JP2006017532A - Pet device and its detector unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide uniform sensitivity on photon pair detection by a direct plane and cross plane. <P>SOLUTION: This PET device is equipped with: a ring-shaped detector module 51 made by layering a plurality of detector rings of thickness w in the specimen body axis direction, the detector rings being made by roundly placing a plurality of detectors 52 in a ring shape around a specimen body axis CL; a septa 53 existing inside the detector module 51 and made by roundly placing flat plates in a screw shape with a pitch w in the direction of the body axis, the flat plates having a prescribed collimation length for collimating γ rays coming flying in a direction substantially vertical to the body axis; a detection circuit 42 capable of determining incoming positions of γ rays coming in the detectors 52; and a simultaneous determination/extraction part 33 for extracting a pair of detection signals detected substantially simultaneously in two detection regions set in positions confronting each other with the specimen put therebetween while performing the setting so that two boundary faces in the body axis direction in one of the detection regions agree with the boundary face of the septa. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a PET (Positron Emission Tomography) apparatus and a detector unit thereof, and more particularly to a PET apparatus and a detector unit thereof in which uniformity of detection plane sensitivity is improved during two-dimensional scanning of the PET apparatus.

  A PET device detects and images a pair of γ-rays (two photons) generated when a positron contained in a radiopharmaceutical (positron nuclide) taken into a subject disappears. It is. When performing a two-dimensional scan with a multi-tomographic PET apparatus having a plurality of detector rings, a shielding plate (also known as a septa or slice collimator) is used to remove radiation that is incident obliquely on the detection surface of each detector ring. Called) on the interface of each detector ring. In this case, the detection tomographic plane includes a direct plane that collects coincidence count data within the same detector ring as tomographic data and a cross plane that collects coincidence count data between adjacent rings. A PET apparatus with n instrument rings can collect 2n-1 plane tomographic data.

Conventionally, a signal sinogram that accumulates and generates coincidence count information in the case of not intersecting any slice collimator among a group of straight lines connecting the light receiving surfaces of a pair of photon detectors that are simultaneously detected, and any one is a slice collimator By using a scattering sinogram that accumulates and generates intersecting coincidence information and reconstructing the image based on the signal sinogram corrected for the influence of the scattering component by the scattering sinogram, the influence of scattered rays while maintaining good photon pair detection sensitivity A PET apparatus that appropriately corrects the above is known (Patent Document 1).
JP2001-330671 (summary, figure)

  However, since the conventional multi-tomographic detector unit has the same ring-shaped septa on the boundary surface of each detector ring, the direct plane and the cross plane have a solid angle with respect to the detection surface of the radiation source. There is a disadvantage that a difference in sensitivity occurs between the two. Hereinafter, this point will be specifically described with reference to the drawings.

  FIGS. 11 and 12 are views (1) and (2) for explaining the prior art. FIG. 11 is a perspective view of a typical detector unit 80 of the related art. In the figure, the detector unit 80 includes a detector module 81 sandwiched between two shield collimators 84a and 84b, and the detector module 81 includes a plurality of detector rings R1 to R5. They are stacked in the direction of the subject body axis CL. Each of the detector rings R1 to R5 includes a number of detectors 82 (referred to as detector blocks 82 in the present specification for convenience of description) provided on the circumference around the subject body axis CL. Each detector block 82 includes a so-called scintillation detector in which a plurality of scintillators 82a made of BGO or the like and a plurality of photomultiplier tubes (PMT) 82b are combined. High energy (511 keV) gamma rays flying from the inside of the detector module 81 are converted into visible light by the scintillator 82a, and the visible light is converted into electric signals by the PMT 82b. When performing 2D scanning, each ring-shaped septa 83 is provided inside the detector module 81.

Inset (a) shows a cross-sectional view of the detector unit 80 taken along the line aa. The conventional scepter 83 is composed of each ring-shaped disk disposed on the boundary surface of each detector ring R1 to R5, and each disk is composed of a member having a large atomic number such as lead or tungsten, and each disk By shielding γ rays that are incident obliquely with respect to the surface, only the γ rays incident substantially parallel to the boundary surface are allowed to pass to the detector block 82 side. Thereby, each detector ring R1-R5 detects only the (gamma) ray which flies from the direction substantially perpendicular to the body axis CL (2D scan). In the case of performing 3D scanning, such a septa is not provided.

  FIG. 12 is a diagram for explaining detection plane-sensitivity characteristics by a conventional PET apparatus, and FIG. 12 (a) shows a front view of the detector unit 80. FIG. The detector module 81 includes a large number of detector blocks 82 arranged on a circumference around the subject body axis CL. For convenience of explanation in this specification, the detection signal of each detector block 82 is detected. Corresponding to channels CH0 to CH359.

  FIG. 12B shows a cross-sectional view of the detector unit 80 taken along the line aa. Discs having a length d in the diametrical direction are arranged at intervals w on the boundary surfaces of the detector rings R1 to R5. The detection plane for tomographic data collected by 2D scanning includes direct planes P1, P3,..., P9 for collecting coincidence events in the same ring, and a cross plane P2, for collecting coincidence events between adjacent rings. P4,..., P8 exist, and generally, (2n-1) planes of tomographic data can be collected with n detector rings.

