JP2009047602A - Positron emission computerd tomograph, attenuation map creating device, and attenuation map creating program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simply and quickly create an attenuation map having the same FOV as a PET image. <P>SOLUTION: A temporary CT image creating part 441 creates a temporary CT image by converting a PET value being a pixel value of an attenuation non-correction PET image re-composed by an attenuation non-correction PET image re-composition part 41 into a CT value being a pixel value of a CT image. A substitution CT image creating part 442 creates a substitution CT image based on the CT value of the temporary CT image from the CT image re-composed by a CT image re-composition part 42. An addition CT image creating part 443 creates an addition CT image adding the temporary CT image to the substitution CT image after matching positions of the temporary CT image and the substitution CT image. An attenuation map creating part 444 creates the attenuation map from the CT value of the addition CT image. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a positron emission computed tomography apparatus, an attenuation map creation apparatus, and an attenuation map creation program.

  Conventionally, positron emission computed tomography (PET) apparatus, X-ray computed tomography (CT) apparatus, and the like are known as radiation diagnostic apparatuses using radiation. These radiological diagnosis apparatuses provide images based on their respective characteristics, thereby enabling medical image diagnosis that is indispensable in today's medical care.

The PET device is one of nuclear medicine diagnostic devices and provides detailed functional information of human body tissues as an image. Specifically, the PET apparatus administers a drug labeled with a positron emitting nuclide to a subject, and emits 511 keV in approximately the opposite direction when the positrons emitted from the administered drug combine with electrons and disappear. These gamma rays are simultaneously detected by, for example, a ring-shaped detector disposed around the subject. Then, by calculating the data of the gamma rays detected simultaneously, an image (hereinafter referred to as PET) showing the distribution of the human tissue that has taken in the administered drug on the plane (tomographic plane) where the ring-shaped detector is located. Image). For example, ¹⁸ F-labeled deoxyglucose (hereinafter referred to as FDG) labeled with “ ¹⁸ F (fluorine)”, which is a positron emitting nuclide, is efficiently taken up by cancer cells having an enhanced sugar metabolism function. Therefore, the PET apparatus reconstructs the distribution of cancer tumor tissue with enhanced glucose metabolism function in the human tissue of the subject by imaging the subject after administering FDG to the subject. The PET image can be provided.

  However, since the PET image only represents the state of accumulation and distribution of positron emitting nuclides, detailed morphological information such as where it exists in human body tissue is not necessarily clear. In addition, gamma rays emitted in the body of the subject are absorbed and attenuated in the body before being detected outside the body, so the PET image is reconstructed using the detected gamma ray data as it is. However, the image does not show an accurate distribution. Therefore, when reconstructing a PET image, it is necessary to attenuate and correct the detected gamma ray data as preprocessing.

  Therefore, in recent years, a PET-CT apparatus in which a PET apparatus and an X-ray CT apparatus are integrated has become widespread. In a PET-CT apparatus, a highly reliable PET image is obtained by using an image reconstructed by an X-ray CT apparatus (hereinafter referred to as a CT image) for attenuation correction of data obtained by the PET apparatus as needed. In addition to shortening the examination time, high-accuracy medical image diagnosis based on a PET image and a CT image that is an image showing morphological information is realized. This will be described in detail below.

  The X-ray CT apparatus is one of transmission type CT apparatuses, and provides detailed morphological information of human body tissues. Specifically, the X-ray CT apparatus rotates an X-ray source and detector installed outside the subject, for example, by rotating the body axis of the subject as a pair, so as to receive X-rays from multiple directions. The intensity of X-rays that are absorbed and attenuated when the specimen is irradiated and transmitted through the body is measured in each direction. Then, by reconstructing the X-ray intensity distribution obtained by the detector, a CT image showing the morphological information of the human body tissue in the subject on the X-ray irradiated surface (tomographic plane) is reconstructed. Do. In other words, the X-ray CT apparatus provides morphological information in the human tissue of the subject as a reconstructed CT image by detecting the X-ray intensity distribution resulting from differences in X-ray transmission of bones, organs, air, etc. can do.

