JP2011092554A - Pet-ct apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a PET-CT apparatus for easily confirming a positional deviation between a PET image and a CT image. <P>SOLUTION: A CT image generating part 17 generates data of the CT image concerning a tank phantom. A PET scanner 5 detects a gamma ray to be discharged from the tank phantom. A PET projection data collecting part 13 collects PET projection data concerning the tank phantom. An attenuation correcting part 19 corrects the attenuation of the PET projection data, on the basis of the CT image. A PET image generating part 21 generates data of the PET image concerning the tank phantom, on the basis of the attenuation-corrected PET projection data. A positional deviation detecting part 23 detects the positional deviation between the CT image and the PET image, on the basis of a difference between the CT image and the PET image. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a PET-CT apparatus in which a PET (positron emission tomography) apparatus and an X-ray computed tomography apparatus (hereinafter referred to as an X-ray CT apparatus) are combined.

  A PET-CT apparatus in which a PET scanner and an X-ray CT scanner are combined is used in a hospital or the like. In the PET-CT apparatus, the mechanical misalignment between the PET scanner and the CT scanner is corrected by a serviceman using a line source during installation or regular maintenance. As a method of detecting the positional deviation, the positional deviation is based on the positional deviation between the line source region on the CT image and the line source region on the PET image obtained by scanning the line source.

JP 2008-11922 A

  However, there are the following three problems in misregistration confirmation such as misregistration detection and correction. 1. It is necessary to prepare a line source. 2. The timing for detecting and correcting misalignment is limited to regular maintenance. 3. A customer (person in the hospital, for example, a doctor or engineer) cannot easily detect or correct the misalignment.

  An object of the present invention is to provide a PET-CT apparatus that facilitates confirmation of positional deviation between a PET image and a CT image.

  A PET-CT apparatus according to a first aspect of the present invention includes a first generator that generates CT image data relating to a tank phantom, a detector that detects gamma rays emitted from the tank phantom, and the detector. A collection unit that collects projection data relating to the tank phantom, an attenuation correction unit that attenuates and corrects the projection data based on the CT image, and PET image data relating to the tank phantom based on the attenuation corrected projection data And a detection unit that detects a positional shift between the CT image and the PET image based on a difference between the CT image and the PET image.

  A PET-CT apparatus according to a second aspect of the present invention includes a first generator for generating CT image data relating to a tank phantom, a detector for detecting gamma rays emitted from the tank phantom, and the detector. A collection unit that collects projection data related to the tank phantom, an attenuation correction unit that corrects the projection data based on the CT image, and PET image data related to the tank phantom based on the attenuation-corrected projection data. A calculating unit that calculates a distance and direction between a center of the tank phantom region on the CT image and a center of the tank phantom region on the PET image, and the calculated distance And an alignment unit that aligns the CT image and the PET image based on the direction.

  According to the present invention, it is possible to provide a PET-CT apparatus that facilitates confirmation of positional deviation between a PET image and a CT image.

1 is a configuration diagram of a PET-CT apparatus according to a first embodiment of the present invention. The perspective view which arranged the tank phantom and the line source. FIG. 2 is a functional block diagram of the data processing apparatus in FIG. 1. It is a figure for demonstrating the process of the position shift detection part of FIG. 1, and is a figure which shows the production | generation process of a nonuniform count distribution map. FIG. 2 is a diagram for explaining processing of a misregistration detection unit in FIG. 1 and showing non-uniform count distribution diagrams when there is a misregistration between a CT image and a PET image and when there is no misregistration. The figure for demonstrating the calculation process of the positional offset amount and positional offset direction by the positional offset amount / direction calculation part of FIG.

  Hereinafter, a PET-CT apparatus according to an embodiment of the present invention will be described with reference to the drawings.

  The PET-CT apparatus according to the present embodiment checks the positional deviation between the PET image and the CT image using a tank phantom. The tank phantom is a phantom that is used for IQ (image quality) check performed on a PET-CT apparatus every day, that is, image quality check. The PET-CT apparatus according to this embodiment can be applied to any scene where the tank phantom can be practically used, such as during maintenance by a service person, regardless of the IQ check.

  FIG. 1 is a diagram illustrating a configuration of a PET-CT apparatus 1 according to the present embodiment. As shown in FIG. 1, the PET-CT apparatus 1 has a bed 2. The bed 2 supports the top plate 3 on which the tank phantom T is placed so as to be movable in the longitudinal direction, the lateral direction, and the vertical direction.

