JP4536211B2 - PET equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a PET apparatus capable of imaging the behavior of a substance labeled with a positron emitting isotope (RI radiation source).
[0002]
[Prior art]
A PET (Positron Emission Tomography) device generates a pair of photons (gamma rays) of energy 511 keV that are generated along with the annihilation of electrons and positrons in a living body (subject) to which an RI radiation source is administered and fly in opposite directions. By detecting this, it is an apparatus that can image the behavior of a trace amount substance in the subject. The PET apparatus includes a detection unit having a large number of small photon detectors arranged around a measurement space in which a subject is placed, and simultaneously counts photon pairs generated as a result of electron / positron pair annihilation. And reconstructing an image representing the spatial distribution of the occurrence frequency of photon pairs in the measurement space based on the accumulated coincidence information, that is, projection data. This PET apparatus plays an important role in the field of nuclear medicine and the like, and can be used to study, for example, biological functions and higher-order brain functions. Such PET apparatuses are roughly classified into two-dimensional PET apparatuses and three-dimensional PET apparatuses.
[0003]
FIG. 6 is a diagram illustrating the configuration of the detection unit of the two-dimensional PET apparatus. This figure shows an example of a configuration including seven detector rings, and shows a cross section when the detector is cut along a plane including the central axis. The detection unit 10 of the two-dimensional PET apparatus has detector rings R _{1 to} R ₇ stacked between the shield collimator 11 and the shield collimator 12. Each of the detector rings R _{1 to} R ₇ has a plurality of photon detectors arranged in a ring shape on a plane perpendicular to the central axis. Each photon detector is a scintillation detector that combines a photomultiplier tube with a scintillator such as BGO (Bi ₄ Ge ₃ O ₁₂ ), and detects photons that have arrived from a measurement space including the central axis. . In the two-dimensional PET apparatus, slice collimators S _{1 to} S ₆ are provided inside the detection unit 10. Each of these slice collimators S _{1 to} S ₆ is a ring-shaped material disposed at a position between adjacent detector rings in a direction parallel to the central axis, and is a material having a large atomic number and a high specific gravity (for example, lead And collimating action to shield photons (gamma rays) incident obliquely.
[0004]
The detection unit 10 of the two-dimensional PET apparatus configured as described above simultaneously counts only photon pairs flying from a direction whose angle with the central axis is approximately 90 degrees by the collimating action of the slice collimators S _{1 to} S _6. Can do. That is, the coincidence count information obtained by the detection unit 10 of the two-dimensional PET apparatus, that is, the two-dimensional projection data, is a pair of photon detections included in the same detector ring or adjacent (or very close) detector rings. Limited to equipment. Therefore, the two-dimensional PET apparatus can efficiently remove scattered rays scattered by photon pairs generated at positions outside the measurement space, and can easily perform absorption correction and sensitivity correction for two-dimensional projection data. Since it can be performed, a reconstructed image with good quantitativeness can be obtained.
[0005]
FIG. 7 is a diagram illustrating the configuration of the detection unit of the three-dimensional PET apparatus. This figure also shows a cross section when the detection unit is cut along a plane including the central axis. The configuration of the detection unit 10 of the three-dimensional PET apparatus is the same as that of the two-dimensional PET apparatus. However, the three-dimensional PET apparatus is not equipped with a slice collimator. The detection unit 10 of the three-dimensional PET apparatus configured as described above has a wide solid angle, and can simultaneously count photon pairs flying from a wide direction compared to the two-dimensional PET apparatus. That is, the coincidence counting information obtained by the detection unit 10 of the three-dimensional PET apparatus, that is, the three-dimensional projection data, can be obtained by a pair of photon detectors included in an arbitrary detector ring. Therefore, the three-dimensional PET apparatus can simultaneously count photon pairs with a sensitivity about 5 to 10 times higher than that of the two-dimensional PET apparatus. However, since it is difficult to remove the influence of scattered radiation in the three-dimensional PET apparatus, the quantitativeness of the reconstructed image is not good as compared with the two-dimensional PET apparatus.