  Therefore, by acquiring the PET image reconstructed by the PET apparatus and the CT image reconstructed by the X-ray CT apparatus in the same cross-sectional layer, the functional information acquired by the PET image is acquired by the CT image. Thus, more accurate medical image diagnosis can be performed.

  The X-ray CT apparatus calculates a CT value from the X-ray intensity obtained by the detector and reconstructs a CT image using the calculated CT value. The CT value is an X-ray transmitted through the subject. This is a numerical value calculated based on the attenuation coefficient of “water” and the attenuation coefficient of “air” with respect to X-rays according to the intensity (photon energy), and corresponds to the attenuation coefficient of the scan target region. That is, the CT image is also an attenuation map representing the distribution of attenuation coefficients corresponding to the photon energy of X-rays on the corresponding tomographic plane. The attenuation coefficient is also called an absorption coefficient and quantitatively represents the degree to which photons such as X-rays and gamma rays are attenuated when passing through a certain substance. It is determined by the atomic number. That is, the attenuation coefficient (absorption coefficient) is a photon reaction cross section (reaction probability) for each substance, which is determined depending on the photon energy.

  Therefore, by scaling the “attenuation map corresponding to the photon energy of X-ray” so as to correspond to the photon energy of gamma ray, an attenuation map for performing attenuation correction of the detected gamma ray data can be created.

  However, the effective field of view (Field of View; FOV) of the cross-sectional layer imaged by the X-ray CT apparatus is smaller than the FOV of the cross-sectional layer imaged by the PET apparatus. For this reason, since there is no CT value used for attenuation correction in the portion of the PET image that protrudes from the CT image (hereinafter referred to as the protruding portion), there is a problem that an attenuation map of the protruding portion cannot be created. In particular, when the subject's human body is present at the protruding portion, there is a problem that the image quality of the PET image at the protruding portion is degraded.

  Therefore, Patent Document 1 discloses a technique for enlarging the FOV of the cross-sectional layer imaged by the transmission CT apparatus by calculation and creating an attenuation map of the protruding portion by using the enlarged CT image. Specifically, each of the data obtained by the transmission CT apparatus is subjected to correction processing a plurality of times to estimate a CT image in which the FOV is enlarged.

JP 2006-312027 A

  By the way, the above-described conventional technique has a problem that the processing is complicated and it takes a long time to obtain a calculation result, so that an attenuation map having the same FOV as that of the PET image cannot be created easily and quickly. .

  Accordingly, the present invention has been made to solve the above-described problems of the prior art, and a positron emission computed tomography apparatus capable of easily and quickly creating an attenuation map having the same FOV as that of a PET image. An object of the present invention is to provide an attenuation map creation device and an attenuation map creation program.

  In order to solve the above-described problems and achieve the object, the present invention according to claim 1 attenuates gamma ray detection data, which is data obtained by detecting gamma rays emitted from a positron emitting nuclide administered to a subject. A positron emission computed tomography apparatus for generating an attenuation map used for correction from a CT image that is an image reconstructed by an X-ray computed tomography apparatus, wherein the gamma ray detection data is reconstructed without attenuation correction A temporary CT image creating means for creating a temporary CT image by converting a pixel value of an attenuated uncorrected image, which is a reduced image, into a CT value that is a pixel value of the CT image, and the temporary CT image creating means An added CT image for creating an added CT image obtained by adding the CT image to the temporary CT image after aligning the positions of the temporary CT image and the CT image And creating means, characterized in that and a attenuation map generating means for generating the attenuation map from the CT value of the adding CT image created by the addition CT image creating device.

  According to a fourth aspect of the present invention, there is provided an attenuation map used for attenuation correction of gamma ray detection data acquired by detecting gamma rays emitted from a positron emitting nuclide administered to a subject. An attenuation map creation device that creates a CT image that is an image reconstructed by the device, the pixel value of an attenuation-uncorrected image that is an image reconstructed without attenuation correction of the gamma ray detection data. A provisional CT image creation means for creating a provisional CT image by converting it into a CT value that is a pixel value of the image, and a position of the provisional CT image created by the provisional CT image creation means and the CT image Adding CT image creating means for creating an added CT image obtained by adding the CT image to the provisional CT image; and the addition created by the added CT image creating means And attenuation map generating means for generating the attenuation map from the CT value of T images, characterized by comprising a.

