JP3904220B1 - Positron emission tomography apparatus and transmission imaging control method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a PET device for a head that makes it possible to image a target area in a short time using a point source and prevent unnecessary exposure.
A gantry 1 of a PET apparatus 100 includes a detector ring 2, a radiation source housing 3, an external radiation source 4, a rotation gear 5, a rotation driving device 6, a rectilinear driving device 7, a radiation source shield 8 and a radiation source housing. A support bar 9 is provided. At the start of transmission imaging, the radiation source housing 3 and the external radiation source 4 go straight to the end of the detector ring 2 on the side close to the shoulder of the examinee 10 by the straight drive 7, and then the radiation source housing support rod 9. Is passed to the rotating gear 5. The rotation drive device 6 rotates the rotation gear 5 to rotate the radiation source housing support rod 9, the radiation source housing 3, and the external radiation source 4 around the examinee 10. The γ rays from the external source 4 are irradiated in the direction in which the imaging region of the detector ring 2 and the detector region overlap with each other through the four surfaces of the portion of the source housing 3 that is penetrated.
[Selection] Figure 1

Description

  The present invention relates to a data collection mechanism of a head positron emission tomography apparatus (hereinafter referred to as a head PET (Positron Emission Tomography) apparatus), and more particularly to a radiation source mechanism suitable for measuring transmission data. .

  The PET apparatus includes a radiation detector ring and an external radiation source. In an examination using a PET apparatus, positron radiopharmaceutical (hereinafter referred to as PET drug) is administered to a subject to be examined, and γ-ray data (hereinafter referred to as emission data) emitted from the inside of the subject. ) And a transmission scan for collecting absorption correction data (hereinafter referred to as transmission data) using an external radiation source.

In an inspection using a PET apparatus (hereinafter referred to as an FDG test) performed by administering radioactive fluorine 18 ( ¹⁸ F) -labeled fluorodeoxyglucose (hereinafter abbreviated as FDG), the test is usually performed after FDG is administered to a subject. After a time of about 30 to 60 minutes when sufficient FDG uptake into the site can be expected, transmission data is collected by rotating an external radiation source around the subject, and 511 keV gamma rays (hereinafter referred to as γ rays). Emission data is collected for each subject imaging region.

  The emission scan includes two-dimensional imaging in which a septa is provided between the detectors and imaging, and three-dimensional imaging in which no septa is provided. In two-dimensional imaging, the detection sensitivity in the gantry axis direction becomes uniform and the influence of scattered radiation can be suppressed due to the presence of the septa, but the sensitivity of the entire gantry is low, and data collection takes a long time. On the other hand, in 3D imaging, although there are problems such as the distribution of sensitivity in the gantry axis direction and the possibility of noise contamination due to scattered radiation and random coincidence (accidental coincidence), the entire gantry has high sensitivity, so data Collection time is short. For this reason, three-dimensional imaging has become the mainstream in recent years due to the demand for improved throughput. In addition, since the data of the whole body of the subject cannot be collected at once with the normal gantry length of the PET apparatus, the gantry or bed (bed) of the PET apparatus is moved and imaged in several times while overlapping the imaging range. Is done.

Generally, ⁶⁸ Ge- ⁶⁸ Ga, ¹³⁷ Cs, or the like is used as an external radiation source used for transmission data collection. In the case of ⁶⁸ Ge- ⁶⁸ Ga which is a positron nuclide, a rod-shaped radiation source arranged in the gantry axis direction is generally used. Since the rod-shaped radiation source emits gamma ray pairs having energy of 511 keV, the PET apparatus simultaneously counts the gamma ray pairs and collects absorption correction data between the detectors. By rotating the rod-shaped radiation source, data necessary for correcting all cross sections in the field of view in the body axis direction can be acquired at once. This technique is described in Non-Patent Document 1, for example.

