JP5672061B2 - Positron emission tomography system - Google Patents

Description

  The present invention relates to a positron emission tomography apparatus that detects paired annihilation photons from a subject to which a radiopharmaceutical has been administered and images the distribution of the radiopharmaceutical in the subject, and more particularly to a technique for positioning the subject. .

  A positron emission tomography apparatus (also referred to as a PET (Positron Emission Tomography) apparatus: hereinafter referred to as “PET apparatus” as appropriate) is a 511 keV pair annihilation photon emitted in a 180 ° opposite direction from a subject administered with a radioactive drug ( For example, γ rays (hereinafter referred to as “γ rays” as appropriate) are detected by a detector ring in which a plurality of detectors provided in the PET gantry are arranged in a ring shape. The time when this γ-ray is detected is measured, and when the difference in detection time between the two detectors is within a certain time, it is counted as a pair of γ-rays (simultaneous counting). And the generation | occurrence | production point of a gamma ray is specified as what exists on the straight line of the two detectors. Thus, data of a line connecting the detectors from which two γ-rays are detected, that is, LOR (Line of Response) data is collected and accumulated, and reconstruction processing is performed to obtain a tomographic image.

  In addition, since it is known that the speed of γ-ray is about 30 cm / ns, there is a method for identifying the generation point of γ-ray from the difference in detection time of γ-ray counted simultaneously by two detectors. . Gamma ray generation point data acquired by this method, that is, TOF (time of flight) data is collected and accumulated, and image reconstruction processing is performed to obtain a tomographic image (see, for example, Patent Document 1). ).

International Publication No. 2008/102422

  However, the conventional example having such a configuration has the following problems. In other words, the conventional PET apparatus can image any object in any position in the detector ring. However, when the centers of a plurality of detectors arranged in a ring shape, that is, the center and end of the gantry are compared, the spatial resolution changes greatly as shown in FIG. This is because the spatial resolution deteriorates due to the fact that γ-rays enter from an oblique direction and are detected by an adjacent detector as it is located at the end (that is, the coincidence count of the adjacent detector is counted). Excluding true coincidence counts reduced). For example, when the spatial resolution of two points separated by 2 cm in the radial direction of the detector ring is compared between the center and the end of the gantry, the spatial resolution is high at the two points and the difference (change amount) is small. On the other hand, at the end, the resolution is low and the difference is large. Therefore, it is preferable to place the subject at the center of the gantry having a high spatial resolution and a small difference in spatial resolution. In the case of collection for correction such as normalization and cross calibration using a phantom, collection is performed on the assumption that the phantom is arranged at the center of the country. In order to obtain an accurate correction value, it is preferable to place the phantom at the center of the gantry with high accuracy.

  However, in the conventional PET apparatus, the operator manually positions the subject in the cross section and in the body axis direction by using a laser marker or the like. That is, the operator positions the subject by visually moving a top plate or the like on which the subject including the phantom is placed vertically and horizontally. Therefore, the position is finally determined by the subjectivity of the operator, and the position or the like varies depending on the operator or the like.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a positron emission tomography apparatus capable of facilitating positioning of a subject.

  In order to achieve such an object, the present invention has the following configuration. That is, the positron emission tomography apparatus according to the present invention is configured to detect pair annihilation photons emitted from a subject to which a radiopharmaceutical is administered, in which a detector ring in which a plurality of detectors are arranged in a ring shape is configured in multiple layers. A multi-layer detector ring for detection, and a TOF data collecting unit for collecting TOF data indicating a generation point of pair annihilation photons calculated from a difference in detection time of pair annihilation photons simultaneously counted by two detectors of the multi-layer detector ring A positional deviation amount detection unit for detecting a positional deviation amount between a central axis position of the multilayer detector ring and a central position of a vertical section of the subject using the collected TOF data, and based on the positional deviation amount And a mechanism control unit that moves the center position of the vertical cross section of the subject to the center axis position of the multilayer detector ring.

  According to the positron emission tomography apparatus according to the present invention, the TOF data collection unit determines the generation point of the pair annihilation photon calculated from the difference in detection time of the pair annihilation photon simultaneously counted by the two detectors of the multilayer detector ring. The positional deviation amount detection unit detects the positional deviation amount between the central axis position of the multilayer detector ring and the central position of the vertical cross section of the subject using the collected TOF data. The mechanism control unit moves the center position of the vertical cross section of the subject to the center axis position of the multilayer detector ring based on the positional deviation amount. That is, the collected TOF data can be used to easily position the subject to the center position of the multilayer detector ring. Thereby, the subject can be moved to the central axis position of the multilayer detector ring without depending on the subjectivity of the operator.