Further, according to the present invention, the attenuation map used for attenuation correction of the gamma ray detection data acquired by detecting the gamma rays emitted from the positron emitting nuclide administered to the subject is obtained by X-ray computed tomography. An attenuation map creation program for causing a computer to execute an attenuation map creation method created from a CT image that is an image reconstructed by an apparatus,
Temporary CT image creation procedure for creating a temporary CT image by converting pixel values of an attenuation-uncorrected image, which is an image reconstructed without attenuation correction of the gamma ray detection data, into CT values that are pixel values of the CT image And adding the CT image to the provisional CT image after adding the positions of the provisional CT image and the CT image created by the provisional CT image creation procedure, The computer is caused to execute a procedure and an attenuation map creating procedure for creating the attenuation map from the CT value of the added CT image created by the added CT image creating procedure.

  According to the first, fourth, or fifth aspect of the present invention, it is possible to easily and quickly create an attenuation map having the same FOV as the PET image.

  Exemplary embodiments of a positron emission computed tomography apparatus, an attenuation map creation apparatus, and an attenuation map creation program according to the present invention will be described below in detail with reference to the accompanying drawings. In this embodiment, the case where the present invention is applied to a PET-CT apparatus in which a positron emission computed tomography apparatus (PET apparatus) and an X-ray computed tomography apparatus (X-ray CT apparatus) are integrated will be described. .

  First, the configuration of the PET-CT apparatus in the present embodiment will be described. FIG. 1 is a diagram for explaining a configuration of a PET-CT apparatus according to the present embodiment. As shown in FIG. 1, the PET-CT apparatus includes a PET scanner 1, an X-ray CT scanner 2, a bed 3, a data processing device 4, and an input / output device 5.

  The PET scanner 1 includes a ring-shaped gamma ray detector that detects gamma rays, and sequentially emits a pair of gamma rays emitted from a drug labeled with a positron emitting nuclide incorporated into a human tissue of a patient during a predetermined monitoring period. Detect with a gamma ray detector. Then, projection data based on the detected gamma ray count value is generated and collected in association with the gamma ray detection position and the gamma ray incident direction in the gamma ray detector.

  The X-ray CT scanner 2 includes an X-ray generator that generates X-rays and an X-ray detector that detects X-rays. The patient is irradiated with X-rays generated by the X-ray generator and transmitted through the patient. X-rays are detected by an X-ray detector. Specifically, the X-ray CT scanner 2 rotates a pair of an X-ray generator and an X-ray detector around the patient's body axis to irradiate the subject with X-rays from multiple directions, X-ray intensity absorbed and attenuated when passing through is detected in each direction. Then, the detected X-ray projection data is generated and collected in association with the X-ray detection position in the X-ray detector.

  The bed 3 is a bed on which a patient is placed. The data processing device 4 processes the projection data generated and collected by the PET scanner 1 and the X-ray CT scanner 2 to reconstruct a PET image and a CT image. The input / output device 5 includes buttons, a keyboard for the user to input instructions to the PET-CT device, a monitor for outputting and displaying the PET image and the CT image reconstructed by the data processing device 4, and the like. Have.

  The PET-CT apparatus in the present embodiment first collects X-ray projection data by moving the PET scanner 1 and the X-ray CT scanner 2 from left to right in FIG. It is assumed that projection data based on the count value is collected.

  Here, the data processing device 4 that constitutes the PET-CT apparatus in the present embodiment uses the X-ray CT scanner 2 to collect the attenuation map used when the gamma ray projection data collected by the PET scanner 1 is attenuated. The main feature is that the attenuation map having the same FOV as the PET image FOV (Field Of View; FOV) is easily and quickly created from the CT image reconstructed by the line projection data.

