JP2019197026A - Attenuation coefficient map generation device, attenuation coefficient map generation method, and program - Google Patents

Abstract

To provide a new generation technique of an attenuation coefficient map.SOLUTION: An attenuation coefficient map generation device comprises: an input part 11 for inputting bone SPECT image data of a subject; an interest region setting part 21 for setting an interest region in a right lung upper leaf in bone SPECT image data while avoiding a costa; a region determination part 24 for, with a constant multiple of an average count value of VOI as a threshold, classifying regions into a region A in which the count value is equal to or more than the threshold, a region B in which the count value is equal to or more than the average count value and less than the threshold, and a region C in which the count value is less than the average count value; and an attenuation coefficient map generation part 26 for converting the region A into a CT value corresponding to a bone region, the region B into a CT value corresponding to a soft tissue or water, the region C into a CT value corresponding to air, in a CT image of a template, for generating a virtual CT image, then using the virtual CT image, generating an attenuation coefficient map for performing attenuation correction of the bone SPECT image data.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a technique for creating an attenuation coefficient map used for attenuation correction of a positron emission tomography (hereinafter referred to as “PET”) image and a single photon emission tomography (hereinafter referred to as “SPECT”) image. The present invention relates to a technique for creating an attenuation coefficient map used for attenuation correction of bone SPECT.

  Nuclear medicine images represented by PET images and SPECT images are effective in diagnosing various diseases including heart diseases and cancers. These images are administered with a drug labeled with a specific radioisotope (hereinafter referred to as “radiopharmaceutical”), and γ rays emitted directly or indirectly from the drug are detected by a dedicated camera. Obtained by rebuilding. Nuclear medicine images not only have excellent properties such as high specificity and sensitivity to diseases, but also have characteristics not found in other diagnostic images that can provide information on the function of lesions. Yes.

  Nuclear medicine images are obtained by detecting gamma rays emitted directly or indirectly from a radiopharmaceutical administered to a subject. Since gamma rays interact with constituents in the body, such as absorption and scattering, and are attenuated, the count of detected gamma rays is attenuated according to the depth from the body surface and is underestimated. . Therefore, in order to accurately reconstruct a nuclear medicine image using the detected γ-ray count, it is necessary to perform attenuation correction in consideration of attenuation of γ-rays in the living body.

  Attenuation correction means that in a section of the captured nuclear medicine image space, γ rays emitted from an arbitrary source (for example, Tc-99m source) travel radially in the section, This is a method of adding the attenuation to the detection data by calculating the photon attenuation that occurs until the detector located outside is reached.

  As methods for performing such attenuation correction, there are attenuation correction using an external radiation source and attenuation correction using X-ray CT (Non-Patent Document 1). In the attenuation correction method using an external radiation source, a map of attenuation coefficients is obtained using transmission data when there is an attenuation body and blank data when there is no attenuation body. In the attenuation correction method using X-ray CT, an X-ray CT image of a subject is taken, and an attenuation coefficient map is obtained by estimating a line attenuation coefficient from the CT value.

Satoshi Ujiie, Kazuya Uno, Junji Kanno, Tatsumi Morita “Comparison of Absorption Correction Methods (External Sources and X-ray CT) in PET Examinations—Correspondence in Absorption Correction Methods and Exposure in Clinical Practices” Journal of Science No.6 (2008)

  In recent years, the quantitative evaluation in the bone examination region has attracted attention due to the development of the SPECT / CT apparatus. For this quantitative evaluation, attenuation correction is essential. A SPECT / CT apparatus is required to capture CT data corresponding to bone SPECT for a whole body examination. However, there are many facilities that do not have a SPECT / CT apparatus, and depending on the facility, it may be difficult to perform attenuation correction of bone SPECT data and perform quantitative evaluation in the bone examination region.

  Conventionally, in facilities that do not have a SPECT / CT apparatus, attenuation correction using the Chang method has been performed. However, the method of attenuation correction of bone SPECT uses the conventional Chang method because the structure of the trunk is complex. It was difficult. Accordingly, an object of the present invention is to provide a new technique for creating an attenuation coefficient map.