In addition to whole body data collection using FDG, there is a brain function test using FDG, which is expected to be used for diagnosis of Alzheimer's disease and the like. In order to collect the whole body data, the whole body must enter the gantry, so the gantry opening diameter is about 600 mm to 700 mm, and the detector ring diameter is about 800 mm to 900 mm. Therefore, when brain function diagnosis using a whole-body PET apparatus is performed, details cannot be imaged because the head is small relative to the ring diameter. Therefore, a head PET apparatus for diagnosing the head exclusively has been proposed. The PET device for the head has a gantry opening diameter of about 300 mm into which the head enters and a detector ring diameter of about 400 mm, so that a detailed drug distribution can be imaged.
Japanese translation of PCT publication No. 2002-512374 Japanese translation of PCT publication No. 2002-512375 JP 2000-284051 A “The Journal of Nuclear Medicine”, Vol.44, No.2, p.291-315, February 2003

As described above, when a rod-shaped radiation source using ⁶⁸ Ge- ⁶⁸ Ga positron nuclide is used as a transmission radiation source in the head PET apparatus, there is an advantage that the field of view in the body axis direction is wide. However, since the energy of γ rays emitted from the radiation source and the energy of γ rays emitted from the PET drug administered to the subject are both 511 keV, transmission data is collected after the PET drug is administered to the subject. In the case of post-injection imaging that performs the above, noise due to mixing into each other's data increases. In order to obtain data with less noise, it is conceivable to increase the source intensity or lengthen the acquisition time. However, in the ⁶⁸ Ge- ⁶⁸ Ga rod-shaped radiation source, since the count rate is limited by a detector close to the radiation source, the intensity of the radiation source to be raised is limited. This is described in Non-Patent Document 1, for example. In addition, the ⁶⁸ Ge- ⁶⁸ Ga radiation source needs to be replaced in about one year due to a half-life limitation.

Therefore, it has been proposed to use ¹³⁷ Cs, which is a single-photon emission nuclide, as a transmission radiation source. The source is geometrically a point source if necessary to identify the emission location. The area around the point source is shielded to limit the irradiation range to a conical shape, and the absorption rate between the detector position where the emitted γ-ray is detected and the source position is obtained. ^Since the energy of γ-rays radiated from ¹³⁷ Cs is 662 keV, it can be distinguished from γ-rays from PET drugs, and there is little mixing in each other's data. In the point source, the irradiation range is limited by shielding, so that the source intensity can be increased and data with less noise can be acquired. Furthermore, since the ¹³⁷ Cs radiation source has a long half-life of about 30 years and does not need to be replaced during the lifetime of the apparatus, it has recently become widely preferred.

  Further, in the conventional transmission imaging method using a point source, the point source is disposed at the center of the detector ring body axis and rotated around the subject.

  However, since irradiation is performed from a point source, the field of view in the body axis direction in the gantry is limited, and therefore it is necessary to capture images so that the imaging ranges overlap when the gantry or bed is moved.

  Furthermore, the following problems occur when performing transmission imaging using a point source in the head PET apparatus. As described above, the gantry opening diameter in the head PET apparatus is about 300 to 350 mm. However, when the subject is an adult, the shoulder width is 400 mm or more, so the shoulder of the subject hits the end of the gantry and the inside of the gantry. It is not possible to completely insert the subject. Therefore, there arises a problem that the head and neck cannot be imaged.

Therefore, an object of the present invention is to provide a head-use PET apparatus that can perform transmission imaging of a target area in a short time using a point source and prevent unnecessary exposure.

The present invention that solves the above problems includes a bed on which a subject is placed, radiation generating means for generating radiation, and a radiation detector annular body in which a plurality of radiation detectors for detecting radiation generated from the radiation generating means are arranged in a ring shape. A positron emission tomography apparatus having a rotating means for holding the radiation generating means and rotating along the radiation detector ring, wherein the radiation generating means emits a beam of a point-like single photon emission nuclide; A housing in which the single-photon emission nuclide is stored and a radiation emission port is formed so that the beam is shaped to look into the radiation detector annular body. The radiation generating means is rotated in the circumferential direction of the radiation detector annular body at the end of the subject insertion side.