  Further, in the positron emission tomography apparatus according to the present invention, the displacement amount detection unit detects a boundary between both ends of the subject from TOF data on a coincidence line passing through a central axis of a plurality of detectors arranged in a ring shape. A center position of the subject boundary detection unit and a boundary between both ends of the subject, and a position shift for calculating a positional shift amount between the center axis position of the multilayer detector ring and the center position of the boundary between the subject ends. It is preferable to include an amount calculation unit, a maximum value extraction unit that extracts the maximum value from the positional deviation amount, and a coordinate conversion unit that converts the maximum value of the positional deviation amount into coordinates. That is, the misregistration amount detection unit first detects the boundary between both ends of the subject from the TOF data on the coincidence line passing through the centers of a plurality of detectors arranged in a ring shape among the collected TOF data. Then, the center position is calculated from the boundary between both ends of the subject, and the positional shift amount between the center axis position of the multilayer detector ring and the center position of the boundary between both ends of the subject is calculated. The maximum value is extracted from the calculated positional deviation amount, and the maximum value of the positional deviation amount is converted into coordinates. Thereby, it is possible to easily detect the displacement amount of the subject using the TOF data.

  In addition, the positron emission tomography apparatus according to the present invention includes a pair of annihilation photons emitted from a subject to which a radiopharmaceutical is administered, in which a detector ring in which a plurality of detectors are arranged in a ring shape is formed in multiple layers. A multi-layer detector ring to be detected, a LOR data collecting unit for collecting LOR data indicating a line connecting two detectors simultaneously counted by the multi-layer detector ring, and a projection data of the collected LOR data are created. A projection data generation unit; a positional deviation amount detection unit that detects a positional deviation amount between a central axis position of the multilayer detector ring and a central position of a vertical section of the subject using the projection data; and the positional deviation amount. And a mechanism control unit that moves the center position of the vertical cross section of the subject to the center axis position of the multilayer detector ring.

  According to the positron emission tomography apparatus according to the present invention, the LOR data collection unit collects LOR data indicating a line connecting two detectors simultaneously counted by the multilayer detector ring, and the projection data creation unit collects the data. The projection data of the LOR data thus created is created. The positional deviation amount detection unit detects the positional deviation amount between the central axis position of the multilayer detector ring and the central position of the vertical section of the subject using the created projection data. The mechanism control unit moves the center position of the vertical cross section of the subject to the center axis position of the multilayer detector ring based on the amount of displacement. In other words, it is possible to easily position the subject within the multilayer detector ring using projection data created to obtain a tomographic image from the collected TOF data. Thereby, the subject can be moved to the central axis position of the multilayer detector ring without depending on the subjectivity of the operator.

  In the positron emission tomography apparatus according to the present invention, the positional deviation amount detection unit includes a subject boundary detection unit that detects a boundary between both ends of the subject from the projection data, and a center position from the boundary between both ends of the subject. A positional deviation amount calculation unit for calculating a positional deviation amount between the central axis position of the multilayer detector ring and the center position of the boundary between both ends of the subject, and a maximum value for extracting the maximum value from the positional deviation amount It is preferable to include an extraction unit and a coordinate conversion unit that converts the maximum value of the positional deviation amount into coordinates. That is, the positional deviation amount detection unit detects the boundary between both ends of the subject using the projection data created by collecting the LOR data, calculates the center position from the boundary between both ends of the subject, and detects multiple layers. The amount of positional deviation between the center axis position of the instrument ring and the center position of the boundary between both ends of the subject is calculated. Then, the maximum value is extracted from the calculated positional deviation amount, and the maximum value of the positional deviation amount is converted into coordinates. Thereby, it is possible to easily detect the positional deviation amount of the subject using the projection data.

Moreover, in the positron emission tomography apparatus according to the present invention, the positional deviation amount detection unit includes a predetermined position in the body axis direction of the subject and a center position in the layer direction of the multilayer detector ring in the body axis direction of the subject. It is preferable that the amount of positional deviation is detected, and the mechanism control unit moves the predetermined position to the center position in the layer direction of the multilayer detector ring based on the amount of positional deviation of the subject in the body axis direction. In the layer direction of the multilayer detector ring, the spatial resolution is higher at the center of the detector rings arranged in multiple layers. Therefore, for example, when the length of the subject in the body axis direction is smaller than the length of the multilayer detector ring in the layer direction (effective field of view), the positional deviation amount detection unit detects the boundary between both ends of the subject, From the center position in the body axis direction of the subject and the center position in the layer direction of the multilayer detector ring, the amount of positional deviation in the body axis direction of the subject is detected. Then, the center position of the subject in the body axis direction is moved to the center position of the multilayer detector ring in the layer direction. Thereby, positioning of the subject in the body axis direction within the multilayer detector ring can be easily performed.

  According to the positron emission tomography apparatus according to the first aspect of the present invention, the TOF data collection unit includes a pair annihilation photon calculated from a difference between detection times of pair annihilation photons simultaneously counted by the two detectors of the multilayer detector ring. TOF data indicating the point of occurrence is collected, and the positional deviation amount detection unit uses the collected TOF data to determine the positional deviation amount between the central axis position of the multilayer detector ring and the central position of the vertical section of the subject. To detect. The mechanism control unit moves the center position of the vertical cross section of the subject to the center axis position of the multilayer detector ring based on the positional deviation amount. That is, the collected TOF data can be used to easily position the subject to the center position of the multilayer detector ring. Thereby, the subject can be moved to the central axis position of the multilayer detector ring without depending on the subjectivity of the operator.

