JP2012245235A - Image generating apparatus, x-ray ct scanner, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a low exposure level in contrast radiography performed by X-ray CT scanning.SOLUTION: Dual energy scanning of a subject, to whom a contrast medium containing iodine is administered, is performed, and a virtual contrast image of the subject is generated on the basis of obtained data. An iodine density image indicating density distribution of iodine in the subject, which is based on a model expressing the subject by the synthesis of iodine and a predetermined substance except iodine, is generated on the basis of the data. Furthermore, a virtual non-contrast image is generated by performing the subtraction or weighted subtraction of the iodine density image from the virtual contrast image. Thus, both an image corresponding to the contrast image and an image corresponding to the non-contrast image can be acquired by performing the scanning once.

Description

  The present invention relates to an image generation apparatus, an X-ray CT (Computed Tomography) apparatus, and a program therefor, and more particularly, to a technique for reducing exposure using dual energy imaging in a contrast examination.

  Conventionally, when performing a contrast examination of a subject using an X-ray CT apparatus, a simple image obtained by simple imaging before administration of a contrast agent and a contrast image obtained by contrast imaging after administration of the contrast agent are obtained, and these Are often read and compared with each other (see, for example, the summary of Patent Document 1).

JP 2002-850401 A

  In order to acquire a simple image and a contrast image, it is usually necessary to separately perform simple imaging and contrast imaging of the subject, so that the exposure of the subject is larger than that of a general examination.

Under such circumstances, it is desired to reduce the exposure of the subject in the contrast examination.

  The first aspect of the invention is based on data obtained by X-ray CT dual energy imaging of a subject to which a contrast medium containing iodine is administered. The subject is subjected to X of a desired effective X-ray energy. First generation means for generating a virtual contrast image corresponding to an image obtained when X-ray CT imaging is performed using a line, and synthesis of the subject with iodine and a predetermined substance other than iodine based on the data And a second generation means for generating an iodine density image representing a virtual iodine density distribution in the subject based on a model expressed by: subtracting or weighting subtracting the iodine density image from the virtual contrast image Thus, there is provided an image generation apparatus including a third generation unit that generates a virtual non-contrast image corresponding to an image obtained by non-contrast imaging of the subject.

  The invention of the second aspect uses X-rays having a desired effective X-ray energy based on data obtained by X-ray CT dual energy imaging of a subject to which a contrast medium containing iodine is administered. A first generation unit that generates a virtual contrast image corresponding to an image obtained when X-ray CT imaging is performed, and a model that represents the subject by synthesis of iodine and a predetermined substance other than iodine based on the data And a second generation means for generating an iodine density image representing a virtual iodine density distribution in the subject, and a process for converting a negative pixel value to zero with respect to the iodine density image. And a virtual non-contrast image corresponding to an image obtained by non-contrast imaging of the subject is generated by subtracting or weighted subtraction of the processed iodine density image from the virtual contrast image. An image generation apparatus including the generation unit is provided.

  The invention of a third aspect provides the image generating apparatus according to the first aspect or the second aspect, wherein the predetermined substance is a substance having an X-ray absorption coefficient larger than water and smaller than iodine.

  The invention according to a fourth aspect provides the image generating apparatus according to the third aspect, wherein the predetermined substance is calcium.

  According to a fifth aspect of the invention, the data includes: first projection data based on X-rays having a first energy; and second projection data based on X-rays having a second energy different from the first energy. And the first generation means obtains two types of projection data by performing a weighted subtraction process on the first projection data and the second projection data by using two types of weighting. Each image is subjected to image reconstruction processing to represent a virtual density distribution of the first substance in the subject based on a model that represents the subject by combining different first substances and second substances. A first substance density image and a second substance density image representing a virtual density distribution of the second substance in the subject are obtained, and weighted addition processing is performed on the first and second substance density images. The virtual contrast image To provide an image generating apparatus according to any one aspect of the fourth aspect of the first aspect of formed.

  According to a sixth aspect of the invention, the data includes: first projection data based on X-rays having a first energy; and second projection data based on X-rays having a second energy different from the first energy. And the first generation means obtains two types of images by performing image reconstruction processing on the first projection data and the second projection data, respectively. The two types of images are converted into two types of images. A first that represents a density distribution of the virtual first substance in the subject based on a model that represents weighting and subtracting by weighting to represent the subject by combining different first and second substances. And a second substance density image representing a virtual density distribution of the second substance in the subject, and weighted addition processing is performed on the first and second substance density images. The above for generating the virtual contrast image From one aspect provides an image generating apparatus according to any one aspect of the fourth aspect.