  FIG. 2 is a perspective view in which the tank phantom T and the line source L are arranged. As shown in FIG. 2, the tank phantom T has a cylindrical shape and has a diameter larger than that of the line source L. For example, the tank phantom T has a diameter of about 20 cm, and the line source L has a diameter of about 3 cm. In the tank phantom T and the line source L, radioisotopes are arranged uniformly. Radioisotopes repeatedly emit positrons. The emitted positron combines with surrounding electrons. When positrons and electrons are combined, a pair of gamma rays is emitted in the direction of about 180 degrees.

  The PET-CT apparatus 1 includes a CT scanner 4 and a PET scanner 5. The CT scanner 4 and the PET scanner 5 are each formed with a hollow portion 6 and a hollow portion 7 having a substantially cylindrical shape into which the top plate 3 is fed. The CT scanner 4 and the PET scanner 5 are arranged so that the center line of the hollow portion 6 and the center line of the hollow portion 7 substantially coincide.

  The CT scanner 4 performs a CT scan of the tank phantom T with X-rays. Specifically, the CT scanner 4 is mounted with an X-ray tube and an X-ray detector so as to face each other with the hollow portion 6 interposed therebetween. The X-ray tube generates X-rays. The X-ray detector detects X-rays generated from the X-ray tube and transmitted through the tank phantom T, and generates an electrical signal corresponding to the detected X-ray energy. The X-ray tube and the X-ray detector repeat X-ray generation and X-ray detection while rotating around the hollow portion 6.

  The PET scanner 5 scans the tank phantom T with gamma rays. Specifically, the PET scanner 5 includes a gamma ray detector arranged in a ring shape around the hollow portion 7. The gamma ray detector repeatedly detects the gamma rays emitted from the tank phantom T and repeatedly generates an electrical signal corresponding to the detected gamma ray energy.

  The PET-CT apparatus 1 further includes a data processing apparatus 10 that executes data processing. The data processing device 10 receives an electrical signal generated by the CT scanner 4. Further, the data processing device 10 receives an electrical signal generated by the PET scanner 5. The data processing device 10 detects a positional shift between the CT image based on the electrical signal from the CT scanner 4 and the PET image based on the electrical signal from the PET scanner 5. Further, the data processing apparatus 10 corrects the positional deviation between the CT image and the PET image according to the positional deviation amount and the positional deviation direction between the CT image and the PET image.

  FIG. 3 is a functional block diagram of the data processing apparatus 10. As shown in FIG. 3, the data processing apparatus 10 includes a CT projection data collection unit 11, a PET projection data collection unit 13, a storage unit 15, a CT image generation unit 17, an attenuation correction unit 19, a PET image generation unit 21, a positional deviation. It has a detection unit 23, a positional deviation amount / direction calculation unit 25, a positioning unit 27, a display unit 29, an operation unit 31, and a control unit 33.

  The CT projection data collection unit 11 performs preprocessing on the electrical signal from the CT scanner 4 and collects projection data (hereinafter referred to as CT projection data). Preprocessing for generating CT projection data includes logarithmic conversion, sensitivity correction, beam hardening correction, and the like.

  The PET projection data collection unit 13 performs signal processing on the electrical signal from the PET scanner 5 to generate projection data (hereinafter referred to as PET projection data). The signal processing includes position calculation processing, energy calculation processing, coincidence counting processing, preprocessing, and the like. The pre-processing for generating the PET projection data includes, for example, sensitivity correction, random correction, and scattered ray correction.

  The storage unit 15 stores CT projection data and PET projection data. The CT projection data is stored in association with the X-ray incident position and angle on the X-ray detector, for example. The PET projection data is stored in association with the gamma ray incident position and angle on the gamma ray detector, for example.

  The CT image generation unit 17 generates CT image data related to a predetermined reconstruction cross section based on the CT projection data. The pixel value assigned to each pixel constituting the CT image has a CT value corresponding to the X-ray attenuation coefficient (absorption coefficient) related to the substance on the X-ray transmission path. The CT image includes a tank phantom area that is a pixel area corresponding to the tank phantom T.

  The attenuation correction unit 19 attenuates and corrects the PET projection data based on the CT image. The attenuation-corrected PET projection data relates to the reconstructed cross section calculated to be a reconstructed cross section that is substantially the same as the reconstructed cross section of the CT image. Specifically, the attenuation correction unit 19 first generates a gamma ray attenuation correction map based on the CT image. The attenuation correction map is generated by calculating a gamma ray attenuation coefficient by applying a predetermined conversion formula to the CT value. Then, the attenuation correction unit 19 attenuates and corrects the PET projection data by multiplying the attenuation correction map with the PET projection data.