  According to the positron emission tomography apparatus according to the second aspect of the present invention, the LOR data collection unit collects LOR data indicating a line connecting the two detectors simultaneously counted by the multilayer detector ring, and generates projection data. The unit creates projection data of the collected LOR data. The positional deviation amount detection unit detects the positional deviation amount between the central axis position of the multilayer detector ring and the central position of the vertical section of the subject using the created projection data. The mechanism control unit moves the center position of the vertical cross section of the subject to the center axis position of the multilayer detector ring based on the amount of displacement. In other words, it is possible to easily position the subject within the multilayer detector ring using projection data created to obtain a tomographic image from the collected TOF data. Thereby, the subject can be moved to the central axis position of the multilayer detector ring without depending on the subjectivity of the operator.

1 is a schematic configuration diagram of a positron emission tomography apparatus (PET apparatus) according to Example 1. FIG. It is a figure which shows an example of arrangement | positioning of the detector seen from the A direction of FIG. It is a figure with which it uses for description of the positional offset amount detection part using TOF data. It is a figure with which it uses for description of the position shift amount detection part using TOF data, (a)-(d) shows the position shift amount on the coincidence line which connects the detector pair in each angle. 3 is a flowchart for explaining automatic positioning of a subject according to the first embodiment. 3 is a schematic configuration diagram of a positron emission tomography apparatus (PET apparatus) according to Example 2. FIG. It is a figure with which it uses for description of the position shift amount detection part using a sinogram, (a)-(d) shows the projection data in each angle. It is a figure with which it uses for description of the position shift amount detection part using a sinogram, and is a figure which shows an example of a sinogram. It is a figure which shows an example of a sinogram which does not have a position shift. 10 is a flowchart for explaining automatic positioning of a subject according to a second embodiment. It is a figure where it uses for description of the automatic positioning of the body axis direction of the subject which concerns on a modification. It is a figure where it uses for description of the automatic positioning of the body axis direction of the subject which concerns on a modification. It is a figure with which it uses for description that spatial resolution differs by the center and edge of a gantry, a vertical axis | shaft shows the count of true coincidence, and a horizontal axis shows the radial direction of a gantry.

  Embodiment 1 of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of a positron emission tomography apparatus (PET apparatus) according to the first embodiment, and FIG. 2 is a diagram illustrating an example of the arrangement of detectors as viewed from the direction A in FIG. FIG. 3 is a diagram for explaining a positional deviation amount detection unit using TOF data, and FIG. 4 is a diagram for explaining a positional deviation amount detection unit using TOF data. ) Indicates the amount of positional deviation on the coincidence line connecting the detector pairs at each angle.

  Please refer to FIG. The PET apparatus 1 includes a bed apparatus 3 having a top plate 2 on which a subject M is placed and a gantry 5 having an opening 4. The bed apparatus 3 is configured to move the top 2 in the vertical direction (Y direction) and the horizontal direction (XZ direction). The bed apparatus 3 is controlled by the mechanism control unit 6 and moves the subject M placed on the top 2 to the inside or outside of the opening 4 of the gantry 5. A detector ring 7 that detects γ rays generated from the subject M is provided on the outer periphery of the opening 4 of the gantry 5.

  As shown in FIG. 2, the detector ring 7 includes a plurality of detectors 9 arranged in a ring shape including a polygonal shape. Further, as shown in FIG. 1, the detector ring 7 is configured to be stacked in multiple layers in the layer direction (the central axis direction or the body axis direction of the subject M). The detector ring 7 stacked in multiple layers is referred to as a multilayer detector ring 11. In the present embodiment, the detector ring 7 is described as being a multilayer detector ring 11 configured in multiple layers, but may be configured as a single layer.

  The detector 9 is composed of a detector block (not shown) including, for example, a scintillator block, a light guide, and a photomultiplier tube. The scintillator block is composed of a plurality of scintillators. The scintillator block converts γ-rays generated from the subject M to which the radiopharmaceutical is administered into light, and the light guide guides the converted light, and the photomultiplier tube photoelectrically converts and outputs an electrical signal. .

  The TOF data collection unit 13 collects TOF data indicating the generation point of pair annihilation γ-rays calculated from the difference in detection time of pair annihilation γ-rays simultaneously counted by the two detectors 9 of the multilayer detector ring 11. The image reconstruction unit 15 performs image reconstruction using the TOF data subjected to the correction process. Thereby, a tomographic image can be acquired.