[0006]
As described above, the two-dimensional PET apparatus having the slice collimator can efficiently remove scattered radiation and easily perform the absorption correction and the sensitivity correction, although the two-dimensional PET apparatus having the slice collimator has a low detection sensitivity of the photon pair. Therefore, there is an advantage that a reconstructed image with excellent quantitativeness can be obtained.
[0007]
[Problems to be solved by the invention]
However, the conventional PET apparatus has the following problems. In other words, both the two-dimensional PET apparatus and the three-dimensional PET apparatus are required to improve the resolution in the reconstructed image. In order to improve the resolution, it is essential to reduce the size of each photon detector.
[0008]
However, in the case of a two-dimensional PET apparatus, as the photon detector becomes smaller, the interval between the slice collimators becomes narrower, so that the aperture ratio decreases and the photon pair detection sensitivity decreases. With respect to this problem, in the two-dimensional PET apparatus, if each slice collimator is made thin and short in accordance with the downsizing of the photon detector, the aperture ratio can be suppressed, but the effect of shielding photons (gamma rays) can be suppressed. That is, since the collimating effect is lowered, it becomes impossible to efficiently exclude scattered rays, and the quantitativeness of the reconstructed image is lowered.
[0009]
On the other hand, in the case of a three-dimensional PET apparatus, even if the photon detector is downsized, the slice collimator is not provided, so that there is no problem of a decrease in aperture ratio or a decrease in photon pair detection sensitivity. However, as described above, in the three-dimensional PET apparatus, it is difficult to remove the influence of scattered radiation, and thus the reconstructed image is not quantitative.
[0010]
The present invention has been made to solve the above problems, and provides a PET apparatus capable of ensuring good photon pair detection sensitivity and quantitativeness while improving resolution in a reconstructed image. Objective.
[0011]
[Means for Solving the Problems]
In the PET apparatus according to the present invention, (1) a plurality of photon detectors that respectively detect photons flying from a measurement space including a central axis are two-dimensionally arranged on a cylinder surrounding the central axis and are parallel to the central axis. A plurality of cylindrical detectors corresponding to a structure in which a plurality of detector rings in which a single layer of photon detectors is arranged in a ring shape in a direction parallel to the central axis are formed. Detectors arranged in a direction parallel to the central axis, and (2) at least between the measurement space and the detector, alternately arranged with the cylindrical detector in the direction parallel to the central axis, and measured Multiple slice collimators that allow only photons flying from space to pass almost parallel to a predetermined plane orthogonal to the central axis, and (3) Relative to the subject placed in the measurement space Integrated detector and multiple slice collimators And (4) a pair included in the detection unit during a period in which the detection unit and the plurality of slice collimators are moving relative to the subject by the movement unit. A coincidence information accumulating unit that obtains coincidence information of photon pairs detected by the photon detector of the photon, converts the coincidence information into a coordinate system fixed to the subject and accumulates it, and (5) coincidence counting An image reconstructing unit configured to reconstruct an image representing a spatial distribution of the occurrence frequency of photon pairs in the measurement space based on the coincidence counting information accumulated by the information accumulating unit.
[0012]
According to the PET apparatus of the present invention, the detection unit and the plurality of slice collimators are moved together by the moving unit in a direction parallel to the central axis relative to the subject placed in the measurement space. Of the photon pairs generated in the measurement space during the movement period, those that reach the detection unit without being shielded by the slice collimator are simultaneously detected by a pair of photon detectors included in the detection unit. Is converted into a coordinate system fixed to the subject by the coincidence information storage unit and stored. When the coincidence information accumulation by the coincidence information accumulation unit is completed, an image representing the spatial distribution of the occurrence frequency of photon pairs in the measurement space is reconstructed by the image reconstruction unit based on the accumulated coincidence information. Is done.
