JP2011172803A - X-ray ct apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray CT apparatus for improving reading efficiency. <P>SOLUTION: The X-ray CT apparatus includes: photographing units (10, 20, 51) for photographing a subject by dual energy so as to obtain first photographing data by the first X-ray and second photographing data by the second X-ray; a reconstitution unit (52) for reconstituting a prescribed image, based on the obtained photographing data; an acquiring part (531) for acquiring a prescribed feature amount concerning the pixel values of pixel positions concerning the respective pixel positions of the prescribed image; a specifying part (532) for specifying X-ray energy associated with the acquired feature amount; a calculating part (534) for calculating the pixel values of the pixel positions on the image corresponding to the image to be acquired when photographing the subject by the X-ray of the specified X-ray energy; and a generator (53) for generating the image where the calculated pixel values are defined as the pixel values of the pixel positions corresponding to the pixel positions with the calculated pixel values. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to X-ray CT (Computed
In particular, the present invention relates to an X-ray CT apparatus that performs dual energy imaging.

  There is known a technique for reconstructing an image corresponding to an image obtained when imaging is performed using X-rays having arbitrary effective X-ray energy by dual energy imaging using an X-ray CT apparatus (for example, Patent Documents). 1, abstract, patent document 2, FIGS. 4-5 etc.). According to this method, an image of desired effective X-ray energy can be obtained in a short amount of time and with a low exposure.

  On the other hand, the energy of X-rays at the time of X-ray CT imaging for obtaining a CT image suitable for observation differs depending on the type of substance to be observed. For example, calcification and bone tissue are easier to observe because images with higher energy X-rays have less bleeding. Conversely, contrast blood vessels and soft tissues have better contrast and a larger amount of information in images taken with lower energy X-rays.

  However, in actual image interpretation, it is often the case that a plurality of parts with different substances are observed or a part composed of a plurality of substances is observed. In such cases, the energy of X-rays (usually It is necessary to observe a plurality of images having different X-ray tube voltages).

US2009 / 0052612A1 JP 2009-1553829 A

  Therefore, it is conceivable to observe a plurality of images of desired effective X-ray energy from dual energy imaging by using the above-described method, and display these images on a monitor.

  However, when a plurality of images are observed in this way, the amount of interpretation is increased, and the burden on the interpreter is also increased, resulting in poor interpretation efficiency.

  Under such circumstances, an X-ray CT apparatus capable of improving the interpretation efficiency is desired.

  In the invention of the first aspect, the subject is subjected to dual energy imaging, the first projection data by the first X-ray, and the second X-ray by the second X-ray having energy different from the first X-ray. Imaging means for obtaining projection data, reconstruction means for reconstructing a predetermined image of the subject based on the first projection data and / or the second projection data, and the first and second A calculation unit that calculates a pixel value at a desired pixel position in an image corresponding to an image obtained when the subject is imaged with X-rays having desired X-ray energy based on the projection data; For each pixel position in the image, an acquisition unit that can specify a substance corresponding to the pixel position and acquires a predetermined feature amount related to the pixel value of the pixel position, and is associated with the acquired feature amount, In the pixel position And a specifying unit that specifies X-ray energy corresponding to an image suitable for observation of the corresponding substance, and an image obtained when the subject is imaged with X-rays having the specified X-ray energy The pixel value of the pixel position in the image corresponding to is calculated by the calculation unit, and the generated pixel value is used as the pixel value of the pixel position corresponding to the pixel position for which the pixel value is calculated. An X-ray CT apparatus comprising the means is provided.

  According to a second aspect of the invention, the reconstruction means performs image reconstruction processing on the first and second projection data, respectively, to obtain first and second images, and the first and second images are obtained. The images are weighted and subtracted by two different weights to obtain third and fourth images, and the third and fourth images are weighted and summed by two different weights, The sixth image is reconstructed as the predetermined image, and the predetermined feature amount is a ratio or difference of pixel values at the same pixel position in the fifth and sixth images. A CT apparatus is provided.

  According to a third aspect of the invention, the reconstructing means obtains third and fourth projection data by performing weighted subtraction processing on the first and second projection data using two different types of weights. The third and fourth projection data are respectively subjected to image reconstruction processing to obtain first and second images, and the first and second images are subjected to weighted addition processing by two different types of weighting, 3 and 4 are reconstructed as the predetermined image, and the predetermined feature amount is a ratio or difference of pixel values at the same pixel position in the third and fourth images. An X-ray CT apparatus is provided.

  According to a fourth aspect of the invention, the reconstruction means performs image reconstruction processing on the first and second projection data, respectively, and reconstructs the first and second images as the predetermined image, The X-ray CT apparatus according to the first aspect is provided in which the predetermined feature amount is a ratio or difference between pixel values at the same pixel position in the first and second images.

  According to a fifth aspect of the invention, the reconstruction means performs image reconstruction processing on the first or second projection data to reconstruct the predetermined image, and the predetermined feature amount is a pixel value. The X-ray CT apparatus according to the first aspect as it is is provided.