  The PET image generation unit 21 generates PET image data related to the reconstructed cross section at substantially the same position as the reconstructed cross section of the CT image, based on the PET projection data subjected to attenuation correction. The pixel value assigned to each pixel constituting the PET image has a count value corresponding to the concentration of the radioisotope. The PET image includes a tank phantom area that is a pixel area corresponding to the tank phantom T. It is assumed that the tank phantom area on the PET image and the tank phantom area on the CT image are misaligned. Here, the positional deviation means that the two tank phantoms are not at the same coordinates (coordinates defined on the image).

  The misregistration detection unit 23 detects misregistration between the CT image and the PET image based on the difference between the CT image and the PET image. Specifically, the positional deviation detection unit 23 determines whether or not the difference is larger than a threshold value. When it is determined that the difference is larger than the threshold value, the positional deviation detection unit 23 determines that a positional deviation has occurred between the CT image and the PET image. When it is determined that the difference is smaller than the threshold value, the positional deviation detection unit 23 determines that no positional deviation has occurred between the CT image and the PET image.

  The positional deviation amount / direction calculation unit 25 calculates the positional deviation amount and the positional deviation direction between the CT image and the PET image. Specifically, the positional deviation amount / direction calculation unit 25 calculates the distance and direction between the center of the tank phantom region on the CT image and the center of the tank phantom region on the PET image. The calculated distance is the amount of displacement, and the calculated direction is the displacement direction.

  The alignment unit 27 aligns the CT image and the PET image according to the displacement amount and the displacement direction.

  The display unit 29 displays the aligned CT image and PET image in an overlapping manner. Further, the display unit 29 displays information indicating that the positional deviation has been detected when the positional deviation detection unit 23 detects the positional deviation. On the other hand, when the positional deviation detection unit 23 does not detect the positional deviation, the display unit 29 displays information indicating that no positional deviation has been detected.

  The operation unit 31 receives instructions and information input from a user via an input device. As an input device, a keyboard, a mouse, various switches, a touch panel, and the like can be used.

  The control unit 33 functions as the center of the data processing device 10. The control unit 33 controls each unit to perform a positional deviation detection process between the CT image and the PET image and an alignment display process between the CT image and the PET image.

  Next, the operation of the PET-CT apparatus 1 will be specifically described. First, the misregistration detection process performed by the misregistration detection unit 23 according to control by the control unit 33 will be described.

  As described above, the displacement detection unit 23 detects the displacement between the CT image and the PET image based on the difference between the CT image and the PET image. The positional deviation detection unit 23 uses, for example, a non-uniform count distribution diagram generated based on the difference between the CT image and the PET image as the difference between the CT image and the PET image.

  First, the generation process of the non-uniform count distribution map generated by the misalignment detection unit 23 will be described with reference to FIG. In the following description, it is assumed that the pixel value range that can be taken by the tank phantom region on the CT image is converted (scaled) to the pixel value range that can be taken by the tank phantom region on the PET image.

  FIG. 4A is a diagram showing a superimposed image of a PET image and a CT image arranged in a single coordinate system (hereinafter referred to as an image processing coordinate system). In the superimposed image, a tank phantom region TRP on the PET image and a tank phantom region TRC on the CT image are overlaid. The CT image and the PET image are images related to the axial cross section of the tank phantom. As shown in FIG. 4A, the center of the image processing coordinate system is coincident with the center PS of the center point PP of the tank phantom area TRP and the center point PC of the tank phantom area TRC. In the image processing coordinate system, the x direction is defined as the transverse direction of the top 3 and the y direction is defined as the vertical direction of the top 3. In order to explain specifically, it is assumed that the tank phantom region TRC and the tank phantom region TRP are displaced along the x-axis. As the cause of the positional deviation, for example, the positional deviation of the tank phantom T on the top board 3, the deviation of the photographing position between the CT scanner 4 and the PET scanner 5, and the like can be mentioned.

  First, as shown in FIG. 4A, a plurality of lines S (for example, S1, S2, S3) crossing the CT image and the PET image are set on the image processing coordinate system. The plurality of lines S are set parallel to each other. Here, for simplicity of explanation, it is assumed that a plurality of lines S whose angles with respect to the x axis are 0 degrees are set. The angle of the line S with respect to the x axis corresponds to the rotation angle θ of the generated non-uniform count distribution diagram. The value of the rotation angle θ can be arbitrarily set via the operation unit 31.