[0013]
In the PET apparatus according to the present invention, detection of coincidence counting information may be performed by a pair of photon detectors in the same cylindrical detector included in the detection unit, and each cylindrical detector and each Depending on the size of each slice collimator, the detection may be performed by a pair of photon detectors included in each of two adjacent cylindrical detectors, and a pair of further included in each of two cylindrical detectors. Sometimes performed by a photon detector. In other words, the coincidence information is detected not only in the same detector ring (one layer of photon detectors arranged in a ring shape in the direction parallel to the central axis) but also adjacent to each other. It may be performed between two detector rings, and may also be performed between two detector rings that are further apart. That is, the PET apparatus according to the present invention has an intermediate configuration between a conventional two-dimensional PET apparatus and a conventional three-dimensional PET apparatus, and has a sensitivity several times that of the conventional two-dimensional PET apparatus. Therefore, the PET apparatus according to the present invention can ensure good photon pair detection sensitivity and quantitativeness while improving the resolution of the reconstructed image.
[0014]
In particular, in the PET apparatus according to the present invention, the coincidence information is accumulated during the period in which the detection unit and the slice collimator are integrally moved relative to the subject by the moving unit in the direction parallel to the central axis. Since the reconstructed image is obtained by the image reconstruction unit based on the accumulated coincidence information, even in the configuration of the detection unit in which the cylindrical detectors and the slice collimators are alternately arranged, Photon pairs can be detected with uniform sensitivity in the body axis direction of the subject, and quantitativeness in the reconstructed image can be made uniform.
[0015]
In the PET apparatus according to the present invention, the cylindrical detector includes a plurality of two-dimensional position detectors that detect a two-dimensional incident position on the light receiving surface when a photon is incident on the light receiving surface. It is characterized by being arranged in a shape. In this case, it is preferable to downsize each photon detector to improve the resolution of the reconstructed image.
[0016]
In the PET apparatus according to the present invention, each of the plurality of slice collimators passes through a space between two adjacent cylindrical detectors among the plurality of cylindrical detectors included in the detection unit. It is provided until it reaches the rear part. Moreover, it is preferable that each of the plurality of slice collimators is fixed to each other at the rear portion, for example. In this case, the accuracy of the relative positional relationship between each cylindrical detector and each slice collimator is excellent, and each cylindrical detector and each slice collimator are always alternately positioned in a direction parallel to the central axis. The incident efficiency of the photon to each cylindrical detector is excellent, and the performance can be sufficiently exhibited. In addition, since it is not necessary to strictly manage the processing accuracy and assembly accuracy of each cylindrical detector, each slice collimator, and the holding plate, manufacturing is easy and inexpensive. Moreover, it is suitable for moving the detection unit and the slice collimator together in a direction parallel to the central axis.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.
[0018]
FIG. 1 is an overall schematic configuration diagram of a PET apparatus 1 according to the present embodiment. In this figure, about the detection part 10 and the slice collimator 21, the cross section when cut | disconnected by the surface containing a central axis is shown. The PET apparatus 1 according to the present embodiment includes a detection unit 10, slice collimators 21 _{1 to} 21 ₁₁ , a bed 31, a support base 32, a moving unit 40, a coincidence information storage unit 50, an image reconstruction unit 60, and a display unit 70. I have. In this figure, a subject 2 to be examined by the PET apparatus 1 is also shown. In addition, a space in which the PET apparatus 1 can detect coincidence information of photon pairs is shown as a measurement space 3.
[0019]
In the detection unit 10, cylindrical detectors 13 _{1 to} 13 ₁₂ are arranged in a direction parallel to the central axis between a ring-shaped shield collimator 11 and a shield collimator 12. Each cylindrical detector 13 _n is a two-dimensional array of a plurality of photon detectors that respectively detect photons flying from the measurement space 3 including the central axis on a cylinder surrounding the central axis. That is, each cylindrical detector 13 _n is configured by stacking a plurality of detector rings in which a plurality of photon detectors are arranged in a ring shape on a plane perpendicular to the central axis in a direction parallel to the central axis. It corresponds to. The slice collimators 21 _{1 to} 21 ₁₁ are alternately arranged with the cylindrical detectors 13 _{1 to} 13 _{12 in the} direction parallel to the central axis at least between the measurement space 3 and the detection unit 10, and fly from the measurement space 3. Only the photons that are substantially parallel to the predetermined surface are passed toward the detection unit 10. Details of the detection unit 10 and the slice collimators 21 _{1 to} 21 ₁₁ will be described later.