  In a seventh aspect of the invention, the second generation means performs a weighted addition process on the first and second substance density images by two types of weighting, and the subject is subjected to the first effective X-ray energy. Obtained when X-ray CT imaging is performed using a first image corresponding to an image obtained when X-ray CT imaging is performed using X-rays and an X-ray of the subject with second effective X-ray energy. A fifth image corresponding to the image, and generating the iodine density image by performing a weighted subtraction process on the first and second images so as to eliminate the component of the predetermined substance. Alternatively, an image generation apparatus according to a sixth aspect is provided.

  In an eighth aspect of the invention, the second generation means performs a weighted subtraction process on the first projection data and the second projection data so that the component of the predetermined substance is erased. There is provided the image generating apparatus according to the fifth aspect or the sixth aspect, wherein projection data is obtained and the iodine density image is generated by performing image reconstruction processing on the third projection data.

  In a ninth aspect of the invention, the second generation means obtains two types of images by performing image reconstruction processing on the first projection data and the second projection data, respectively, and the two types of images. The image generation apparatus according to the fifth aspect or the sixth aspect of the present invention that generates the iodine density image by performing weighted subtraction processing so that the component of the predetermined substance is eliminated.

  The invention according to a tenth aspect provides the image generating apparatus according to any one of the fifth to ninth aspects, wherein the first and second substances are water and iodine.

  The eleventh aspect of the invention provides an X-ray CT apparatus including the image generating apparatus according to any one of the first to tenth aspects.

  The invention of the twelfth aspect provides a program for causing a computer to function as the image generating apparatus according to any one of the first to tenth aspects.

  The “density” mentioned here is not an actual density but an imaginary density. Two predetermined types of substances are used as a base substance, and an X-ray absorption coefficient of a certain substance is set to X of the two types of base substances. When expressed by the weighted addition value of the linear absorption coefficient, it corresponds to a weighting coefficient to be multiplied by the X-ray absorption coefficient of the two types of base materials. Therefore, for example, a water density image when water and iodine are a set of base materials is the X-ray absorption coefficient of the substance represented by each pixel in the image to be imaged, the X-ray absorption coefficient of water and the X-ray of iodine. When expressed by a weighted addition value with an absorption coefficient, a distribution diagram of values corresponding to the weighting coefficient multiplied by the water X-ray absorption coefficient is obtained.

  According to the invention of the above aspect, a virtual contrast image and an iodine density image are generated by X-ray CT dual energy imaging of a subject to which a contrast medium containing iodine is administered, and the iodine density image is subtracted from the virtual contrast image or A virtual non-contrast image can be obtained by weighted subtraction. As a result, both the image corresponding to the contrast image and the image corresponding to the non-contrast image can be obtained by one dual energy imaging, and it is not necessary to perform contrast imaging and non-contrast imaging, respectively. Low exposure can be realized.

It is a figure which shows the structure of the X-ray CT apparatus by 1st embodiment. It is a figure which shows the flow of a process in the X-ray CT apparatus which concerns on 1st embodiment. It is a figure for demonstrating the extrapolation process by a calcium density image and an iodine density image. It is a figure which shows the flow of a process in the X-ray CT apparatus which concerns on 2nd embodiment. It is a figure which shows the flow of a process in the X-ray CT apparatus which concerns on 3rd embodiment.

(First embodiment)
First, the configuration of the X-ray CT apparatus according to the first embodiment will be described.

  FIG. 1 is a diagram showing a configuration of an X-ray CT apparatus 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 performs control of various units and various calculations for scanning the subject 40, and data acquired by the scanning gantry 20. A data collection buffer (buffer) 5, a monitor 6 for displaying images, and a storage device 7 for storing programs and data.

  The imaging table 10 includes a cradle 12 on which the subject 40 is placed and carried into and out of the opening of the scanning gantry 20. The cradle 12 is moved up and down and horizontally moved by a motor built in the imaging table 10.

