JP2010005016A - X-ray ct apparatus and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress burdens on an object such as exposure, a contrast medium amount and restriction time, when obtaining two or more kinds of tomographic images of different time resolutions. <P>SOLUTION: The plurality of tomographic images of high time resolutions are obtained from each of two or more pieces of projection data obtained by one scan without separately performing scan, weighting addition of them is executed in a time base direction and the tomographic images of low time resolutions are obtained. For instance, the projection data corresponding to each of 32 slices 16A-16B are reconfigured into images in each of the first rotation, second rotation and third rotation of a gantry, and the tomographic images of the high time resolutions such as Image_0.3sec, 16A, r1 to Image_0.3sec, 16B, r1 are obtained. They are sectioned by every 8 slices and every 3 rotations of the gantry for instance, and the weighting addition is executed respectively. Thus, the tomographic images of the low time resolutions such as Image_0.9sec, 2A'(5 mm), 1 corresponding to 3 rotations of the gantry for four slices 2A'-2B' whose slice thickness is 8 times are obtained. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an X-ray CT apparatus for X-ray CT (Computed Tomography) imaging of a subject and a program therefor.

In the field of radiological image diagnosis, a plurality of types of CT tomographic images having different time resolutions may be required depending on the type of diagnosis. For example, in the diagnosis of ischemic disease in the head region, a blood flow test called CT perfusion and angiography called CT angio are performed using an X-ray CT apparatus (for example, a patent) Reference 1 and Patent Reference 2). In CT perfusion, in order to obtain a tomographic image with a high S / N ratio, the head is scanned at a relatively slow speed to obtain a tomographic image with a relatively low time resolution, and blood flow in the head region. Observe. On the other hand, in CT angio, the head is scanned at a relatively high speed to obtain a tomographic image having a relatively high time resolution, and the detailed state of the blood vessel is observed.
JP 2004-159983 A JP 2005-6772 A

  As described above, when CT tomograms having different temporal resolution are required, generally, a scan for obtaining a tomographic image with a high temporal resolution and a scan for obtaining a tomographic image with a low temporal resolution are separated. To do.

  However, when scanning is performed separately, the exposure dose to the subject increases, and in contrast, an angiographic scan also increases the amount of contrast agent administered to the subject, which places a heavy burden on the subject.

  In view of the above circumstances, an object of the present invention is to provide an X-ray CT apparatus capable of obtaining a plurality of types of tomographic images having different time resolutions while suppressing a burden on a subject, and a program therefor. .

  In a first aspect, the present invention provides an X-ray CT scan of a predetermined part of a subject, each corresponding to the predetermined part in each of a plurality of first time ranges arranged in the time axis direction, and an image Based on at least one of the plurality of projection data sets, imaging means for obtaining a plurality of projection data (data set) including view data (view-data) for the number of views (view) necessary for reconstruction, First image generation means for reconstructing and generating a first tomographic image representing the predetermined part in at least one of a plurality of first time ranges; and the plurality of projection data sets or the first An X-ray CT apparatus comprising: a second image generating unit configured to generate a second tomographic image representing the predetermined portion in a second time range in which the time is longer than the first time range based on the tomographic image; provide.

  In a second aspect, the present invention relates to the second tomography, wherein the second image generation means reconstructs an image based on a projection data set obtained by weighted addition of the plurality of projection data sets. An X-ray CT apparatus according to the first aspect for generating an image is provided.

  In a third aspect, the present invention provides the second image generation means, wherein the first image generation means generates a plurality of first tomographic images each corresponding to each of the plurality of projection data sets. However, the X-ray CT apparatus according to the first aspect, which generates the second tomographic image by weighting and adding the plurality of first tomographic images, is provided.

  In a fourth aspect, according to the present invention, the predetermined portion includes a plurality of slices arranged in one direction, and the first tomographic image corresponds to each of the plurality of slices. Any one of the first to third aspects is a plurality of tomographic images, wherein the second tomographic image is a tomographic image corresponding to a single slice including the plurality of slices. An X-ray CT apparatus according to one aspect is provided.

  In a fifth aspect, the present invention provides that the first time range has a time width of less than 0.5 seconds, the second time range has a time width of 0.5 seconds or more, The X-ray CT apparatus according to the fourth aspect, wherein each of the plurality of slices has a slice thickness of less than 2 millimeters, and the single slice has a slice thickness of 2 millimeters or more.