[0020]
The bed 31 is used to place the subject 2 and is supported by the support base 32. The moving means 40 moves the detection unit 10 and the slice collimators 21 _{1 to} 21 ₁₁ together in a direction parallel to the central axis relative to the subject 2 placed in the measurement space 3. Specifically, the moving unit 40 may move the detection unit 10 and the slice collimators 21 _{1 to} 21 ₁₁ together in a direction parallel to the central axis, or the bed 31 (that is, the subject 2) as the central axis. It may be moved in a parallel direction. Further, the movement may be only in one direction during the measurement period, or may be a reciprocating movement. The relative movement by the moving means 40 is performed so that the measurement site of the subject 2 moves in the measurement space 3 by a distance of ½ or more of the arrangement pitch of each cylindrical detector 13 _n during the measurement period. . Preferably, the relative movement of the measurement site of the subject 2 within the measurement space 3 during the measurement period is performed by a distance that is an integral multiple of the pitch, and is performed at a constant speed. In addition, when the measurement site of the subject 2 exists over a certain range in the central axis direction, the time during which each site within the certain range remains in the measurement space 3 during the measurement period is substantially constant. Is preferred.
[0021]
The coincidence information storage unit 50 includes a pair of photons included in the detection unit 10 during a period in which the detection unit 10 and the slice collimators 21 _{1 to} 21 ₁₁ are moved relative to the subject 2 by the moving unit 40. The coincidence information of the photon pairs detected by the detector is accumulated. When accumulating the coincidence count information, the coincidence count information detected by the detection unit 10 based on the relative displacements of the detection unit 10 and the slice collimators 21 _{1 to} 21 ₁₁ with respect to the subject 2 Then, the coordinate system is converted to a fixed coordinate system, and the coincidence count information subjected to the coordinate conversion is stored. In addition, what was calculated | required with the encoder etc. may be used for a relative displacement amount, and what the movement means 40 grasped | ascertained may be used.
[0022]
The image reconstruction unit 60 reconstructs an image representing the spatial distribution of the occurrence frequency of photon pairs in the measurement space 3 based on the coincidence counting information accumulated by the coincidence counting information accumulation unit 50. The image reconstruction unit 60 also performs sensitivity correction for correcting variation in detection sensitivity of each photon detector of the detection unit 10, absorption correction for correcting photon absorption in the subject 2, and photon scattering in the subject 2. Scatter correction is also performed. The display unit 70 displays the reconstructed image obtained by the image reconstruction unit 60. The control unit 80 also performs relative movement by the moving unit 40, accumulation of coincidence count information by the coincidence count information accumulation unit 50, image reconstruction by the image reconstruction unit 60, and display of a reconstructed image by the display unit 70. To control.
[0023]
FIG. 2 is a diagram illustrating the configuration of the detection unit 10 and the slice collimator 21 of the PET apparatus according to the present embodiment. This figure shows a cross section when the detection unit 10 and the slice collimators 21 _{1 to} 21 ₁₁ are cut along a plane including the central axis. The detection unit 10 of the PET apparatus according to the present embodiment includes cylindrical detectors 13 _{1 to} 13 ₁₂ stacked in a direction parallel to the central axis between a ring-shaped shield collimator 11 and a shield collimator 12, respectively. It is out. Each of the ring-shaped slice collimators 21 _{1 to} 21 ₁₁ is disposed at least between the measurement space and the detection unit 10 and is alternately arranged with the cylindrical detector 13 _{n in} a direction parallel to the central axis. That is, each slice collimator 21 _n is arranged at a position between the cylindrical detector 13 _n and the cylindrical detector 13 _{n + 1} that are adjacent to each other. Each slice collimator 21 _n is made of a material having a large atomic number and a high specific gravity (for example, lead or tungsten), a thickness of several mm (for example, 5 mm to 6 mm), and a photon (gamma ray) flying from the measurement space. ), A photon substantially parallel to a plane perpendicular to the central axis is allowed to pass toward the detection unit 10, and a collimating action is performed to shield obliquely incident photons.