  Hereinafter, this main feature will be described with reference to FIGS. 2 is a functional block diagram showing the configuration of the data processing apparatus, FIG. 3 is a diagram for explaining the set value storage unit, and FIG. 4 is a diagram for explaining the provisional CT image creation unit. FIG. 5 is a diagram for explaining an alternative CT image creation unit, FIG. 6 is a diagram for explaining an addition CT image creation unit, and FIG. 7 is created in the present embodiment. It is a figure for demonstrating an example of the addition CT image.

  As shown in FIG. 2, the data processing device 4 constituting the PET-CT apparatus in this embodiment includes an attenuation-uncorrected PET image reconstruction unit 41, a CT image reconstruction unit 42, a set value storage unit 43, And a correction processing unit 44.

  The CT image reconstruction unit 42 receives and processes X-ray projection data collected by the X-ray CT scanner 2 to reconstruct a CT image.

  The attenuation-uncorrected PET image reconstruction unit 41 receives gamma ray projection data collected by the PET scanner 1 and processes it without attenuation correction, thereby reconstructing an attenuation-uncorrected PET image.

  The set value storage unit 43 stores various set values input by the user via the input / output device 5. For example, as shown in FIG. 3, “0” is stored as “PET value threshold (X)”, “0” is stored as “water CT value”, “−1000” is stored as “air CT value”, “300” is stored as “maximum setting value (Y)”, and “0” is stored as “alternative setting value (Z)”. These various setting values will be described in detail later.

  The correction processing unit 44 creates and creates an attenuation map using the CT image reconstructed by the CT image reconstruction unit 42 and the attenuation-uncorrected PET image reconstructed by the attenuation-uncorrected PET image reconstruction unit 41. As shown in FIG. 2, a provisional CT image creation unit 441, a substitute CT image creation unit 442, and an addition CT image creation are performed to reconstruct an attenuation correction PET image subjected to attenuation correction processing using an attenuation map. 443, an attenuation map creation unit 444, and an attenuation correction PET image reconstruction unit 445.

  The provisional CT image creation unit 441 uses the PET value (unit: Bq / ml), which is the pixel value of the attenuation-uncorrected PET image reconstructed by the attenuation-uncorrected PET image reconstruction unit 41, as the pixel value of the CT image. A temporary CT image is created by converting the value (unit: Hounsfield Unit). Specifically, as illustrated in FIG. 4, the provisional CT image creation unit 441 refers to the various setting values stored in the setting value storage unit 43 illustrated in FIG. 3, and displays “PET value: When “P” is a value equal to or greater than “PET value threshold (X) = 0”, it is converted to “water CT value = 0” which is a CT value corresponding to water, and “PET value of attenuation-uncorrected PET image” : P ”is smaller than“ PET value threshold (X) = 0 ”, it is converted to“ air CT value = −1000 ”, which is a CT value corresponding to air, to create a temporary CT image.

  In other words, in the attenuation-uncorrected PET image, the pixel portion where “PET value: P” is a value equal to or greater than “0” is regarded as corresponding to the body in which the drug labeled with the positron emitting nuclide is taken in. The “water CT value = 0” corresponding to the water as the main component of is provided as the CT value “CT” of the temporary CT image. In addition, a pixel portion having a “PET value: P” smaller than “0” is regarded as outside the body in which a drug labeled with a positron emitting nuclide is not taken in, and “air CT value = − corresponding to air”. 1000 ”is given as the CT value“ CT ”of the provisional CT image.

  In this embodiment, the case where “0” is set as “PET value threshold (X)” has been described. However, the present invention is not limited to this, and measurement errors and statistical errors in the PET scanner 1 are not limited to this. In consideration, “PET value threshold (X)” taking into account the allowable range may be set (for example, “PET value threshold (X) = 0 ± 0.01”).

  The alternative CT image creation unit 442 creates an alternative CT image from the CT image reconstructed by the CT image reconstruction unit 42. Here, when the patient wears metal or the like (for example, dental implant), the CT value in the CT image becomes higher than the value corresponding to bone in the periphery (metal artifact), If a part of the patient's body protrudes from the FOV of the X-ray CT scanner 2, the CT value in the CT image may be higher than the value corresponding to the bone in the periphery (extruding artifact). Are known.