  In a sixth aspect, the present invention provides the X-ray according to any one of the first to fifth aspects, wherein the plurality of first time ranges are arranged adjacent to each other in the time axis direction. A CT apparatus is provided.

  In a seventh aspect, the present invention provides the first time range according to any one of the first to fifth aspects, wherein the plurality of first time ranges are arranged adjacent to each other in the time axis direction. An X-ray CT apparatus is provided.

  In an eighth aspect, the present invention relates to the seventh to seventh aspects, wherein the number of views required for the image reconstruction is a view number corresponding to a half scan or a full scan. An X-ray CT apparatus according to any one of the aspects is provided.

  In a ninth aspect, the present invention relates to a computer corresponding to the predetermined portion in each of a plurality of first time ranges arranged in the time axis direction, and the number of views required for image reconstruction. Based on at least one of a plurality of projection data sets including view data, a first tomographic image representing the predetermined part in at least one of the plurality of first time ranges is generated by image reconstruction. A second tomographic image representing the predetermined part in a second time range in which the time is longer than the first time range, based on one image generation means and the plurality of projection data sets; A program for functioning as an image generation means is provided.

  According to the present invention, a tomographic image having a relatively high time resolution is obtained from a plurality of projection data sets obtained by one scan, and a tomographic image having a relatively low time resolution is obtained from the plurality of projection data sets as a whole. Therefore, it is not necessary to perform scanning separately, and a plurality of types of tomographic images having different time resolutions can be obtained while suppressing the burden on the subject.

  Further, according to the present invention, since only one scan is required, the imaging time is shortened as a whole, and the diagnostic efficiency is improved.

Embodiments according to the present invention will be described below with reference to the drawings.
(First embodiment)

  FIG. 1 is a block diagram showing an X-ray CT apparatus 100 according to an embodiment of the present invention. The X-ray CT apparatus 100 includes an operation console 1, an imaging table 8, and a scanning gantry 9.

  The operation console 1 includes an input device 2, a central processing unit 3, a control interface (interface) 4, a data collection buffer (buffer) 5, and a monitor 6. The input device 2 accepts operator instructions and information. The central processing unit 3 executes scan control processing, image reconstruction processing, projection data or tomographic weighted addition processing, and the like. The control interface 4 outputs a control signal and the like to the imaging table 8 and the scanning gantry 9 under the control of the central processing unit 3. The data collection buffer 5 collects data acquired by the scanning gantry 9. The monitor 6 displays an operation screen, a tomographic image, and the like.

  The imaging table 8 moves the placed subject along its body axis (hereinafter referred to as z direction) and conveys it to the cavity of the scanning gantry 9.

  The scanning gantry 9 has a cavity including an imaging space, and includes a rotating unit 7 that rotates around the cavity. The rotation unit 7 includes an X-ray controller 10, an X-ray tube 11, a collimator 12, an X-ray detector 13, a data collection unit 14, and a rotation controller 15. The X-ray controller 10 controls tube voltage and tube current of the X-ray tube 11, on / off of X-ray irradiation, and the like. The collimator 12 shapes the X-ray beam emitted from the X-ray tube 11. The X-ray detector 13 is a so-called multi-row detector having a plurality of detector rows in the slice direction in which a plurality of detector elements are arranged in the channel direction. A signal corresponding to the intensity is output. The data collection unit 14 performs A / D (analog-digital) conversion on the output signal of the X-ray detector 13 to collect projection data of the subject and sends it to the data collection buffer 5. The rotation controller 15 controls the rotation speed of the rotating unit 7, on / off of rotation, and the like. The X-ray tube 11 and the X-ray detector 13 are disposed to face each other with the cavity portion interposed therebetween.

  The central processing unit 3 and the operation gantry 9 are examples of photographing means in the present invention. The central processing unit 3 is an example of a first image generation unit and a second image generation unit in the present invention.

  FIG. 2 is a flowchart showing a flow of scan processing in the X-ray CT apparatus 100 according to the first embodiment. FIG. 3 is a conceptual diagram showing the flow of the scanning process.

  In step S1, scanning is performed. Specifically, an imaging space including a predetermined part of the subject is continuously scanned, and a plurality of projection data sets corresponding to the predetermined part are collected.