  According to a sixth aspect of the invention, the reconstruction means obtains third projection data by performing weighted subtraction processing on the first and second projection data, and performs image reconstruction processing on the third projection data. Then, the X-ray CT apparatus according to the first aspect is provided in which the predetermined image is reconstructed and the predetermined feature amount is a pixel value itself.

  In a seventh aspect of the invention, the reconstruction means performs image reconstruction processing on the first and second projection data to obtain first and second images, respectively, and the first and second images The X-ray CT apparatus according to the first aspect is provided in which the predetermined image is reconstructed by performing weighted subtraction processing, and the predetermined feature amount is a pixel value itself.

  According to an eighth aspect of the invention, the reconstruction means performs image reconstruction processing on the first and second projection data, respectively, to obtain first and second images, and the first and second images The images are weighted and subtracted by two different types of weights to obtain third and fourth images, the third and fourth images are weighted and summed to reconstruct the predetermined image, and The X-ray CT apparatus according to the first aspect, wherein the predetermined feature amount is the pixel value itself.

  In a ninth aspect of the invention, the reconstruction means performs weighted subtraction processing on the first and second projection data by two different types of weights to obtain third and fourth projection data, Image reconstruction processing is performed on the third and fourth projection data, respectively, to obtain first and second images, and the first and second images are weighted and added to reconstruct the predetermined image. The X-ray CT apparatus according to the first aspect, wherein the predetermined feature amount is a pixel value itself.

  According to a tenth aspect of the present invention, the calculation unit calculates the first and second images obtained by performing image reconstruction processing on the first and second projection data, respectively, by two different types of weighting. The pixel value at the same pixel position in the third and fourth images obtained by the weighted subtraction process is weighted and added by the weight corresponding to the specified X-ray energy, and the pixel value at the pixel position is calculated. An X-ray CT apparatus according to any one of the first to ninth aspects is provided.

  According to an eleventh aspect of the invention, the calculation unit performs image reconstruction on third and fourth projection data obtained by performing weighted subtraction on the first and second projection data using two different types of weighting. The pixel value at the same pixel position in the first and second images obtained by performing the configuration process is weighted and added by weighting corresponding to the specified X-ray energy to obtain the pixel value at the pixel position. An X-ray CT apparatus according to any one of the first to ninth aspects to be calculated is provided.

  According to the X-ray CT apparatus of the invention of the above aspect, each substance of the subject can provide a single image represented by image information with X-ray energy suitable for observation for interpretation. Therefore, the amount of interpretation can be reduced and the interpretation efficiency can be improved.

It is a figure which shows the structure of the X-ray CT apparatus by 1st Embodiment. It is a mechanism block diagram of the X-ray CT apparatus by 1st Embodiment. It is a figure which shows roughly the process of reconstructing a tube voltage image, a material density image, and a monochromatic (monochromatic) image in steps. It is a figure which shows roughly the process of calculating | requiring the pixel value of a monochromatic composite image. It is a figure which shows an example of the correspondence of CT value ratio and effective X-ray energy. It is a flow figure showing the flow of processing in the X-ray CT apparatus of a 1st embodiment. It is a flowchart of the composite image generation process in 1st Embodiment. It is a mechanism block diagram of the X-ray CT apparatus by 2nd Embodiment. It is a flowchart of the composite image generation process in 2nd Embodiment. It is a mechanism block diagram of the X-ray CT apparatus by 3rd Embodiment. It is a flowchart of the composite image generation process in 3rd Embodiment. It is a figure which shows an example of the correspondence of CT value and effective X-ray energy. It is a mechanism block diagram of the X-ray CT apparatus by 4th Embodiment. It is a flowchart of the composite image generation process in 4th Embodiment. It is a mechanism block diagram of the X-ray CT apparatus by 5th Embodiment. It is a flowchart of the synthesized image generation process in 5th Embodiment.

  Embodiments of the invention will be described below.

(First embodiment)
FIG. 1 is a diagram showing the configuration of the X-ray CT apparatus according to the present embodiment.

  The X-ray CT apparatus 100 includes an operation console 1, an imaging table 10, and a scanning gantry 20. The imaging table 10 and the scanning gantry 20 are examples of data collection means in the invention.

  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 B 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. Here, the body axis direction of the subject 40, that is, the horizontal linear movement direction of the cradle 12 is the z direction, the vertical direction is the y direction, and the horizontal direction perpendicular to the z direction and the y direction is the x direction.

  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 22 that controls the X-ray tube 21, and a collimator 23 that collimates the X-rays 81 generated from the X-ray tube 21. 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 acquisition device (DAS;) that converts and collects the output of the X-ray detector 24 into projection data. Data Acquisition System) 25 and a rotating unit controller 26 for controlling the X-ray controller 22, the collimator 23, and the DAS 25 are mounted. The X-ray detector 24 is a multi-row detector in which, for example, 256 detector rows are arranged in the z direction. 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.