  Therefore, the alternative CT image creation unit 442 has a CT value “C” of the CT image reconstructed by the CT image reconstruction unit 42 equal to or greater than “maximum set value (Y) = 300” stored in the set value storage unit 43. And the CT value “CT” of the pixel at the same position as the pixel having the CT value “C” among the pixels constituting the temporary CT image created by the temporary CT image creating unit 441 is “water”. If CT value = 0, the CT value “C” is changed to “alternative setting value (Z) = 0” stored in the setting value storage unit 43 (see (1) in FIG. 5). That is, even if the CT value “C” indicates a value greater than or equal to “maximum set value (Y) = 300”, the alternative CT image creation unit 442 determines that the CT value “CT” of the corresponding pixel in the temporary CT image is If it is “0” corresponding to water, it is considered that a high CT value “C” is obtained due to artifacts in spite of being in the body of the patient, and “alternative setting value corresponding to water as the main component in the body” (Z) = 0 ”.

  Further, the alternative CT image creation unit 442 has a CT value “C” of the CT image reconstructed by the CT image reconstruction unit 42 equal to or greater than “maximum set value (Y) = 300” stored in the set value storage unit 43. And the CT value “CT” of the pixel at the same position as the pixel having the CT value “C” among the pixels constituting the temporary CT image created by the temporary CT image creating unit 441 is “air” If CT value = −1000, the CT value “C” is changed to “maximum set value (Y) = 300” (see (2) in FIG. 5). That is, even if the CT value “C” indicates a value greater than or equal to “maximum setting value (Y) = 300”, the alternative CT image creation unit 442 has “−1000” where the CT value “CT” corresponds to air. If this is the case, it is considered as a value that does not adversely affect the creation of the attenuation map, assuming that the drug administered to the subject does not exist, that is, a metal outside the human body (air) that does not have the function of metabolizing the drug. Is converted to “maximum setting value (Y) = 300”.

  The alternative CT image creation unit 442 also has a CT value “C” of the CT image reconstructed by the CT image reconstruction unit 42 smaller than “maximum set value (Y) = 300” stored in the set value storage unit 43. In this case, the CT value “C” is used as it is (see (3) in FIG. 5).

  In this embodiment, the case where “300” is set as the “maximum setting value (Y)” has been described. However, the “maximum setting value (Y)” may be a value that does not adversely affect the creation of the attenuation map. Usually, it is considered appropriate to set a value in the range of “200 to 400”.

  The added CT image creation unit 443 aligns the positions of the temporary CT image created by the temporary CT image creation unit 441 and the alternative CT image created by the alternative CT image creation unit 442, and then substitutes the temporary CT image. An added CT image is created by adding the CT images. That is, as shown in FIG. 6, among the areas captured in the temporary CT image, “FOV (CT) area” that is an area protruding from the “FOV (CT) area” that is the area captured in the alternative CT image. “CT) outside region” has a CT value of the temporary CT image, and “FOV (CT) region” has an added CT having a CT value obtained by adding the CT value of the temporary CT image and the CT value of the alternative CT image. Create an image.

  For example, as shown in FIG. 7, the added CT image creation unit 443 performs provisional CT in the “outside FOV (CT) region” of the temporary CT image created from the attenuation-uncorrected PET image by the temporary CT image creation unit 441. In the “FOV (CT) region”, a CT value obtained by adding the CT value of the temporary CT image and the CT value of the alternative CT image created from the CT image by the alternative CT image creation unit 442 is obtained. An added CT image is created. Thereby, an addition CT image having the same FOV as the FOV of the attenuation-uncorrected PET image can be created. Further, by the processing of the alternative CT image creation unit 442, an added CT image in which the “protrusion artifact” in the CT image shown in FIG. 7 is corrected can be created. FIG. 7 shows an example of an added CT image created when the FOV of the attenuation-uncorrected PET image (and the provisional CT image) has a diameter of 683 mm and the CT image (and the alternative CT image) has a diameter of 500 mm. It is a figure for demonstrating.