  FIG. 4 is a diagram showing a photographing space. Here, as shown in FIG. 4, the imaging space R is divided into 32 slices 16A to 1A and 1B to 16B arranged in the z direction, and projection data for each slice is collected. Further, view data of the number of views necessary for image reconstruction of one slice is considered as one projection data, and here, view data of the number of views corresponding to a full scan, that is, a view angle of 360 ° is set to one Let it be a projection data set. As scanning conditions, the slice thickness is 0.625 mm, the rotation speed of the rotating unit 7 is 0.3 second / rotation, and the scanning time is 0.9 second (for three rotations of the rotating unit 7).

  By performing such a scan, a plurality of projection data as shown in the upper part of FIG. 3, Proj_0.3 sec, 16A, r1 to Proj_0.3 sec, 16B, r1, Proj_0.3 sec, 16A, r2 to Proj_0.3 sec , 16B, r2, and Proj_0.3sec, 16A, r3 to Proj_0.3sec, 16B, r3. That is, a plurality of time ranges arranged in the time axis direction, t = 0 to 0.3 seconds (first rotation), t = 0.3 to 0.6 seconds (second rotation), t = 0.6 to 0. At each of 9 seconds (third rotation), a projection data set corresponding to each of the slices 16A to 1A and 1B to 16B is collected. The projection data set Proj_0.3 sec, 16A, r1 means the projection data set for the first rotation of the slice 16A when the time width is 0.3 seconds and the slice thickness is 0.625 mm.

  In step S2, image reconstruction processing is performed. Specifically, a plurality of high-resolution tomographic images (first tomographic images) are reconstructed by applying a back projection method or the like to each of the plurality of projection data sets obtained in the previous step. And generate. Thereby, a plurality of tomographic images as shown in the center of FIG. 3, Image_0.3sec, 16A, r1 to Image_0.3sec, 16B, r1, Image_0.3sec, 16A, r2 to Image_0.3sec, 16B, r2, and Image_0 .3sec, 16A, r3 ~ Image_0.3sec, 16B, r3 are obtained.

  In step S3, a tomographic weighted addition process is performed. Specifically, the plurality of tomographic images obtained in the previous step are divided into predetermined space widths and predetermined time widths, and the tomographic images are weighted and added for each of the divided tomographic image groups. A plurality of time-resolution tomographic images (second tomographic images) are generated. Here, the predetermined space width is divided into eight slices, that is, 5 millimeters, and the predetermined time width is divided into three rotations of the rotating unit 7, that is, 0.9 seconds, and weighted addition is performed. Thus, the imaging space R is divided into four slices 2A ′ to 2B ′ having a slice thickness of 5 mm, and the tomographic image of each slice when the time range is set to t = 0 to 0.9 seconds, that is, in FIG. Multiple tomographic images with low temporal resolution and low spatial resolution as shown below Image_0.9sec, 2A '(5mm), 1, Image_0.9sec, 1A' (5mm), 1, Image_0.9sec, 1B '(5mm ), 1 and Image_0.9 sec, 2B ′ (5 mm), 1. That is, tomogram Image_0.3sec, 16A, r1 to Image_0.3sec, 9A, r1, Image_0.3sec, 16A, r2 to Image_0.3sec, 9A, r2, Image_0.3sec, 16A, r3 to Image_0.3sec, 9A, A tomographic image Image_0.9 sec, 2A ′ (5 mm), 1 is generated by weighted addition of r3. Similarly, tomogram Image_0.3sec, 8A, r1 to Image_0.3sec, 1A, r1, Image_0.3sec, 8A, r2 to Image_0.3sec, 1A, r2, Image_0.3sec, 8A, r3 to Image_0.3sec, 1A , r3 is weighted and added, and a tomographic image Image_0.9 sec, 1A ′ (5 mm), 1 is generated. Tomography Image_0.3sec, 1B, r1 ~ Image_0.3sec, 8B, r1, Image_0.3sec, 1B, r2 ~ Image_0.3sec, 8B, r2, Image_0.3sec, 1B, r3 ~ Image_0.3sec, 8B, r3 A tomographic image Image_0.9 sec, 1B ′ (5 mm), 1 is generated by weighted addition. Tomography Image_0.3sec, 9B, r1 ~ Image_0.3sec, 16B, r1, Image_0.3sec, 9B, r2 ~ Image_0.3sec, 16B, r2, Image_0.3sec, 9B, r3 ~ Image_0.3sec, 16B, r3 A tomographic image Image_0.9 sec, 2B ′ (5 mm), 1 is generated by weighted addition.

  Here, one form of the tomographic image weighted addition processing will be described by taking a case where a tomographic image Image_0.9 sec, 2A ′ (5 mm), 1 is generated as an example.

