JP2010075443A - Tomographic image processing device, x-ray ct apparatus, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suitably perform beam hardening correction when generating tomograms by dual energy photographing. <P>SOLUTION: On the basis of the ratio of the CT values of corresponding pixels between two kinds of tomograms different in X-ray tube voltage in photographing, a material image corresponding to a predetermined material in the tomograms is extracted (S3), and the extracted material image is virtually projected again (S4). Obtained re-projection data are worked according to the kind of the material and the X-ray tube voltage in photographing (S5), and image reconstitution is performed on the basis of the worked re-projection data (S6). The original tomogram and the newly obtained new material image are subjected to weighted addition to generate a new tomogram (S7). Consequently, the image of the material to be corrected is extracted precisely, and beam hardening correction suitable to the image is suitably performed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a tomographic image processing apparatus for processing a tomographic image obtained by dual energy imaging, and an X-ray CT (Computed).
Tomography) apparatus, and a program therefor.

  A dual energy imaging method is known as a method of X-ray CT imaging. There are two types of dual energy imaging methods, in which the same part of the subject is X-ray CT imaged with a low X-ray tube voltage and a high X-ray tube voltage, for example, and the X-ray energy distribution used for the imaging is different. Is an imaging method for obtaining a tomographic image (see, for example, Patent Document 1). The two types of tomographic images obtained in this way are used when generating various images effective for image diagnosis. For example, by separating the CT values of corresponding pixels between these two types of tomographic images, a material separation image representing each material such as bone, contrast agent, and soft part in the tomographic image of the subject is separated. Can be generated.

  On the other hand, in X-ray CT imaging, a phenomenon called beam hardening or beam hardening occurs, so that beam hardening correction is generally performed when generating a tomographic image.

  As a method of beam hardening correction, for example, a method of estimating the beam hardening effect on the assumption that the entire subject is water and correcting the entire projection data (hereinafter referred to as a first method) is known. This first method takes into account that the subject includes many soft parts, and the soft parts have an X-ray absorption rate close to that of water, and can correct the entire tomographic image on average.

  Also, for example, CT value threshold processing is performed on the tomographic image to extract a bone part image corresponding to the bone part, and the bone part image is virtually reprojected to the X-ray detector to obtain reprojection data, A technique (hereinafter referred to as a second technique) is known in which a new bone part image is obtained by processing reprojection data and reconstructing an image, and the new bone part image is weighted and added to the original tomographic image. (See, for example, Patent Document 2, [0047] to [0051]). This second method considers that the beam hardening phenomenon appears strongly in the bone part having a high X-ray absorption rate, and corresponds to a bone part in the tomographic image that cannot be corrected by the first method. The part can be corrected.

In the beam hardening correction, the optimum correction parameter varies depending on the type of substance to be corrected and the X-ray tube voltage at the time of imaging.
JP 2008-125900 A Japanese Patent Application Laid-Open No. 2004-195050

  However, in the second method, since the bone part image is extracted by a simple CT value threshold process, an iodine-based contrast agent whose CT value range partially overlaps the bone part is used. There is a high possibility that the image cannot be completely separated from the bone part and an image in which the bone part and the contrast medium are mixed is extracted as the bone part image. That is, there is a high possibility that correction for the bone portion will be applied to an image other than the bone portion, and it is difficult to appropriately perform the beam hardening correction.

  In view of the above circumstances, an object of the present invention is to provide a tomographic image processing apparatus, an X-ray CT apparatus, and a program therefor capable of performing beam hardening correction more appropriately.

  In a first aspect, the present invention relates to a pixel corresponding to a first tomographic image of a subject based on a first X-ray tube voltage and a second tomographic image of the subject based on a second X-ray tube voltage. Based on the ratio or difference of the values, a substance image specifying means for specifying a substance image corresponding to a predetermined substance in an arbitrary tomographic image based on an arbitrary X-ray tube voltage of the subject; Reprojection means for calculating reprojection data (data) by projecting, correction image generation means for generating a correction image by reconstructing an image based on the reprojection data, and the correction image using the correction image. Provided is a tomographic image processing apparatus including correction means for correcting an arbitrary tomographic image.

  Here, “arbitrary X-ray tube voltage” is generally allowed to be taken with the X-ray tube voltage in consideration of the amount of exposure of the subject, and a meaningful image is obtained as a diagnostic image by the imaging. It is assumed that the voltage range is such that For example, when the subject is a human body, an X-ray tube voltage in the range from several tens kV to several hundreds kV can be obtained.