[0024]
FIG. 3 is an enlarged view showing a part of the detection unit 10 and the slice collimator 21 of the PET apparatus according to the present embodiment (the part in the frame surrounded by the one-dot chain line in FIG. 2). FIG. 4 is a diagram illustrating the configuration of the cylindrical detector 13 _n and the slice collimator 21 _n of the PET apparatus according to the present embodiment. FIG. 4 shows the relationship between the cylindrical detector 13 _n and the slice collimator 21 _n when viewed in the direction parallel to the central axis. Each cylindrical detector 13 _n has a plurality of block detectors 14 _{1 to} 14 _M arranged in a ring shape on the same circumference on a plane perpendicular to the central axis. Each block detector 14 _m is a two-dimensional position detector that detects a two-dimensional incident position on the light receiving surface when a photon enters the light receiving surface. Each slice collimator 21 _n is provided through the space between the adjacent cylindrical detectors 13 _n and 13 _{n + 1} to reach the rear part of each cylindrical detector 13 _n. In the rear part, they are integrally fixed to each other by the holding plate 22.
[0025]
FIG. 5 is a configuration diagram of the block detector 14. As shown in this figure, each block detector 14 _m is a scintillation detector in which a scintillator block 15 composed of segments of P × Q (P ≧ 2, Q ≧ 2) and a position detection type photomultiplier tube 16 are combined. In addition to detecting the photons that have arrived from the measurement space and reached the light receiving surface of the scintillator block 15, the two-dimensional incident position on the light receiving surface is detected. That is, each block detector 14 _m corresponds to a two-dimensional array of P × Q small photon detectors. Further, the cylindrical detector 13 _n configured by arranging such block detectors 14 _m in a ring shape has a plurality of small photon detectors arranged in a ring shape on a plane perpendicular to the central axis. A detector ring is configured, and this detector ring corresponds to a plurality of detector rings stacked in a direction parallel to the central axis. In the block detector 14 _m , together with the scintillator block 15 and the position detection photomultiplier tube 16, a resistor array for applying a predetermined voltage to each electrode in the position detection photomultiplier tube 16, A preamplifier for inputting a current signal output from the anode electrode of the position detection type photomultiplier tube 16 and outputting it as a voltage signal is housed in a light shielding case.
[0026]
For example, as the scintillator block 15, BGO (Bi ₄ Ge ₃ O ₁₂ ), GSO (Gd ₂ SiO ₅ (Ce)), LSO (Lu ₂ SiO ₅ (Ce)), PWO (PbWO ₄ ) and the like are preferably used. . The scintillator block 15 is composed of 8 × 8 segments, the size of each segment is 6 mm × 6 mm × 20 mm, and the width of the photocathode of the position detection type photomultiplier tube 16 is 50 mm × 50 mm. Then, 60 block detectors 14 _m including the scintillator block 15 and the position detection type photomultiplier tube 16 are arranged in a ring shape to constitute a cylindrical detector 13 _n . At this time, the inner diameter of each cylindrical detector 13 _n is about 1000 mm. Each slice collimator 21 _{n has} an inner diameter of 600 mm. Furthermore, the thickness (that is, the field of view in the body axis direction) of such cylindrical detectors 13 _{1 to} 13 ₁₂ and slice collimators 21 _{1 to} 21 ₁₁ alternately stacked in the direction parallel to the central axis is about 670 mm. .