  FIG. 5 is a diagram showing the concept of tomographic weighting addition processing.

  To generate a tomographic image Image_0.9 sec, 2A ′ (5 mm), 1, the projection data sets Proj_0.3 sec, 16A, r1 to Proj_0.3 sec, 9A, r1, Proj_0.3 sec, 16A, r2 to Proj_0.3 sec, 9A, r2, and Proj_0.3sec, 16A, r3 to Proj_0.3sec, 9A, r3, respectively, 24 tomographic images obtained, ie, tomographic images Image_0.3sec, 16A, r1 to Image_0.3sec, 9A, r1, Image_0.3sec, 16A, r2 to Image_0.3sec, 9A, r2, and Image_0.3sec, 16A, r3 to Image_0.3sec, 9A, r3 are used.

  As shown in FIG. 5, each of the tomographic images Image_0.3sec, 16A, r1 to Image_0.3sec, 9A, r1 is sequentially multiplied and added by weighting factors ww1 to ww8 (ww1 +... + Ww8 = 1), and time A tomographic image of slice 2A ′ is obtained in the range t = 0 to 0.3 seconds. In addition, each of the tomographic images Image_0.3sec, 16A, r2 to Image_0.3sec, 9A, r2 is sequentially multiplied and added by weighting factors ww1 to ww8, and the time range t = 0.3 to 0.6 seconds, slice A 2A ′ tomographic image is obtained. Similarly, weight coefficients ww1 to ww8 are sequentially multiplied and added to each of the tomographic images Image_0.3sec, 16A, r3 to Image_0.3sec, 9A, r3, and the time range t = 0.6 to 0.9 seconds, A tomographic image of slice 2A ′ is obtained. Further, weighting coefficients w1 to w3 (w1 + w2 + w3 = 1) are sequentially multiplied and added to each of these three tomographic images, and the tomographic image of slice 2A ′ in time range t = 0 to 0.9 seconds. Get. This is expressed by the following equation.

Image_0.9sec, 2A '(5mm), 1
= W1 × {ww1 × Image_0.3sec, 16A, r1 +… + ww8 × Image_0.3sec, 9A, r1}
+ W2 × {ww1 × Image_0.3sec, 16A, r2 +… + ww8 × Image_0.3sec, 9A, r2}
+ W3 × {ww1 × Image_0.3sec, 16A, r3 +… + ww8 × Image_0.3sec, 9A, r3}
However, w1 + w2 + w3 = 1, ww1 + ww2 +… + ww8 = 1 (Formula 1)

  The weight coefficients wi and wwj may be assigned values such that the contribution ratio of each tomographic image is equal, or the contribution ratio of the tomographic image corresponding to a specific time range or a specific slice is increased. You may assign different values.

  As described above, according to the present embodiment, a tomographic image having a relatively high temporal resolution is obtained from a plurality of projection data sets obtained by one scan, and the temporal resolution is compared from the plurality of projection data sets as a whole. Therefore, a plurality of types of tomographic images with different temporal resolution can be obtained while suppressing the burden on the subject.

  In addition, according to the present embodiment, since a plurality of tomographic images are weighted and added not only in the time axis direction but also in the spatial axis direction, a high time resolution and high time resolution tomographic image, a low time resolution and A tomographic image with low spatial resolution can be generated.

In general, a CT angiographic tomographic image is required to have a high temporal resolution, and the slice thickness is less than 2 millimeters, more limited to about 0.625 to 1.25 millimeters, and the time width is less than 0.5 seconds. If limited, the time is about 0.3 to 0.4 seconds. In addition, a tomogram for CT perfusion is required to have a high S / N ratio, and the slice thickness is set to 2 mm or more, and further limited to about 4 to 6 mm, and the time width is further set to 0.5 seconds or more. If so, the time is about 0.8 to 3.5 seconds. In the present embodiment, for a tomographic image with high temporal resolution and high spatial resolution, the corresponding slice thickness is 0.625 mm, the time width of the corresponding time range is 0.3 seconds, and the tomographic image has low temporal resolution and low spatial resolution. Since the corresponding slice thickness is 5 mm and the time width of the corresponding time range is 0.9 second, the tomographic image for CT angiography with a high temporal resolution and the CT perfusion with a high S / N ratio are used. And tomographic images of both.
(Second Embodiment)

  In the first embodiment, the time ranges of tomographic images with high temporal resolution are arranged adjacent to each other in the time axis direction, but adjacent to each other in a part of the time axis direction. Good.