  The scanning gantry 20 includes a rotating unit 15 and a support unit 16 that rotatably supports the rotating unit 15. The rotating unit 15 includes an X-ray tube 21, an X-ray controller (controller) 22 that controls the X-ray tube 21, and a collimator that collimates and shapes the X-ray 81 generated from the X-ray tube 21. ) 23, an X-ray detector 24 that detects X-rays 81 irradiated from the X-ray tube 21 and transmitted through the subject 40, and a data collection device that converts and collects the output of the X-ray detector 24 into projection data (DAS; Data Acquisition System) 25 and an X-ray controller 22, a collimator 23, and a rotating unit controller 26 that controls the DAS 25 are mounted. The support unit 16 includes a control controller 29 that communicates control signals and the like with the operation console 1 and the imaging table 10. The rotating part 15 and the support part 16 are electrically connected via a slip ring 30.

  Hereafter, the flow of processing in the X-ray CT apparatus according to the first embodiment will be described.

  In this process, using a predetermined model representing the subject by combining two types of base materials, images corresponding to a contrast image and a non-contrast image of the subject are obtained by one X-ray CT dual energy imaging, respectively. It is processing.

  In this example, from the two types of projection data obtained by X-ray CT dual energy imaging of the subject using the above model, an iodine density representing the virtual contrast image of the subject and the virtual iodine density distribution of the subject. Ask for an image. Further, a virtual non-contrast image is obtained by subtracting the iodine density image from the virtual contrast image.

  Hereinafter, the above process will be described in detail for each step.

  FIG. 2 is a diagram showing a flow of processing in the X-ray CT apparatus according to the first embodiment.

  In step S1, X-ray CT dual energy imaging of the subject 40 is performed. Thereby, the first tube voltage projection data Pv1 and the second tube voltage projection data Pv2 are collected.

  The first tube voltage projection data Pv1 is projection data of a plurality of views by X-rays when the X-ray tube voltage is the first X-ray tube voltage V1. The second tube voltage projection data Pv2 is projection data of a plurality of views by X-rays when the X-ray tube voltage is the second X-ray tube voltage V2 different from the first X-ray tube voltage.

  X-ray CT dual energy imaging is performed as follows, for example.

  A scan of the subject 40 is performed while alternately switching the X-ray tube voltage between the first X-ray tube voltage V1 and the second X-ray tube voltage V2 in units of one or several views, and 180 ° + X-ray beam (beam) Collect projection data with a fan angle of α ° or more. In this case, the projection data of the missing view in the set of projection data having the same X-ray tube voltage is obtained by weighted addition processing of the projection data of the view adjacent to the missing view.

  Alternatively, the X-ray tube voltage is set to the first X-ray tube voltage V1 and scanning is performed to collect projection data of 180 ° + fan angle α ° or more, and then the X-ray tube voltage is converted to the second X-ray tube voltage V2. Then, scanning is performed to collect projection data of 180 ° + fan angle α ° or more.

  Here, as an example, the first X-ray tube voltage V1 is 80 kVp, and the second X-ray tube voltage V2 is 140 kVp.

  In steps S2 and S3, the water density image Gw (w, io) and the iodine density image Gio (w, io) are reconstructed based on the first and second tube voltage projection data Pv1 and Pv2.

  The water density image Gw (w, io) and the iodine density image Gio (w, io) are respectively models representing the subject 40 by the synthesis of two kinds of base materials, for example, US Pat. No. 7724865 (US2009 / 0052612). In the model described in (1), etc., a substance density image representing a virtual density distribution of the base substance in the subject 40. That is, the water density image Gw (w, io) is an image representing a virtual water density distribution in the subject 40 when the base material of the model is water and iodine. The iodine density image Gio (w, io) is an image representing a virtual iodine density distribution in the subject 40 when the base material of the model is water and iodine.

  Based on the above model, the water density image Gw (w, io) and the iodine density image Gio (w, io) are weighted and added, so that the subject 40 is X-ray CT with X-rays having a desired effective X-ray energy. It is possible to reconstruct a monochrome image corresponding to an image obtained when the image is taken. The monochrome image can be used as a virtual contrast image of the subject 40.

  The two types of base materials of the model may be basically any materials, but when reconstructing an image of the subject 40 such as a human body as a monochrome image, water and iodine are used. Good. This is because most of the substances contained in the human body have an X-ray absorption coefficient larger than that of water and smaller than iodine, so that each pixel value in the subject image is interpolated between a pixel value representing water and a pixel value representing iodine. This is because extrapolation with low accuracy can be avoided as much as possible.

  Therefore, in this example, the water density image Gw (w, io) and iodine density image Gio (w, io) when the base material of the model is water and iodine are used as the material density image used for the reconstruction of the monochromatic image. ).