  The correction table 17 stores a correction value for sensitivity correction for correcting variation for each detector 9 and a calibration coefficient obtained by cross calibration. The calibration factor converts the co-counted count into a radioactivity concentration (Bq / ml). Data collection for sensitivity correction is obtained by normalization collection. On the other hand, in the cross calibration, first, water in which a radiopharmaceutical is dissolved is put into a cylindrical phantom, and the cylindrical phantom is accommodated in the multilayer detector ring 11 to collect data. After collecting the data, remove a part of the water from the cylindrical phantom and measure the radioactivity concentration with a dose calibrator. Then, a calibration coefficient is obtained from the count collected by the multilayer detector ring 11 and the radiation concentration measured by the dose calibrator. The image reconstruction unit 15 performs image reconstruction with reference to the correction table.

  The PET apparatus 1 includes a main control unit 19, a display unit 21, a memory unit 23, and an input unit 25. The main control unit 19 controls each component centrally. The display unit 21 is composed of a liquid crystal display panel or the like, and displays a tomographic image obtained by reconstructing an image. The memory unit 23 stores tomographic images and the like, and is configured by a storage medium such as a ROM (Read-only Memory), a RAM (Random-Access Memory), or a hard disk. The input unit 25 is configured with input settings and various operations, and includes a keyboard, a mouse, and the like.

  In addition, the PET apparatus 1 includes a positional deviation amount detection unit 27 that detects the positional deviation amount between the central axis position of the multilayer detector ring 11 and the central position of the vertical cross section of the subject M using the collected TOF data. I have. As shown in FIG. 3, when the subject M is arranged inside a plurality of detectors 9 (detector rings 7) arranged in a ring shape, the positional deviation amount detection unit 27 includes the subject M. The amount of positional deviation between the center of the cross section perpendicular to the body axis and the center axis position of the plurality of detectors 9 arranged in a ring shape is detected. The positional deviation amount detection unit 27 includes an object boundary detection unit 29, a positional deviation amount calculation unit 31, a maximum value extraction unit 33, and a coordinate conversion unit 35.

  The subject boundary detection unit 29 detects the boundary between both ends of the subject M from the TOF data on the coincidence line passing through the centers of the plurality of detectors 9 arranged in a ring shape. That is, first, as shown in FIG. 3, the subject boundary detection unit 29 extracts the TOF data on the coincidence line passing through the centers of the plurality of detectors 9 from the TOF data collected by the TOF data collection unit 13. Extract at each angle. For example, when θ = 0 °, as shown in FIG. 4A, TOF data having the horizontal axis as the radial direction and the vertical axis as the count of occurrence positions of γ rays is extracted. When θ = 60 °, 90 °, and 150 °, TOF data shown in FIGS. 4B to 4D is extracted. Then, the subject boundary detection unit 29 detects the boundaries of both ends of the subject M from the extracted TOF data counts at the respective angles.

  The extracted TOF data has a gentle slope at both ends of the subject M. For detection of the boundary, for example, a half width is used. As shown in FIG. 4A, when the maximum value of the TOF data count is h, the full width at half maximum is the range sandwiched between the h / 2 radial positions of the profile curve. represented by r. A half-value width boundary (h / 2) is detected as a boundary between both ends of the subject M. Further, as shown in FIG. 3 or FIG. 4, the subject boundary detection unit 29 sequentially detects boundaries in the range of 0 ° to 180 °, for example, when the horizontal coincidence line is set to 0 °.

  Note that the subject boundary detection unit 29 is not limited to detecting the boundary between both ends of the subject M using the half width, and detects the boundary as long as the count is equal to or greater than a predetermined value. Also good.

  The positional deviation amount calculation unit 31 calculates the center position of the boundary of the subject M from the boundary between both ends of the subject M, and the positional deviation between the central axis position of the detector ring 7 and the central position of the boundary of the subject M. Calculate the amount. The center position of the boundary of the subject M is obtained from the center of the half width, that is, the boundary given by the half width. The center axis position of the detector ring 7 is obtained from the center position of the coincidence line from which the center position of the boundary of the subject M is obtained. Then, the amount of positional deviation is obtained from the difference between the center position of the boundary of the subject M and the center position of the coincidence counting line (FIGS. 4A to 4D). The detection of the positional deviation amount is sequentially performed in the range of 0 ° to 180 ° where the boundary is detected.

  The maximum value extraction unit 33 extracts the maximum value from the positional deviation amount. That is, the maximum value is extracted from the positional shift amount of each angle sequentially calculated by the positional shift amount calculation unit 31 in the range of 0 ° to 180 °. The maximum positional deviation amount on the coincidence line corresponds to the positional deviation amount between the center of the subject M and the central axis position of the multilayer detector ring 11.

  The coordinate conversion unit 35 converts the maximum value of the positional deviation amount into coordinates. That is, the coordinate conversion unit 35 decomposes the coordinates in the X direction and the Y direction from the positional deviation amount extracted by the maximum value extraction unit 33 and the angle of the coincidence line having the positional deviation amount.

  The positional deviation amount converted into the coordinates in the X direction and the Y direction by the coordinate conversion unit 35 is transmitted to the mechanism control unit 6. The mechanism control unit 6 moves the center position of the vertical cross section of the subject M to the center axis position of the detector ring 7 based on the amount of displacement. The mechanism control unit 6 operates the bed apparatus 3 to move the top plate 2 on which the subject M is placed, so that the central position of the vertical cross section of the subject M is the central axis position of the multilayer detector ring 11. To match.