The present invention is also a positron emission tomography apparatus, wherein the radiation emission port of the housing limits the radiation direction of the beam so that the beam does not protrude from the imaging region of the radiation detector annular body. A substantially planar first surface and a second surface, and an approximately provided on the subject insertion side that limits the radiation direction of the beam so that the beam does not protrude from the detector region of the radiation detector annular body. A flat third surface and a fourth curved surface provided on the opposite side of the subject insertion side that limit the radiation direction of the beam so that the beam does not protrude from the detector region of the radiation detector annular body. It is characterized by providing these surfaces. The present invention includes another positron emission tomography apparatus and a transmission imaging control method in the positron emission tomography apparatus.

ADVANTAGE OF THE INVENTION According to this invention, in the PET apparatus for heads, transmission imaging of the target area can be performed in a short time using a point source, and unnecessary exposure can be prevented.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

≪Device configuration and overview≫
A head PET apparatus, which is a preferred embodiment of the present invention, will be described with reference to FIG. In the present embodiment, a PET apparatus including an external radiation source using ¹³⁷ Cs (cesium 137) which is a point photon emission nuclide will be described as an example of the head PET apparatus 100. The radiation detector according to the present embodiment may have a configuration using a scintillation detector that converts radiation detection into light and then converts it into an electrical signal, or directly converts the detector signal into an electrical signal. A configuration using a semiconductor detector may also be used.

  A gantry 1 (imaging device) provided in the PET apparatus 100 includes a detector ring (radiation detector annular body) 2, a radiation source housing 3 as a radiation shield, and an external radiation source (single photon emission nuclide). 4, a rotation gear 5, a rotation drive device 6, a straight drive device 7, a radiation source shield 8, and a radiation source housing support rod 9. The gantry 1 has a substantially cylindrical shape having a hole (penetrating part) 13, and a plurality of detector rings 2 are arranged around the hole 13 and in the body axis direction. As shown in FIG. 1B, the rotation gear 5 has the same central axis as the detector ring 2 and is installed on the opposite side of the detector ring 2 from the insertion side of the examinee 10. The rotation drive device 6 is a motor that rotates the rotation gear 5, and is installed on a side farther from the rotation gear 5 when viewed from the central axis. In FIG. 1B, the rotary drive device 6 is shown as being below the rotary gear 5, but the invention is not limited to this. The rectilinear drive device 7 is installed on the opposite side of the detector ring 2 with the rotation gear 5 interposed therebetween. The radiation source shield 8 is installed on the opposite side of the detector ring 2 with the rotation gear 5 interposed therebetween, so that the radiation from the external radiation source 4 can be shielded when the radiation source housing 3 is stored. Installed closer to the rotary gear 5 than the linear drive device 7.

  The examinee (subject) 10 can move in the body axis direction in the hole 13 by the bed driving device 12 moving the bed 11 while lying on the bed 11. When storing the external radiation source 4, the radiation source housing 3, the external radiation source 4, and the radiation source housing support rod 9 are held by the linear drive device 7, and the external radiation source 4 is placed outside the gantry 1 by the radiation source shield 8. Shielded from leaking radiation from When the external radiation source 4 is delivered, the radiation source housing 3 and the external radiation source 4 are moved together with the radiation source housing support rod 9 in the axial direction of the gantry 1 by the linear drive device 7 and are held by the rotating gear 5 and rotated. It is rotated by the drive device 6. Rather than fixing the radiation source housing 3 in this manner, the delivery and storage are performed because the radiation source housing 3 scatters when performing emission imaging to detect γ rays emitted from the PET drug collected at the affected area. Since it becomes a body and adversely affects imaging, the radiation source housing 3 is unloaded in the case of transmission imaging, and is stored in other cases.

  The radiation source housing 3 and the external radiation source 4 are collectively referred to as radiation generation means or radiation generation apparatus. The rotation gear 5, the rotation drive device 6, and the radiation source housing support rod 9 are collectively referred to as rotation means. The linear drive device 7 and the radiation source housing support rod 9 are collectively referred to as moving means.