  Now, focusing on the direct plane P3, for example, the pair of γ rays (L1a, L1b) and (L2a, L2b) emitted in the direction within the solid angle α of the plane on the body axis CL are blocked by the scepter 83. Without being detected simultaneously by CH0 and CH180 of the detector ring R2, a pair of γ rays L3 emitted at an angle larger than α are not detected simultaneously by the ring R2. Even within the solid angle α, the pair of γ rays L4 emitted from the position deviated from the point P3 on the body axis are not simultaneously detected by the ring R2. The same applies to the other direct planes P1, P5 and the like. Therefore, if the inner diameter of the detector ring R is D and the width of the detector ring R (ie, the interval between the septa) is w, the solid angle α of the plane with respect to the direct plane is expressed by equation (1):

It is represented by

  Next, focusing on the cross plane P8, the pair of γ rays L5 and L6 emitted in the direction within the solid angle β of the plane on the body axis CL are not obstructed by the septa 83, and the detector rings R4 and R4 are not obstructed. The solid angle β of the plane of this cross plane detected simultaneously by CH0 and CH180 of R5 is the formula (2):

It is represented by

  When the solid angles α and β are compared, in a practical range where w / D is small, there is a nearly double difference between α and β. Therefore, the direct plane and the cross plane are detected simultaneously. However, there is a disadvantage that the photon pair detection sensitivity is greatly different.

  The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to provide a PET apparatus capable of obtaining uniform photon pair detection sensitivity between a direct plane and a cross plane.

  The above problem is solved by the configuration shown in FIGS. That is, the PET apparatus of the present invention (1) is a PET apparatus that detects and images a pair of γ-rays generated when a positron contained in a radiopharmaceutical incorporated into a subject disappears. A ring-shaped detector module in which a plurality of detector rings having a thickness w, in which a plurality of detectors 52 having a plurality of detection surfaces are provided in a ring shape around the subject body axis CL, are stacked in the body axis direction. 51 and a flat plate having a predetermined collimating length for collimating γ-rays that are interposed inside the detector module 51 and fly in a direction substantially perpendicular to the body axis of the subject at a pitch w in the direction of the body axis A septum 53 formed in a spiral shape, a detection circuit 42 capable of specifying the incident position of γ rays incident on the detection surface based on the detection signal of the detector 52, and a position opposite to each other with the subject interposed therebetween. Abbreviation in two set detection areas A simultaneous determination and extraction unit 33 for extracting a pair of detection signals detected at times, and setting so that both boundary surfaces in the body axis direction of the one detection region coincide with the boundary surface of the septa It is.

  In the present invention (1), the configuration in which the spiral septa 53 is provided inside the ring-shaped detector module 51 allows one detection region to be viewed in the direction of the body axis in any detection plane on the subject body axis. These boundary surfaces can be set to coincide with the boundary surface of the scepter. This will be specifically described with reference to FIG.

  For example, in the direct plane P3, when one detection region is the channel CH0 of the detector ring R2, both boundary surfaces in the body axis direction coincide with the boundary surface of the septa 53, and the scattering is mixed into the detection region. The line can be effectively shielded. On the other hand, the septa 53 do not exist on both boundary surfaces of the channel CH 180 which is the opposite surface region, but by extracting a pair of detection signals detected almost simultaneously with the one detection region, both boundaries on the channel CH 180 side are extracted. The same effect as the presence of the septa 53 on the surface can be obtained. The same applies to the other direct planes P1, P5, P7 and the like.

  Next, in the cross plane P6, when one detection region is the latter half of the channel CH180 of the detector ring R3 and the first half of the channel 180 of the detector ring R4, both boundary surfaces in the body axis direction are the same as the boundary surface of the septa 53. Therefore, it is possible to effectively shield scattered rays that are mixed in the detection region. On the other hand, the septa 53 do not exist on both the boundary surfaces of the channel CH0 second half of the detector ring R3 and the channel 0 first half of the detector ring R4, which are opposite surface areas, but are detected almost simultaneously with the one detection area. By extracting the pair of detection signals, it is possible to obtain the same effect as if the septa 53 exist on both boundary surfaces on the channel CH0 side. The same applies to the other cross planes P2, P4, and P8. From the above, the planar solid angles of the direct plane and the cross plane are both α, thereby obtaining uniform photon pair detection sensitivity in all planes in the body axis direction.

  In the present invention (2), in the above-mentioned present invention (1), the simultaneous determination extraction unit is detected in the one detection region among the signals detected in the other detection region facing the one detection region. Only the signal detected almost simultaneously with the signal is extracted.

  According to the present invention (2), image reconstruction can be performed by a simple method of extracting only signals detected substantially simultaneously with signals detected in one detection region out of signals detected in the other detection region. A useful pair of detection signals can be extracted efficiently.

  In the present invention (3), in the above-mentioned present invention (1), a septa is detachably provided inside the detector module. This facilitates not only two-dimensional scanning but also three-dimensional scanning.

  The above-described problem is solved by the configurations of FIGS. That is, the PET apparatus of the present invention (4) is a PET apparatus that detects and images a pair of γ-rays generated when the positron contained in the radiopharmaceutical incorporated into the subject disappears. A plurality of detectors 52 having a detection surface are spirally arranged around the subject body axis CL at a pitch w and are disposed inside the detector module 55; A scepter 53 in which a flat plate having a predetermined collimating length for collimating γ rays flying in a direction substantially perpendicular to the subject body axis is spirally provided in the direction of the body axis at a pitch w, and the detection The detection circuit 42 that can specify the incident position of the γ-ray incident on the detection surface based on the detection signal of the detector 52, and a pair of detection areas that are detected substantially simultaneously in the two detection areas that are set to face each other with the subject sandwiched therebetween Extracting detection signal There determination extracting unit 33, which both interface body axis direction of the one of the detection area is set to coincide with the boundary surface of the septum, but with a city.