  Further, the substance image specifying unit specifies the substance image based on, for example, a result of threshold processing of a ratio or difference of pixel values of the corresponding pixels.

  In a second aspect, the present invention provides that the arbitrary tomographic image is the first and second tomographic images, and the material image specifying means corresponds to a predetermined material in the first tomographic image. A first substance image, a second substance image corresponding to the predetermined substance in the second tomographic image is identified, and the reprojection means virtually identifies the first and second substance images. And the first and second reprojection data are calculated, and the correction image generation means reconstructs an image based on the first and second reprojection data, thereby generating the first and second reprojection data. A correction image is generated, and the correction unit corrects the first tomographic image using the first correction image to obtain a first new tomographic image, and the second correction image. A second new tomographic image is obtained by correcting the second tomographic image using Providing a tomographic image processing apparatus of the serial first aspect.

  In a third aspect, the present invention provides that the arbitrary tomographic image is the first and second tomographic images, the predetermined substance is the first substance and the second substance, and the substance image The specifying unit specifies a first substance image corresponding to the first substance in the first tomographic image and a second substance image corresponding to the second substance, and the second tomographic image A third substance image corresponding to the first substance and a fourth substance image corresponding to the second substance are identified, and the reprojection means virtually each of the first to fourth substance images. The first to fourth reprojection data is calculated, and the correction image generation means reconstructs the image based on the first to fourth reprojection data, and performs the first to fourth reprojection data. And the correction means uses the first and second correction images to generate the first correction image. A first new tomographic image is obtained by correcting the second tomographic image, and a second new tomographic image is obtained by correcting the second tomographic image using the third and fourth correction images. A tomographic image processing apparatus according to the first aspect is provided.

  In a fourth aspect, the present invention relates to the first new tomographic image or the first new tomographic image based on a ratio or difference of corresponding pixel values of the first new tomographic image and the second new tomographic image. The tomographic image processing apparatus according to the second aspect or the third aspect is further provided with image generating means for generating an image in which substances in the two new tomographic images are separated.

  In a fifth aspect, the present invention further includes image generating means for generating an image in which a specific substance is suppressed by weighted addition of the first new tomographic image and the second new tomographic image. A tomographic image processing apparatus according to the second aspect or the third aspect is provided.

  In a sixth aspect, the present invention weights and adds the first new tomographic image and the second new tomographic image to suppress the first material-suppressed tomographic image in which the substance A is suppressed and the material B is suppressed. The second material-suppressed tomogram is generated, and the first material-suppressed tomogram and the second material-suppressed tomogram are weighted and added to generate the third tomogram of the subject. Provided is the tomographic image processing apparatus according to the second aspect or the third aspect, further comprising image generation means.

  In a seventh aspect, the present invention refers to the storage means for storing the type of substance and the X-ray tube voltage in association with the processing to be executed, and the information stored in the storage means, The correction image further includes processing means for specifying a processing process associated with the type of substance corresponding to the reprojection data and the X-ray tube voltage, and executing the processing process on the reprojection data. The generation means provides the tomographic image processing apparatus according to any one of the first to sixth aspects, in which the correction image is generated based on the reprojection data on which the processing has been executed.

  In an eighth aspect, the present invention provides the seventh tomographic image processing apparatus, wherein the associated processing is a linear transformation process or a nonlinear transformation process.

  In a ninth aspect, the present invention relates to the third aspect, wherein the first substance is bone containing calcium as a main component, and the second substance is a contrast agent containing iodine as a main component. A tomographic image processing apparatus according to the above aspect is provided.

  In a tenth aspect, the present invention relates to the tomographic image processing apparatus according to any one of the first to ninth aspects, and the first tomographic image and the first tomographic image of the subject by X-ray CT. An X-ray CT apparatus including imaging means for obtaining two tomographic images is provided.

  In an eleventh aspect, the present invention provides a program for causing a computer to function as each means constituting the tomographic image processing apparatus according to any one of the first to ninth aspects.

  According to the present invention, a substance image corresponding to a predetermined substance in a tomographic image of a subject is obtained based on a ratio or difference of pixel values of corresponding pixels between two types of tomographic images having different X-ray tube voltages at the time of imaging. Since the specified substance image is processed according to the type of substance and the X-ray tube voltage at the time of imaging, the image of the substance to be corrected is specified with higher accuracy and suitable for that image. Correction can be performed, and beam hardening correction for a tomographic image can be performed more appropriately.