  FIG. 2 is a mechanism block diagram functionally showing the configuration of the X-ray CT apparatus according to the present embodiment. In this figure, the main part of the operation console is functionally represented.

  The operation console 1 of the X-ray CT apparatus 100 includes a dual energy imaging control unit 51, an image reconstruction unit 52, a composite image generation unit 53, and a display control unit 54.

  The dual energy imaging control unit 51 controls the imaging table 10 and the scanning gantry 20, performs dual energy imaging on the subject 40, and collects projection data. For example, scanning is performed while alternately switching the X-ray tube voltage between a relatively high first tube voltage HV and a relatively low second tube voltage LV in units of one view or several views. Collect projection data for the viewing angle. Alternatively, scanning is performed with the X-ray tube voltage set to the first tube voltage HV, projection data for a predetermined view angle is collected, the X-ray tube voltage is switched to the second tube voltage LV, and scanning is performed. Projection data for a predetermined view angle is collected. As a result, the first projection data PHV based on the X-ray having the first tube voltage HV and the second projection data PLV based on the X-ray having the second tube voltage LV are collected. The first and second tube voltages HV and LV are, for example, 140 [kV] and 80 [kV]. The predetermined view angle is, for example, a fan angle α [rad] or 2π [rad] of a π + X-ray beam.

  Based on the first and second projection data PHV and PLV, the image reconstruction unit 52 reconstructs an image of the subject 40 whose pixel values change according to the type of substance. Here, a tube voltage image, a material density image, and a monochromatic image are reconstructed step by step as such an image. The tube voltage image is a tomographic image normally obtained when X-ray CT imaging of the subject 40 is performed using X-rays when the X-ray tube voltage is a predetermined tube voltage. The substance density image is a tomographic image representing the density distribution of a predetermined substance in the subject 40. A monochrome image is an image obtained by weighted addition processing of two types of substance density images, and is an image corresponding to an image photographed by monochromatic X-rays having a predetermined effective X-ray energy. Details of the image reconstruction unit 52 will be described later.

  Based on the image reconstructed by the image reconstruction unit 52, the composite image generation unit 53 has different effective X-ray energies so that each substance in the subject 40 is represented in a mode suitable for observation of the substance. A monochrome composite image corresponding to an image obtained by combining a plurality of monochrome images in units of pixels is generated. Details of the composite image generation unit 53 will be described later.

  The display control unit 54 controls the monitor 6 so as to display the generated composite image Ga.

  Here, details of the image reconstruction unit 52 will be described.

  As shown in FIG. 2, the image reconstruction unit 52 includes a tube voltage image reconstruction unit 521, a material density image reconstruction unit 522, and a monochrome image reconstruction unit 523.

  FIG. 3 is a diagram schematically showing a process of reconstructing a tube voltage image, a material density image, and a monochrome image in a stepwise manner.

  As shown in FIG. 3, first, the tube voltage image reconstruction unit 521 uses the first and second projection data PHV and PLV to represent the first subject 40 that is imaged with the first tube voltage HV. The second tube voltage image GHV and the second tube voltage image GLV representing the subject 40 photographed by the second tube voltage LV are reconstructed. Specifically, first, predetermined pre-processing including logarithmic conversion, correction of radiation quality, correction of sensitivity of the X-ray detector, and the like is performed on the first and second projection data PHV and PLV. Next, a predetermined reconstruction function is superimposed on the preprocessed first and second projection data PHV and PLV. The first and second projection data PHV and PLV on which the reconstruction function is superimposed are respectively backprojected to obtain first and second tube voltage images GHV and GLV.

  Next, the substance density image reconstruction unit 522 performs weighted subtraction processing on the first tube voltage image GHV and the second tube voltage image GLV to strongly express the density distribution of the first substance in the subject 40. The first material density image and the second material density image that strongly represents the density distribution of the second material in the subject 40 are obtained. Here, as an example, the first substance is water and the second substance is iodine, and a water density image Gw representing the density distribution of water and an iodine density image Gio representing the density distribution of iodine are obtained.

  The projection data of the subject or an image reconstructed based on the projection data can be approximately expressed by the density distributions of two different types of substances and their X-ray absorption coefficients. Based on this approximate model, first and second material density images can be obtained. That is, the first material is obtained by performing weighted subtraction processing on the first tube voltage image GHV and the second tube voltage image GLV so that the pixel value of the pixel corresponding to the water that is the first material becomes zero. As a second substance density image, an iodine density image Gio that strongly suppresses the density component of the water and suppresses the density distribution of iodine as the second substance. Similarly, the first tube voltage image GHV and the second tube voltage image GLV are subjected to weighted subtraction processing so that the pixel value of the pixel corresponding to iodine as the second substance becomes zero, thereby obtaining the second tube voltage image GHV. A component of iodine which is a substance is suppressed, and a water density image Gw which strongly represents the density distribution of water which is the first substance is obtained as the first substance density image.