  Here, in step S2, the first tube voltage projection data Pv1 and the second tube voltage projection data Pv2 are weighted and subtracted so that iodine components are eliminated, and the base material of the model is water and iodine. Then, water density projection data Pw (w, io) representing the water component in the subject 40 is generated. Further, the subject when the first tube voltage projection data Pv1 and the second tube voltage projection data Pv2 are weighted and subtracted so that the water component is eliminated, and the base material of the model is water and iodine. Iodine density projection data Pio (w, io) representing the component of iodine at 40 is generated. The weighted subtraction process for the first and second tube voltage projection data Pv1 and Pv2 may be a linear first-order weighted subtraction process, but here a non-linear multi-order weighted subtraction process is used, and a multi-order weighting coefficient is used. Beam hardening correction is also performed by adjusting.

  The weighting coefficient used for the weighted subtraction processing of the first and second tube voltage projection data Pv1 and Pv2 is the first and second X-ray tube voltages V1 and V2, and two types of base materials (here, water and Iodine) and a component to be erased by weighted subtraction or a component to be retained, and can be obtained in advance by a predetermined calculation based on the above model.

  In step S3, the water density projection data Pw (w, io) is subjected to image reconstruction processing by back projection processing or the like to reconstruct the water density image Gw (w, io). Further, iodine density projection data Pio (w, io) is subjected to image reconstruction processing to reconstruct an iodine density image Gio (w, io).

  In this example, as described above, a virtual non-contrast image is obtained by subtracting the iodine density image from the virtual contrast image. The iodine density image used here is basically a weighted subtraction process so that the base material of the model is a predetermined substance other than iodine and iodine, and two types of tube voltage images are erased so that the components of the predetermined substance are erased. The iodine density image obtained as described above or an image based on the iodine density image may be used.

  In that sense, it is possible to use the iodine density image Gio (w, io) obtained in step S3 when the base material of the above model is water and iodine as the iodine density image to be subtracted from the virtual contrast image. is there.

  However, in the iodine density image to be subtracted from the virtual contrast image, it is better that components other than iodine among substances in the subject 40 are removed as much as possible. For this reason, the predetermined substance is preferably a substance that actually constitutes the subject, that is, a substance having an X-ray absorption coefficient larger than water and smaller than iodine.

  In addition, in the iodine density image that is subtracted from the virtual contrast image, the above-mentioned predetermined substance is another substance whose iodine component is actually constituting the subject and whose X-ray absorption coefficient is close to iodine, such as a bone part. It is more preferable that the substance has an X-ray absorption coefficient close to that of iodine so that it can be accurately separated and extracted from calcium contained in a large amount.

  Therefore, here, an iodine density image when the two types of base substances of the above model are calcium and iodine is used as an iodine-weighted image to be subtracted from the virtual contrast image when obtaining a virtual non-contrast image.

  In step S4, the first monochrome image Gme1, the second monochrome image Gme2, and the third monochrome image Gme3 are reproduced based on the water density image Gw (w, io) and the iodine density image Gio (w, io). Constitute.

  The first to third monochrome images Gme1 to Gme3 are obtained when X-ray CT imaging is performed on the subject 40 to which the contrast agent is administered using the X-rays of the first to third effective X-ray energies E1 to E3, respectively. This is an image corresponding to the obtained image.

  Here, as an example, the first effective X-ray energy E1 is set to 65 keV corresponding to the energy of the X-ray at the X-ray tube voltage of 120 kVp. The second effective X-ray energy E2 is set to 50 keV corresponding to the X-ray energy at the X-ray tube voltage of 80 kVp. The third effective X-ray energy E3 is set to 80 keV corresponding to the X-ray energy at the X-ray tube voltage 140 kVp.

  That is, the first monochrome image Gme1 is an image corresponding to a tube voltage image obtained by image reconstruction of projection data by X-rays having an X-ray tube voltage of 120 kVp. Here, the first monochrome image Gme1 is used as a virtual contrast image of the subject 40.

  The second monochrome image Gme2 is an image corresponding to the first tube voltage image Gv1 obtained by reconstructing the projection data of the X-ray with the X-ray tube voltage of 80 kVp, that is, the first tube voltage projection data Pv1. The third monochrome image Gme3 is an image corresponding to the second tube voltage image Gv2 obtained by reconstructing the projection data of the X-ray with the X-ray tube voltage of 140 kVp, that is, the second tube voltage projection data Pv2. However, the second and third monochrome images Gme2 and Gme3 in this example are images obtained by performing beam hardening correction on the actual first and second tube voltage images Gv1 and Gv2. Here, the second and third monochrome images Gme2 and Gme3 are used as original images for generating an iodine density image to be subtracted from the virtual contrast image when the virtual non-contrast image is obtained.