  Embodiments according to the present invention will be described below with reference to the drawings.

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

  The operation console 1 includes an input device 2, a central processing unit 3, a control interface (interface) 4, a data collection buffer (buffer) 5, and a monitor 6. The input device 2 accepts operator instructions and information. In addition to scan control processing, the central processing unit 3 performs pixel value ratio calculation processing, material image extraction processing (material image identification processing), reprojection processing, reprojection data processing processing, image reconstruction processing (correction image) Generation processing), weighted addition processing (correction processing), and the like. The control interface 4 outputs a control signal and the like to the imaging table 8 and the scanning gantry 9 under the control of the central processing unit 3. The data collection buffer 5 collects data acquired by the scanning gantry 9. The monitor 6 displays an operation screen, a tomographic image, and the like.

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

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

  The central processing unit 3 is an example of a substance image specifying unit, a reprojection unit, a processing unit, a correction image generation unit, a correction unit, and an image generation unit in the present invention. Further, the central processing unit 3 and the scanning gantry 9 are examples of photographing means in the present invention.

  FIG. 2 is a flowchart showing the flow of material separation image generation processing in the X-ray CT apparatus 100 according to the first embodiment.

  In step S1, dual energy imaging is performed. Here, it is assumed that a contrast medium is administered to a subject and the abdomen thereof is subjected to dual energy imaging. Specifically, the subject is placed on the imaging table 8, transported to the cavity of the scanning gantry 9, and an iodine-based contrast agent is injected into the blood vessel of the subject. Next, the abdomen of the subject is scanned by setting the X-ray tube voltage to 80 kV, the first projection data is collected, and the same part of the subject is scanned by setting the X-ray tube voltage to 140 kV, and the second projection Collect data. Then, an image is reconstructed based on the first projection data to generate a first tomographic image g80 (x, y), and an image is reconstructed based on the second projection data to produce a second tomographic image g140. (X, y) is generated. Note that the pixel values of the first tomographic image g80 (x, y) and the second tomographic image g140 (x, y) are both CT values.

  3A shows an example of the first tomographic image g80 (x, y), and FIG. 3B shows an example of the second tomographic image g140 (x, y). In each tomogram shown in FIG. 3, the coordinates (x1, y1) are the stomach, the coordinates (x2, y2) are the artery, the coordinates (x3, y3) are the spinal cord, the coordinates (x4, y4) are the spine, and the coordinates (x5, y5). ) Is located on each rib. The stomach is a soft tissue and contains a lot of water. In the spinal cord and arteries, iodine, which is the main component of the contrast agent, is concentrated due to the large blood flow. In addition, calcium, which is the main component of bone, is concentrated in the spine and ribs.

  Accordingly, in the first tomographic image g80 (x, y), the pixel value g80 (x1, y1) is a CT value corresponding to the soft part when the X-ray tube voltage is 80 kV, and here is +100 as an example. . Pixel values g80 (x2, y2) and g80 (x3, y3) are CT values corresponding to iodine when the X-ray tube voltage is 80 kV, and here are +1200 and +600, respectively, as an example. The pixel values g80 (x4, y4) and g80 (x5, y5) are CT values corresponding to calcium when the X-ray tube voltage is 80 kV, and here are, for example, +1500 and +1200, respectively.

  In the second tomographic image g140 (x, y), the pixel value g140 (x1, y1) is a CT value corresponding to the soft part when the X-ray tube voltage is 140 kV, and here is +90 as an example. . Pixel values g140 (x2, y2) and g140 (x3, y3) are CT values corresponding to iodine when the X-ray tube voltage is 140 kV, and here are +650 and +320, respectively, as an example. Pixel values g140 (x4, y4) and g140 (x5, y5) are CT values corresponding to calcium when the X-ray tube voltage is 140 kV, and here are, as examples, +1000 and +800, respectively.

  In step S2, calculation processing of the ratio of pixel values between tomographic images is executed. Specifically, a pixel value ratio r (x, y) for each corresponding pixel between the first tomographic image g80 (x, y) and the second tomographic image g140 (x, y), that is, The ratio of CT values is calculated. This is expressed by the following equation.