  In the present invention (4), the configuration in which the helical detector 53 is provided inside the helical detector module 55 makes it possible to display one detection region in the direction of the body axis in any detection plane on the subject body axis. These boundary surfaces can be set to coincide with the boundary surface of the scepter. In addition, since the one detection area can always coincide with the detection surface of the detector 52, the simultaneous detection process can be simplified and highly reliable. This will be specifically described with reference to FIG.

  For example, in the direct plane P3, when one detection region is the channel CH0 of the detector ring R2, both boundary surfaces in the body axis direction coincide with the boundary surface of the septa 53, and the scattering is mixed into the detection region. The line can be effectively shielded. On the other hand, the septa 53 does not exist on both boundary surfaces of the detection area consisting of the latter half of the channel CH180 of the detector ring R1 and the first half of the channel CH180 of the detector ring R2, which are the opposing surface areas. By extracting a pair of detection signals that are detected almost simultaneously, the same effect as the presence of the septa 53 on both boundary surfaces on the channel CH 180 side can be obtained. The same applies to the other direct planes P1, P5, P7 and the like.

  Next, in the cross plane P6, when one detection region is the channel CH180 of the detector ring R3, both boundary surfaces in the body axis direction coincide with the boundary surface of the septa 53 and are mixed into the detection region. Scattered rays can be effectively shielded. On the other hand, the septa 53 do not exist on both boundary surfaces of the detection area consisting of the second half of the channel CH0 of the detector ring R3 and the first half of the channel 0 of the detector ring R4, which are the opposing surface areas. By extracting a pair of detection signals detected at substantially the same time, the same effect as when the septa 53 exist on both boundary surfaces on the channel CH0 side can be obtained. The same applies to the other cross planes P2, P4, and P8. From the above, the planar solid angles of the direct plane and the cross plane are both α, thereby obtaining uniform photon pair detection sensitivity in all planes in the body axis direction.

  In the present invention (5), in the above-mentioned present invention (4), the simultaneous determination extraction unit is detected in the one detection region out of the signals detected in the other detection region facing the one detection region. Only the signal detected almost simultaneously with the signal is extracted.

  According to the present invention (5), image reconstruction can be performed by a simple method of extracting only signals detected at the same time as signals detected at one detection region from signals detected at the other detection region. A useful pair of detection signals can be extracted efficiently.

  In the present invention (6), in the above-mentioned present invention (4), a septa is detachably provided inside the detector module. This facilitates not only two-dimensional scanning but also three-dimensional scanning.

  The detector unit of the present invention (7) detects and images a pair of gamma rays generated when the positron contained in the radiopharmaceutical incorporated into the subject disappears, for example, as shown in FIG. In the detector unit of the PET apparatus, a plurality of detector rings having a thickness w in which a plurality of detectors 52 having a detection surface of a predetermined size are provided in a ring shape around the subject body axis CL are provided in the body axis direction. A ring-shaped detector module 51 formed by stacking, and a flat plate having a predetermined collimating length for collimating γ-rays that are interposed inside the detector module 51 and fly in a direction substantially perpendicular to the subject body axis. And a scepter 53 formed in a spiral shape with a pitch w in the direction of the body axis.

  The detector unit of the present invention (8) detects and images a pair of γ-rays generated when the positron contained in the radiopharmaceutical incorporated into the subject disappears, for example, as shown in FIG. In the detector unit of the PET apparatus, a spiral detector module 55 in which a plurality of detectors 52 having a detection surface of a predetermined size are spirally arranged around the subject body axis CL at a pitch w; A flat plate having a predetermined collimating length for collimating γ-rays flying in a direction substantially perpendicular to the subject body axis is spirally arranged at a pitch w in the direction of the body axis. And a scepter 53 formed around.

  As described above, according to the present invention, there is no difference in sensitivity and difference in the degree of mixed scattered radiation between the direct plane and the cross plane, and the sensitivity uniformity in the body axis direction is greatly improved.

  Hereinafter, a plurality of preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that the same reference numerals denote the same or corresponding parts throughout the drawings. FIG. 1 is an external view of a PET apparatus according to an embodiment. This apparatus uses a γ-ray detector unit to collect projection data necessary for creating a tomographic image of a subject, and a subject to a top plate 21. An imaging table 20 mounted on the gantry and moved into the cavity of the gantry, a data processing unit 30 for reconstructing a PET tomographic image of the subject based on projection data collected by the gantry 40, and remote control of each of these units, And a console unit 10 operated by an engineer or the like.