  Note that the pixel values corresponding to the first and second substances in the first and second tube voltage images GHV and GLV, respectively, can be estimated from the imaging conditions of dual energy imaging. Therefore, the weight to be used for the weighted subtraction process can be specified from the ratio of these estimated pixel values.

  The water density image Gw and the iodine density image Gio can be obtained, for example, by performing a weighted subtraction process according to the following formula.

  Here, kw is a conversion coefficient for expressing the pixel value Gw (x, y) of the water density image in terms of water density [mg / ml], and kio is the pixel value Gio (x, y) of the iodine density image. Conversion coefficient for expressing density [mg / ml], rio is the dual energy ratio of iodine in the first tube voltage HV and the second tube voltage LV, rw is the first tube voltage HV and the second tube voltage It is the dual energy ratio of water in LV.

  In Equation 1 representing the weighted subtraction process for obtaining the water density image Gw, the weighting coefficient to be multiplied by the pixel value GLV (x, y) of the second tube voltage image is kw, and the pixel of the first tube voltage image The weighting factor by which the value GHV (x, y) is multiplied is kW · rio. Further, in Equation 2 representing the weighted subtraction process for obtaining the iodine density image Gio, the weight coefficient to be multiplied by the pixel value GLV (x, y) of the second tube voltage image is kio, and the first tube voltage image. The weighting coefficient by which the pixel value of GHV (x, y) is multiplied is kio · rw.

  The dual energy ratio rio is a pixel value (CT value) GCio, LV (x, y) corresponding to iodine on the image GCLV (x, y) obtained when the X-ray is taken with the second tube voltage LV. ) Is divided by the pixel value GCio, HV corresponding to iodine on the image GCHV (x, y) obtained when X-rays are taken with the first tube voltage HV (CT value ratio) It is. Further, the dual energy ratio rw is obtained by converting the pixel value GCw, LV (x, y) corresponding to the water on the image GCLV (x, y) to the pixel value GCw, LV corresponding to the water on the image GCHV (x, y). A value obtained by dividing by HV (x, y).

  Next, as shown in FIG. 3, the water density image Gw and the iodine density image Gio are weighted and added, and a monochrome image Gm corresponding to an image photographed using X-rays having a predetermined effective X-ray energy. Get.

  The monochromatic image Gm can be obtained, for example, by performing a weighted addition process according to the following formula.

  Here, E1 is the effective X-ray energy, μw (E1) is the X-ray absorption coefficient of water with respect to the X-ray with the effective X-ray energy E1, and μio (E1) is the X-ray absorption of iodine with respect to the X-ray with the effective X-ray energy E1. The coefficient kc is a conversion coefficient for converting a pixel value into a CT value. As is well known, the CT value is a value indicating the degree of X-ray absorption of a substance, the CT value of air is represented by -1000 [HU], and the CT value of water is represented by 0 [HU].

  In Equation 5 representing the weighted addition process for obtaining the monochrome image Gm, the weighting coefficient to be multiplied to the water density image Gw is kc · μw (E1), and the weighting factor to be multiplied to the iodine density image Gio is kc · μio ( E1).

  By the way, in the above method, the first and second projection data are respectively subjected to image reconstruction processing to obtain two types of images, and these two types of images are subjected to weighted subtraction processing using different first and second weights. Thus, first and second substance density images are obtained. However, the first and second projection data are subjected to weighted subtraction with different first and second weights to obtain two types of projection data, and these two types of projection data are respectively subjected to image reconstruction processing, First and second material density images can also be obtained.

  Further, the weighted subtraction process and the weighted addition process are not limited to the linear linear weighted subtraction process and the linear linear weighted addition process, and a high-order linear weighted subtraction process, a high-order linear weighted addition process, and the like can also be used.

  The monochromatic image reconstruction unit 523 can reconstruct a monochromatic image corresponding to a desired effective X-ray energy by adjusting the weighting in the weighted addition process of the first and second material density images. In the present embodiment, the monochrome image reconstruction unit 523 includes a first monochrome image GmHV corresponding to an effective X-ray energy of 100 [keV] and a second monochrome image corresponding to an effective X-ray energy of 60 [keV]. Reconstruct monochrome image GmLV.

  For details of the reconstruction process of the monochrome image Gm, refer to, for example, US Patent Document US2009 / 0052612A1.

  Next, details of the composite image generation unit 53 will be described.

  As illustrated in FIG. 2, the composite image generation unit 53 includes a CT value ratio calculation unit 531, an X-ray energy identification unit 532, a CT value ratio versus X-ray energy storage unit 533, and a monochrome image pixel value calculation unit 534. ing.

  FIG. 4 is a diagram schematically illustrating a process of obtaining pixel values of a monochrome composite image.