  As specific processing in step S4, the water density image Gw (w, io) and the iodine density image Gio (w, io) are respectively given predetermined weights corresponding to the first to third effective X-ray energies E1 to E3. That is, weighted addition processing is performed using weighting coefficients to reconstruct the first to third monochrome images Gme1 to Gme3.

  For details of the reconstruction method of each material density image and monochrome image, refer to Japanese Patent Application Laid-Open No. 2010-172590, US Patent Document: US Pat. No. 7724865 (US2009 / 0052612), and the like. I want.

  In step S5, the second monochrome image Gme2 and the third monochrome image Gme3 are subjected to weighted subtraction processing as shown in the following equation, and the virtual substance in the subject 40 when the base material of the model is iodine and calcium. An iodine density image Gio (ca, io) representing a typical iodine density distribution is reconstructed.

Gio (ca, io) = Gme2 × w2-Gme3 × w3 (Formula 1)
w2 = 1, w3 = 1.5

  These weighting factors w2 and w3 correspond to the case where the first and second X-ray tube voltages V1 and V2 are 80 kVp and 140 kVp, respectively, the base material of the model is iodine and calcium, and the component to be erased is calcium. It is an example of a weighting coefficient.

  Thereby, an iodine density image Gio (ca, io) can be obtained when the base material of the model is iodine and calcium. The iodine density image Gio (ca, io) is an image in which the component of iodine is emphasized by removing the component having an X-ray absorption coefficient equal to or less than the calcium equivalent value from the contrast image of the subject 40.

  The images used for the weighted addition for obtaining the iodine density image Gio (ca, io) may be the first and second tube voltage images Gv1 and Gv2, but the second and third monograms corresponding to these images. The chromatic images Gme2 and Gme3 are preferable in that beam hardening correction has been completed. Since the beam hardening correction is performed, an iodine density image Gio (ca, io) with better image quality can be obtained.

  The iodine density image is an image containing a large amount of iodine components that are components of a contrast agent. Therefore, if such an iodine density image is subtracted from the virtual contrast image, a non-contrast image from which the iodine component is removed from the contrast image can be virtually obtained.

  Therefore, in step S6, the iodine density image Gio (ca, io) is subtracted or weighted from the first monochrome image Gme1 as a virtual contrast image to obtain a virtual non-contrast image Gvnc.

  At this time, the iodine density image Gio (ca, io) is subjected to a process of cutting negative pixel values, that is, a process of converting negative pixel values (density values) to 0 (zero). The processed iodine density image Gio (ca, io) ′ may be subtracted or weighted from the contrast image. The reason will be described below.

  FIG. 3 shows, for each substance of iodine and calcium, the pixel value of the substance in the CT image when the X-ray tube voltage is 80 kVp and the pixel value of the substance in the CT image when the X-ray tube voltage is 140 kVp. It is a graph showing the relationship.

  Each straight line in the graph of FIG. 3 corresponds to each substance, and the slope of the straight line has a correlation with the magnitude of the X-ray absorption coefficient of the substance. The vector along the straight line of the substance corresponds to the pixel value in the substance density image of each substance, that is, the density of the substance. Specifically, the vector Vio along the iodine straight line Lio corresponds to the pixel value in the iodine density image, that is, the iodine density, and the vector Vca along the calcium straight line Lca is the pixel value in the calcium density image. That is, it corresponds to the density of calcium. Therefore, the pixel value of each pixel in the monochrome image can be represented by a weighted addition process of the pixel value of the corresponding pixel in the iodine density image and the pixel value of the corresponding pixel in the calcium density image. It can be expressed by a linear addition sum of the vector Vio and the calcium vector Vca.

  Here, the pixel value of the substance Q1 whose X-ray absorption coefficient is larger than calcium and smaller than iodine, the pixel value of the substance Q2 whose X-ray absorption coefficient is smaller than calcium, and the pixel value (calcium vector Vca) representing the density of calcium. It is assumed that each pixel value is expressed by weighted addition (linear addition sum) with a pixel value (iodine vector Vio) representing the density of iodine.