FIG. 2 shows a configuration diagram of a main part of the PET apparatus according to the embodiment. The gantry 40 includes a γ-ray detector unit 50, and the subject 100 is carried into a central cavity (bore). Of each pair of γ rays generated inside the subject, those not blocked by the septa 53 are incident on the surrounding detector 52 and converted into visible light, and also converted into an electrical signal by the PMT, and a pair of output pulses. Is formed.
In this specification, in order to clearly call out the part of the detector 52 as an example among various other components (detector unit 50, detector module 51, detector rings R1 to R5, etc.), For convenience of explanation, the detector 52 is referred to as a detector block 52, and its detection surface is referred to as a block detection surface. However, the detector 52 of the present invention is not limited to the block shape.
The pair of detection pulses thus formed is input to a preprocessing circuit (ACEM) 42 provided corresponding to each detector block 52, where the γ-ray detection position (channel number CH of the detector block 52). And a predetermined signal including detection timing information in the block, detection timing, detection energy, and the like. Hereinafter, an example of the detector unit 50 and the preprocessing circuit 42 will be described in detail.

  FIG. 3 is an external perspective view of the detector unit 50 according to the first embodiment, and shows a case where a spiral septa 53 is provided inside a ring-shaped detector module 51. The detector unit 50 includes a ring-shaped detector module 51 sandwiched between two front and rear shield collimators 54a and 54b, and the detector module 51 includes a plurality of detector rings R1 to R5. They are stacked in the direction of CL. Each detector ring R1 to R5 includes a large number of detector blocks 52 arranged on a circumference around the subject body axis CL, and each detector block 52 flies from the inside of the detector module 51. High energy (511 keV) gamma rays are detected. Further, a spiral shielding board (scepter) 53 formed of a member having a large atomic number (lead, tungsten, etc.) is provided inside the ring-shaped detector module 51.

  Inset (a) shows a cross-sectional view of the detector unit 50 taken along the line aa. Since the septa 53 is formed in a spiral shape with the same pitch width as the detector ring width, on one side thereof (for example, the upper surface side in the figure), each septa board surface is just on the boundary surface of the detector rings R1 to R5. However, at the opposite position (the lower surface side in the figure), each septum board surface is arranged at an intermediate position between the detector rings R1 to R5, and is incident substantially parallel to such septa board surface. It has a so-called collimating action that allows only γ rays to pass to the detector block 52 side.

  FIG. 4 is a diagram for explaining the detector block 52 according to the first embodiment, and FIG. 4A shows an external perspective view of the detector block 52. The detector block 52 has a structure in which combinations of an arbitrary plurality of scintillators 52a and photomultiplier tubes (PMT) 52b are arranged in a matrix. FIG. 4A is a 2 × 2 for simplicity of explanation. A total of four detection systems A to D are present.

  FIG. 4B shows a side view of the detector block 52. Γ rays incident from the lower side of the figure are converted into visible light by the scintillator 52a, the light is emitted and incident on a plurality of PMTs 52b, and detection signals B and D corresponding to the amount of incident light are output from each PMT 52b. . The same applies to the detection signals A and C. The preprocessing circuit 42 generates a signal for specifying which block detection surface position of the detector block 52 the γ ray is incident on the basis of the detection signals A to D.

  FIG. 5 is a diagram for explaining the preprocessing circuit 42 according to the first embodiment. FIG. 5A shows a block diagram of the preprocessing circuit 42. In the figure, an edge detection circuit (EGD) 43 detects an edge of signal generation based on a combined signal of detection signals A to D, and outputs an edge pulse signal EP at the same timing. Further, the preprocessing circuit 42 generates block address information BA unique to the detector block 52 to which this circuit is connected. Further, the energy encoder (EE) 44 amplifies and A / D converts the sum (A + B + C + D) of the detection signals A to D to generate an energy signal E. The X position encoder (XE) 45 amplifies and A / D converts the sum (A + C) of the detection signals A and C to generate a signal X for indicating a detection position in the X axis direction in the detection block. A Z position encoder (ZE) 46 amplifies and A / D converts the sum (C + D) of the detection signals C and D to indicate a detection position in the Z axis (body axis) direction in the detection block. Is generated. These signals EP, BA, E, X, and Z are converted into serial signals by a parallel-serial converter (P / S) 47 and sent to the address generation circuit 32 of the data processing unit 30 in real time.

FIG. 5B shows an example method for specifying the γ-ray incident position in the block detection surface. This processing is performed by each address generation circuit (DCEM) 32 provided corresponding to each preprocessing circuit 42. In the figure, the row address ROW corresponding to the X-axis direction in the block detection surface is, for example, (
3) Formula,

And the column address COL corresponding to the Z-axis (body axis) direction is, for example, equation (4),

It is calculated by. Each address ROW, COL is normalized to a value within a range of 0 to 1 by the detection energy E, and has sufficient resolution to specify the γ-ray incident position in the detector block with a required accuracy.

  Returning to FIG. 2, a signal generated by each preprocessing circuit 42 of the gantry 40 is a time stamp signal TS indicating the timing at which a corresponding address generation circuit (DCEM) 32 detects a predetermined address signal POS or γ-ray. Etc. The address signal POS includes a block address signal BA of the detector block 52 and address signals ROW and COL indicating the detected positions of γ rays in the block. The simultaneous determination extraction unit 33 faces each other across the subject 100 (that is, the detection signals (POSi, TSi) of the two detection channels i and j that are opposite to each other (that is, the combination of two γ-ray tracks forms a straight line), (POSj, TSj) are compared, and an address signal pair PAIR satisfying the simultaneous condition included in the predetermined gate time width is extracted and stored in the memory 34.