[0027]
Under such conditions, detection of a pair of photons (gamma rays) of energy 511 keV that is generated in association with the annihilation of electrons and positrons in the measurement space 3 and flies in the opposite directions, that is, detection of coincidence information is the same. may be done by the cylindrical detector 13 _n block detector 14 of the pair of the, also, a pair included in each cylindrical detector 13 _n and the cylindrical detector 13 n _{+ 1} adjacent to each other block This may be done by the detector 14. The coincidence counting information may be detected by a pair of block detectors 14 included in two cylindrical detectors 13 that are further apart from each other. In other words, the coincidence information is detected not only within the same detector ring, but also between two detector rings adjacent to each other, and even between two detector rings that are further apart. Sometimes done.
[0028]
That is, the PET apparatus 1 according to the present embodiment has an intermediate configuration between the conventional two-dimensional PET apparatus and the conventional three-dimensional PET apparatus. When the sensitivity per unit axial length (cm) in the body axis direction under the above conditions is calculated, the sensitivity of the PET apparatus 1 according to the present embodiment is about 1.3 kcps / (kBq · ml), which is the conventional three-dimensional. Compared to the sensitivity of a conventional two-dimensional PET device (about 0.28 kcps / (kBq · ml)), it is about half that of the sensitivity of a PET device (about 2.58 kcps / (kBq · ml)). And about 4 to 5 times.
[0029]
Next, the operation of the PET apparatus 1 according to this embodiment will be described. The subject 2 to which the RI radiation source is administered is placed on the bed 31, and the measurement site of the subject 2 is positioned in the measurement space 3. Then, under the control of the control unit 80, the PET apparatus 1 operates as follows. First, the detection unit 10 and the slice collimators 21 _{1 to} 21 ₁₁ start moving in a direction parallel to the central axis relative to the subject 2 placed in the measurement space 3 by the moving unit 40.
[0030]
Among the pairs of photons (gamma rays) of energy 511 keV that are generated in association with the annihilation of electrons and positrons in the measurement space 3, the detection unit 10 is not shielded by the slice collimators 21 _{1 to} 21 _11. The arrivals are simultaneously detected by a pair of photon detectors included in the detection unit 10. The coincidence information of the photon pairs simultaneously detected by the detection unit 10 during the relative movement period is based on the relative displacement amounts of the detection unit 10 and the slice collimators 21 _{1 to} 21 ₁₁ with respect to the subject 2. The coordinate system is converted into a coordinate system fixed with respect to the subject 2 and accumulated by the coincidence counting information accumulation unit 50.
[0031]
When the predetermined measurement period ends, the accumulation of coincidence counting information by the coincidence counting information accumulation unit 50 is terminated, and the relative movement by the moving unit 40 is also terminated. Then, the image reconstructing unit 60 reconstructs an image representing the spatial distribution of the occurrence frequency of photon pairs in the measurement space 3 based on the coincidence counting information accumulated by the coincidence counting information accumulating unit 50. The image reconstruction unit 60 also performs sensitivity correction, absorption correction, and scattering correction. The reconstructed image obtained by the image reconstruction unit 60 is displayed by the display unit 70.
[0032]
As described above, the detection unit 10 of the PET apparatus 1 according to the present embodiment includes the cylindrical detectors 13 _{1 to} 13 ₁₂ arranged in a direction parallel to the central axis. _n is a plurality of photon detectors arranged two-dimensionally on a cylinder surrounding the central axis. The cylindrical detectors 13 _{1 to} 13 ₁₂ and the slice collimators 21 _{1 to} 21 ₁₁ are alternately arranged in the direction parallel to the central axis. By configuring the detection unit 10 in this way, it is possible to improve the resolution of the reconstructed image by downsizing the individual photon detectors. Further, instead of providing a slice collimator between the detector ring, by providing the slice collimator 12 _n between the cylindrical detector 13 _n, to secure the spacing of each slice collimator 12 _n, suppressing a decrease in aperture ratio In addition, photon pair detection sensitivity can be ensured. Furthermore, since it is not necessary to make each slice collimator 12 _n thin, the collimating effect can be maintained, scattered rays can be efficiently excluded, and the quantitativeness of the reconstructed image can be ensured. Thus, the PET apparatus 1 according to the present embodiment can ensure good photon pair detection sensitivity and quantitativeness while improving the resolution of the reconstructed image.