  The attenuation coefficient map creating apparatus of the present invention includes an input unit that inputs nuclear medicine image data of a subject, a region of interest setting unit that sets a region of interest in a region where the degree of attenuation is uniform in the nuclear medicine image, A region determination unit for classifying a nuclear medicine image of a subject into a first region having an average count value equal to or greater than the threshold and a second region less than the threshold, with a constant multiple of the average count value of the region of interest as a threshold; In the CT image of the template, the pixel value of the first region is converted into a CT value corresponding to the bone region, the pixel value of the second region is converted into a CT value corresponding to the region other than the bone, And an attenuation coefficient map creating unit that creates an attenuation coefficient map for performing attenuation correction of the nuclear medicine image using the virtual CT image.

  The attenuation coefficient map creating apparatus of the present invention includes an input unit that inputs nuclear medicine image data of a subject, a region of interest setting unit that sets a region of interest in a region where the degree of attenuation is uniform in the nuclear medicine image, A region determination unit for classifying a nuclear medicine image of a subject into a first region having an average count value equal to or greater than the threshold and a second region less than the threshold, with a constant multiple of the average count value of the region of interest as a threshold; CT information for converting the pixel value of the first region into a CT value corresponding to a bone region, converting the pixel value of the second region into a CT value corresponding to a region other than the bone, and constituting a CT image And an attenuation coefficient map creating unit for creating an attenuation coefficient map for performing attenuation correction of the nuclear medicine image using the virtual CT image.

  According to the present invention, an appropriate attenuation coefficient map is created by classifying a region of a nuclear medicine image of a subject using a constant multiple of an average count value of a region of interest set in a region where the degree of attenuation is uniform as a threshold. it can. In addition, the present invention generates a virtual CT image in which CT values are set based on the classified region, and generates an attenuation coefficient map from the virtual CT image. Therefore, an attenuation coefficient map is generated from the X-ray CT image of the subject. A conventional method (for example, Non-Patent Document 1) can be used. Note that the CT image of the subject may be a CT image of the subject, or an average CT image other than the subject may be used.

  Here, the region-of-interest setting unit only needs to be able to set the region of interest in a region where the degree of attenuation is uniform in the nuclear medicine image of the subject. The region where the degree of attenuation is uniform is a region where the radiopharmaceutical is uniformly distributed and the radiation emitted therefrom is attenuated to the same extent. As a specific example, the region-of-interest setting unit may set the region of interest in the lung while avoiding the rib region, or may be set in the liver.

  The area of the lung that does not show bone or soft tissue is uniform in terms of radiation attenuation and can be considered almost the same as air, so there is virtually no attenuation by setting the area of interest in the lung. The count value can be used as a reference. Moreover, since the radioactivity is uniformly distributed in the liver region, the degree of attenuation is uniform, so that an appropriate threshold value can be obtained by setting the region of interest. If there is an area in the nuclear medicine image where the degree of attenuation is evaluated to be uniform even in areas other than the lungs and liver, an area of interest is set within the area, and an average serving as a threshold reference A count value may be obtained.

  In the attenuation coefficient map creation device of the present invention, the region determination unit includes a third region in which the count value is greater than or equal to the average count value, and a fourth region in which the count value is less than the average count value. The attenuation coefficient map creating unit converts the pixel value of the third region into a CT value corresponding to the soft tissue or the water region, and the pixel value of the fourth region corresponds to the air region. An attenuation coefficient map creating unit that creates a virtual CT image by converting to a CT value to be generated, and creates an attenuation coefficient map that performs attenuation correction of the nuclear medicine image. With this configuration, regions other than bone are divided into soft tissue or water regions and air regions, converted into CT values corresponding to each region, a virtual CT image is generated, and attenuation with a fine attenuation coefficient set A coefficient map can be created.

  In the attenuation coefficient map creating apparatus of the present invention, the nuclear medicine image may be bone SPECT image data. The present invention can be suitably applied to bone SPECT image data having a complicated trunk structure.

  The present invention can appropriately create an attenuation coefficient map based on a nuclear medicine image of a subject.

It is a figure which shows the structure of the image processing apparatus provided with the attenuation coefficient map production apparatus of 1st Embodiment. It is a figure which shows operation | movement of the image processing apparatus of 1st Embodiment. It is a figure which shows the structure of the image processing apparatus provided with the attenuation coefficient map production apparatus of 2nd Embodiment. It is a figure which shows operation | movement of the image processing apparatus of 2nd Embodiment.