As shown in FIG. 1, the radiation source housing 3 includes an external radiation source 4 (for example, a ¹³⁷ Cs point radiation source) 4 for transmission. In the present embodiment, the radiation source housing 3 has a shape as shown in FIG. 2, and the shape is determined by the position of the external radiation source 4, the imaging region, and the shape of the detector ring 2. Note that the external radiation source 4 does not necessarily have to be a point radiation source, and may be a substantially point shape. Hereinafter, the radiation source housing 3 and the external radiation source 4 will be described in detail with reference to FIG.

  FIG. 2A shows a side view of the radiation source housing 3, and FIG. 2B shows a plan view of the radiation source housing 3. The radiation source housing 3 is a cylindrical body, and has a γ-ray emission port (radiation emission port) 20 having a shape that penetrates a part of the cylindrical body. The γ-ray emission port 20 has four surfaces P1 (first surface), P2 (second surface), P3 (third surface), and P4 (fourth surface). Then, the external radiation source 4 is installed at the starting point of the four surfaces in the radiation source housing 3. Gamma rays are emitted from the external source 4 and emitted within a range of directions defined by the four planes P1, P2, P3 and P4. The γ rays emitted to other than the γ ray emission port 20 are shielded by the radiation source housing 3. Note that the shape of the radiation source housing 3 in which the γ-ray emission port 20 is formed is not necessarily a cylindrical body, and may be a rectangular parallelepiped or other shapes. Further, the radiation source housing 3 may be constituted by a plurality of members.

  The surfaces P1 and P2 are substantially planar in order to prevent γ rays from leaking outside (in a direction not passing through the hole 13) of the hole (measurement space) 13 of the gantry 1 shown in FIG. Provided. According to this, not only is it meaningless because effective data is not acquired even if γ rays are emitted in a space other than the hole 13 (imaging region), that is, where an imaging target cannot exist, Since it is useless to increase the load of the detection system for detecting unnecessary data, it is possible to suppress such γ-ray emission.

  When the radiation source housing 3 is located at the insertion side end of the examinee 10 of the detector ring 2, the surface P <b> 3 is outside the insertion side end of the examinee 10 of the detector ring 2 in the axial direction of the gantry 1. In order to prevent leakage of γ rays, it is formed in a substantially flat shape. The surface P3 substantially coincides with a part of the side surface of the oblique cone that connects the external radiation source 4 and the inner circumference of the end of the detector ring 2 on the insertion side of the examinee 10. Further, the surface P4 is such that when the radiation source housing 3 is located at the end of the detector ring 2 on the insertion side of the examinee 10, γ rays leak from the detector ring 2 to the rotating gear 5 side in the axial direction of the gantry 1. In order not to be, it is formed in a curved surface shape. The surface P4 substantially coincides with a part of the side surface of the oblique cone connecting the external radiation source 4 and the inner circumference of the end of the detector ring 2 opposite to the insertion side end of the examinee 10 (see FIG. 3). ). According to this, even if γ-rays are emitted to a place without the detector ring 2 (detector region), it is not detected because it is not detected, and in that case, there is a possibility of unnecessary exposure. Such γ-ray emission can be suppressed. This effect cannot be obtained when this embodiment in which γ rays are emitted from the external radiation source 4 located at the end of the gantry 1 is not used. In order to solve the problem with which the shoulder hits described in [Problems to be Solved by the Invention], for example, when the external radiation source 4 irradiates the gantry 1 at the center or the end while changing the position in the axial direction, any position In order to acquire valid data, the shape that suppresses invalid exposure cannot be used as in the radiation source housing 3 of the present embodiment.

≪Transmission imaging and emission imaging methods≫
Hereinafter, transmission imaging and emission imaging methods in the present embodiment will be described. In the present embodiment, a case where a post-injection method in which transmission imaging and emission imaging are continuously performed will be described by taking static imaging of the head examination of the examinee 10 as an example (see FIG. 1 as appropriate).

  Before conducting the PET examination, a PET drug (for example, FDG) is preliminarily administered to the subject to be examined 10 by injection. The examinee 10 is put on standby for a required time (about 30 to 60 minutes) until the PET drug administered to the examinee 10 diffuses into the body and is taken into and accumulated in the brain as the examination site. Thereafter, the examinee 10 is laid on the bed 11.