  Inset (a) shows an example of two-dimensional projection data (sinogram) stored in the memory 34. The horizontal axis represents the channel number CH of the detection device block (including in-block addresses ROW and COL), the vertical axis represents the projection angle θ of the subject, and the depth represents the direct and cross detection plane numbers P. The CPU 35 reconstructs the PET tomographic image of the subject based on the projection data stored in the memory 34 by, for example, the back projection method and displays it on the console 10. Next, the detection plane-sensitivity characteristics according to the first embodiment will be specifically described.

  6 and 7 are diagrams (1) and (2) for explaining the detection plane-sensitivity characteristics of the PET apparatus according to the first embodiment. FIG. 6 is a cross-sectional view of the detector module 51 including CH0 and CH180. The detection operation when viewed is shown. FIG. 6A shows a front view of the detector unit, and FIG. 6B shows an aa cross-sectional view of the detector unit. In the first embodiment, since the spiral septa 53 is inserted inside the ring-shaped detector module 51, for example, on the upper side (CH0 side) of the detector module 51, just on the boundary surface of each detector ring R1 to R5. A scepter board having a length d in the diametrical direction is arranged at an interval w. On the other hand, on the lower side (CH 180 side) of the module 51, a scepter board having a length d is also provided on the center plane of each detector ring R1 to R5. Are arranged at intervals w. With this configuration, the direct planes P1, P3,..., P9 that collect coincidence events in the same ring and the cross planes P2, P4,. Consider each count in.

  For example, in the data collection of the direct plane P3, among the γ rays detected in the other detection region (CH 180 of the detector ring R2), γ rays detected in one detection region (CH0 of the ring R2) opposite to this. Only a pair of γ rays satisfying the simultaneous detection condition are extracted. In this way, the pair of γ rays (L1a, L1b), (L2a, L2b) and the like emitted in the direction within the solid angle α of the plane at the point P3 on the body axis are not blocked by the scepter 53. The ring R2 is simultaneously detected by CH0 and CH180, but the pair of γ rays L3 emitted at an angle larger than that are not simultaneously detected by the ring R2. Further, even if the solid angle is α, the pair of γ rays L4a and L4b emitted from the position deviated from the point P3 are not simultaneously detected by the ring R2.

  In this case, since γ rays incident on CH0 of the ring R2 are sufficiently collimated by the septa 53 located at both ends of the CH0 detection surface, mixing of scattered rays can be effectively prevented at the time of detection. . On the other hand, for γ rays incident on the CH 180 of the ring R2, the scepter 53 is located at the midpoint of the detection surface, and therefore, the scattered rays cannot be removed at the time of detection, but the γ rays incident on the CH0 of the ring R2 By extracting only those satisfying the simultaneous detection condition, the mixing of scattered rays can be effectively prevented in the same manner. From the above, the solid angle of detection in the direct plane P3 is α, and the detection sensitivity corresponding to the solid angle is obtained. The same applies to the other direct planes P1, P5, P7 and the like.

  Next, for example, in the data collection of the cross plane P6, the other detection areas (the CH0 second half w / 2 of the detector ring R3 and the CH0 first half w / 2 of the ring R4) oppose this. Only those that are detected substantially simultaneously with the γ-rays detected in one detection region (CH 180 second half w / 2 of ring R3 and CH 180 first half w / 2 of ring R4) are extracted. In this way, each pair of γ rays L5, L6, etc. emitted in a direction within the solid angle α of the plane from the point P6 on the body axis is not blocked by the septa 53, and the CH0 second half of the ring R3 and It is detected almost simultaneously on each detection surface consisting of the CH0 first half of the ring R4, the CH180 second half of the ring R3, and the CH180 first half of the ring R4, but a pair of γ rays emitted at a larger angle, A pair of γ rays emitted from a position shifted from the point P6 on the body axis are not simultaneously detected by the detection surface.

  In this case, the γ rays incident on the CH180 side of the rings R3 and R4 are sufficiently collimated by the septa 53 located at both ends of the detection region on the CH180 side, and therefore detection of the mixed scattered radiation is detected. It can be effectively prevented at the time. On the other hand, for the γ rays incident on the CH0 side of the rings R3 and R4, since the septa 53 is located at the midpoint of the detection region on the CH0 side, mixing of scattered rays cannot be removed at the time of detection, but the CH180 By extracting only those that are detected substantially simultaneously with the γ-rays incident on the side, it is possible to effectively prevent mixing of scattered rays in the same manner. From the above, the solid angle of detection in the cross plane P6 is also α, and this is the same for the other cross planes P2, P4 and the like.

  FIG. 7 shows a detection operation when the detector module 51 is viewed in a cross section including CH90 and CH270. FIG. 7A shows a front view of the detector unit, and FIG. 7B shows a bb cross-sectional view of the detector unit. Since the detector module 51 is ring-shaped, the cut surface including CH90 and CH270 is the same as the cut surface including CH0 and CH180. On the other hand, since the septa 53 has a spiral shape, the ceptor board is shifted in the body axis direction by the detection ring width w every time it rotates at any CH. Accordingly, when viewed from the cut plane including CH90 and CH270, as shown in the figure, CH90 is displaced by w / 4 from the boundary surface, and CH270 is displaced by 3w / 4 from the boundary surface. Accordingly, the direct and cross detection planes P1 'to P9' are also considered to be shifted by w / 4 from the reference position in the case of FIG.