  Hereinafter, an attenuation coefficient map creating apparatus according to an embodiment of the present invention will be described with reference to the drawings. In the embodiment described below, an example in which a bone SPECT image is used as a nuclear medicine image is described. However, the present invention can also be applied to a nuclear medicine image such as a SPECT image other than bone or a PET image.

(First embodiment)
FIG. 1 is a diagram illustrating a configuration of an image processing apparatus 10 including the attenuation coefficient map creating apparatus according to the first embodiment.
The image processing apparatus 10 has a function of performing attenuation correction of the bone SPECT image data of the subject imaged by the nuclear medicine image imaging apparatus 30. The image processing device 10 includes an image input unit 11 that inputs bone SPECT image data captured by the nuclear medicine image capturing device 30, an arithmetic processing unit 12 that performs attenuation correction of the bone SPECT image data, and an image that has been subjected to attenuation correction. Is output. The image input unit 11 also has a function of inputting a CT image of a subject. Note that the CT image of the subject input here does not have to be aligned with the SPECT image like the CT image captured by the SPECT / CT apparatus. The input CT image is stored in the CT form image data storage unit 16.

  The arithmetic processing unit 12 is a processing unit 20 corresponding to an attenuation coefficient map creating apparatus that creates an attenuation coefficient map used for performing attenuation correction, and attenuation that performs attenuation correction of the bone SPECT image using the created attenuation coefficient map. It has a correction unit 28 and an image reconstruction unit 29 for reconstructing an attenuation-corrected image.

  The processing unit 20 corresponding to the attenuation coefficient map creation device will be described. The region-of-interest setting unit 21 has a function of setting a region of interest (hereinafter also referred to as “VOI”) for the bone SPECT image of the subject. The region-of-interest setting unit 21 sets a VOI in an area without a rib in the upper lobe of the subject's right lung with reference to the axial image and the coronal image of the subject's bone SPECT data image. . As an example, the VOI has a spherical shape with a diameter of about 60 mm. The position and shape data of the VOI to be set is stored in the VOI data storage unit 14, and the region-of-interest setting unit 21 reads out the VOI shape data from the VOI data storage unit 14 and uses it.

  The VOI average value calculation unit 22 has a function of calculating an average count value of the set VOI. Here, the average count value is “L”. The numerical comparison unit 23 compares the count value of each pixel of the subject's bone SPECT image data with a threshold value. 5L that is five times the average count value L is used as the first threshold, and the average count value L is used as the second threshold. What values are used as the first threshold value and the second threshold value are stored in the area segment threshold value data storage unit 15. The numerical value comparison unit 23 acquires and uses threshold data from the area division threshold data storage unit 15. Here, 5 times the average count value is used as the first threshold value, but 5 times is an example. For example, a numerical value of another constant multiple of the average count value L (4 times, 6 times, etc.) ) May be used.

  Based on the comparison result by the numerical value comparison unit 23, the region determination unit 24 determines the region where the average count value is equal to or greater than the first threshold value A, the region where the average count value is equal to or greater than the second threshold value and less than the first threshold value. The area B and the area where the average count value is less than the second threshold value are determined as the area C.

  The numerical value conversion unit 25 reads the CT image stored in the CT form image data storage unit 16 and converts the CT value of the read CT image in accordance with the region type (A region, B region, C region type). . That is, the read CT image is used as a template and is replaced with a CT value corresponding to the type of region. The area determined as the A area converts the pixel value to 300 or 400, the area determined as the B area has a pixel value of 50, and the area determined as the C area has a pixel value of −1000. Whether the pixel value is 300 or 400 in the A region is determined according to the age and case of the subject. If the subject has osteoporosis or is 50 years of age or older, the pixel value is 300, otherwise 400. Thereby, a virtual CT image of the subject is generated. In addition, the numerical value used for conversion here is an example, and may be converted to another value.

  The attenuation coefficient map creation unit 26 creates an attenuation coefficient map using the virtual CT image of the subject generated by the numerical value conversion unit 25. A conventional method can be applied to the generation of the attenuation coefficient map by the attenuation coefficient map creating unit 26.

  FIG. 2 is a diagram illustrating an operation of the image processing apparatus 10 according to the first embodiment. First, a bone SPECT image of a subject is captured by the nuclear medicine image capturing device 30 (S10), and then CT image data of the subject is read and input (S12). The image processing apparatus 10 reads and inputs the bone SPECT image data imaged by the nuclear medicine image imaging apparatus 30 (S14).