  As shown in FIG. 4B, when a plurality of lines S are set, a difference distribution diagram for each line S is generated. Specifically, the difference between the CT image and the PET image is calculated along the line S, and the calculated difference is plotted on a graph in which the vertical axis is a pixel value and the horizontal axis is a position on the line S. To do. When the plot is completed, the difference distribution diagram is completed. For example, the pixel value (difference) of the non-overlapping portion on the difference distribution diagram has the value V1, and the pixel value of the overlapping portion has the value 0.

  As shown in FIG. 4 (c), when the difference distribution chart for each line S is generated, the difference distribution chart for each line S is added and averaged to generate a difference distribution chart (non-uniform count distribution chart) for the rotation angle θ. . In other words, the non-uniform count distribution diagram relating to the rotation angle θ is a projection of the difference distribution diagram relating to each line S from the normal direction of each line S. The position coordinate center of the non-uniform count distribution diagram corresponds to the center point PS of the image processing coordinate system. The non-uniform count distribution diagram is line symmetric with respect to the center line LA. This is because the CT scanner 4 and the PET scanner 5 scan the same tank phantom T, so the diameter of the tank phantom region TRC on the CT image is the same as the diameter of the tank phantom region TRP on the PET image. To do.

  Next, the positional deviation detection process by the positional deviation detection unit 23 will be described. FIG. 5 is a diagram showing non-uniform count distribution diagrams in the case where there is no positional deviation between the CT image and the PET image. FIG. 5A shows a case where there is no positional deviation, and FIG. 5B shows a case where there is a positional deviation. As shown in FIG. 5A, when there is no positional deviation, in an ideal system without noise, the pixel value on the non-uniform count distribution chart becomes a constant value regardless of the position. The constant value is a difference between a pixel value that can be taken by the tank phantom region TRC and a pixel value that can be taken by the tank phantom region TRP. The constant value is 0 in the case of FIG. On the other hand, as shown in FIG. 5B, when there is a positional shift, in an ideal system without noise, the pixel value of the portion where the tank phantom TRC and the tank phantom region TRP overlap is a constant value (FIG. 5). In this case, the pixel value of the portion that has 0) and does not overlap has a value larger than a certain value (0 in FIG. 5).

  The misregistration detection unit 23 detects misregistration between the CT image and the PET image by using such characteristics of the non-uniform count distribution diagram. Specifically, the positional deviation is detected based on the pixel value of the non-uniform count distribution chart and the threshold Th. For example, the lower limit of the threshold Th is 0, and the upper limit is the minimum pixel value that can be taken by the tank phantom area. Then, the magnitude relation between the threshold value Th set to such a value and the pixel value on the non-uniform count distribution chart is compared. If the non-uniform count distribution chart has a pixel value larger than the threshold value Th, it is determined that a positional deviation has occurred between the CT image and the PET image. Note that the value of the threshold Th can be arbitrarily set via the operation unit 31.

  When it is determined that the positional deviation has occurred, the display unit 29 displays a message indicating that the positional deviation has occurred, for example, “position deviation has been detected”. On the other hand, if the non-uniform count distribution map does not have a pixel value larger than the threshold Th, it is determined that no positional deviation has occurred between the CT image and the PET image. When it is determined that no positional deviation has occurred, the display unit 29 displays a message indicating that no positional deviation has occurred, for example, “No positional deviation was detected”.

  When the position shift is detected by the position shift detector 23, it is preferable to display the CT image and the PET image in alignment. For example, when a message indicating that a displacement has been detected is displayed on the display unit 29, the user inputs an instruction to start the alignment process via the operation unit 31. When the start instruction is input, the control unit 33 starts the alignment display process.

  In the alignment display processing, first, the positional deviation amount / direction calculation unit 25 performs calculation processing of the positional deviation amount and the positional deviation direction. FIG. 6 is a diagram showing a tank phantom region TRP on the PET image and a tank phantom region TRC on the CT image arranged on a single coordinate system (hereinafter referred to as a PET center position coordinate system). . The center of the PET center position coordinate system coincides with the center point PP of the tank phantom region TRP. The x direction of the PET center position coordinate system is defined as the transverse direction of the top 3 and the y direction is defined as the vertical direction of the top 3.