  FIG. 6 is a diagram showing the concept of tomographic weighting addition processing when the time ranges of tomographic images with high temporal resolution partially overlap each other. For example, as shown in FIG. 6, the time range t = 0 to 0.3 seconds, the projection data sets Proj_0.3 sec, 16A, t1 to Proj_0.3 sec, 9A, t1 corresponding to the slices 16A to 9A, and the time range t = 0.1 to 0.4 seconds, projection data sets Proj_0.3sec, 16A, t2 to Proj_0.3sec, 9A, t2 corresponding to slices 16A to 9A, time range t = 0.2 to 0.5 seconds, Based on the projection data sets Proj_0.3sec, 16A, t3 to Proj_0.3sec, 9A, and t3 corresponding to the slices 16A to 9A, the images are reconstructed to obtain 24 tomographic images Image_0.3sec, 16A, t1 to Image_0. Obtain .3 sec, 9A, t1, Image_0.3 sec, 16A, t2 to Image_0.3sec, 9A, t2, and Image_0.3sec, 16A, t3 to Image_0.3sec, 9A, t3. Then, these 24 tomographic images are weighted and added to generate a tomographic image having a time range t = 0 to 0.5 seconds and a slice thickness of 5 mm.

According to the second embodiment, the time width of the tomographic image with low temporal resolution is not limited to a multiple of the time width of the tomographic image with high temporal resolution, and can be set more finely. Further, if a tomographic image with low temporal resolution is used as a tomographic image for CT perfusion, it is possible to observe a finer temporal change in blood flow, and an improvement in calculation accuracy of blood flow (CBF) can be expected.
(Third embodiment)

  In the first embodiment, the tomographic image with high temporal resolution is weighted and added also in the spatial axis direction, but of course, only the time axis direction may be weighted and added.

  FIG. 7 is a diagram showing the concept of tomographic weighting addition processing in the case of adding only in the time axis direction. For example, as shown in FIG. 7, the time range t = 0 to 0.3 seconds, the projection data set Proj_0.3 sec, 16A, r1 corresponding to the slice 16A, and the time range t = 0.3 to 0.6 seconds, Image reconstruction based on the projection data set Proj_0.3 sec, 16A, r2 corresponding to the slice 16A and the time range t = 0.6 to 0.9 sec, the slice 16A projection data set Proj_0.3sec, 16A, r3 Thus, three tomographic images Image_0.3 sec, 16A, r1, Image_0.3 sec, 16A, r2, and Image_0.3 sec, 16A, r3 are obtained. These three tomographic images are weighted and added to generate a tomographic image having a time range of t = 0 to 0.9 seconds and a slice thickness of 0.625 mm.

According to the third embodiment, a tomographic image with a high temporal resolution and a low S / N ratio and a tomographic image with a low temporal resolution and a high SN ratio can be obtained for the same slice, with priority given to the temporal resolution. A tomographic image and a tomographic image giving priority to image quality can be observed simultaneously.
(Fourth embodiment)

  In the first to third embodiments, the weighted addition process is performed in the image data space. In the present embodiment, the weighted addition process is performed in the projection data space.

  FIG. 8 is a flowchart showing the flow of scan processing in the X-ray CT apparatus 100 according to the fourth embodiment. FIG. 9 is a conceptual diagram showing the flow of the scanning process.

  In step S11, scanning is performed under the same conditions as in step S1. Thereby, a plurality of projection data sets as shown in the upper part of FIG. 9, Proj_0.3 sec, 16A, r1 to Proj_0.3 sec, 16B, r1, Proj_0.3 sec, 16A, r2 to Proj_0.3 sec, 16B, r2, and Collect Proj_0.3sec, 16A, r3 to Proj_0.3sec, 16B, r3.

  In step S12, the same image reconstruction process as in step S2 is performed as the first image reconstruction process. Thus, a plurality of high-resolution tomographic images as shown in the center of FIG. 9, Image_0.3 sec, 16A, r1 to Image_0.3 sec, 16B, r1, Image_0.3 sec, 16A, r2 to Image_0.3 sec, 16B, r2 and Image_0.3sec, 16A, r3 to Image_0.3sec, 16B, r3 are obtained.