  The CT value ratio calculation unit 531 has the CT value GmHV (x, y), which is the pixel value of the coordinate (x, y) of the first monochrome image GmHV, and the second monochrome image for the coordinate (x, y). The ratio of the CT value GmLV (x, y), which is the pixel value of the coordinates (x, y) of the image GmLV, that is, the CT value ratio GmLV (x, y) / GmHV (x, y) is calculated.

  The CT value ratio GmLV (x, y) / GmHV (x, y) changes so as to take different values depending on the type of substance represented by the pixel at the coordinates (x, y). This is well known because the X-ray energy absorption distribution of a substance varies depending on the type of the substance. Therefore, according to this CT value ratio, it is possible to relatively accurately discriminate between bone tissue and contrasted blood vessels and bone tissue and calcification, which are difficult to discriminate only with CT values.

  The CT value ratio vs. X-ray energy storage unit 533 observes the CT value ratio and the effective X-ray energy of a monochromatic image in which the substance is expressed in a desirable mode when observing the substance specified by the CT value ratio. Is stored.

  FIG. 5 is a diagram illustrating an example of a correspondence relationship between the CT value ratio and the effective X-ray energy.

  In this example, an effective X-ray energy of about 70 [keV] is associated with a CT value ratio corresponding to water of about 1.0. In addition, effective X-ray energy of about 90 to 120 [keV] is associated with the CT value ratio corresponding to bone tissue = 1.35 to 1.45. Further, an effective X-ray energy of about 120 to 130 [keV] is associated with the vicinity of the CT value ratio corresponding to calcification = 1.45 to 1.55. Effective X-ray energy of about 60 [keV] is associated with other CT value ratios.

  In general, when the X-ray energy of X-rays at the time of radiography is increased, the amount of X-ray absorption of the substance is reduced, and the influence of beam hardening is reduced. Thus, blurring of the outline of the substance is suppressed, but the contrast tends to decrease. Further, if the X-ray energy of X-rays at the time of X-ray imaging is lowered, the amount of X-ray absorption of the substance increases and the intensity of transmitted X-rays of the subject 40 decreases. Therefore, the contrast is increased, but noise tends to increase. The effective X-ray energy associated with each substance is determined in consideration of these balances.

  The X-ray energy specifying unit 532 is associated with the CT value ratio GmLV (x, y) / GmHV (x, y) based on the correspondence relationship stored in the CT value ratio vs. X-ray energy storage unit 533. The effective X-ray energy E (x, y) is specified. That is, the effective X-ray energy of the monochromatic image suitable for observing the substance represented by the pixel at the coordinates (x, y) is specified.

  The monochromatic image pixel value calculation unit 534 uses the X-ray having the specified effective X-ray energy E (x, y) by a predetermined calculation process based on the first and second projection data PHV and PLV. A pixel value GmE (x, y) at the coordinates (x, y) in an image GmE corresponding to an image obtained when the subject 40 is imaged is obtained.

  This predetermined calculation process is a calculation process in which the effective X-ray energy E1 is set to the above-identified E (x, y) in the weighted addition process for obtaining the monochrome image of Formula 5, and can be expressed by the following formula. it can.

  The composite image generation unit 53 obtains the above GmE (x, y) for each coordinate (x, y) by each of these units, and sets the pixel value of each coordinate (x, y) as GmE (x, y), respectively. The image to be generated is generated as a monochromatic composite image Gma.

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

  FIG. 6 is a flowchart showing the flow of processing in the X-ray CT apparatus of this embodiment.

  In step S1, dual energy imaging is performed, and first and second projection data PHV and PLV are collected.

  In step S2, the first and second tube voltage images GHV and GLV are reconstructed based on the first and second projection data PHV and PLV.

  In step S3, the water density image Gw and the iodine density image Gio are reconstructed by performing weighted subtraction processing on the first and second tube voltage images GHV and GLV with two different weights.

  In step S4, the water density image Gw and the iodine density image Gio are weighted and added by two different weights to reconstruct the first and second monochrome images GmHV and GmLV.

  In step S5, a monochromatic composite image Gma is generated.

  In step S6, the generated monochromematic composite image Gma is displayed.

  Note that the generation of the monochromatic composite image Gma in step S5 is performed, for example, by executing the following composite image generation process.

  FIG. 7 is a flowchart of the composite image generation process in this embodiment.

  In step T1, a pixel position number i corresponding to the coordinates of each pixel in the image of the subject 40 is initialized and i = 1 is set.

  In step T2, with respect to the coordinates (xi, yi) of the pixel position number i, the CT value GmHV (xi, yi) of the coordinates (xi, yi) of the first monochrome image GmHV and the second monochrome image GmLV The ratio of the coordinates (xi, yi) to the CT value GmLV (xi, yi), that is, the CT value ratio GmLV (xi, yi) / GmHV (xi, yi) is calculated.

  In step T3, the effective X-rays associated with the CT value ratio GmLV (xi, yi) / GmHV (xi, yi) based on the correspondence relationship stored in the CT value ratio vs. X-ray energy storage unit 533. Specify energy E.