  When transmission imaging by the PET apparatus 100 is started, the operator operates a button provided on an operator console (not shown) to give an instruction to start imaging. Using the button operation as a trigger, an inspection start signal is output to the overall control unit (not shown). The overall control unit that has input the examination start signal outputs information related to the examination target range of the examinee 10 and the bed movement start signal to the bed movement control unit (not shown). The bed movement control unit that has input the bed movement start signal issues an instruction to the bed driving device 12 based on the input information, so that the brain to be examined by the examinee 10 enters the γ-ray detection region of the PET apparatus 100. The bed 11 is moved to enter. At this time, the bed 11 may be moved to a limit where the shoulder of the examinee 10 does not contact the gantry 1. In this state, transmission imaging is started.

<Transmission imaging>
In starting transmission imaging, first, the radiation source housing 3 and the external radiation source 4 are moved by the linear drive device 7 together with the radiation source housing support rod 9 to the end of the detector ring 2 on the side close to the shoulder of the examinee 10 (end portion). ) And then the source housing support rod 9 is passed to the rotating gear 5. The rotation drive device 6 rotates the rotation gear 5 to rotate the radiation source housing support rod 9, the radiation source housing 3, and the external radiation source 4 around the examinee 10. The rotational position of the external radiation source 4 is obtained from a signal indicating the rotational speed output from the rotational driving device 3 by previously obtaining the relationship between the rotational speed of the rotational driving device 3 and the rotational amount of the rotational gear 5. Further, since the position in the gantry 1 in the body axis direction is constant, the position information is used.

  The radiation source housing 3 has the shape shown in FIG. 2, and this shape irradiates the detector region where the detector ring 2 shown in FIG. 3 is present, so that γ rays leak to the outside of the gantry 1. It is possible to collect transmission data with little excess and deficiency.

  FIG. 4 is a diagram showing a configuration of a γ-ray detection processing system that detects γ-rays in a PET apparatus and processes the detection signals. The γ-ray detection processing system 101 is a system incorporated in the PET apparatus 100 of FIG. 1 and includes a detector ring 2, a data processing apparatus 31, and a display apparatus 32. The detector ring 2 includes a plurality of radiation detectors 21, analog ASICs (Application Specific Integrated Circuits) 22, and digital ASICs 23 in the circumferential direction. The data processing device 31 includes an absorption correction data creation device 310, a coincidence counting device 311, a storage device 312, and a tomographic image creation device 313. Hereinafter, processing of the γ-ray detection processing system 101 will be described.

  The γ-rays emitted from the external radiation source 4 pass through the examinee 10 and are detected by the radiation detector 21 in the detector ring 2. The radiation detector 21 that has detected the γ-ray outputs an electrical signal (hereinafter referred to as a γ-ray detection signal) corresponding to the energy of the γ-ray to the analog ASIC 22. The analog ASIC 22 generates a timing signal for specifying the detection time of the γ-ray based on the γ-ray detection signal input from the radiation detector 21, and transmits the generated timing signal to the digital ASIC 23. The analog ASIC 22 generates γ-ray peak value information based on the γ-ray detection signal, and transmits the generated peak value information to the digital ASIC 23.

The digital ASIC 23 determines the detection time of γ rays based on the timing signal received from the analog ASIC 22 and specifies the detector ID (ID for identifying the radiation detector 21). The digital ASIC 23 converts the peak value information corresponding to the radiation detector 21 of the detector ID into digital information. When the nuclide of the external radiation source 4 is ¹³⁷ Cs, the peak value level is different from the emission-derived γ-ray, so it can be determined at which point the γ-ray detection signal is derived (if none is Data may be rejected at this point). When it is determined that the external radiation source 4 is derived, the origin radiation source information is derived from the external radiation source. Further, the digital ASIC 23 adds time information and a detector ID to these digital information to generate packet data. Packet data including four pieces of information (time information, detector ID, origin source information, and peak value information) is transmitted to the data processing device 31.