  In the case of the substance Q1, the weighted addition process corresponds to an “interpolation process” using a pixel value representing the calcium density and a pixel value representing the iodine density. Therefore, as shown in FIG. 3, both the pixel value (+ w11 · Vca) in the calcium density image used for weighted addition and the pixel value (+ w12 · Vio) in the iodine density image are positive.

  On the other hand, in the case of the substance Q2, the weighted addition processing corresponds to “extrapolation processing” using a pixel value representing the calcium density and a pixel value representing the iodine density. Therefore, as shown in FIG. 3, in the pixel value (+ w21 · Vca) in the calcium density image used for weighted addition and the pixel value (−w22 · Vio) in the iodine density image, the pixel value in the iodine density image is negative. Become.

  That is, a pixel having a negative pixel value in the iodine density image Gio (ca, io) when the base material of the model is iodine and calcium represents a substance having an X-ray absorption coefficient smaller than calcium.

  It is assumed that the component of the substance whose X-ray absorption coefficient is smaller than calcium remains in the iodine density image actually obtained without being completely separated. However, a pixel representing such a substance is not a pixel to be subtracted from the virtual contrast image when obtaining the virtual non-contrast image. Therefore, it is preferable to remove such pixels from the object of subtraction in advance.

  In step S7, the first monochrome image Gme1 as the virtual contrast image and the virtual non-contrast image Gvnc are displayed on the monitor.

(Second embodiment)
In the first embodiment, the iodine density image subtracted from the virtual contrast image when obtaining the virtual non-contrast image, that is, the iodine density image Gio (ca, io) when the base material of the model is calcium and iodine, It is obtained by weighted subtraction processing of the second and third monochrome images Gme2, Gme3.

  On the other hand, in the second embodiment, the iodine density image Gio (ca, io) to be subtracted from the virtual contrast image when obtaining the virtual non-contrast image is subjected to weighted subtraction processing on the first and second tube voltage projection data Pv1, Pv2. The iodine density projection data io (ca, io) obtained in this way is obtained by image reconstruction processing.

  FIG. 4 is a diagram showing a flow of processing in the X-ray CT apparatus according to the second embodiment.

  In step T1, similarly to step S1, X-ray CT dual energy imaging is performed to collect first tube voltage projection data Pv1 and second tube voltage projection data Pv2.

  In step T2, the first tube voltage projection data Pv1 and the second tube voltage projection data Pv2 are weighted and subtracted to obtain water density projection data Pw (w, io) when the base material of the model is water and iodine. ) And iodine density projection data Pio (w, io). Also, the first tube voltage projection data Pv1 and the second tube voltage projection data Pv2 are weighted and subtracted to generate iodine density projection data Pio (ca, io) when the base material of the model is calcium and iodine. To do.

  In step T3, the water density projection data Pw (w, io) and the iodine density projection data Pio (w, io) are each subjected to image reconstruction processing, and the water density image when the base material of the model is water and iodine. Gw (w, io) and iodine density image Gio (w, io) are reconstructed. The iodine density projection data Pio (ca, io) is subjected to image reconstruction processing to reconstruct an iodine density image Gio (ca, io) when the base material of the model is calcium and iodine.

  In step T4, the water density image Gw (w, io) and the iodine density image Gio (w, io) are weighted and added to reconstruct the first monochrome image Gme1.

  In step T5, as in step S6, the iodine density image Gio (ca, io) as the iodine extraction image is subtracted or weighted from the first monochrome image Gme1 as the virtual contrast image, and the virtual non-image is obtained. A contrast image Gvnc is obtained. At this time, as in the first embodiment, “processing for converting negative pixel values to zero” is performed on the iodine density image.

  In step T6, as in step S7, the first monochrome image Gme1 as the virtual contrast image and the virtual non-contrast image Gvnc are displayed on the monitor.

(Third embodiment)
In the first embodiment, the water density image Gw (w, io) and the iodine density image Gio (w, io) used for the weighted addition process when reconstructing a monochrome image are used as the first and second tube voltage projection data. It is obtained by image reconstruction processing of water density projection data Pw (w, io) and iodine density projection data io (w, io) obtained by weighted subtraction processing of Pv1 and Pv2. Further, when obtaining a virtual non-contrast image, an iodine density image to be subtracted from the virtual contrast image, that is, an iodine density image Gio (ca, io) when the base material of the model is calcium and iodine, are second and third. It is obtained by weighted subtraction processing of monochrome matic images Gme2 and Gme3.