  In step T4, based on Equation 6, the pixel value Gw (xi, yi) of the coordinates (xi, yi) of the water density image Gw and the pixel value Gio (xi, xi) of the coordinates (xi, yi) of the iodine density image Gio. yi) is weighted and added with a predetermined weighting that depends on the specified effective X-ray energy E (xi, yi) to calculate a pixel value GmE (xi, yi). This pixel value GmE (xi, yi) is the pixel value of the coordinates (xi, yi) in the monochromatic composite image Gma.

  In step T5, it is determined whether the pixel position number i is the last number. If it is the last, the monochromatic composite image Gma is completed (step T7), and the process ends. If not the last, the pixel position number is incremented by 1 (step T6), and the process returns to step T2.

  The monochromatic composite image Gma generated in this way is obtained by representing each substance of the subject 40 by image information with X-ray energy suitable for observation. As a result, for example, for the calcification in the blood vessel, a phenomenon called blooming, in which the calcification point is expressed in an enlarged manner, can be suppressed, and for the tissue in the blood vessel, An optimum CNR (Contrast Noise Ratio) can be maintained. Therefore, the state inside the blood vessel is clearly extracted, and observation inside the blood vessel becomes easy. Further, for example, the bone tissue appears clearly with little bleeding.

  As described above, according to the present embodiment, each substance of the subject 40 can provide a single image represented by image information with X-ray energy suitable for observation for interpretation. And the interpretation efficiency can be improved.

  In addition, the number of images to be saved can be reduced, and the burden on the server that saves the image data can be reduced.

  In addition, when X-ray energy is specified for each pixel position, a CT value ratio with high accuracy of specifying the type of substance is used instead of a simple CT value. Appropriateness increases.

  In addition, since a monochromatic image corresponding to an image photographed with monochromatic X-rays is used for the calculation of the CT value ratio, the range of values that can be taken by the CT value ratio according to the type of substance becomes narrower. The appropriateness of the X-ray energy allocated to the substance is further increased.

(Second Embodiment)
FIG. 8 is a functional block diagram of the X-ray CT apparatus 100a according to the second embodiment. FIG. 9 is a flowchart of the composite image generation process in the second embodiment.

  In the present embodiment, as shown in FIG. 8, the image reconstruction unit 52 includes a tube voltage image reconstruction unit 521 and a material density image reconstruction unit 522, but a monochrome image reconstruction unit 523. Does not have.

  The CT value ratio calculation unit 531 calculates the CT value ratio at each pixel position from the tube voltage image, not from the monochrome image. That is, as shown in step T2 of FIG. 9, the CT value GHV (x, y) of the coordinates (x, y) of the first tube voltage image GHV and the coordinates (x, y) of the second tube voltage image GLV. ) CT value ratio GLV (x, y) / GHV (x, y), which is a ratio of the CT value to the CT value GLV (x, y).

  As shown in step T3 of FIG. 9, the X-ray energy specifying unit 532 uses the CT value ratio GLV (x, y) / GHV based on the correspondence relationship stored in the CT value ratio vs. X-ray energy storage unit 533. The effective X-ray energy E associated with (x, y) is specified.

  Others are the same as in the first embodiment. Also in the present embodiment, a monochrome composite image can be generated as in the first embodiment.

(Third embodiment)
FIG. 10 is a functional block diagram of an X-ray CT apparatus 100b according to the third embodiment. FIG. 11 is a flowchart of the composite image generation process in the third embodiment.

  In the present embodiment, as illustrated in FIG. 10, the composite image generation unit 53 includes a CT value specifying unit 535 instead of the CT value ratio calculation unit 531, and a CT value ratio vs. X-ray energy storage unit 533. Instead of this, a CT value vs. X-ray energy storage unit 536 is provided.

  The monochromatic image reconstruction unit 523 reconstructs a monochromatic image Gm corresponding to predetermined effective X-ray energy.

  The CT value specifying unit 535 specifies the CT value of each pixel position in the monochrome image GmV as shown in step T2 of FIG.

  The CT value vs. X-ray energy storage unit 536 observes the CT value in the monochrome image Gm and the substance specified by the CT value, and the effective X-ray of the monochrome image in which the substance is expressed in a desirable mode. A relationship in which energy is associated is stored.

  FIG. 12 is a diagram illustrating an example of a correspondence relationship between CT values and effective X-ray energy.

  The X-ray energy specifying unit 532 is associated with the CT value Gm (x, y) based on the correspondence relationship stored in the CT value versus X-ray energy storage unit 536, as shown in Step T3 of FIG. The effective X-ray energy E (x, y) is specified.

  Others are the same as in the first embodiment. In this embodiment as well, a monochrome composite image can be generated as in the first embodiment.

(Fourth embodiment)
FIG. 13 is a functional block diagram of an X-ray CT apparatus 100c according to the fourth embodiment. FIG. 14 is a flowchart of the composite image generation process in the fourth embodiment.