  The absorption correction data creation device 310 of the data processing device 31 performs absorption correction data creation processing based on the packet data transmitted from the digital ASIC 23 and originating from the external radiation source 4. Specifically, first, from the time information of the packet data and the table (not shown) indicating the correspondence between the time and the position of the external radiation source 4 stored in advance in the storage device 312, when γ-ray is detected. The position of the external radiation source 4 is specified. Next, the position of the radiation detector 21 that has detected γ-rays from the detector ID is specified. Then, the direction in which the γ rays have passed is specified by a line connecting these two positions. Information on the direction specified in this way is accumulated and counted. By calculating the γ-ray absorptance in each direction by normalizing the count in each direction with the corresponding directional count obtained in the same manner as when there is nothing in the imaging area, the calculated absorptance The data is stored in the storage device 312 as part of the absorption rate distribution data. Further, the absorption distribution data in all directions is calculated based on the absorption data. This calculation can be realized by, for example, the Segmentation Attenuation Correction method described in Non-Patent Document 1.

  After the transmission imaging, the radiation source housing 3, the external radiation source 4, and the radiation source housing support rod 9 are rotated to the same position as when the external radiation source 4 is unloaded and passed to the linear drive device 7. The linear drive device 7 moves the radiation source housing 3 together with the radiation source housing support rod 9 to the position of the radiation source shield 8 and stores the external radiation source 4.

<Emission imaging>
From the body of the examinee 10 lying on the bed 11, many γ rays generated due to the PET drug are emitted in all directions. When the radiation detector 21 in the detector ring 2 detects γ-rays emitted from the body of the examinee 10, the radiation detector 21 outputs an electrical signal corresponding to the energy (hereinafter referred to as a γ-ray detection signal). The analog ASIC 22 generates a timing signal for specifying the detection time of the γ-ray based on the γ-ray detection signal, and transmits the generated timing signal to the digital ASIC 23. The analog ASIC 22 generates γ-ray peak value information based on the γ-ray detection signal, and transmits the generated peak value information to the digital ASIC 23.

The digital ASIC 23 determines the detection time of the γ ray based on the timing signal received from the analog ASIC 22 and specifies the detector ID. The digital ASIC 23 converts the peak value information corresponding to the radiation detector 21 of the detector ID into digital information. When ¹³⁷ Cs is used for the nuclide of the external radiation source 4, the γ-ray signal derived from the emission and the signal derived from the external radiation source 4 can be distinguished at this stage (if it is neither, the data may be rejected at this time) . If the emission-derived γ-ray signal is determined, the origin source information is set to emission origin. Further, the digital ASIC 23 adds packet source information and peak value information to the time information and the detector ID to generate packet data. Packet data including four pieces of information (time information, detector ID, origin source information, and peak value information) is transmitted to the data processing device 31.

  The coincidence counting device 311 of the data processing device 31 performs coincidence counting processing based on the packet data transmitted from the digital ASIC 23. The pair of γ rays counted simultaneously is counted as one, and the positions of the two radiation detectors 21 that have detected the pair of γ rays are specified from their detector IDs. From the paired data of the specified detector ID, the direction in which the 511 keV γ-ray is detected is specified. The detection information in each direction is accumulated and counted, and the count data is stored in the storage device 312. At this time, the γ-ray absorptance distribution data of each direction previously stored in the storage device 312 is used for correcting the detection information. Then, the tomographic image creation device 313 creates tomographic image information based on the identified detector positions. The generated tomographic image information is displayed on the display device 32.

≪Shooting field of view≫
A method in which a radiation source is placed at the center in the body axis direction of a conventional detector ring with respect to an imaging field of view that can be realized when transmission imaging is performed using the point-like external radiation source 4 of the present embodiment (hereinafter, conventional method). And will be described. As an index indicating the imaging range, an FOV (Field Of View) representing a cross-sectional range and an AFOV (Axial FOV) representing a body axis direction range are used. In FIG. 5, the conventional method is shown in (a) and the present embodiment is shown in (b) with respect to the positional relationship between the external radiation source and the detector and the imaging range. Although there is no difference in the overall configuration between the FOV conventional method and this embodiment, the range of AFOV is different. In other words, as described in [Problems to be Solved by the Invention], the PET apparatus 100 for the head cannot sufficiently insert the examinee 10 into the gantry 1, so only AFOVs according to the conventional method can be imaged. Although the head and neck of the examinee 10 cannot be imaged, if the AFOV according to the present embodiment can be imaged, not only the head but also a part of the neck can be imaged. Although a part of the neck can be imaged also by a method in which the point-like external radiation source 4 is moved in the axial direction relative to the gantry 1, even if the radiation source housing 3 is used in this method. The irradiation range of γ rays cannot be limited, and unnecessary exposure cannot be suppressed.

