. It is a conceptual diagram which shows the backprojection pixel data D2 of each line on a reconstruction area | region in view = 90 degrees. It is a conceptual diagram which shows the backprojection pixel data D2 of each pixel on a reconstruction area | region in view = 90 degrees. It is explanatory drawing which shows the state which obtains backprojection data D3 by adding all the views to backprojection pixel data D2 corresponding to a pixel. It is explanatory drawing of the schematic example in which only one calcification part which penetrates the imaging | photography range exists. It is explanatory drawing at the time of applying Example 1 to the schematic example in which only one calcification part which penetrates the imaging | photography range exists. It is explanatory drawing at the time of applying a prior art to the schematic example in which only one calcification part which penetrates the imaging | photography range exists. It is explanatory drawing at the time of applying a prior art to the schematic example in which only one short calcification part exists in the center of an imaging | photography range. It is explanatory drawing at the time of applying Example 1 to the schematic example in which only one short calcification part exists in the center of an imaging | photography range. It is a block diagram which shows the X-ray CT apparatus which concerns on Example 2. FIG. FIG. 6 is a flowchart showing the operation of the X-ray CT apparatus according to the second embodiment. It is explanatory drawing at the time of applying Example 2 to the schematic example in which only one calcification part which penetrates the imaging | photography range exists. It is explanatory drawing at the time of applying a prior art to the schematic example in which only one short calcification part exists from the center of an imaging | photography range near one side. It is explanatory drawing at the time of applying Example 2 to the schematic example in which only one short calcification part exists from the center of an imaging | photography range near one side.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Operation console 3 Central processing unit 20 Scanning gantry 21 X-ray tube 24 Multi-detector 24 'Dual detector G1, ..., G5 Tomographic image P Reconstruction area Q Calcified part V1 Average tomographic image

Claims (14)