  In the region-of-interest setting unit 21, the image processing apparatus 10 sets a spherical VOI in the upper right lobe of the bone SPECT image data (S16), and calculates an average count value L of the VOI (S18). Subsequently, the image processing apparatus 10 classifies the bone SPECT image data into the A region, the B region, and the C region using the first threshold value (5L) and the second threshold value (L) obtained from the average count value L. (S20). Next, the image processing apparatus 10 uses the CT image data read from the CT image data storage unit 16 as a CT corresponding to the type of region, with the A region as bone, the B region as soft tissue or water, and the C region as air. A virtual CT image is generated by converting the value (S22). The image processing apparatus 10 creates an attenuation coefficient map based on the virtual CT image (S24).

  Next, the image processing apparatus 10 corrects the bone SPECT image data using the created attenuation coefficient map, and performs image reconstruction (S26). Then, the image processing apparatus 10 outputs the reconstructed image (S28).

  The configuration of the image processing apparatus 10 including the attenuation coefficient map creating apparatus according to the present embodiment has been described above. Examples of hardware of the image processing apparatus 10 described above are a CPU, a RAM, a ROM, a hard disk, a display, and a keyboard. , A computer equipped with a mouse, a communication interface, and the like. The above-described image processing apparatus 10 is realized by storing a program having modules for realizing the above functions in a RAM or a ROM and executing the program by the CPU. Such a program is also included in the scope of the present invention.

  The image processing apparatus 10 including the attenuation coefficient map creating apparatus according to the first embodiment generates a virtual CT image based on the subject's bone SPECT image data using the subject's X-ray CT image data as a template, and generates a virtual CT image. An attenuation coefficient map can be created based on the CT image data. In the present embodiment, an example in which a virtual CT image is generated using a CT image of a subject as a template has been described. However, a CT image used as a template may not be a CT image of a subject, but a CT image of a third party. May be used as a template.

  In the first embodiment, the bone SPECT image of the subject is classified into regions that are considered to correspond to bone, soft tissue, or water and air, respectively, thereby reducing the bone SPECT image having a complicated trunk structure. A coefficient map can be appropriately created.

  Further, the CT image used in the present embodiment does not have to be aligned with the SPECT image like the image captured by the SPECT / CT image, and therefore has a SPECT / CT imaging apparatus. This embodiment can be used even in facilities that are not.

(Second Embodiment)
FIG. 3 is a diagram illustrating a configuration of the image processing apparatus 10 including the attenuation coefficient map creating apparatus according to the second embodiment. Similar to the image processing apparatus 10 of the first embodiment, the image processing apparatus 10 of the second embodiment classifies the bone SPECT image data of the subject into an A area, a B area, and a C area. In the image processing apparatus 10 according to the second embodiment, in order to create an attenuation coefficient map from a virtual CT image, CT information of the CT image is used without using a template of the CT image. The following description will focus on the points that differ from the first embodiment.

  The attenuation coefficient map creating apparatus according to the second embodiment includes a CT information storage unit 17 that stores CT information constituting a CT image. The CT information is information constituting a CT image, for example, imaging conditions, reconstruction conditions, and the like. The CT image includes a CT value representing the form of the subject and CT information. In the present embodiment, the CT information stored in the CT information storage unit 17 is a computer-readable medium such as a CD, DVD, hard disk, or semiconductor memory in a format usable by a computer such as DICOM. The data provided in the state stored in may be used.

  The numerical value conversion unit 25 converts the pixel value of the nuclear medicine image into a CT value corresponding to the region type (A region, B region, C region type). The area determined as the A area converts the pixel value to 300 or 400, the area determined as the B area has a pixel value of 50, and the area determined as the C area has a pixel value of −1000. Whether the pixel value is 300 or 400 in the A region is determined according to the age and case of the subject. If the subject has osteoporosis or is 50 years of age or older, the pixel value is 300, otherwise 400. Thereby, a virtual CT image of the subject is generated. In addition, the numerical value used for conversion here is an example, and may be converted to another value. A virtual CT image is generated based on the converted CT value and the CT information read from the CT information storage unit 17.

  The attenuation coefficient map creation unit 26 creates an attenuation coefficient map based on the virtual CT image. The attenuation coefficient map output unit 27 outputs the created attenuation coefficient map to the attenuation correction unit 28. Thereby, the attenuation correction unit 28 can perform the attenuation correction using the attenuation coefficient map.