  Note that the addition CT image creation unit 443 prevents the CT value in the addition boundary region between the “FOV (CT) outside region” in the temporary CT image and the alternative CT image from changing discontinuously and rapidly. Correction processing may be performed so that the value is continuously smooth.

  The attenuation map creation unit 444 creates an attenuation map from the CT value of the addition CT image created by the addition CT image creation unit 443. That is, attenuation of gamma ray projection data collected by the PET scanner 1 is performed by scaling the CT value of the added CT image corresponding to the “attenuation map corresponding to photon energy of X-ray” to correspond to the photon energy of gamma ray. Create an attenuation map for correction.

  The attenuation correction PET image reconstruction unit 445 corrects the gamma ray projection data collected by the PET scanner 1 using the attenuation map created by the attenuation map creation unit 444, and has already been attenuated corrected from the corrected gamma ray projection data. Of the PET image.

  For this reason, the data processing apparatus 4 constituting the PET-CT apparatus in the present embodiment does not expand the FOV of the CT image by complicated calculation processing, and is the same as the FOV of the PET image as described above. It is possible to easily and quickly create an attenuation map having an FOV.

  Next, attenuation correction PET image reconstruction processing of the PET-CT apparatus in the present embodiment will be described with reference to FIG. FIG. 8 is a diagram for explaining attenuation-corrected PET image reconstruction processing of the PET-CT apparatus according to the present embodiment.

  As shown in FIG. 8, the PET-CT apparatus according to the present embodiment, when a cross-sectional attenuation-uncorrected PET image corresponding to the reconstructed CT image is reconstructed (Yes in step S801), the provisional CT image creation unit Step 441 creates a temporary CT image from the attenuation-uncorrected PET image (step S802).

  That is, in the PET-CT apparatus according to the present embodiment, first, X-ray projection data by the X-ray CT scanner 2 is collected, and then gamma-ray projection data by the PET scanner 1 is collected. The CT image reconstruction unit 42 reconstructs a CT image as needed from the X-ray projection data collected by the X-ray CT scanner 2, and the temporary CT image creation unit 441 reconstructs the CT image reconstruction unit 42. Each time an attenuated / uncorrected PET image reconstruction unit 41 reconstructs the cross-sectional attenuated / uncorrected PET image corresponding to the CT image, a temporary CT image is created from the attenuated / uncorrected PET image.

  Specifically, as illustrated in FIG. 4, the provisional CT image creation unit 441 refers to the various setting values stored in the setting value storage unit 43 illustrated in FIG. 3, and displays “PET value: When “P” is a value equal to or greater than “PET value threshold (X) = 0”, it is converted to “water CT value = 0” which is a CT value corresponding to water, and “PET value of attenuation-uncorrected PET image” : P ”is smaller than“ PET value threshold (X) = 0 ”, it is converted to“ air CT value = −1000 ”, which is a CT value corresponding to air, to create a temporary CT image.

  Then, the alternative CT image creation unit 442 creates an alternative CT image from the CT image reconstructed by the CT image reconstruction unit 42 (step S803). Specifically, the alternative CT image creating unit 442 has a CT value “C” of the CT image that is equal to or greater than “maximum set value (Y) = 300” stored in the set value storage unit 43, and If the CT value “CT” of the pixel at the same position as the pixel having the CT value “C” among the pixels constituting the temporary CT image created by the CT image creating unit 441 is “water CT value = 0” The CT value “C” is changed to “alternative setting value (Z) = 0” (see (1) in FIG. 5). Further, the alternative CT image creating unit 442 has a CT value “C” of the CT image equal to or greater than “maximum setting value (Y) = 300”, and among the pixels constituting the temporary CT image, If the CT value “CT” of the pixel at the same position as the pixel having the CT value “C” is “air CT value = −1000”, the CT value “C” is set to “maximum set value (Y) = 300”. Change (see (2) in FIG. 5). Further, when the CT value “C” of the CT image is smaller than “maximum setting value (Y) = 300”, the alternative CT image creating unit 442 adopts the CT value “C” as it is ((( 3)).