  In step S13, weighted addition processing of projection data is performed. Specifically, the plurality of projection data sets obtained in step S11 are divided into predetermined space widths and predetermined time widths, and weighted addition of the projection data sets is performed for each divided projection data set group. Then, a projection data set for reconstructing a plurality of tomographic images with low temporal resolution is generated. Here, the predetermined space width is divided into eight slices, that is, 5 millimeters, and the predetermined time width is divided into three rotations of the rotating unit 7, that is, 0.9 seconds, and weighted addition is performed. Thereby, the imaging space R is divided into four slices 2A ′ to 2B ′ having a slice thickness of 5 mm, and a tomographic image of each slice is reconstructed when the time range is t = 0 to 0.9 seconds. Projection data, that is, a plurality of projection data sets Proj_0.9sec, 2A ′ (5mm), 1, Proj_0.9sec, 1A ′ (5mm), 1, Proj_0.9sec, 1B ′ as shown in the lower right of FIG. (5 mm), 1 and Proj_0.9 sec, 2B ′ (5 mm), 1. That is, projection data sets Proj_0.3sec, 16A, r1 to Proj_0.3sec, 9A, r1, Proj_0.3sec, 16A, r2 to Proj_0.3sec, 9A, r2, Proj_0.3sec, 16A, r3 to Proj_0.3sec, 9A , r3 by weighted addition, a projection data set Proj_0.9 sec, 2A ′ (5 mm), 1 is generated. Similarly, projection data sets Proj_0.3sec, 8A, r1 to Proj_0.3sec, 1A, r1, Proj_0.3sec, 8A, r2 to Proj_0.3sec, 1A, r2, Proj_0.3sec, 8A, r3 to Proj_0.3sec, A projection data set Proj_0.9 sec, 1A ′ (5 mm), 1 is generated by weighted addition of 1A, r3. Projection data set Proj_0.3sec, 1B, r1 to Proj_0.3sec, 8B, r1, Proj_0.3sec, 1B, r2 to Proj_0.3sec, 8B, r2, Proj_0.3sec, 1B, r3 to Proj_0.3sec, 8B, r3 Projection data set Proje_0.9 sec, 1B ′ (5 mm), 1 is generated. Projection data set Proj_0.3sec, 9B, r1 to Proj_0.3sec, 16B, r1, Proj_0.3sec, 9B, r2 to Proj_0.3sec, 16B, r2, Proj_0.3sec, 9B, r3 to Proj_0.3sec, 16B, r3 Projection data set Proj_0.9 sec, 2B ′ (5 mm), 1 is generated.

  In step S14, a second image reconstruction process is performed. Specifically, the projection data sets Proj_0.9 sec, 2A ′ (5 mm), 1, Proj_0.9 sec, 1A ′ (5 mm), 1, Proj_0.9 sec, 1B ′ (5 mm), 1, obtained in the previous step, Image reconstruction is performed for each of Proj_0.9 sec, 2B ′ (5 mm), 1, and a plurality of tomographic images with low temporal resolution, Image_0.9 sec, 2A ′ (5 mm), 1, Image_0, as shown in the lower part of FIG. .9 sec, 1A ′ (5 mm), 1, Image_0.9 sec, 1B ′ (5 mm), 1, Image_0.9 sec, 2B ′ (5 mm), 1 are obtained.

  Here, one form of weighted addition processing of the projection data set will be described by taking as an example the case of generating a tomographic image Image_0.9 sec, 2A ′ (5 mm), 1.

  FIG. 10 is a diagram showing the concept of the weighted addition process of projection data and the subsequent image reconstruction process.

  To generate a tomogram Image_0.9 sec, 2A ′ (5 mm), 1, 24 projection data Proj_0.3 sec, 16A, r1 to Proj_0.3 sec, 9A, r1, Proj_0.3 sec, 16A, r2 to Proj_0. 3 sec, 9A, r2, and Proj_0.3 sec, 16A, r3 to Proj_0.3 sec, 9A, r3 are weighted and added to obtain a projection data set Proj_0.9 sec, 2A ′ (5 mm), 1. That is, as shown in FIG. 10, each of the projection data sets Proj_0.3 sec, 16A, r1 to Proj_0.3 sec, 9A, r1 is sequentially multiplied and added by weighting factors ww1 to ww8 (ww1 +... + Ww8 = 1). Then, a projection data set for reconstructing a tomographic image of the slice 2A ′ in the time range t = 0 to 0.3 seconds is obtained. Further, each of the projection data sets Proj_0.3 sec, 16A, r2 to Proj_0.3 sec, 9A, r2 is sequentially multiplied and added by weighting factors ww1 to ww8, and the time range t = 0.3 to 0.6 seconds, A projection data set for reconstructing a tomographic image of slice 2A ′ is obtained. Similarly, weighting factors ww1 to ww8 are sequentially multiplied and added to each of the projection data sets Proj_0.3sec, 16A, r3 to Proj_0.3sec, 9A, r3, and the time range t = 0.6 to 0.9 seconds. A projection data set for reconstructing a tomographic image of slice 2A ′ is obtained. Further, weighting coefficients w1 to w3 (w1 + w2 + w3 = 1) are sequentially multiplied and added to each of these three projection data sets, and the tomographic slice of slice 2A ′ is obtained with a time range t = 0 to 0.9 seconds. A projection data set for reconstructing the image is obtained. This is expressed by the following equation.