  In the present embodiment, as shown in FIG. 13, the image reconstruction unit 52 includes a tube voltage image reconstruction unit 521 and a material density image reconstruction unit 522, but a monochrome image reconstruction unit 523. Does not have. The composite image generation unit 53 includes a CT value specifying unit 535 instead of the CT value ratio calculation unit 531, and instead of the CT value ratio vs. X-ray energy storage unit 533, the CT value vs. X-ray energy. A storage unit 536 is provided.

  The CT value specifying unit 535 specifies the CT value at each pixel position in the first tube voltage image GHV or the second tube voltage image GLV as shown in Step T2 of FIG.

  The CT value versus X-ray energy storage unit 536 is a mode in which the substance is desirable in observing the CT value in the first tube voltage image GHV or the second tube voltage image GLV and the substance specified by the CT value. The relationship which matched the effective X-ray energy of the monochrome image represented by these is memorize | stored.

  As shown in Step T3 of FIG. 14, the X-ray energy specifying unit 532 uses the CT value GLV (x, y) or GHV (xHV) based on the correspondence relationship stored in the CT value vs. X-ray energy storage unit 536. , Y), the effective X-ray energy E (x, y) associated with the specified X-ray energy is specified.

  Others are the same as in the first embodiment. In this embodiment as well, a monochrome composite image can be generated as in the first embodiment.

(Fifth embodiment)
FIG. 15 is a functional block diagram of an X-ray CT apparatus 100d according to the fifth embodiment. FIG. 16 is a flowchart of the composite image generation process in the fifth embodiment.

  In the present embodiment, as shown in FIG. 15, the image reconstruction unit 52 includes a tube voltage image reconstruction unit 521 and a material density image reconstruction unit 522, but a monochrome image reconstruction unit 523. Does not have. The composite image generation unit 53 includes a pixel value specifying unit 537 instead of the CT value ratio calculation unit 531, and instead of the CT value ratio vs. X-ray energy storage unit 533, the pixel value vs. X-ray energy. A storage unit 538 is included.

  The pixel value specifying unit 537 specifies the pixel value (density value) at each pixel position in the water substance image Gw or the iodine substance image Gio as shown in Step T2 of FIG.

  The pixel value versus X-ray energy storage unit 538 displays the pixel value in the water density image Gw or the iodine density image Gio and the material specified by the pixel value in a desirable mode when observing the substance specified by the pixel value. A relationship in which the effective X-ray energy of the image is associated is stored.

  As shown in step T3 of FIG. 16, the X-ray energy specifying unit 532 uses the pixel value Gw (x, y) or Gio (xio) based on the correspondence relationship stored in the pixel value versus X-ray energy storage unit 538. , Y), the effective X-ray energy E (x, y) associated with the specified X-ray energy is specified.

  Others are the same as in the first embodiment. In this embodiment as well, a monochrome composite image can be generated as in the first embodiment.

  Although the embodiments of the invention have been described above, the embodiments of the invention are not limited to those described above, and various modifications and additions can be made without departing from the spirit of the invention.

  For example, the X-ray energy specifying unit 532 specifies the effective X-ray energy based on the difference between the CT values at the same pixel position in the first and second tube voltage images and the first and second monochrome images. Also good. Alternatively, the X-ray energy specifying unit 532 may calculate the CT value in the tube voltage image or the monochromatic image, the CT value ratio or CT of the same pixel position in the first and second tube voltage images or the first and second monochromatic images. The effective X-ray energy may be specified based on two or more values among the value difference and the pixel value in the material density image.

  For example, if the tube voltage image is not used, the tube voltage image reconstruction unit 521 is not included, and the substance density image reconstruction unit 522 uses the first and second projection data PHV and PLV different from each other. Two types of projection data are obtained by weighted subtraction processing by weighting, and these two types of projection data are respectively subjected to image reconstruction processing to reconstruct the first and second substance density images (water density image and iodine density image). It may be configured.

  Also, for example, a plurality of monochrome images having different effective X-ray energies are generated in advance, and effective X-ray energies that are the same as or close to the effective X-ray energies specified for the pixel positions are generated for each pixel position. A monochrome image may be selected, and the pixel value at the pixel position in the selected monochrome image may be used as the pixel value of the monochrome composite image Gma.