  On the other hand, in the third embodiment, the water density image Gw (w, io) and iodine density image Gio (w, io) used for the weighted addition process when reconstructing a monochrome image are used as the first and second tube voltages. The projection data Pv1 and Pv2 are obtained by weighted subtraction processing of the first and second tube voltage images Gv1 and Gv2 obtained by image reconstruction processing. Further, the iodine density image Gio (ca, io) to be subtracted from the virtual contrast image Gme1 when obtaining the virtual non-contrast image Gvnc is obtained by weighted subtraction processing of the first and second tube voltage images Gv1, Gv2.

  FIG. 5 is a diagram showing a flow of processing in the X-ray CT apparatus according to the third embodiment.

  In Step U1, as in Step S1, X-ray CT dual energy imaging is performed to collect first tube voltage projection data Pv1 and second tube voltage projection data Pv2.

  In step U2, the first tube voltage projection data Pv1 is subjected to image reconstruction processing to reconstruct the first tube voltage image Gv1. Further, the second tube voltage projection data Pv2 is subjected to image reconstruction processing to reconstruct the second tube voltage image Gv2.

  In step U3, the first tube voltage image Gv1 and the second tube voltage image Gv2 are divided into the first and second X-ray tube voltages of 80 kVp and 140 kVp, the base materials of the model are water and iodine, and the material to be deleted. The water density image Gw (w, io) when the base material of the above model is water and iodine is reconstructed by performing weighted subtraction with a corresponding weight when the component is iodine. Further, the first tube voltage image Gv1 and the second tube voltage image Gv2 are divided into the first and second X-ray tube voltages of 80 kVp and 140 kVp, the base material of the model is water and iodine, and the components of the material to be erased By performing weighted subtraction with a corresponding weighting when water is water, an iodine density image Gio (w, io) when the base material of the model is water and iodine is reconstructed. Further, the first tube voltage image Gv1 and the second tube voltage image Gv2 are divided into the first and second X-ray tube voltages of 80 kVp and 140 kVp, the base materials of the model are calcium and iodine, and the components of the material to be deleted By performing a weighted subtraction process with a weighting corresponding to when is a calcium, an iodine density image Gio (ca, io) when the base material of the model is calcium and iodine is reconstructed.

  In step U4, the water density image Gw (w, io) and the iodine density image Gio (w, io) are weighted and added to reconstruct the first monochrome image Gme1.

  In step U5, similar to step S6, the iodine density image Gio (ca, io) as the iodine extraction image is subtracted or weighted from the first monochrome image Gme1 as the virtual contrast image, and the virtual non-image is obtained. A contrast image Gvnc is obtained. At this time, as in the first embodiment, “processing for converting negative pixel values to zero” is performed on the iodine density image.

  In step U6, as in step S7, the first monochrome image Gme1 as the virtual contrast image and the virtual non-contrast image Gvnc are displayed on the monitor.

  As described above, according to each of the above embodiments, a virtual non-contrast image can be obtained with high accuracy by X-ray CT dual energy imaging of a subject to which a contrast medium containing iodine is administered. As a result, both a monochrome image corresponding to a contrast image and a virtual non-contrast image corresponding to a non-contrast image can be obtained by one dual energy imaging, and it is necessary to perform contrast imaging and non-contrast imaging, respectively. In addition, low exposure in contrast examination can be realized.

  As mentioned above, although embodiment of invention was described, embodiment of invention is not limited to said thing, In the range which does not deviate from the meaning of invention, various forms can be taken. That is, a virtual contrast image of the subject and an iodine density image representing the virtual iodine density distribution of the subject are obtained from projection data obtained by X-ray CT dual energy imaging of the subject, and the virtual contrast image is obtained from the virtual contrast image. Any form may be used as long as the virtual non-contrast image is obtained by subtracting the iodine density image.

  For example, in each of the above embodiments, the monochromatic image is generated based on the water density image and the iodine density image, but may be generated based on a material density image using another substance as a base substance.

  Also, for example, in each of the above embodiments, when the iodine density image is subtracted or weighted subtracted from the virtual contrast image, a process for converting the negative pixel value to zero is performed on the iodine density image. This process can be omitted.

  Further, for example, each of the above embodiments is an X-ray CT apparatus, but an image generation apparatus having a virtual non-contrast image generation function as described above is also an embodiment of the invention.

  Further, for example, a program for causing a computer to function as the above-described image generation apparatus is also an embodiment of the invention.