Proj_0.9sec, 2A '(5mm), 1
= W1 × {ww1 × Proj_0.3sec, 16A, r1 +… + ww8 × Proj_0.3sec, 9A, r1}
+ W2 x {ww1 x Proj_0.3sec, 16A, r2 + ... + ww8 x Proj_0.3sec, 9A, r2}
+ W3 x {ww1 x Proj_0.3sec, 16A, r3 + ... + ww8 x Proj_0.3sec, 9A, r3}
However, w1 + w2 + w3 = 1, ww1 + ww2 +… + ww8 = 1 (Formula 2)

  The weighting factors wi and wwj may be assigned values such that the contribution ratio of each projection data set is equal, or the contribution ratio of the projection data set corresponding to a specific time range or a specific slice is large. Such a value may be assigned.

After that, by reconstructing the image based on the projection data set Proj_0.9 sec, 2A ′ (5 mm), 1, the tomographic image Image_0.9 sec, 2A ′ of the time range t = 0 to 0.9 seconds and the slice 2A ′ (5mm), 1 can be obtained.
(Fifth embodiment)

  In the fourth embodiment, the time ranges of the projection data set for reconstructing a tomographic image with high time resolution are arranged adjacent to each other in the time axis direction, but adjacent to each other in the time axis direction. It may be arranged in duplicate.

FIG. 11 is a diagram illustrating the concept of weighted addition processing of projection data sets when the time ranges of projection data sets for reconstructing a tomographic image with high temporal resolution partially overlap each other. For example, as shown in FIG. 11, the time range t = 0 to 0.3 seconds, the projection data sets Proj_0.3 sec, 16A, t1 to Proj_0.3 sec, 9A, t1 corresponding to the slices 16A to 9A, and the time range t = 0.1 to 0.4 seconds, projection data sets Proj_0.3sec, 16A, t2 to Proj_0.3sec, 9A, t2 corresponding to slices 16A to 9A, time range t = 0.2 to 0.5 seconds, The projection data sets Proj_0.3sec, 16A, t3 to Proj_0.3sec, 9A, t3 corresponding to the slices 16A to 9A are weighted and added, and a tomogram with a time range t = 0 to 0.5 seconds and a slice thickness of 5 mm A projection data set for reconstructing is generated. In this way, the time width of the tomographic image with low time resolution is not limited to a multiple of the time width of the tomographic image with high time resolution, and can be set more finely.
(Sixth embodiment)

  In the fourth embodiment, the projection data set for reconstructing a tomographic image with high temporal resolution is weighted and added also in the spatial axis direction, but of course, only the time axis direction may be weighted and added. .

  FIG. 12 is a diagram showing the concept of the weighted addition process of projection data when adding only in the time axis direction. For example, as shown in FIG. 12, the time range t = 0 to 0.3 seconds, the projection data set Proj_0.3 sec, 16A, r1 corresponding to the slice 16A, and the time range t = 0.3 to 0.6 seconds, The projection data set Proj_0.3sec, 16A, r2 corresponding to the slice 16A and the time range t = 0.6 to 0.9 seconds, and the slice 16A projection data set Proj_0.3sec, 16A, r3 are weighted and added to obtain a time. A projection data set for reconstructing a tomographic image having a range t = 0 to 0.9 seconds and a slice thickness of 0.625 mm is generated.

  The present invention is not limited to the above-described embodiments, and various modifications and additions can be made without departing from the spirit of the present invention.

In the above embodiment, as one scan, a so-called cine scan in which a certain portion of the subject is continuously axially scanned is described as an example. However, this one scan is performed by, for example, alternately scanning different ranges included in a predetermined part of the subject.
a so-called axial shuttle scan, or a relatively wide range of helical scans.
It may be a so-called helical shuttle scan that reciprocates by scanning.