  After that, the addition CT image creation unit 443 aligns the positions of the temporary CT image created by the temporary CT image creation unit 441 and the alternative CT image created by the alternative CT image creation unit 442, and then adds the temporary CT image. An added CT image is created by adding the image to the alternative CT image (step S804, see FIG. 6).

  Further, the attenuation map creating unit 444 creates an attenuation map from the CT value of the added CT image created by the added CT image creating unit 443 (step S805), and the attenuation corrected PET image reconstruction unit 445 is operated by the PET scanner 1. The collected gamma ray projection data is corrected using the attenuation map created by the attenuation map creation unit 444, and an attenuation-corrected PET image is reconstructed from the corrected gamma ray projection data (step S806). finish.

  In the present embodiment, the case where the attenuation map is created using the CT image of the corresponding cross section every time the attenuation-uncorrected PET image is reconstructed from the gamma ray projection data by the PET scanner 1 has been described. The invention is not limited to this, and after all the attenuation-uncorrected PET images are reconstructed from the projection data of the gamma rays by the PET scanner 1, the attenuation maps are collectively used using the corresponding CT images of the cross sections. May be created.

  As described above, in this embodiment, the provisional CT image creation unit 441 converts the PET value, which is the pixel value of the attenuation-uncorrected PET image reconstructed by the attenuation-uncorrected PET image reconstruction unit 41, into the CT image. A temporary CT image is created by converting the CT value, which is a pixel value, and the alternative CT image creation unit 442 creates a temporary CT image created by the temporary CT image creation unit 441 from the CT image reconstructed by the CT image reconstruction unit 42. An alternative CT image is created based on the CT value of the CT image. Then, the addition CT image creation unit 443 aligns the positions of the temporary CT image created by the temporary CT image creation unit 441 and the alternative CT image created by the alternative CT image creation unit 442, and then adds the temporary CT image. Is added to the alternative CT image, and the attenuation map creation unit 444 creates an attenuation map from the CT value of the addition CT image created by the addition CT image creation unit 443.

  Therefore, in the FOV of the PET image, the portion that protrudes from the FOV of the CT image (the protruding portion) is converted into a CT value estimated from the PET value of the PET image, so that the FOV of the CT image is subjected to complicated calculation processing. It is possible to easily and quickly create an attenuation map having the same FOV as the PET image without expanding.

  In addition, by using the generated attenuation map, it is possible to avoid a reduction in the accuracy of the image quality of the protruding portion in the reconstructed PET image. Further, it is not necessary to instruct the specimen to change the posture so that the protruding portion is not allowed, and the burden on the subject can be reduced.

  In addition, since the CT image has a high CT value due to the artifact, the attenuation coefficient on the attenuation map is calculated to be high, thereby creating a substitute CT image for the risk of reducing the image quality accuracy of the reconstructed PET image. Therefore, it is possible to maintain the accuracy of the image quality of the PET image.

  In the present embodiment, the PET-CT apparatus in which the PET apparatus and the X-ray CT apparatus are integrated has been described. However, the present invention is not limited to this, and the PET apparatus and the X-ray CT apparatus include The present invention can be similarly applied to a PET apparatus that is separately installed and uses a CT image reconstructed by an X-ray CT apparatus for attenuation correction.

  As described above, the positron emission computed tomography apparatus, attenuation map creating apparatus, and attenuation map creating program according to the present invention are useful for PET-CT apparatuses and PET apparatuses that use CT images for attenuation correction, and in particular, PET images. It is suitable for making it possible to easily and quickly create an attenuation map having the same FOV.