(Equation 1)
r (x, y) = g80 (x, y) / g140 (x, y) (Formula 1)
FIG. 3C is a diagram illustrating an example of a ratio image having the pixel value ratio r (x, y) as a pixel value. In this ratio image r (x, y), as shown in FIG. 3C, r (x1, y1) = + 100 / + 90 = 1.11 and r (x2, y2) = + 1200 / + 650 = 1. .85, r (x3, y3) = + 600 / + 320 = 1.88, r (x4, y4) = + 1500 / + 1000 = 1.50, r (x5, y5) = + 1200 / + 800 = 1.50.

  In step S3, a substance image extraction process is executed. Specifically, the first bone image g80b corresponding to the bone portion (calcium) in the first tomographic image g80 (x, y) is obtained by the threshold processing of the pixel value ratio calculated in step S2. A first contrast agent image g80i corresponding to the contrast agent (iodine) is extracted. Similarly, in the second tomogram g140 (x, y), a second bone image g140b corresponding to the bone (calcium) and a second contrast agent image g140i corresponding to the contrast agent (iodine) are extracted. To do.

  Here, the relationship between the type of substance and the ratio of pixel values will be described.

  FIG. 4 is a diagram showing a correspondence relationship between the type of substance and the ratio of pixel values, that is, the range of the ratio of pixel values corresponding to each substance. In the graph shown in FIG. 4, the vertical axis represents the pixel value (CT value) L-HU of the tomographic image taken at an X-ray tube voltage of 80 kV, and the horizontal axis represents the image taken at an X-ray tube voltage of 140 kV. The tomographic image pixel value (CT value) H-HU. Each region divided so as to be sandwiched by straight lines in the graph indicates a range of pixel value ratios (L-HU / H-HU) determined according to the type of substance. The ratio of pixel values is determined according to the type of substance, but various noises such as X-ray absorption by a tissue other than the target substance and a background component on the detection signal of the X-ray detector 13. Considering (noise), it is determined as a range with a certain width. The range of the ratio of pixel values corresponding to iodine (L-HU / H-HU) is, for example, 1.7 to 2.0, and the ratio of pixel values corresponding to calcium (L-HU / H-HU). The range is 1.4 to 1.6, for example.

  Therefore, here, in the first tomographic image g80 (x, y), a pixel having a pixel value ratio of 1.4 ≦ r (x, y) ≦ 1.6 is defined as 1 in the first bone image g80b. A pixel that has a pixel value ratio of 1.7 ≦ r (x, y) ≦ 2.0 is specified as one pixel of the first contrast agent image g80i. Similarly, in the second tomographic image g140 (x, y), a pixel having a pixel value ratio of 1.4 ≦ r (x, y) ≦ 1.6 is set as one pixel of the second bone image g140b. The pixel having a pixel value ratio of 1.7 ≦ r (x, y) ≦ 2.0 is specified as one pixel of the second contrast agent image g140i.

  Thus, for example, the pixels at coordinates (x2, y2) and (x3, y3) have pixel value ratios of 1.85 and 1.88, respectively, so these pixels are specified as one pixel of the contrast agent image. Is done. In addition, the pixels at the coordinates (x4, y4) and (x5, y5) have pixel value ratios of 1.5 and 1.5, respectively, and thus these pixels are specified as one pixel of the bone part image. On the other hand, the pixel at the coordinates (x1, y1) has a pixel value ratio of 1.1, and thus is not specified in either the bone part image or the contrast agent image.

  FIG. 5 is a diagram illustrating an example of a substance image extracted by threshold value processing of pixel value ratios. In step S3, the first threshold image g80b as shown in FIG. 5A is obtained by performing the threshold processing as described above on the first tomographic image g80 (x, y). The first contrast agent image g80i as shown in FIG. Similarly, the second bone image g140b and the second contrast agent image g140i are extracted from the second tomographic image g140 (x, y) by performing the threshold processing as described above.

  The pixels to be processed in step S3 may be all pixels in the tomographic image, but it is more efficient to use pixels excluding pixels that are clearly considered to represent substances other than iodine and calcium. For example, a pixel having a pixel value, that is, a CT value smaller than +200, is considered to be a pixel corresponding to a substance other than iodine or calcium, such as water, a soft part, or air having a small X-ray absorption coefficient. Therefore, for example, the processing target may be limited to pixels of + 200 ≦ g80 (x, y) and + 200 ≦ g140 (x, y). Further, the pixel values corresponding to water and soft parts are close to zero, and the range of the pixel value ratio (L-HU / H-HU) tends to vary widely. Therefore, when extracting the image corresponding to the soft part, the pixel value itself or the difference between the corresponding pixel values is separated and extracted by threshold processing instead of the ratio of the corresponding pixel values between tomographic images. It is good to do.