For example, in the data acquisition of the direct plane P3 ′, the other detection area (detector ring R
2 of the CH 270 second half 3W / 4 and the ring R3 CH 270 first half w / 4), which is opposite to the detection region (the CH 90 second half 3W / 4 of the ring R2 and the ring R3 of the ring R3). It is only necessary to extract those satisfying the simultaneous condition with the gamma rays detected in the first half of CH90 w / 4).

  In this case, the γ-rays incident on the CH90 side of the rings R2 and R3 are sufficiently collimated by the septa 53 located at both ends of the detection region on the CH90 side, so detection of scattered radiation is detected. It can be effectively prevented at the time. On the other hand, for the γ rays incident on the CH 270 side of the rings R2 and R3, since the septa 53 is located at the midpoint of the detection region on the CH 270 side, mixing of scattered radiation cannot be removed at the time of detection. By extracting only those that are detected substantially simultaneously with the γ rays incident on the CH90 side of R2 and R3, mixing of scattered rays can be effectively prevented in the same manner. From the above, the solid angle of detection in the direct plane P3 'is also α, and this is the same for the other direct planes P1', P5 ', P9' and the like.

  Next, for example, in the data collection of the cross plane P6 ′, among the γ rays detected in the other detection region (the CH90 second half w / 4 of the detector ring R3 and the CH90 first half 3w / 4 of the ring R4), Only those that satisfy the conditions of simultaneous detection with the γ-rays detected in one detection region (CH270 second half w / 4 of ring R3 and CH270 first half 3w / 4 of ring R4) opposite to It ’s fine.

  In this case, the γ rays incident on the CH 270 side of the rings R3 and R4 are sufficiently collimated by the septa 53 located at both ends of the detection region on the CH 270 side, and therefore detection of the mixed scattered radiation is detected. It can be effectively prevented at the time. On the other hand, for the γ rays incident on the CH90 side of the rings R3 and R4, since the septa 53 is located at the midpoint of the detection surface on the CH90 side, mixing of scattered rays cannot be removed at the time of detection, but the CH270 By extracting only those that are detected substantially simultaneously with the γ-rays incident on the side, it is possible to effectively prevent mixing of scattered rays in the same manner. From the above, the solid angle of detection in the cross plane P6 'is also α, and this is the same for the other cross planes P2', P4 'and the like.

  Although the above description has focused on the detection when the γ-ray passes on the body axis, the same applies to the detection when the γ-ray does not pass on the body axis. For example, in the detection of the γ rays L10 and L11 shown in FIGS. 6A and 7A, the positional relationship between the detector rings R1 to R5 and the helical scepter board 53 is known for any detection plane. Therefore, it is always possible to appropriately set one detection area for each detection plane and the other detection area that faces the subject with the object sandwiched therebetween. Efficiently collects high-quality data without lines.

  Thus, according to the first embodiment, uniform (required quality and sensitivity) projection data can be collected by the direct and cross detection planes at each projection angle, and these can be reconstructed by the back projection method or the like. Thus, a high-quality two-dimensional PET tomographic image can be obtained.

  FIG. 8 is an external perspective view of the detector unit 50 according to the second embodiment. Here, not only the septa 53 but also the detector module 55 is formed in a spiral shape. In the second embodiment, since the positional relationship between the detector block 52 and the scepter board 53 is always constant, the simultaneous detection process of γ rays is greatly simplified as compared to the first embodiment. Is done.

In this detector module 55, a large number of detector blocks 52 arranged on the circumference around the subject body axis CL are spirally developed at a pitch w in the direction of the subject body axis. Further, on the inner side of the spiral detector module 55, a spiral scepter 5 that is also deployed at a pitch W is provided.
3 is provided. Other configurations may be the same as those described in FIG.

  Inset (a) shows a cross-sectional view of the detector unit 50 taken along the line aa. Since not only the septa 53 but also each detector block 52 of the detector module 55 is spirally developed, the surface of the scepter board is located just on the boundary surface of the detector block 52 in relation to any detector block 52. ing.

  9 and 10 are diagrams (1) and (2) for explaining the detection plane-sensitivity characteristics of the PET apparatus according to the second embodiment. FIG. 9 is a cross-sectional view of the detector module 55 including CH0 and CH180. The detection operation when viewed is shown. FIG. 9A is a front view of the detector unit, and FIG. 9B is a cross-sectional view taken along the line aa of the detector unit. In the second embodiment, since the same spiral septa 53 is inserted inside the spiral detector module 55, the positional relationship between the detector block 52 and the septa board 53 is the same for all detector blocks 52. is there. That is, the scepter board 53 is always located on the boundary surface of the detector block 52. With such a configuration, consider the collection of projection data in each of the direct and cross detection planes P1 to P9 as in the conventional case. In this specification, for simplicity of explanation, a group of detector blocks belonging to one rotation of each spiral is referred to as rings R1 to R5.

  For example, in the data collection of the direct plane P3, one of the γ-rays detected in the other detection region (the CH 180 second half w / 2 of the ring R1 and the CH 180 first half w / 2 of the ring R2) is opposed to this. It is only necessary to extract those satisfying the simultaneous detection condition with the γ-rays detected in the region (CH0 of ring R2). In this case, the γ rays incident on CH0 of the ring R2 are sufficiently collimated by the septa 53 located at both ends of the detection surface of the CH0, so that mixing of scattered rays is effectively prevented at the time of detection. it can. On the other hand, for γ rays incident on the CH 180 side of the rings R1 and R2, the septa 53 is located at the midpoint of the detection region on the CH 180 side, and therefore, mixing of scattered rays cannot be removed at the time of detection. By extracting only those that are detected substantially simultaneously with the γ rays incident on CH0 of the ring R2, it is possible to effectively prevent scattered rays from being mixed in the same manner. From the above, the detection solid angle of the plane in the direct plane P3 is α, and projection data of required quality and sensitivity can be collected. The same applies to the other direct planes P1, P5, P9 and the like.