<Operation of PET apparatus 1>
Next, regarding the operation of the PET apparatus 1, an operation for aligning the center position of the vertical cross section of the subject M with the center axis position of the multilayer detector ring 11, that is, automatic positioning will be described. FIG. 5 is a flowchart for explaining the automatic positioning of the subject according to the first embodiment.

  The subject M is administered with a radiopharmaceutical labeled with a positron radioisotope (radioisotope: RI). Then, the bed apparatus 3 controlled by the mechanism control unit 6 drives the top plate 2 on which the subject M is placed, and moves the subject M to an arbitrary position within the opening 4 of the gantry 5.

[Step S01] Collection of TOF Data Two γ-rays radiated from the subject M in the opposite direction by 180 ° are detected by the detectors 9 of the multilayer detector ring 11. Based on the electrical signal (detection signal) output from each detector 9, the TOF data collection unit 13 is calculated from the detection time difference of the pair annihilation photons simultaneously counted by the two detectors 9 of the multilayer detector ring 11. Collect TOF data indicating the point of occurrence of pair annihilation photons.

[Step S02] Detection of subject boundary From the collected TOF data, the subject boundary detection unit 29 detects the subject boundary from TOF data on a coincidence line passing through the centers of a plurality of detectors 9 arranged in a ring shape. A boundary between both ends of the specimen M is detected. The detection of the boundary is performed, for example, by obtaining a half width, and is performed from the TOF data on the coincidence line having an angle of 0 ° to 180 °.

[Step S03] Calculation of Misalignment The misalignment calculating unit 31 calculates the center position of the subject M from the boundaries of both ends of the subject M on the detected simultaneous counting lines of the respective angles, and multi-layer detector rings. A positional deviation amount between the center axis position of 11 and the center position of the subject M boundary is calculated.

[Step S04] Extraction of Maximum Value The maximum value extraction unit 33 extracts the maximum value from the amount of positional deviation of the subject M on the coincidence counting line of each calculated angle. The maximum positional deviation amount on the coincidence line passing through the central axis of the detector ring 7 corresponds to the actual positional deviation amount between the central position of the vertical cross section of the subject M and the central axis position of the detector ring 7.

[Step S05] Coordinate Conversion The coordinate conversion unit 35 converts the maximum value of the extracted positional deviation amount into coordinates in the X direction and the Y direction.

[Step S06] Alignment The amount of displacement of the subject M detected by being converted into coordinates in the X direction and the Y direction is transmitted to the mechanism control unit 6. The mechanism control unit 6 controls the top plate 2 of the bed apparatus 3 to perform alignment so that the center position of the vertical cross section of the subject M coincides with the center axis position of the detector ring 7. That is, the alignment is performed so that the positional deviation amount becomes 0 (zero). As described above, automatic positioning of the subject M is performed.

  Thereafter, correction data to be stored in the correction table 17 such as normalization and cross calibration is collected using a phantom (subject M). Further, actual data collection is performed to obtain an RI distribution image such as a tomographic image of the subject M.

  According to the PET apparatus 1 according to the present embodiment, the TOF data collection unit 13 determines the generation point of the γ ray calculated from the difference in the detection time of the γ ray simultaneously counted by the two detectors 9 of the multilayer detector ring 11. The positional deviation amount detection unit 27 detects the positional deviation amount between the central axis position of the multilayer detector ring 11 and the central position of the vertical cross section of the subject M using the collected TOF data. To do. The mechanism control unit 6 moves the center position of the vertical section of the subject M to the center axis position of the multilayer detector ring 11 based on the amount of displacement. That is, it is possible to easily position the subject M to the center position of the multilayer detector ring 11 using the collected TOF data. Thereby, the subject M can be moved to the center axis position of the multilayer detector ring 11 without depending on the subjectivity of the operator.

  Thereby, it is possible to perform imaging in a state where the center position of the vertical cross section of the subject M is aligned with the center axis position of the multilayer detector ring 11. Therefore, in the case of collection for correction such as normalization or cross calibration using a phantom, an accurate correction value can be obtained, and a tomographic image with high spatial resolution can be obtained.

  Next, Embodiment 2 of the present invention will be described with reference to the drawings. FIG. 6 is a schematic configuration diagram of a positron emission tomography apparatus (PET apparatus) according to the second embodiment. FIG. 7 is a diagram for explaining a positional deviation amount detection unit using a sinogram, and (a) to (d) show projection data at each angle. Note that the description of the same configuration as that of the above-described embodiment is omitted.

  In the first embodiment, the PET apparatus 1 that performs automatic positioning using TOF data has been described. In the second embodiment, a PET apparatus 41 that performs automatic positioning using sinograms will be described.