これによれば、撮像領域の大きさは共に同じであるが、本実施形態では従来法と比較して被検診者１０の頭頚部を撮像することが可能となる。なお、頭頚部より上の頭部については、寝台１１を移動させることにより撮像することができる。 Next, the size of AFOV that can be imaged according to the conventional method and the present embodiment will be compared using FIG. Considering the coordinates shown in FIG. 6, if the detector ring diameter (inner circumference) is ringD, the length of the detector ring body axis direction is ringL, and the rotational radius of the external source 4 is rotR, z of the external source The coordinates are ringL / 2 in the conventional method, and ringL in the present embodiment. In both the conventional method and the present embodiment, the size of AFOV is represented by the distance between ABs in FIG.

According to this, although the magnitude | size of an imaging region is the same, in this embodiment, it becomes possible to image the head and neck part of the examinee 10 compared with the conventional method. Note that the head above the head and neck can be imaged by moving the bed 11.

According to the present embodiment, the following effects can be obtained.
(1) This embodiment uses a point source as an external source for transmission, rotates the point source at the gantry end close to the subject's shoulder, and performs transmission imaging, thereby widening the imaging range of the head. And the imaging time can be shortened. Specifically, transmission imaging of the head and neck can be performed, and a highly quantitative image in which attenuation of γ rays within the subject within a wide range can be obtained.
(2) In the present embodiment, the radiation source housing 3 having the surfaces P1, P2, P3 and P4 and the external radiation source 4 are provided, so that the region is determined by the shape of the gantry 1, the position of the external radiation source 4, and the imaging range. Irradiation with gamma rays can reduce ineffective exposure. That is, since γ rays are emitted from the external radiation source 4 in a direction in which the imaging region and the detector region of the detector ring 2 overlap, it is possible to eliminate irradiation of invalid γ rays as detection data, Unnecessary exposure can be prevented.
(3) Since the surface P3 of the radiation source housing 3 is positioned at the insertion side end of the examinee 10 of the detector ring 2, transmission data relating to the neck of the examinee 10 can be collected without excess or deficiency.
(4) When transmission imaging is not performed, the radiation from the external radiation source 4 is shielded by the radiation source shield 8 so as not to leak, so that unnecessary exposure can be prevented.

<< Other embodiments >>
An example of the preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment, and can be appropriately changed without departing from the spirit of the present invention. For example, the following embodiments can be considered.

(1) In this embodiment, the point source is ¹³⁷ Cs, but ⁵⁷ Co (cobalt 57), ^99m Tc (technetium 99m), ^123m Te (tellurium 123m), ¹³⁹ Ce (cerium 139), ¹⁵³ Gd (gadolinium 153) ), ²⁴¹ Am (Americium 241).

(2) In the present embodiment, the post-injection method in which transmission imaging and emission imaging are continuously performed has been described as an example. However, when transmission imaging is performed before the PET drug is administered, the emission / transmission simultaneous acquisition method ( Hereinafter, it can also be employed in the case of the ET simultaneous collection method). The ET simultaneous acquisition method performs emission imaging and transmission imaging simultaneously.

It is a figure which shows the structure of the PET apparatus for heads which is preferable one Embodiment of this invention, (a) shows sectional drawing by the surface orthogonal to a body axis, (b) is a perpendicular | vertical surface containing a body axis FIG. It is a figure which shows the shape of the radiation source housing which is one suitable embodiment of this invention, (a) shows a side view, (b) shows a top view. It is a figure which shows the gamma ray irradiation range formed with the radiation source housing which is one suitable embodiment of this invention. It is a figure which shows the structure of a gamma ray detection processing system. It is a figure which shows the imaging range by the difference in an external radiation source position, (a) shows a conventional method, (b) shows this embodiment. It is a figure which shows the coordinate setting for calculating | requiring AFOV at the time of using a point source, (a) shows a conventional method, (b) shows this embodiment.