  FIG. 4 is a diagram illustrating an operation of the image processing apparatus 10 according to the second embodiment. First, a bone SPECT image of a subject is captured by the nuclear medicine image capturing device 30 (S10). The image processing apparatus 10 reads and inputs the bone SPECT image data imaged by the nuclear medicine image imaging apparatus 30 (S14).

  The image processing apparatus 10 sets a spherical VOI in the upper right lobe of the bone SPECT image data in the VOI setting unit 21 (S16), and calculates an average count value L of the VOI (S18). Subsequently, the image processing apparatus 10 classifies the bone SPECT image data into the A region, the B region, and the C region using the first threshold value (5L) and the second threshold value (L) obtained from the average count value L. (S20). The image processing apparatus 10 converts the CT region corresponding to each region into a CT value corresponding to each region by using the A region as bone, the B region as soft tissue or water, and the C region as air. A virtual CT image is generated based on the read CT information. Based on the virtual CT image, the image processing apparatus 10 sets an attenuation coefficient corresponding to each region and creates an attenuation coefficient map (S24).

  Next, the image processing apparatus 10 corrects the bone SPECT image data using the created attenuation coefficient map, and performs image reconstruction (S26). Then, the image processing apparatus 10 outputs the reconstructed image (S28).

  The configuration and operation of the image processing apparatus 10 according to the second embodiment have been described above. Similar to the image processing apparatus 10 of the first embodiment, the image processing apparatus 10 of the second embodiment can create an attenuation coefficient map based on the bone SPECT image of the subject. In the second embodiment, an attenuation coefficient map is generated from an X-ray CT image for a virtual CT image by generating a virtual CT image based on the CT information and the bone SPECT image data of the subject. Conventional techniques for creating can be used. Moreover, the image processing apparatus 10 of this Embodiment can produce | generate an attenuation coefficient map, without a test subject's CT image.

  Since the count value of the SPECT image depends not only on the metabolic activity of the bone tissue but also on the tissue blood flow and blood clearance, the bone / soft tissue / air in the virtual CT image data converted based on the average count value of the lung The range of is slightly different compared to true CT data. However, it was confirmed from clinical data that there was little error between the count value of the SPECT image by attenuation correction using virtual CT data and the count value of the SPECT image by attenuation correction using true CT data. Therefore, an appropriate attenuation coefficient map can be created by a method using a virtual CT image as in the present embodiment.

  As described above, the configuration of the attenuation coefficient map creating apparatus of the present invention has been described in detail with reference to the embodiment. However, the attenuation coefficient map creating apparatus of the present invention is not limited to the above-described embodiment.

  In the above-described embodiment, an example in which the region of the bone SPECT image data is classified into the three regions A to C has been described. However, the region may not necessarily be classified into the three regions. For example, the first threshold (5L ) May be classified into two regions. An attenuation coefficient map can be created by classifying a region according to whether or not the region is assumed to be a bone.

  At this stage, it is difficult to separate soft tissue and water based on SPECT images. On the other hand, since it is considered that the accuracy improvement of attenuation correction by separating the soft tissue and water is slight, it is not separated in the present embodiment. However, when a technique capable of separating soft tissue or water appears in the future, the B region may be classified into a soft tissue and a water region.

  In the embodiment described above, an example in which a VOI is set in the upper right lobe has been described. However, the VOI setting area is not necessarily limited to the upper right lobe, and may be the upper lobe of the left lung, the middle lobe of the right lung, or the like. However, the upper lobe of the right lung is preferable in the sense of avoiding the ribs and the heart. In addition, when the lung is not included in the bone SPECT image of the subject, the VOI may be set in a region where the degree of attenuation is evaluated to be uniform. In addition to the lung, a VOI may be set in the liver as a region where the degree of attenuation is evaluated to be uniform.

  The present invention is useful as an apparatus for creating an attenuation coefficient map used for attenuation correction of nuclear medicine images.