  Please refer to FIG. The PET apparatus 41 includes an LOR data collection unit 43 that collects LOR (Line of Response) data indicating a line connecting the two detectors 9 that are simultaneously counted by the multilayer detector ring 11, and projection data of the collected LOR data. A projection data creation unit 45 for creating

  As shown in FIG. 7A, it is assumed that the subject M is arranged inside a plurality of detectors 9 (detector rings 7) arranged in a ring shape. The projection data creation unit 45 creates projection data for each angle, and creates a sinogram by arranging the projection data for each angle in order. As shown in FIGS. 7A to 7D, the projection data creation unit 45 creates, for example, projection data of 0 ° to 180 °, and arranges the projection data of each angle in order as shown in FIG. Create a sinogram with FIG. 8 is a diagram illustrating an example of a sinogram.

  The positional deviation amount detection unit 47 detects the positional deviation amount between the central axis position of the detector ring 7 and the central position of the vertical section of the subject M, using the sinogram created by the projection data creation unit 45. As shown in FIG. 6, the positional deviation amount detection unit 47 includes a subject boundary detection unit 51, a positional deviation amount calculation unit 53, a maximum value extraction unit 55, and a coordinate conversion unit 57.

  The subject boundary detection unit 51 detects the boundaries of both ends of the subject M from the sinogram. That is, the subject boundary detection unit 51 detects the boundary positions of both ends of the subject M from the projection data at each angle of the sinogram (FIG. 8) created by the projection data creation unit 45. First, the subject boundary detection unit 51 extracts projection data at each angle as shown in FIGS. As the projection data at each angle, for example, θ = 0 ° shown in FIG. 7A is given with the horizontal axis representing the radial direction and the vertical axis representing the LOR count. At both ends of the subject M, the count has a gentle slope. Then, the subject boundary detection unit 51 detects, from the extracted projection data at each angle, the position in the radial direction of the ½ value of the maximum count as a boundary using, for example, a half width. Further, if the count is not less than a predetermined value set in advance, it may be detected as a boundary of the subject M.

  The positional deviation amount calculation unit 53 calculates the center position from the boundary between both ends of the subject M, and calculates the positional deviation amount between the central axis position of the multilayer detector ring 11 and the central position of the boundary between both ends of the subject M. . The positional deviation amount calculation unit 53 obtains the center position using the boundary positions of both ends of the subject M detected from the projection data of each angle of the sinogram. Then, the positional deviation amount calculation unit 53 calculates the positional deviation amount between the center position of the boundary between both ends of the subject M and the central axis position of the detector ring 7. At this time, the center axis positions of the plurality of detectors 9 arranged in a ring shape correspond to the center positions in the horizontal axis direction shown in FIG. 8 of the sinogram. That is, the horizontal axis of the sinogram indicates the radial direction of the plurality of detectors 9 arranged in a ring shape, and the center position thereof becomes the center axis position of the detector ring 7.

  The maximum value extraction unit 55 extracts the maximum value from the positional deviation amount calculated by the positional deviation amount calculation unit 53. The maximum value extraction unit 55 extracts the maximum value from the positional deviation amount of the projection data at each angle of the sinogram. The maximum value of the positional deviation amount, that is, the positional deviation amount of the projection data at the angle having the maximum positional deviation amount corresponds to the actual positional deviation amount.

  The coordinate conversion unit 57 converts the maximum value of the positional deviation amount into coordinates. That is, the coordinate conversion unit 57 decomposes the coordinates in the X direction and the Y direction from the positional deviation amount extracted by the maximum value extraction unit 55 and the angle of the projection data having this positional deviation amount.

  The positional deviation amount converted into the X-direction and Y-direction coordinates by the coordinate conversion unit 57, that is, the positional deviation amount output from the positional deviation amount detection unit 47 is transmitted to the mechanism control unit 6. The mechanism control unit 6 moves the center position of the vertical cross section of the subject M to the center axis position of the detector ring 7 based on the transmitted positional deviation amount. That is, the mechanism control unit 6 controls the bed apparatus 3 to move the center position of the vertical cross section of the subject M placed on the top 2 to the center position of the detector ring 7 so as to match. FIG. 9 shows a sinogram having no positional deviation.

<Operation of PET apparatus 41>
Next, regarding the operation of the PET apparatus 41, automatic positioning of the subject M will be described in particular. FIG. 10 is a flowchart for explaining the automatic positioning of the subject according to the second embodiment.

  A radiopharmaceutical is administered to the subject M. Then, the mechanism control unit 6 controls the bed apparatus 3 to drive the top 2 on which the subject M is placed, and moves the subject M to an arbitrary position within the opening 4 of the gantry 5.

[Step S11] Collection of LOR Data Two γ rays radiated from the subject M in the opposite direction by 180 ° are detected by the detectors 9 of the multilayer detector ring 11. Based on the electrical signal (detection signal) output from each detector 9, the LOR data collection unit 43 collects LOR data indicating a line connecting the two detectors 9 that are simultaneously counted by the detector ring 9.