[0033]
Further, coincidence count information is accumulated during a period in which the detection unit 10 and the slice collimators 21 _{1 to} 21 ₁₁ are integrally moved in the direction parallel to the central axis relative to the subject 2 by the moving unit 40. The reconstructed image is obtained by the image reconstructing unit 60 based on the accumulated coincidence information. Therefore, in the present embodiment, even with the configuration of the cylindrical detectors 13 _{1 to} 13 ₁₂ and the slice collimators 21 _{1 to} 21 ₁₁ as described above, the photon pair is detected with uniform sensitivity in the body axis direction of the subject 2. It can be detected, and the quantitativeness in the reconstructed image can be made uniform.
[0034]
In the present embodiment, a plurality of two-dimensional position detectors (block detectors 14 _m ) that detect a two-dimensional incident position on the light receiving surface when a photon enters the light receiving surface are arranged in a ring shape to form a cylinder. A state detector 13 _n is constructed. Therefore, this case is suitable for reducing the size of each photon detector and improving the resolution of the reconstructed image.
[0035]
In the present embodiment, the slice collimator 21 _n is provided until it reaches the rear part of each cylindrical detector 13 _n through the space between the cylindrical detector 13 _n and the cylindrical detector 13 _{n + 1.} And fixed to each other by the holding plate 22 at the rear portion. Therefore, in this case, excellent accuracy of the relative positional relationship between each cylindrical detector 13 _n and each slice collimator 21 _n, parallel to each cylindrical detector 13 _n and each slice collimator 21 _n and the center axis Since they are always alternately positioned in the right direction, the incident efficiency of the photons to each cylindrical detector 13 _n is excellent, and the performance can be sufficiently exhibited. Further, since it is not necessary to strictly manage the processing accuracy and assembly accuracy of each cylindrical detector 13 _n , each slice collimator 21 _n, and the holding plate 22, manufacturing is easy and inexpensive. Moreover, it is suitable for moving the detection unit 10 and the slice collimators 21 _{1 to} 21 ₁₁ together in a direction parallel to the central axis.
[0036]
【The invention's effect】
As described above in detail, according to the present invention, detection of coincidence counting information may be performed by a pair of photon detectors in the same cylindrical detector included in the detection unit, Depending on the size of the cylindrical detector and each of the slice collimators, the detection may be performed by a pair of photon detectors included in two adjacent cylindrical detectors. May be performed by a pair of photon detectors. In other words, the coincidence information is detected not only within the same detector ring, but also between two detector rings adjacent to each other, and even between two detector rings that are further apart. Sometimes done. That is, the PET apparatus according to the present invention has an intermediate configuration between a conventional two-dimensional PET apparatus and a conventional three-dimensional PET apparatus, and has a sensitivity several times that of the conventional two-dimensional PET apparatus. Therefore, the PET apparatus according to the present invention can ensure good photon pair detection sensitivity and quantitativeness while improving the resolution of the reconstructed image.
[0037]
In particular, the coincidence information is accumulated by the coincidence information accumulation unit during the period in which the detection unit and the slice collimator are integrally moved in the direction parallel to the central axis relative to the subject by the moving unit. Since the reconstructed image is obtained by the image reconstruction unit based on the coincidence information, even in the configuration of the detection unit in which the cylindrical detectors and the slice collimators are alternately arranged, the body axis direction of the subject is uniform. A photon pair can be detected with high sensitivity, and quantitativeness in the reconstructed image can be made uniform.
[0038]
When a cylindrical detector is configured by arranging a plurality of two-dimensional position detectors for detecting a two-dimensional incident position on the light receiving surface when a photon enters the light receiving surface in a ring shape on a predetermined surface. For this reason, it is preferable to downsize individual photon detectors to improve the resolution of the reconstructed image.