  In step S4, a substance image reprojection process is executed. Specifically, the material image extracted in step S3 is virtually displayed for each view direction included in the view angle required for reconstruction, for example, for each view direction obtained by dividing 360 ° into 1000 views. And reprojected to the X-ray detector 13 to calculate reprojection data.

  FIG. 6 is a diagram illustrating an example of reprojection data calculated by reprojecting a substance image. In step S4, by reprojecting the first bone image g80b, reprojection data rp80b (0) for the 0 ° direction and reprojection data rp80b (270) for the 270 ° direction as shown in FIG. The first bone reprojection data rp80b (θ), which is the reprojection data for each θ ° direction, is calculated. In addition, the first contrast agent image g80i is reprojected in each θ ° direction to calculate first contrast agent reprojection data rp80i (θ). Similarly, the second bone portion image g140b is re-projected in each θ ° direction to calculate second bone portion reprojection data rp140b (θ), and the second contrast agent image g140i is re-projected in each θ ° direction. The second contrast agent reprojection data rp140i (θ) is calculated by projection.

  In step S5, reprojection data processing is executed. Specifically, for each reprojection data calculated in step S4, a processing process associated with the type of substance and the X-ray tube voltage corresponding to the reprojection data is specified and executed. As processing, linear conversion processing that multiplies the reprojection data by a predetermined weighting factor or nonlinear conversion processing that squares the reprojection data itself can be considered. Here, the former linear conversion processing is adopted. To do. In addition, here, a table T associating the type of substance, the X-ray tube voltage and the weighting coefficient as shown in Table 1 is stored in a storage unit in the central processing unit 3 or other storage device (not shown). Referring to this table T, the weighting factor for the reprojection data to be processed is specified. Then, the reprojection data is obtained by multiplying the reprojection data by this weight coefficient.

例えば、第１の骨部再投影データｒｐ８０ｂ（θ）に対する加工処理の場合、物質の種類は骨部でありＸ線管電圧は８０ｋＶであるから、テーブルＴを参照して重み係数ｋ（ｂ，８０）を特定する。そして、次式のように、特定した重み係数ｋ（ｂ，８０）を第１の骨部再投影データｒｐ８０ｂ（θ）に乗算する。

For example, in the case of the processing for the first bone reprojection data rp80b (θ), since the material type is bone and the X-ray tube voltage is 80 kV, the weight coefficient k (b, 80) is specified. Then, the first bone reprojection data rp80b (θ) is multiplied by the specified weight coefficient k (b, 80) as in the following equation.

(Equation 2)
rp80b (θ) ′ = k (b, 80) × rp80b (θ) (Formula 2)
Thereby, as shown in FIG. 6, the first processed bone reprojection composed of data rp80b (0) ′ for the view angle 0 °, data rp80b (270) ′ for the view angle 270 °, and the like. Data rp80b (θ) ′ is calculated.

  In addition, the first contrast medium reprojection data rp80i (θ) is multiplied by a weight coefficient k (io, 80) to calculate the first processed contrast medium reprojection data rp80i (θ) ′. . Similarly, the second bone reprojection data rp140b (θ) ′ is calculated by multiplying the second bone reprojection data rp140b (θ) by the weight coefficient k (b, 140). In addition, the second processed contrast agent reprojection data rp140i (θ) ′ is calculated by multiplying the second contrast agent reprojection data rp140i (θ) by the weighting factor k (io, 140). To do.

  In step S6, an image reconstruction process for a new substance image is executed. Specifically, each processed reprojection data calculated in step S5 is backprojected to reconstruct a new substance image.

  For example, in the case of the first processed bone reprojection data rp80b (θ) ′, as shown in FIG. 7, the data rp80b (0) ′ for the 0 ° direction and the data rp80b (270) for the 270 ° direction. The processed reprojection data such as 'is backprojected to reconstruct the first new bone image g80b (x, y)'. Further, the first processed contrast agent reprojection data rp80i (θ) ′ is backprojected to reconstruct the first new contrast agent image g80i (x, y) ′. Similarly, the second processed contrast medium reprojection data rp140b (θ) ′ is backprojected to reconstruct the second new bone part image g140b (x, y) ′, and the second processed image is processed. The contrast agent reprojection data rp140i (θ) ′ is backprojected to reconstruct a second new contrast agent image g140i (x, y) ′.