[Step S12] Creation of Sinogram The projection data creation unit 45 creates projection data at each angle (for example, 0 ° to 180 °) from the LOR data collected by the LOR data collection unit 43 as shown in FIG. A sinogram is created by arranging projection data for each angle in order.

[Step S13] Detection of the Boundary of the Subject The subject boundary detection unit 51 detects the boundary positions at both ends of the subject M from the projection data at each angle of the sinogram. The subject boundary detection unit 51 detects the boundary using, for example, a half width.

[Step S14] Calculation of Misalignment The misalignment calculating unit 53 calculates the center position from the boundary of both ends of the subject M, and the center position of the center axis of the detector ring 7 and the boundary of both ends of the subject M. The positional deviation amount is calculated.

[Step S15] Extraction of Maximum Value The maximum value extraction unit 55 extracts the maximum value from the positional deviation amount calculated by the positional deviation amount calculation unit 53.

[Step S16] Coordinate Conversion The coordinate conversion unit 57 converts the maximum value of the extracted positional deviation amount into coordinates in the X direction and the Y direction.

[Step S <b> 17] Positioning The position shift amount of the center of the subject M detected by being converted into coordinates in the X direction and the Y direction is transmitted to the mechanism control unit 6. The mechanism control unit 6 controls the top plate 2 of the bed apparatus 3 to perform alignment so that the center position of the vertical cross section of the subject M coincides with the center axis position of the multilayer detector ring 11.

  According to the PET apparatus 41 according to the present embodiment, the LOR data collection unit 43 collects LOR data indicating a line connecting two detectors 9 that are simultaneously counted by the multilayer detector ring 11, and generates a projection data creation unit 45. Creates projection data of the collected LOR data. The positional deviation amount detection unit 47 detects the positional deviation amount between the central axis position of the multilayer detector ring 11 and the central position of the vertical section of the subject M using the created projection data. The mechanism control unit 6 moves the center position of the vertical section of the subject M to the center axis position of the multilayer detector ring 11 based on the amount of displacement. That is, it is possible to easily position the subject M within the multilayer detector ring 11 using projection data created to obtain a tomographic image from the collected TOF data. Thereby, the subject M can be moved to the center axis position of the multilayer detector ring 11 without depending on the subjectivity of the operator.

  Thereby, it is possible to perform imaging in a state where the center position of the vertical cross section of the subject M is aligned with the center axis position of the multilayer detector ring 11. Therefore, in the case of collection for correction such as normalization or cross calibration using a phantom, an accurate correction value can be obtained, and a tomographic image with high spatial resolution can be obtained.

  The present invention is not limited to the above embodiment, and can be modified as follows.

  (1) In each of the above-described embodiments, a positional deviation amount in a cross section substantially perpendicular to the body axis of the subject M is detected, and a plurality of the center positions of the subject M arranged in a ring shape are detected. It was moved so as to coincide with the center position of the detector 9. However, it is also possible to detect the amount of positional deviation in the body axis direction of the subject M of the multilayer detector ring 11 and move it so as to coincide with the center of the multilayer detector ring 11 in the layer direction. In the layer direction of the detector ring 7 configured to be stacked in multiple layers, the sensitivity of the detector ring 7 at the center position is high, and the sensitivity decreases toward the outside.

  The positional deviation amount detection units 27 and 47 detect the positional deviation amount of the subject M in the body axis direction. The mechanism control unit 6 moves the center position of the subject M in the body axis direction to the center position in the layer direction of the detector ring 9 configured in multiple layers based on the positional deviation amount of the subject M in the body axis direction. .

  In the case of a phantom or the like in which the subject M is entirely contained in the multilayer detector ring 11 (FIG. 11), the positional deviation amount detection units 27 and 47 detect the boundary between both ends of the phantom (subject M) in the body axis direction. Then, the center position is calculated. Then, the mechanism control unit 6 moves the subject M so as to coincide with the center position of the multilayer detector ring 11 in the layer direction.

  Further, when the length of the subject M in the body axis direction is larger than the multilayer detector ring 11 (for example, when aligning the head of the subject M) (FIG. 12), for example, one end of the head is used as a reference position. The mechanism control unit detects the boundary in the body axis direction of the head (subject M) and makes the center position of the multilayer detector ring 11 in the layer direction and one end of the head have a predetermined distance set in advance. 6 to move the head (subject M). Accordingly, the head (subject M) is moved to the center position of the multilayer detector ring 11 in the layer direction.

  The boundary of the subject M in the body axis direction is detected by, for example, setting the width of the subject M in advance based on TOF data or sinogram (projection data) collected in a cross section perpendicular to the body axis direction of the subject M. If it is equal to or greater than the predetermined value, the boundary of the subject M in the body axis direction may be determined.

  With this configuration, for example, when the length of the subject in the body axis direction is smaller than the length of the multilayer detector ring 11 in the layer direction (effective visual field), the positional deviation amount detection unit The boundary between both ends is detected, and the amount of positional deviation in the body axis direction of the subject is detected from the center position in the body axis direction of the subject and the center position in the layer direction of the multilayer detector ring. Then, the center position of the subject in the body axis direction is moved to the center position of the multilayer detector ring in the layer direction. Thereby, positioning of the subject in the body axis direction within the multilayer detector ring can be easily performed. In addition, the subject M can be aligned without depending on the subjectivity of the operator.