A plurality of tomographic images Ga (a = 1, 2,...) Are reconstructed with a tomographic image interval smaller than the column interval in the direction in which the plurality of detector rows of the multi-detector are arranged, and each tomographic image in the tomographic images Ga A method for measuring a calcification index, characterized in that a calcification index C is calculated by setting a portion having a CT value at a region of interest in an image equal to or greater than a threshold as a calcification portion . 2. The calcification index measurement method according to claim 1, wherein a plurality of tomographic images arranged at a tomographic image interval smaller than a column interval in a direction in which the plurality of detector rows of the multi-detector are arranged correspond to the tomographic images. An image is obtained by a three-dimensional backprojection method in which backprojection pixel data is obtained based on the projection data extracted for each reconstruction area, and the backprojection pixel data of all views used for image reconstruction is added to the corresponding pixels to obtain backprojection data. A calcification index measurement method, wherein the plurality of tomographic images Ga are formed by reconstructing. In calcium score measuring method according to claim 2, the formation of the tomographic image G of the plurality of cross-sectional images image Ga, 1 lines or pixels a spacing on the reconstruction area corresponding to the tomographic image G Projection data Dr corresponding to a plurality of parallel lines L is extracted, and the projection data Dr is multiplied by a cone beam reconstruction load to generate projection line data Dp, and the projection line data Dp is filtered. To generate image position line data Df, obtain back projection pixel data D2 of each pixel on the reconstruction portion based on the image position line data Df, and reverse all views used for image reconstruction. A method for measuring a calcification index, which is performed by reconstructing a tomographic image G by a three-dimensional backprojection method in which projection pixel data D2 is added corresponding to each pixel to obtain backprojection data D3. An average tomographic image Vv (v = 1, 2,...) Is created by averaging adjacent tomographic images of a plurality of tomographic images Ga (a = 1, 2,...) Reconstructed at the tomographic image interval ds. Assuming that the average tomographic image Vv is located in the middle of the tomographic images to be processed, a portion where the CT value of the region of interest in each tomographic image in the original tomographic image Ga and the average tomographic image Vv is a threshold value or more is defined as a calcified portion. A method for measuring a calcification index, wherein the calcification index C is calculated. The calcification index measurement method according to any one of claims 1 to 4 , wherein a weight based on an area and a CT value is calculated for each calcification portion Rab (b = 1, 2, ...) in the calcification portion. The product Cab is obtained, and the sum of the products Cab of all the parts Rab of all the tomographic images Ga is multiplied by a coefficient H corresponding to the tomographic image interval ds or the number of tomographic images, thereby calculating the calcification index of the region of interest of the patient. A method for measuring a calcification index, wherein C is obtained. The calcification index measurement method according to claim 5 , wherein an area Aab is obtained for each calcification portion Rab in the calcification portion, a weight Wab is determined according to the highest CT value of each calcification portion Rab, and each calcification is determined. A method for measuring a calcification index, comprising multiplying a weight Rab of a portion Rab and an area Aab to obtain a product Cab = Wab × Aab of the calcification portion Rab. The calcification index measurement method according to claim 6 , wherein when the region of interest is a coronary artery, the threshold value is 130, and the highest CT value of each calcification portion Rab is 130 to 199, the weight Wab A calcification index measurement method, characterized in that a weight Wab = 2 when 200 to 299, a weight Wab = 3 when 300-399, and a weight Wab = 4 when 400 or more. X-ray tube, multi-detector having a plurality of detector rows, scanning means for collecting projection data while rotating at least one of the X-ray tube or multi-detector around an imaging target, and multi-detector Reconstructing a plurality of tomographic images Ga (a = 1, 2,...) At a tomographic image interval ds smaller than the column interval dr in the direction in which the plurality of detector rows are arranged, and the plurality of tomographic images An X-ray CT apparatus comprising: a calcification index calculating means for calculating a calcification index C using a portion where a CT value at a region of interest in each tomographic image in Ga is equal to or greater than a threshold as a calcification portion . The X-ray CT apparatus according to claim 8, wherein the image reconstruction unit includes a plurality of tomographic images arranged at a tomographic image interval smaller than a column interval in a direction in which the plurality of detector columns of the multi-detector are arranged. Back projection pixel data is obtained based on the projection data extracted for each reconstruction area corresponding to each tomographic image, and the back projection pixel data of all views used for image reconstruction is added in correspondence with the pixels to obtain back projection data 3 An X-ray CT apparatus, wherein the plurality of tomographic images Ga are formed by reconstructing an image by a three-dimensional backprojection method. In X-ray CT apparatus according to claim 9, wherein the image reconstruction means, the formation of the tomographic image G of the plurality of cross-sectional images image Ga, 1 present on the reconstruction area P corresponding to the tomographic image G Projection data Dr corresponding to a plurality of parallel lines L spaced by a plurality of pixels or a plurality of parallel pixels L is extracted, and projection line data Dp is generated by multiplying the projection data Dr by a cone beam reconstruction load. The line data Dp is filtered to create each position line data Df of the image. Based on each position line data Df of the image, back projection pixel data D2 of each pixel on the reconstructed portion is obtained, and the image reconstruction is performed. X-ray C, characterized in that the three-dimensional back projection method for obtaining the backprojection data D3 backprojected pixel data D2 is added to the pixel-corresponding all views used in construction carried out by reconstructing a tomographic image G Apparatus. An X-ray tube, a multi-detector having a plurality of detector rows, scanning means for collecting projection data while rotating at least one of the X-ray tube or the multi-detector around an imaging target, and a tomographic image interval Image reconstruction means for reconstructing a plurality of tomographic images Ga (a = 1, 2,...) with ds, and a plurality of tomographic images Ga (a = 1, 2,...) reconstructed with a tomographic image interval ds. It is assumed that the average tomographic image creation means for creating an average tomographic image Vv (v = 1, 2,...) That averages adjacent tomographic images, and the average tomographic image Vv is located between the adjacent tomographic images. And a calcification index calculating means for calculating a calcification index C using a portion of the tomographic image Ga and the average tomographic image Vv where the CT value of the region of interest is equal to or greater than a threshold as a calcification portion. To Line CT apparatus. 12. The X-ray CT apparatus according to claim 8 , wherein the calcification index calculating means has an area for each calcification portion Rab (b = 1, 2,...) In the calcification portion. And a weight product Cab based on the CT value, and a sum of the products Cab of all calcified portions Rab of all tomographic images Ga is multiplied by a coefficient H corresponding to the tomographic image interval ds or the number of tomographic images. An X-ray CT apparatus characterized by obtaining a calcification index C of a region of interest of the patient. 13. The X-ray CT apparatus according to claim 12 , wherein the calcification index calculating means obtains an area Aab for each calcification portion Rab in the calcification portion, and weights according to the highest CT value of each calcification portion Rab. An X-ray CT apparatus characterized by determining Wab and multiplying a weight Wab of each calcified portion Rab by an area Aab to obtain a product Cab = Wab × Aab of the calcified portion Rab. 14. The X-ray CT apparatus according to claim 13 , wherein when the region of interest is a coronary artery, the threshold value is 130, and the highest CT value of each calcified portion Rab is 130 to 199, the weight Wab = 1. An X-ray CT apparatus characterized in that the weight Wab = 2 when 200-299, the weight Wab = 3 when 300-399, and the weight Wab = 4 when 400 or more.

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