  In step S7, a new tomographic image generation process is executed. Specifically, the first tomographic image g80 (x, y), the first new bone part image g80b (x, y) ′, and the first new contrast agent image g80i (x, y) ′ are weighted and added. Thus, the first new tomographic image g80 (x, y) ′ is generated. Further, the second tomographic image g140 (x, y), the second new bone part image g140b (x, y) ′ and the second new contrast agent image g140i (x, y) ′ are weighted and added. A second new tomographic image g140 (x, y) ′ is generated. The new tomographic image obtained by weighted addition of the original tomographic image and the new material image corresponds to a tomographic image in which an appropriate beam hardening correction is performed on the material image portion.

  Here, as shown in FIG. 8 and the following equation, the first new bone image g80b (x, y) ′ is multiplied by the weighting factor t1, and the first new contrast agent image g80i (x, y) ′. Is multiplied by a weighting factor t2, and these are added to the first tomographic image g80 (x, y) to obtain a first new tomographic image g80 (x, y) ′.

(Equation 3)
g80 (x, y) ′ = g80 (x, y) + t1 × g80b (x, y) ′ + t2 × g80i (x, y) ′ (Formula 3)
Similarly, the second new bone image g140b (x, y) ′ is multiplied by a weighting factor t1, and the second new contrast agent image g140i (x, y) ′ is multiplied by a weighting factor t2, A second new tomographic image g140 (x, y) ′ is obtained by adding to the second tomographic image g140 (x, y).

  FIG. 9A shows an example of the first new tomographic image g80 (x, y) ′, and FIG. 9B shows an example of the second new tomographic image g 140 (x, y) ′. In the first new tomographic image g80 (x, y) ′, the pixel value g80 (x1, y1) ′ is +120 as an example. The pixel values g80 (x2, y2) ′ and g80 (x3, y3) ′ are, for example, +1380 and +720, respectively. As an example, pixel values g80 (x4, y4) ′ and g80 (x5, y5) ′ are +1800 and +1430, respectively.

  The pixel value g140 (x1, y1) ′ is +100 as an example. As an example, the pixel values g140 (x2, y2) ′ and g140 (x3, y3) ′ are +720 and +370, respectively. As an example, the pixel values g140 (x4, y4) ′ and g140 (x5, y5) ′ are +1150 and +900, respectively.

  In step S8, a material separation image generation process is executed. Specifically, the pixel value ratio r (x, y) ′ of the corresponding pixel between the first new tomographic image g80 (x, y) ′ and the second new tomographic image g140 (x, y) ′. Based on the above, a material separation image dm (x, y) ′ is generated by separating and representing materials in the first new tomographic image g80 (x, y) ′ or the second new tomographic image g140 (x, y) ′. To do.

  For example, in the first new tomographic image g80 (x, y) ′, a pixel having a pixel value ratio of 1.4 ≦ r (x, y) ′ ≦ 1.6 is specified as one pixel of the bone image. A pixel having a pixel value ratio of 1.7 ≦ r (x, y) ′ ≦ 2.0 is specified as one pixel of the contrast agent image. In the first new tomographic image g80 (x, y) ′, the bone part image is colored with a first color, for example, blue, and the contrast agent image is colored with a second color, for example, green. A substance separation image dm (x, y) ′ is generated by separating the contrast medium and the contrast agent.

  FIG. 10 is a diagram showing an example of the substance separation image dm (x, y) ′ generated in this way. The pixel value ratios r (x1, y1) ′ to r (x5, y5) ′ in the pixels (x1, y1) to (x5, y5) are 1.20, 1 as shown in FIG. .92, 1.95, 1.57, 1.59. Therefore, the contrast agent image including dm (x2, y2) ′ and dm (x3, y3) ′ is colored in green, and the bone image including dm (x4, y4) ′ and dm (x5, y5) ′ is blue. Colored with.

  Note that the first new tomographic image g80 (x, y) ′ and the second new tomographic image g140 (x, y) ′ are tomographic images in which beam hardening correction is appropriately performed. The boundary between the bone part image and the contrast agent image shown on dm (x, y) ′ is more accurate than the bone part image and the contrast agent image extracted in step S3, and the substance is separated with high accuracy.

  The substance separation image dm (x, y) ′ generated in this way is displayed on the screen of the monitor 6 and used for image diagnosis and the like.