  (2) In each Example mentioned above, although the mechanism control part 6 controlled the bed apparatus 3 and moved the top plate 2 to the up-down direction and the horizontal direction, it is not limited to this structure. For example, the multilayer detector ring 11 (gantry 5) may be moved in the vertical direction and the horizontal direction.

  (3) In each Example mentioned above, although the detector 9 was comprised by the detector block, it is not limited to this structure. For example, it may be a semiconductor camera in which the detection element is made of cadmium telluride (CdTe) or the like, which is a semiconductor, and detects charges generated by incidence of γ rays.

  (4) In each of the embodiments described above, among the detector rings 7 configured in multiple layers of the multilayer detector ring 11, for example, the subject M is automatically positioned by the detector ring 7 disposed in the center. May be. Further, automatic positioning may be performed based on the average position of the positional deviation amounts detected by the two or more detector rings 7.

  (5) In each of the above-described embodiments, for example, an external radiation source may be provided to collect transmission data, and alignment may be performed based on the transmission data. Moreover, you may comprise so that another correction | amendment may be performed as needed.

DESCRIPTION OF SYMBOLS 1,41 ... PET apparatus 6 ... Mechanism control part 7 ... Detector ring 9 ... Detector 11 ... Multi-layer detector ring 13 ... TOF data collection part 17 ... Correction table 19 ... Main control part 27, 47 ... Position shift amount detection part 29, 51 ... Object boundary detection unit 31, 53 ... Position shift amount calculation unit 33, 55 ... Maximum value extraction unit 35, 57 ... Coordinate conversion unit 43 ... LOR data collection unit 45 ... Projection data creation unit

Claims (5)

A multi-layer detector ring configured to detect a pair of annihilation photons emitted from a subject to which a radiopharmaceutical is administered, in which a detector ring in which a plurality of detectors are arranged in a ring shape is configured in multiple layers;
A TOF data collection unit that collects TOF data indicating a generation point of pair annihilation photons calculated from a difference in detection time of pair annihilation photons simultaneously counted by two detectors of the multilayer detector ring;
A positional deviation amount detection unit for detecting a positional deviation amount between the central axis position of the multilayer detector ring and the central position of the vertical section of the subject using the collected TOF data;
A mechanism control unit that moves the center position of the vertical cross section of the subject to the center axis position of the multilayer detector ring based on the positional shift amount;
A positron emission tomography apparatus comprising: The positron emission tomography apparatus according to claim 1,
The positional deviation amount detection unit
A subject boundary detection unit for detecting a boundary between both ends of the subject from TOF data on a coincidence counting line passing through a central axis of a plurality of detectors arranged in a ring;
A position shift amount calculation unit that calculates the center position from the boundary between both ends of the subject, and calculates a position shift amount between the center axis position of the multilayer detector ring and the center position of the boundary between both ends of the subject;
A maximum value extraction unit for extracting the maximum value from the positional deviation amount;
A coordinate conversion unit that converts the maximum value of the positional deviation amount into coordinates;
A positron emission tomography apparatus comprising: A multi-layer detector ring configured to detect a pair of annihilation photons emitted from a subject to which a radiopharmaceutical is administered, in which a detector ring in which a plurality of detectors are arranged in a ring shape is configured in multiple layers;
An LOR data collection unit for collecting LOR data indicating a line connecting two detectors simultaneously counted by the multilayer detector ring;
A projection data creation unit for creating projection data of the collected LOR data;
Using the projection data, a positional deviation amount detection unit for detecting a positional deviation amount between the central axis position of the multilayer detector ring and the central position of the vertical section of the subject;
A mechanism control unit that moves the center position of the vertical cross section of the subject to the center axis position of the multilayer detector ring based on the positional shift amount;
A positron emission tomography apparatus comprising: In the positron emission tomography apparatus according to claim 3,
The positional deviation amount detection unit
A subject boundary detection unit for detecting a boundary between both ends of the subject from the projection data;
A position shift amount calculation unit that calculates the center position from the boundary between both ends of the subject, and calculates a position shift amount between the center axis position of the multilayer detector ring and the center position of the boundary between both ends of the subject;
A maximum value extraction unit for extracting the maximum value from the positional deviation amount;
A coordinate conversion unit that converts the maximum value of the positional deviation amount into coordinates;
A positron emission tomography apparatus comprising: In the positron emission tomography apparatus according to any one of claims 1 to 4,
The positional deviation amount detection unit detects a positional deviation amount in the body axis direction of the subject between a predetermined position in the body axis direction of the subject and a center position in the layer direction of the multilayer detector ring ,
The mechanism control unit moves the predetermined position to a center position in the layer direction of the multilayer detector ring based on a positional shift amount of the subject in the body axis direction.

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