  Next, for example, in the data collection of the cross plane P6, among the γ-rays detected in the other detection region (CH0 second half w / 2 of the detector ring R3 and CH0 first half w / 2 of the ring R4), It is only necessary to extract those that are detected substantially simultaneously with the γ rays detected in one of the opposing detection regions (CH 180 of ring R3). In this case, the γ rays incident on the CH 180 of the ring R3 are sufficiently collimated by the septa 53 located at both ends of the detection surface of the CH 180, so that mixing of scattered rays is effective at the time of detection. Can be prevented. On the other hand, for the γ rays incident on each CH0 side of the rings R3 and R4, since the septa 53 is located at the midpoint of the detection region on the CH0 side, mixing of scattered rays cannot be removed at the time of detection. By extracting only those that are detected substantially simultaneously with the γ rays incident on the CH 180, it is possible to effectively prevent the mixing of scattered rays. From the above, the detected solid angle in the cross plane P6 is also α, and projection data of required quality and sensitivity can be collected as in the case of the direct plane. The same applies to the other cross planes P2, P4 and the like.

FIG. 10 shows a detection operation when the detector module 55 is viewed in a cross section including CH90 and CH270. FIG. 10A shows a front view of the detector unit, and FIG. 10B shows a bb cross-sectional view of the detector unit. Since both the detector module 55 and the septa 53 are spiral, each detection channel shifts in the direction of the body axis by the detection ring width w every time it is rotated, and this is viewed on a cut surface including CH90 and CH270. As shown in the figure, CH90 is shifted by w / 4 from CH0, and CH270 is shifted by 3w / 4 from CH0. Accordingly, the direct and cross detection planes P1 ′ to P9 ′ are also considered to be shifted by w / 4 from the reference position shown in FIG.

  For example, in the data collection of the direct plane P3 ′, the other detection region (the CH270 second half W / 2 of the detector ring R1 and the CH270 first half w / 2 of the ring R2) opposes this. It is only necessary to extract those satisfying the same condition with the γ-rays detected in one detection region (CH90 of ring R2). In this case, the γ rays incident on the CH 90 of the ring R2 are sufficiently collimated by the septa 53 located at both ends of the detection surface of the CH 90, so that mixing of scattered rays is effective at the time of detection. Can be prevented. On the other hand, for γ rays incident on each CH 270 side of the rings R1 and R2, since the septa 53 is located at the midpoint of the detection region on the CH 270 side, mixing of scattered rays cannot be removed at the time of detection. By extracting only those that are detected substantially simultaneously with the γ rays incident on the CH 90 of the ring R2, it is possible to effectively prevent scattered rays from being mixed in the same manner. From the above, the detected solid angle in the direct plane P3 'is also α, and projection data of required quality and sensitivity can be collected. The same applies to the other direct planes P1 ', P5', P9 'and the like.

  Next, for example, in the data acquisition of the cross plane P6 ′, the γ-rays detected in the other detection region (the CH90 second half w / 2 of the detector ring R3 and the CH90 first half w / 2 of the ring R4) It is only necessary to extract those satisfying the simultaneous detection condition with the γ-rays detected in one detection region (CH 270 of the ring R3) opposite to. In this case, the γ rays incident on the CH 270 of the ring R3 are sufficiently collimated by the septa 53 located at both ends of the detection surface of the CH 270, so that mixing of scattered rays is effective at the time of detection. Can be prevented. On the other hand, for γ-rays incident on each CH90 side of the rings R3 and R4, since the septa 53 is located at the midpoint of the detection region on the CH90 side, mixing of scattered radiation cannot be removed at the time of detection. By extracting only those that are detected substantially simultaneously with the γ rays incident on the CH 270 side, mixing of scattered rays can be effectively prevented in the same manner. From the above, the detected solid angle in the cross plane P6 'is also α, and projection data having the required quality and sensitivity similar to those in the direct plane can be collected. The same applies to the other cross planes P2 ', P4' and the like.

  Although the above description has focused on the detection when the γ-ray passes on the body axis, the same applies to the detection when the γ-ray does not pass on the body axis. For example, in the detection of the γ rays L10 and L11 shown in FIGS. 9A and 10A, the positional relationship between the detector module 55 and the helical scepter board 53 is known for any detection plane. For each detection plane, it is always possible to properly set one detection area and the other detection area that faces the object with the object sandwiched between them. Efficient collection of high quality data.

  Thus, according to the second embodiment, uniform (required quality and sensitivity) projection data can be collected for each direct and cross plane corresponding to each projection angle, and these can be reconstructed by the back projection method or the like. By doing so, a high-quality two-dimensional PET tomographic image can be obtained.

  In addition, if the sensitivity difference between the two detection planes and the difference in the scattered radiation mixing degree are eliminated, if the scattered radiation mixing degree in the conventional cross plane is acceptable, the scepter interval is set to w, For example, the ring diameter D of the detector module 51/55 can be set to 1/2, and the scepter length can be set to d / 2. Furthermore, the apparatus itself can be miniaturized.