  According to the present embodiment as described above, it corresponds to a predetermined substance in a tomographic image of a subject based on a ratio or difference of pixel values of corresponding pixels between two types of tomographic images having different X-ray tube voltages at the time of imaging. The substance image to be identified is specified, and the specified substance image is processed according to the type of substance and the X-ray tube voltage at the time of imaging, so the substance image to be corrected is identified with higher accuracy, Correction suitable for the image can be performed, and beam hardening correction for the tomographic image can be performed more appropriately.

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

  For example, in the present embodiment, the first tomographic image g80 (x, y) based on the first X-ray tube voltage obtained directly by dual energy imaging as the correction target and the second based on the second X-ray tube voltage. The tomographic image g140 (x, y) of FIG. 5 may be used, but the correction target may be an arbitrary tomographic image by an arbitrary X-ray tube voltage corresponding to the same slice plane as these tomographic images. If this arbitrary tomographic image is a tomographic image corresponding to the same slice plane as the first and second tomographic images, the ratio or difference between the pixel values of the corresponding pixels of the first tomographic image and the second tomographic image; Based on the coordinates of the corresponding pixel, a substance corresponding to the pixel having the same coordinate as the corresponding pixel in the arbitrary tomographic image can be specified.

  For example, in the present embodiment, a material separation image is finally generated and displayed using the first new tomographic image g80 (x, y) ′ and the second new tomographic image g140 (x, y) ′. However, a substance density image representing the density of the substance corresponding to each pixel may be generated and displayed. In this case, since the first new tomographic image g80 (x, y) ′ and the second new tomographic image g140 (x, y) ′ are appropriately subjected to beam hardening correction, the material density with little error is obtained. Can be provided.

  In addition, for example, a specific material, for example, a material that suppresses a bone part or a contrast agent by weighted addition of the first new tomographic image g80 (x, y) ′ and the second new tomographic image g140 (x, y) ′. A suppression image may be generated.

  Further, for example, the first new tomographic image g80 (x, y) ′ and the second new tomographic image g140 (x, y) ′ are weighted and added to the substance A, for example, the first substance in which water is suppressed. A suppressed tomographic image and a second material suppressed tomographic image in which substance B, for example, iodine is suppressed, are generated, and the first material suppressed tomographic image and the second material suppressed tomographic image are weighted and added. A third tomographic image corresponding to a tomographic image of the subject with an X-ray tube voltage of, for example, 100 kV may be generated.

  Further, for example, in the present embodiment, the target substance for performing beam hardening correction is a bone part and a contrast agent, but the target substance may be a single substance such as only a bone part or only a contrast agent, It is good also as three or more types of substances, such as a contrast agent and a soft part.

  Further, for example, in this embodiment, tomographic images are obtained by dual energy imaging when the X-ray tube voltage is 80 kV and 140 kV, but of course, the present invention is not limited to this, and other X-ray tube voltages are used. May be.

  For example, the present invention can also be applied to the adaptive weighted difference method proposed in Japanese Patent Application No. 2007-292955.

  Unlike the X-ray CT apparatus according to the present embodiment, the first tomographic image of the subject by the first X-ray tube voltage and the second of the subject by the second X-ray tube voltage are not provided. A first material image corresponding to a predetermined substance in the first tomographic image is extracted based on a ratio of pixel values of corresponding pixels between the two tomographic images and the predetermined tomographic image in the second tomographic image; Extraction means for extracting a second substance image corresponding to the substance; reprojection means for virtually reprojecting the first and second substance images to calculate first and second reprojection data; Processing means for processing the first and second reprojection data, and image reconstruction based on the processed first and second reprojection data to generate first and second new substance images The image reconstruction means, the first tomographic image and the first new material image are weighted. A first new tomographic image, and a workstation having addition means for generating a second new tomographic image by weighted addition of the second tomographic image and the second new material image ( A tomographic image processing apparatus such as a workstation) is also an embodiment of the present invention.

  A program for causing a computer to function as each means constituting the tomographic image processing apparatus is also an embodiment of the present invention.