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 (imaging means)
12 Cradle 15 Rotating part 16 Supporting part 20 Scanning gantry (imaging means)
21 X-ray tube 22 X-ray tube controller 23 Collimator 24 X-ray detector 25 Data acquisition device (DAS)
26 Rotation unit controller 29 Control controller 30 Slip ring 40 Subject 51 Dual energy imaging control unit (imaging means)
52 Image reconstruction unit (reconstruction means)
521 Tube voltage image reconstruction unit 522 Material density image reconstruction unit 523 Monochromatic image reconstruction unit 53 Composite image generation unit (generation unit)
531 CT value ratio calculation unit (acquisition unit)
532 X-ray energy identification part (specific part)
533 CT value ratio vs. X-ray energy storage unit 534 Monochromatic image pixel value calculation unit (calculation unit)
535 CT value identification unit (acquisition unit)
536 CT value vs. X-ray energy storage unit 537 Pixel value identification unit (acquisition unit)
538 Pixel value versus X-ray energy storage unit 54 Display control unit 81 X-ray 100 X-ray CT apparatus

Claims (11)

Imaging means for performing dual energy imaging of a subject to obtain first projection data by first X-rays and second projection data by second X-rays having energy different from that of the first X-rays; ,
Reconstruction means for reconstructing a predetermined image of the subject based on the first projection data and / or the second projection data;
Calculation for calculating a pixel value at a desired pixel position in an image corresponding to an image obtained when the subject is imaged with X-rays having desired X-ray energy based on the first and second projection data An acquisition unit for acquiring a predetermined feature amount relating to a pixel value of the pixel position, the acquisition unit being capable of specifying a substance corresponding to the pixel position for each pixel position in the predetermined image, and the acquired feature amount A specifying unit that specifies X-ray energy corresponding to an image suitable for observation of a substance corresponding to the pixel position, and the X-ray having the specified X-ray energy The calculation unit obtains a pixel value of the pixel position in an image corresponding to an image obtained when the subject is imaged, and the obtained pixel value corresponds to the pixel position from which the pixel value is obtained. X-ray CT apparatus and a generation means for generating an image to pixel value of the position. The reconstruction means performs image reconstruction processing on the first and second projection data to obtain first and second images, and the first and second images are weighted in two different ways. To obtain the third and fourth images, and the third and fourth images are weighted and added by two different types of weights to obtain the fifth and sixth images as the predetermined images. Reconstruct as an image,
The X-ray CT apparatus according to claim 1, wherein the predetermined feature amount is a ratio or difference between pixel values at the same pixel position in the fifth and sixth images. The reconstruction means performs weighted subtraction processing on the first and second projection data by using two different types of weights to obtain third and fourth projection data, and the third and fourth projection data are converted into the third and fourth projection data. Image reconstruction processing is performed to obtain first and second images, and the first and second images are weighted and added with two different weights, and the third and fourth images are Reconstruct as a given image,
The X-ray CT apparatus according to claim 1, wherein the predetermined feature amount is a ratio or difference between pixel values at the same pixel position in the third and fourth images. The reconstruction means performs image reconstruction processing on the first and second projection data, respectively, to reconstruct the first and second images as the predetermined image,
The X-ray CT apparatus according to claim 1, wherein the predetermined feature amount is a ratio or a difference between pixel values at the same pixel position in the first and second images. The reconstruction means performs an image reconstruction process on the first or second projection data to reconstruct the predetermined image,
The X-ray CT apparatus according to claim 1, wherein the predetermined feature amount is a pixel value itself. The reconstruction means performs weighted subtraction processing on the first and second projection data to obtain third projection data, performs image reconstruction processing on the third projection data, and reconstructs the predetermined image. Configure
The X-ray CT apparatus according to claim 1, wherein the predetermined feature amount is a pixel value itself. The reconstruction means performs image reconstruction processing on the first and second projection data, respectively, to obtain first and second images, performs weighted subtraction processing on the first and second images, and Reconstruct a given image,
The X-ray CT apparatus according to claim 1, wherein the predetermined feature amount is a pixel value itself. The reconstruction means performs image reconstruction processing on the first and second projection data to obtain first and second images, and the first and second images are weighted in two different ways. To obtain the third and fourth images, perform the weighted addition processing on the third and fourth images, and reconstruct the predetermined image;
The X-ray CT apparatus according to claim 1, wherein the predetermined feature amount is a pixel value itself. The reconstruction means performs weighted subtraction processing on the first and second projection data by using two different types of weights to obtain third and fourth projection data, and the third and fourth projection data are converted into the third and fourth projection data. Image reconstruction processing is performed to obtain first and second images, weighted addition processing is performed on the first and second images, and the predetermined image is reconstructed.
The X-ray CT apparatus according to claim 1, wherein the predetermined feature amount is a pixel value itself.   The calculation unit is obtained by performing weighted subtraction processing on the first and second images obtained by performing image reconstruction processing on the first and second projection data, respectively, using two different types of weighting. The pixel value of the pixel position is calculated by performing weighted addition processing on the pixel value at the same pixel position in the third and fourth images by weighting corresponding to the specified X-ray energy. X-ray CT apparatus as described in any one of these.   The calculation unit is obtained by performing image reconstruction processing on third and fourth projection data obtained by performing weighted subtraction processing on the first and second projection data using two different types of weights, respectively. The pixel value at the pixel position is calculated by performing a weighted addition process on the pixel value at the same pixel position in the first and second images to be weighted with a weight corresponding to the specified X-ray energy. The X-ray CT apparatus according to claim 9.

Images