  In each of the above embodiments, the case where the septa 53 is fixed inside the detector module 51/55 is described, but the present invention is not limited to this. By providing the septa 53 in the detector module 51/55 so as to be insertable / removable, not only two-dimensional scanning but also three-dimensional scanning can be performed.

  Moreover, although several embodiment suitable for the said invention was described, it cannot be overemphasized that the structure of each part, control, a process, and these combination can be variously changed within the range which does not deviate from this invention. .

1 is an external view of a PET apparatus according to an embodiment. It is a principal part block diagram of the PET apparatus by embodiment. It is an external appearance perspective view of the detector unit by 1st Embodiment. It is a figure explaining the detector block by 1st Embodiment. It is a figure explaining the pre-processing circuit by 1st Embodiment. It is a figure (1) explaining the detection plane-sensitivity characteristic of the PET apparatus according to the first embodiment. It is a figure (2) explaining the detection plane-sensitivity characteristic of the PET apparatus by 1st Embodiment. It is an external appearance perspective view of the detector unit by 2nd Embodiment. It is a figure (1) explaining the detection plane-sensitivity characteristic of the PET apparatus by 2nd Embodiment. It is a figure (2) explaining the detection plane-sensitivity characteristic of the PET apparatus by 2nd Embodiment. It is a figure (1) explaining a prior art. It is a figure (2) explaining a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Console part 20 Imaging table 21 Top plate 30 Data processing part 31 Address generation part 32 Address generation circuit (DCEM)
33 Simultaneous determination extraction unit 40 Gantry 41 Preprocessing unit 42 Preprocessing circuit (ACEM)
50 detector unit 51 detector module 52 detector (detector block)
53 Septa (collimator)
54a, 54b Shield collimator R1 to R5 Detector ring 100 Subject

Claims (8)

In a PET apparatus that detects and images a pair of γ-rays generated when a positron contained in a radiopharmaceutical incorporated into a subject disappears,
A ring-shaped detector module in which a plurality of detector rings having a thickness w, in which a plurality of detectors having a detection surface of a predetermined size are provided in a ring shape around the subject body axis, are stacked in the body axis direction. When,
A flat plate having a predetermined collimating length for collimating γ rays flying in a direction substantially perpendicular to the subject body axis is spirally wound in the direction of the body axis at a pitch w. A scepter,
A detection circuit capable of specifying the incident position of γ rays incident on the detection surface based on the detection signal of the detector;
A simultaneous determination extraction unit that extracts a pair of detection signals detected substantially simultaneously in two detection regions set at positions facing each other with a subject interposed therebetween, wherein both boundary surfaces in the body axis direction in the one detection region are septa A PET device comprising: a device set so as to coincide with a boundary surface of the PET device. The simultaneous determination extraction unit extracts only signals detected substantially simultaneously with a signal detected in the one detection area from signals detected in the other detection area facing the one detection area. The PET apparatus according to claim 1. 2. The PET apparatus according to claim 1, wherein a septa is detachably provided inside the detector module. In a PET apparatus that detects and images a pair of γ-rays generated when a positron contained in a radiopharmaceutical incorporated into a subject disappears,
A spiral detector module in which a plurality of detectors having a detection surface of a predetermined size are spirally arranged around a subject body axis at a pitch w;
A flat plate having a predetermined collimating length for collimating γ rays flying in a direction substantially perpendicular to the subject body axis is spirally wound in the direction of the body axis at a pitch w. A scepter,
A detection circuit capable of specifying the incident position of γ rays incident on the detection surface based on the detection signal of the detector;
A simultaneous determination extraction unit that extracts a pair of detection signals detected substantially simultaneously in two detection regions set at positions facing each other with a subject interposed therebetween, wherein both boundary surfaces in the body axis direction in the one detection region are septa A PET device comprising: a device set so as to coincide with a boundary surface of the PET device. The simultaneous determination extraction unit extracts only signals detected substantially simultaneously with a signal detected in the one detection area from signals detected in the other detection area facing the one detection area. The PET apparatus according to claim 4. The PET apparatus according to claim 4, wherein a septa is detachably provided inside the detector module. In the detector unit of the PET apparatus that detects and images a pair of γ rays generated when the positron contained in the radiopharmaceutical incorporated into the subject disappears,
A ring-shaped detector module in which a plurality of detector rings having a thickness w, in which a plurality of detectors having a detection surface of a predetermined size are provided in a ring shape around the subject body axis, are stacked in the body axis direction. When,
A flat plate having a predetermined collimating length for collimating γ rays flying in a direction substantially perpendicular to the subject body axis is spirally wound in the direction of the body axis at a pitch w. A detector unit of a PET apparatus, comprising: a septum provided. In the detector unit of the PET apparatus that detects and images a pair of γ rays generated when the positron contained in the radiopharmaceutical incorporated into the subject disappears,
A spiral detector module in which a plurality of detectors having a detection surface of a predetermined size are spirally arranged around a subject body axis at a pitch w;
A flat plate having a predetermined collimating length for collimating γ rays flying in a direction substantially perpendicular to the subject body axis is spirally wound in the direction of the body axis at a pitch w. A detector unit of a PET apparatus, comprising: a septum provided.

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