DESCRIPTION OF SYMBOLS 10 Image processing apparatus 11 Image input part 12 Arithmetic processing part 13 Output part 14 VOI data memory | storage part 15 Area | region division threshold value data memory | storage part 16 CT form image data memory | storage part 17 CT information memory | storage part 20 Processing part 21 of an attenuation coefficient map preparation apparatus Interest Region setting unit 22 VOI average value calculation unit 23 Numerical comparison unit 24 Region determination unit 25 Numerical conversion unit 26 Attenuation coefficient map creation unit 27 Attenuation coefficient map output unit 28 Attenuation correction unit 29 Image reconstruction unit 30 Nuclear medicine imaging device

Claims (8)

An input unit for inputting nuclear medicine image data of the subject;
A region-of-interest setting unit for setting a region of interest in a region where the degree of attenuation is evaluated to be uniform in the nuclear medicine image;
A region determination unit that classifies a nuclear medicine image of a subject into a first region where the count value is equal to or greater than the threshold and a second region that is less than the threshold, using a constant multiple of the average count value of the region of interest as a threshold;
In the CT image of the template, the pixel value of the first region is converted into a CT value corresponding to the bone region, the pixel value of the second region is converted into a CT value corresponding to the region other than the bone, An attenuation coefficient map creating unit for creating an attenuation coefficient map for generating attenuation images of the nuclear medicine images using the virtual CT images,
An attenuation coefficient map creation device comprising: An input unit for inputting nuclear medicine image data of the subject;
A region-of-interest setting unit for setting a region of interest in a region where the degree of attenuation is evaluated to be uniform in the nuclear medicine image;
A region determination unit that classifies a nuclear medicine image of a subject into a first region where the count value is equal to or greater than the threshold and a second region that is less than the threshold, using a constant multiple of the average count value of the region of interest as a threshold;
CT information for converting the pixel value of the first region into a CT value corresponding to a bone region, converting the pixel value of the second region into a CT value corresponding to a region other than the bone, and constituting a CT image An attenuation coefficient map creating unit that creates a virtual CT image and creates an attenuation coefficient map that performs attenuation correction of the nuclear medicine image using the virtual CT image;
An attenuation coefficient map creation device comprising:   The attenuation region map creating apparatus according to claim 1, wherein the region-of-interest setting unit sets a region of interest in a lung region while avoiding a rib region.   The attenuation region map creating apparatus according to claim 1, wherein the region of interest setting unit sets a region of interest in a liver region. The region determination unit classifies a region of which the count value is equal to or greater than the average count value among the second regions as a third region, and a region of less than the average count value as a fourth region,
The attenuation coefficient map creating unit converts the pixel value of the third region into a CT value corresponding to a soft tissue or a water region, and converts the pixel value of the fourth region into a CT value corresponding to an air region. An attenuation coefficient map creating unit that creates a virtual CT image and creates an attenuation coefficient map that performs attenuation correction of the nuclear medicine image;
An attenuation coefficient map creation device according to any one of claims 1 to 4.   6. The attenuation coefficient map creating apparatus according to claim 1, wherein the nuclear medicine image is bone SPECT image data. A method for generating an attenuation coefficient map used for attenuation correction of a nuclear medicine image from a nuclear medicine image of a subject,
Inputting nuclear medical image data of the subject;
Setting a region of interest in a region where the degree of attenuation is evaluated to be uniform in the nuclear medicine image;
Classifying a nuclear medicine image of a subject into a first region where the count value is equal to or greater than the threshold and a second region where the count value is less than the threshold, with a constant multiple of the average count value of the region of interest as a threshold;
In the CT image of the template, the pixel value of the first region is converted into a CT value corresponding to the bone region, the pixel value of the second region is converted into a CT value corresponding to the region other than the bone, Generating a CT image of
Creating an attenuation coefficient map that performs attenuation correction of the nuclear medicine image using the virtual CT image;
An attenuation coefficient map creation method comprising: A program for generating an attenuation coefficient map used for attenuation correction of a nuclear medicine image from a nuclear medicine image of a subject, comprising:
Inputting nuclear medical image data of the subject;
Setting a region of interest in a region where the degree of attenuation is evaluated to be uniform in the nuclear medicine image;
Classifying a nuclear medicine image of a subject into a first region where the count value is equal to or greater than the threshold and a second region where the count value is less than the threshold, with a constant multiple of the average count value of the region of interest as a threshold;
In the CT image of the template, the pixel value of the first region is converted into a CT value corresponding to the bone region, the pixel value of the second region is converted into a CT value corresponding to the region other than the bone, Generating a CT image of
Creating an attenuation coefficient map for performing attenuation correction of the nuclear medicine image using the virtual CT image;
A program that executes

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