It is a figure for demonstrating the structure of the PET-CT apparatus in a present Example. It is a functional block diagram which shows the structure of a data processor. It is a figure for demonstrating a setting value memory | storage part. It is a figure for demonstrating a temporary CT image creation part. It is a figure for demonstrating an alternative CT image creation part. It is a figure for demonstrating an addition CT image preparation part. It is a figure for demonstrating an example of the addition CT image produced in a present Example. It is a figure for demonstrating the attenuation correction PET image reconstruction process of the PET-CT apparatus in a present Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 PET scanner 2 X-ray CT scanner 3 Bed 4 Data processing apparatus 41 Attenuation / uncorrected PET image reconstruction unit 42 CT image reconstruction unit 43 Set value storage unit 44 Correction processing unit 441 Temporary CT image creation unit 442 Alternative CT image creation unit 443 addition CT image creation unit 444 attenuation map creation unit 445 attenuation correction PET image reconstruction unit 5 input / output device

Claims (5)

An attenuation map used for attenuation correction of gamma ray detection data, which is data acquired by detecting gamma rays emitted from a positron emitting nuclide administered to a subject, is an image reconstructed by an X-ray computed tomography apparatus. A positron emission computed tomography device created from a CT image,
Temporary CT image creation means for creating a temporary CT image by converting pixel values of an attenuation-uncorrected image that is a reconstructed image of the gamma ray detection data without attenuation correction into CT values that are pixel values of the CT image When,
An added CT image creating means for creating an added CT image obtained by adding the CT image to the temporary CT image after aligning the positions of the temporary CT image and the CT image created by the temporary CT image creating means; ,
Attenuation map creating means for creating the attenuation map from the CT value of the added CT image created by the added CT image creating means;
A positron emission computed tomography apparatus comprising:   When the pixel value of the attenuation-uncorrected image is equal to or greater than a predetermined set value, the temporary CT image creation unit converts the pixel value of the attenuation-uncorrected image into a predetermined value. 2. The positron emission computed tomography apparatus (nuclear medicine diagnostic apparatus) according to claim 1, wherein when it is smaller than the set value, the CT value is converted into a CT value corresponding to air. When the CT value of the CT image is an excess CT value that exceeds a predetermined maximum value, the excess CT value is determined among the pixels constituting the temporary CT image created by the temporary CT image creation means. If the CT value of the pixel at the same position as the pixel having the value is equivalent to water, the excess CT value is changed to a predetermined alternative value, and the CT value of the pixel at the same position as the pixel having the excess CT value is air. If it is a substantial value, the CT further includes a substitute CT image creating means for creating a substitute CT image from the CT image by changing the excess CT value to the predetermined maximum value,
The positron emission computed tomography apparatus according to claim 2, wherein the addition CT image creating unit adds the substitute CT image created by the substitute CT image creating unit to the temporary CT image. CT image, which is an image reconstructed by an X-ray computed tomography apparatus, used to correct gamma ray detection data acquired by detecting gamma rays emitted from the positron emitting nuclide administered to the subject. An attenuation map creation device created from
Temporary CT image creation means for creating a temporary CT image by converting pixel values of an attenuation-uncorrected image that is a reconstructed image of the gamma ray detection data without attenuation correction into CT values that are pixel values of the CT image When,
An added CT image creating means for creating an added CT image obtained by adding the CT image to the temporary CT image after aligning the positions of the temporary CT image and the CT image created by the temporary CT image creating means; ,
Attenuation map creating means for creating the attenuation map from the CT value of the added CT image created by the added CT image creating means;
An attenuation map creation device characterized by comprising: CT image, which is an image reconstructed by an X-ray computed tomography apparatus, used to correct gamma ray detection data acquired by detecting gamma rays emitted from the positron emitting nuclide administered to the subject. An attenuation map creation program for causing a computer to execute an attenuation map creation method created from
Temporary CT image creation procedure for creating a temporary CT image by converting pixel values of an attenuation-uncorrected image, which is an image reconstructed without attenuation correction of the gamma ray detection data, into CT values that are pixel values of the CT image When,
An added CT image creation procedure for creating an added CT image obtained by adding the CT image to the temporary CT image after aligning the positions of the temporary CT image and the CT image created by the temporary CT image creation procedure; ,
An attenuation map creating procedure for creating the attenuation map from the CT value of the added CT image created by the added CT image creating procedure;
An attenuation map creating program characterized by causing a computer to execute.

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