It is a block diagram which shows the X-ray CT apparatus by one Embodiment of this invention. It is a flowchart which shows the flow of the material separation image generation process in the X-ray CT apparatus by one Embodiment of this invention. It is a figure which shows an example of two types of tomographic images obtained by dual energy imaging | photography, and its ratio image. It is a figure which shows the correspondence of the kind of substance, and the ratio of a pixel value. It is a figure which shows an example of the substance image extracted by the threshold value process of the ratio of pixel values. It is a figure which shows an example of the reprojection data calculated by reprojection of a material image. It is a figure which shows a mode that a new substance image is reconfigure | reconstructed based on the processed reprojection data. It is a figure which shows a mode that a new tomogram is produced | generated by carrying out weighted addition of the original tomogram and a new material image. It is a figure which shows an example of two types of new tomograms produced | generated by the production | generation process of a new tomogram, and its ratio image. It is a figure which shows an example of the substance separation image produced | generated by the production | generation process of a substance separation image.

Explanation of symbols

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

Claims (11)

Based on the ratio or difference of the pixel values of the corresponding pixels between the first tomogram of the subject by the first X-ray tube voltage and the second tomogram of the subject by the second X-ray tube voltage, A substance image specifying means for specifying a substance image corresponding to a predetermined substance in an arbitrary tomographic image by an arbitrary X-ray tube voltage of a subject;
Reprojection means for virtually reprojecting the material image to calculate reprojection data;
Correction image generation means for generating a correction image by reconstructing an image based on the reprojection data;
A tomographic image processing apparatus comprising: a correcting unit that corrects the arbitrary tomographic image using the correction image. The arbitrary tomographic images are the first and second tomographic images,
The substance image specifying means specifies a first substance image corresponding to a predetermined substance in the first tomographic image, and a second substance image corresponding to the predetermined substance in the second tomographic image. Identify,
The reprojection means virtually reprojects the first and second substance images to calculate first and second reprojection data;
The correction image generation means generates first and second correction images by reconstructing an image based on the first and second reprojection data,
The correction means obtains a first new tomographic image by correcting the first tomographic image using the first correction image, and uses the second correction image to obtain the second second tomographic image. The tomographic image processing apparatus according to claim 1, wherein a second new tomographic image is obtained by correcting the tomographic image. The arbitrary tomographic images are the first and second tomographic images,
The predetermined substances are a first substance and a second substance,
The substance image specifying means specifies a first substance image corresponding to a first substance and a second substance image corresponding to a second substance in the first tomogram, and the second tomogram. Identifying a third substance image corresponding to the first substance and a fourth substance image corresponding to the second substance in an image;
The reprojection means virtually reprojects the first to fourth substance images, respectively, to calculate first to fourth reprojection data,
The correction image generating means reconstructs an image based on the first to fourth reprojection data to generate first to fourth correction images,
The correction means obtains a first new tomographic image by correcting the first tomographic image using the first and second correction images, and obtains the third and fourth correction images. The tomographic image processing apparatus according to claim 1, wherein a second new tomographic image is obtained by correcting the second tomographic image using the second tomographic image.   Substances in the first new tomographic image or the second new tomographic image are separated based on a ratio or difference of pixel values of corresponding pixels between the first new tomographic image and the second new tomographic image. The tomographic image processing apparatus according to claim 2, further comprising image generation means for generating an image.   4. The tomographic image according to claim 2, further comprising image generation means for generating an image in which a specific substance is suppressed by weighted addition of the first new tomographic image and the second new tomographic image. Processing equipment.   A first material-suppressed tomogram in which the substance A is suppressed and a second material-suppressed tomogram in which the substance B is suppressed are weighted and added to the first new tomogram and the second new tomogram. 3, and further comprising an image generation means for generating a third tomographic image of the subject by weighted addition of the first material-suppressed tomographic image and the second material-suppressed tomographic image. The tomographic image processing apparatus according to claim 3. Storage means for storing the type of substance and the X-ray tube voltage in association with the processing to be executed;
With reference to the information stored in the storage means, the type of substance corresponding to the reprojection data and the processing associated with the X-ray tube voltage are specified, and the processing is performed on the reprojection data. Processing means for executing
The tomographic image processing apparatus according to claim 1, wherein the correction image generation unit generates a correction image based on the reprojection data on which the processing process has been executed.   The tomographic image processing apparatus according to claim 7, wherein the associated processing is a linear conversion process or a non-linear conversion process. The first substance is bone;
The tomographic image processing apparatus according to claim 3, wherein the second substance is a contrast agent. A tomographic image processing apparatus according to any one of claims 1 to 9,
An X-ray CT apparatus comprising: an imaging unit that obtains the first tomographic image and the second tomographic image by performing X-ray CT imaging of the subject. Computer
The program for functioning as each means which comprises the tomogram processing apparatus of any one of Claims 1-9.

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