  The conditions such as the number of slices, slice thickness, and scan time are not limited to the above specific examples.

  In addition, the number of detector rows and the number of slices of the X-ray detector 13 do not have to coincide with each other, and projection data for reconstructing a tomographic image with high time resolution derived by weighted addition between projection data. It may be used as

  Note that the computer has a means for generating a plurality of tomographic images with high time resolution based on each of the plurality of projection data obtained by one scan and a low time resolution based on the plurality of projection data. A program for functioning as a means for generating a tomographic image is also an embodiment of the present invention.

1 is a block diagram showing an X-ray CT apparatus according to a first embodiment. 3 is a flowchart showing a flow of scan processing in the X-ray CT apparatus 100 according to the first embodiment. It is a conceptual diagram which shows the flow of the scanning process by 1st Embodiment. It is a figure which shows imaging space. It is a figure which shows the concept of the weighted addition process of a tomogram. It is a figure which shows the concept of the weighting addition process of the tomographic image by 2nd Embodiment. It is a figure which shows the concept of the weighting addition process of the tomogram by 3rd Embodiment. It is a flowchart which shows the flow of the scanning process in the X-ray CT apparatus 100 by 4th Embodiment. It is a conceptual diagram which shows the flow of the scanning process by 4th Embodiment. It is a figure which shows the concept of the weighting addition process of projection data, and the image reconstruction process after that. It is a figure which shows the concept of the weighting addition process of the projection data by 5th Embodiment. It is a figure which shows the concept of the weighting addition process of the projection data by 6th Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 X-ray CT apparatus 1 Operation console 2 Input device 3 Central processing unit 4 Control interface 5 Data acquisition buffer 6 Monitor 7 Rotating part 8 Imaging table 9 Scanning gantry 10 X-ray controller 11 X-ray tube 12 Collimator 13 X-ray detector 14 Data Collection unit 15 Rotation controller

Claims (9)

X-ray CT scan of a predetermined part of the subject, view data corresponding to the predetermined part in each of the plurality of first time ranges arranged in the time axis direction, and the number of views necessary for image reconstruction Photographing means for acquiring a plurality of projection data sets including:
Based on at least one of the plurality of projection data sets, a first image is generated by reconstructing a first tomographic image representing the predetermined part in at least one of the plurality of first time ranges. Generating means;
Based on the plurality of projection data sets or the first tomographic image, a second tomographic image representing the predetermined part in a second time range in which the time is longer than the first time range is generated. An X-ray CT apparatus comprising image generation means.   2. The second image generation unit according to claim 1, wherein the second image generation unit generates the second tomographic image by reconstructing an image based on a projection data set obtained by weighted addition of the plurality of projection data sets. X-ray CT system. The first image generating means generates a plurality of first tomographic images each corresponding to each of the plurality of projection data sets;
The X-ray CT apparatus according to claim 1, wherein the second image generation unit generates the second tomographic image by weighted addition of the plurality of first tomographic images. The predetermined part includes a plurality of slices arranged in one direction,
The first tomogram is a plurality of tomograms each corresponding to each of the plurality of slices;
The X-ray CT apparatus according to claim 1, wherein the second tomogram is a tomogram corresponding to a single slice including the plurality of slices. The first time range has a time width of less than 0.5 seconds;
The second time range has a time width of 0.5 seconds or more,
Each of the plurality of slices has a slice thickness of less than 2 millimeters;
The X-ray CT apparatus according to claim 4, wherein the single slice has a slice thickness of 2 millimeters or more.   The X-ray CT apparatus according to claim 1, wherein the plurality of first time ranges are arranged adjacent to each other in the time axis direction.   6. The X-ray CT apparatus according to claim 1, wherein in the plurality of first time ranges, adjacent ones overlap with each other in the time axis direction.   The X-ray CT apparatus according to claim 1, wherein the number of views necessary for the image reconstruction is a view number corresponding to a half scan or a full scan. Computer
Based on at least one of a plurality of projection data sets each corresponding to the predetermined portion in each of the plurality of first time ranges arranged in the time axis direction and including view data of the number of views necessary for image reconstruction. First image generating means for reconstructing and generating a first tomographic image representing the predetermined part in at least one of the plurality of first time ranges;
To function as a second image generation unit that generates a second tomographic image representing the predetermined part in a second time range that is longer than the first time range based on the plurality of projection data sets. Program.

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