  The positional deviation amount / direction calculating unit 25 first arranges the tank phantom region TRP and the tank phantom region TRC in the PET center position coordinate system while maintaining the relative positional relationship with each other. More specifically, the distance D between the center point PP of the tank phantom area TRP and the center point PC of the tank phantom area TRC in the PET position coordinate system is the center point coordinates of the tank phantom area on the PET image and the tank phantom on the CT image. It arrange | positions so that it may become equal to the space | interval with the center point coordinate of an area | region. Then, the positional deviation amount / direction calculation unit 25 calculates the interval D between the center point PP and the center point PC. The calculated interval D is the amount of displacement. Further, the positional deviation amount / direction calculation unit 25 calculates the direction from the center point PP to the center point PC. For example, the rotation angle θ from the x axis in the PET center position coordinate system to the axis A connecting the center point PP and the center point PC is calculated. The calculated rotation angle θ is the misalignment direction.

  When the position shift amount and the position shift direction are calculated, the alignment unit 27 moves the tank phantom region TRC by the position shift amount D along the position shift direction θ so that the center point PC and the center point PP coincide. Shift. As a result, the CT image and the PET image are aligned. The aligned CT image and PET image are displayed on the display unit 29. The user can carry out IQ check and the like with high accuracy by observing the aligned CT image and PET image.

  As described above, the PET-CT apparatus 1 according to the present embodiment can detect and correct a positional deviation between the CT image and the PET image by using the tank phantom instead of the line source. Since the PET-CT apparatus 1 uses a tank phantom, it is possible to detect and correct misalignment at the time of IQ check performed by the customer every day, instead of during regular maintenance about four times a year. As a result, the PET-CT apparatus 1 can display images with high positional alignment accuracy every day. In addition, since the detection / correction time is not limited to regular maintenance, it is possible to easily detect and correct misalignment at a time desired by the customer. Furthermore, by using the tank phantom, not only customers but also service personnel who perform regular maintenance can easily detect and correct misalignment. Further, since it is not necessary to purchase a line source, the maintenance cost of the PET-CT apparatus 1 can be reduced.

  Thus, according to the present embodiment, it is possible to provide a PET-CT apparatus that facilitates confirmation of positional deviation between a PET image and a CT image.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  As described above, according to the present invention, it is possible to provide a PET-CT apparatus that facilitates confirmation of positional deviation between a PET image and a CT image.

  DESCRIPTION OF SYMBOLS 1 ... PET-CT apparatus, 2 ... Bed, 3 ... Top plate, 4 ... CT scanner, 5 ... PET scanner, 6 ... Hollow part, 7 ... Hollow part, 10 ... Data processing apparatus, 11 ... CT projection data collection part, DESCRIPTION OF SYMBOLS 13 ... PET projection data collection part, 15 ... Memory | storage part, 17 ... CT image generation part, 19 ... Attenuation correction part, 21 ... PET image generation part, 23 ... Position shift detection part, 25 ... Position shift amount / direction calculation part, 27 ... Positioning unit, 29 ... Display unit, 31 ... Operation unit, 33 ... Control unit

Claims (5)

A first generator for generating CT image data relating to the tank phantom;
A detector for detecting gamma rays emitted from the tank phantom;
A collection unit that collects projection data relating to the tank phantom via the detector;
An attenuation correction unit that attenuates and corrects the projection data based on the CT image;
A second generator for generating PET image data relating to the tank phantom based on the attenuation-corrected projection data;
A detection unit that detects a positional deviation between the CT image and the PET image based on a difference between the CT image and the PET image;
PET-CT apparatus comprising:   A display unit displaying a message indicating that the positional deviation has been detected when the detection unit is detected; and displaying a message indicating that the positional deviation has not been detected when the positional deviation is not detected by the detection unit. The PET-CT apparatus according to claim 1, further comprising:   The PET-CT apparatus according to claim 2, wherein the detection unit detects the displacement based on a magnitude relationship between the difference and a threshold value. A first generator for generating CT image data relating to the tank phantom;
A detector for detecting gamma rays emitted from the tank phantom;
A collection unit that collects projection data relating to the tank phantom via the detector;
An attenuation correction unit that attenuates and corrects the projection data based on the CT image;
A second generator for generating PET image data relating to the tank phantom based on the attenuation-corrected projection data;
A calculation unit that calculates the distance and direction between the center of the tank phantom region on the CT image and the center of the tank phantom region on the PET image;
An alignment unit that aligns the CT image and the PET image based on the calculated distance and direction;
PET-CT apparatus comprising:   The PET-CT apparatus according to claim 4, further comprising a display unit that displays the aligned CT image and the PET image in an overlapping manner.

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