[0039]
Each of the plurality of slice collimators is provided until reaching the rear part of each cylindrical detector through a space between two adjacent cylindrical detectors among the plurality of cylindrical detectors included in the detection unit. For example, it is preferable that the rear portions are fixed to each other. In this case, the accuracy of the relative positional relationship between each cylindrical detector and each slice collimator is excellent, and each cylindrical detector and each slice collimator are always alternately positioned in a direction parallel to the central axis. The incident efficiency of the photon to each cylindrical detector is excellent, and the performance can be sufficiently exhibited. In addition, since it is not necessary to strictly manage the processing accuracy and assembly accuracy of each cylindrical detector, each slice collimator, and the holding plate, manufacturing is easy and inexpensive. Moreover, it is suitable for moving the detection unit and the slice collimator together in a direction parallel to the central axis.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an entire PET apparatus according to the present embodiment.
FIG. 2 is a diagram for explaining a configuration of a detection unit and a slice collimator of the PET apparatus according to the present embodiment.
FIG. 3 is an enlarged view showing a part of a detection unit and a slice collimator of the PET apparatus according to the present embodiment.
FIG. 4 is a diagram for explaining a configuration of a cylindrical detector and a slice collimator of the PET apparatus according to the present embodiment.
FIG. 5 is a block diagram of a block detector.
FIG. 6 is a diagram illustrating a configuration of a detection unit of a two-dimensional PET apparatus.
FIG. 7 is a diagram illustrating a configuration of a detection unit of a three-dimensional PET apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... PET apparatus, 2 ... Subject, 3 ... Measurement space, 10 ... Detection part, 11, 12 ... Shield collimator, 13 ... Cylindrical detector, 14 ... Block detector, 15 ... Scintillator block, 16 ... Position detection type Photomultiplier tube, 21 ... slice collimator, 22 ... holding plate, 31 ... bed, 32 ... support base, 40 ... moving means, 50 ... simultaneous counting information storage unit, 60 ... image reconstruction unit, 70 ... display unit.

Claims (3)

A plurality of photon detectors each detecting photons flying from a measurement space including the central axis are two-dimensionally arranged on a cylinder surrounding the central axis, and one layer of photon detectors in a direction parallel to the central axis Includes a plurality of cylindrical detectors corresponding to a configuration in which a plurality of detector rings arranged in a ring shape are stacked in a direction parallel to the central axis, and the plurality of cylindrical detectors are arranged on the central axis. Detectors arranged in parallel directions;
A predetermined surface orthogonal to the central axis among photons flying from the measurement space, alternately arranged with the cylindrical detector in a direction parallel to the central axis, at least between the measurement space and the detection unit A plurality of slice collimators that allow only those substantially parallel to the detection section to pass through,
Moving means for moving the detection unit and the plurality of slice collimators together in a direction parallel to the central axis relative to a subject placed in the measurement space;
Simultaneous photon pairs detected by a pair of photon detectors included in the detection unit during a period in which the detection unit and the plurality of slice collimators are moving relative to the subject by the moving unit. A coincidence information storage unit for acquiring the counting information, converting the accumulative counting information into that of the coordinate system fixed to the subject, and accumulating the information,
Based on the coincidence information accumulated by the coincidence information accumulation unit, an image reconstruction unit that reconstructs an image representing a spatial distribution of the occurrence frequency of photon pairs in the measurement space;
A PET apparatus comprising: The cylindrical detector is configured by arranging a plurality of two-dimensional position detectors that detect a two-dimensional incident position on the light receiving surface when a photon enters the light receiving surface in a ring shape on the predetermined surface. The PET apparatus according to claim 1. Each of the plurality of slice collimators is provided until reaching the rear part of each cylindrical detector through a space between two adjacent cylindrical detectors among the plurality of cylindrical detectors included in the detection unit. The PET apparatus according to claim 1, wherein:

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