DESCRIPTION OF SYMBOLS 1 Operation console 2 Input device 3 Central processing unit 5 Data collection buffer 6 Monitor 7 Storage device 10 Imaging table 12 Cradle 15 Rotation part 16 Support part 20 Scanning gantry 21 X-ray tube 22 X-ray tube controller 23 Collimator 24 X-ray detector 25 Data collection device (DAS)
26 Rotating part controller 29 Control controller 30 Slip ring 40 Subject 81 X-ray

Claims (12)

When X-ray CT imaging of the subject is performed using X-rays having desired effective X-ray energy based on data obtained by X-ray CT dual energy imaging of the subject administered with a contrast medium containing iodine First generation means for generating a virtual contrast image corresponding to the obtained image;
Second generation means for generating an iodine density image representing a virtual iodine density distribution in the subject based on a model representing the subject by synthesis of iodine and a predetermined substance other than iodine based on the data When,
Image generation comprising: third generation means for generating a virtual non-contrast image corresponding to an image obtained by non-contrast imaging of the subject by subtracting or weighted subtraction of the iodine density image from the virtual contrast image apparatus. When X-ray CT imaging of the subject is performed using X-rays having desired effective X-ray energy based on data obtained by X-ray CT dual energy imaging of the subject administered with a contrast medium containing iodine First generation means for generating a virtual contrast image corresponding to the obtained image;
Second generation means for generating an iodine density image representing a virtual iodine density distribution in the subject based on a model representing the subject by synthesis of iodine and a predetermined substance other than iodine based on the data When,
Obtained by non-contrast imaging of the subject by subjecting the iodine density image to a process of converting a negative pixel value to zero and subtracting or weighted subtracting the processed iodine density image from the virtual contrast image And a third generation means for generating a virtual non-contrast image corresponding to the image to be generated.   The image generation apparatus according to claim 1, wherein the predetermined substance is a substance having an X-ray absorption coefficient larger than water and smaller than iodine.   The image generation apparatus according to claim 3, wherein the predetermined substance is calcium. The data includes first projection data by X-rays of a first energy and second projection data by X-rays of a second energy different from the first energy,
The first generation means obtains two types of projection data by performing weighted subtraction processing on the first projection data and the second projection data by two types of weighting, and each of the two types of projection data is converted into an image. A first substance that represents a density distribution of the virtual first substance in the subject based on a model that is reconstructed and represents the subject by combining different first substances and second substances. Obtaining a density image and a second substance density image representing a virtual density distribution of the second substance in the subject, and performing a weighted addition process on the first and second substance density images The image generation apparatus according to claim 1, wherein a contrast image is generated. The data includes first projection data by X-rays of a first energy and second projection data by X-rays of a second energy different from the first energy,
The first generation means obtains two types of images by performing image reconstruction processing on the first projection data and the second projection data, respectively, and performs weighted subtraction of the two types of images by two types of weighting. A first material density image representing a virtual density distribution of the first substance in the subject based on a model that is processed to represent the subject by combining different first and second substances. And a second substance density image representing a virtual density distribution of the second substance in the subject, and the virtual contrast image is obtained by performing weighted addition processing on the first and second substance density images. The image generation device according to any one of claims 1 to 4, wherein   The second generation means performs weighted addition processing of the first and second substance density images by two types of weighting, and the subject is subjected to X-ray CT using X-rays of first effective X-ray energy. A first image corresponding to an image obtained at the time of imaging, and a second image corresponding to an image obtained when X-ray CT imaging is performed on the subject using X-rays having second effective X-ray energy. The image generation apparatus according to claim 5 or 6, wherein the iodine density image is generated by performing weighted subtraction processing on the first and second images so that components of the predetermined substance are erased. .   The second generation means obtains third projection data by performing weighted subtraction processing on the first projection data and the second projection data so that a component of the predetermined substance is eliminated, and the third projection data is obtained. The image generation apparatus according to claim 5, wherein the iodine density image is generated by performing image reconstruction processing on the projection data.   The second generation unit obtains two types of images by performing image reconstruction processing on the first projection data and the second projection data, respectively, and erases the two types of images from the component of the predetermined substance. The image generation apparatus according to claim 5, wherein the iodine density image is generated by performing weighted subtraction processing as described above.   The image generation apparatus according to claim 5, wherein the first and second substances are water and iodine.   An X-ray CT apparatus provided with the image generation apparatus according to claim 1.   The program for functioning a computer as an image generation apparatus as described in any one of Claims 1-10.

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