Explanation of symbols

1 Gantry 2 Detector ring (radiation detector ring)
3 Radiation source housing (housing)
4 External radiation source (single photon emission nuclide)
5 Rotating gear (Rotating means)
6 Rotation drive (rotating means)
7 Straight drive (moving means)
8 Radiation shield (radiation shield)
9 Radiation source housing support rod (rotating means, moving means)
10 Examinee (subject)
11 Sleeper 12 Sleeper Drive 20 Gamma Ray Emission Port (Radiation Emission Port)
100 PET equipment (positron emission tomography equipment)

Claims (6)

A bed on which a subject is placed, radiation generating means for generating radiation, a radiation detector annular body in which a plurality of radiation detectors for detecting radiation generated from the radiation generating means are arranged in an annular shape, and the radiation generating means are held. Rotating means for rotating along the radiation detector annular body;
A positron emission tomography apparatus comprising:
The radiation generating means includes
A point-like single-photon emitting nuclide that emits a beam;
A housing in which the single-photon emission nuclide is stored, and a radiation emission port is formed so that the beam is shaped to look into the radiation detector annular body ;
With
The rotating means rotates the radiation generating means in the circumferential direction of the radiation detector annular body at the end of the radiation detector annular body on the subject insertion side during transmission imaging.
A positron emission tomography apparatus characterized by the above. The radiation emission port of the housing is
A pair of opposing substantially planar first and second surfaces that limit the radiation direction of the beam so that the beam does not protrude from the imaging region of the radiation detector annulus,
A substantially planar third surface provided on the subject insertion side for limiting a radiation direction of the beam so that the beam does not protrude from a detector region of the radiation detector annular body;
A curved fourth surface provided on the opposite side of the subject insertion side to limit the radiation direction of the beam so that the beam does not protrude from the detector region of the radiation detector annular body;
The positron emission tomography apparatus according to claim 1, further comprising: The third surface is
When the radiation generating means is located at the end of the radiation detector annular body on the subject insertion side, the single photon emission nuclide and an inner circumference of the end of the radiation detector annular body on the subject insertion side Approximately coincides with a part of the side of the oblique cone connecting
The fourth surface is
When the radiation generating means is positioned at the end of the radiation detector annular body on the subject insertion side, the single photon emission nuclide and the end of the radiation detector annular body opposite to the end of the subject insertion side The positron emission tomography apparatus according to claim 2, wherein the positron emission tomography apparatus substantially coincides with a part of a side surface of an oblique cone connecting an inner circumferential circle of an end portion. Radiation source shielding means for shielding radiation generated from the radiation generating means;
Moving means for holding the radiation generating means and moving the radiation source shielding means between an installation location of the radiation source shielding means and an end of the radiation detector annular body on the subject insertion side;
The positron emission tomography apparatus according to claim 1, further comprising: A bed on which the subject is placed;
A radiation generator having a point-like single photon emission nuclide that emits a beam, and a housing in which the single photon emission nuclide is stored and a radiation emission port is formed;
A radiation detector annular body in which a plurality of radiation detectors for detecting radiation generated from the radiation generator are arranged in an annular shape; and
Radiation source shielding means for shielding radiation generated from the radiation generator;
A moving means for holding the radiation generating apparatus and moving the radiation source between the installation place of the radiation source shielding means and the end of the radiation detector annular body on the subject insertion side;
A rotating means for holding the radiation generating device and rotating the radiation generating apparatus along the radiation detector annular body;
A transmission imaging control method in a positron emission tomography apparatus comprising:
The moving means moves the radiation generating apparatus from an installation location of the radiation source shielding means to an end of the radiation detector annular body on the subject insertion side,
The rotating means rotates the radiation generating device in a circumferential direction of the radiation detector annular body at an end of the radiation detector annular body on a subject insertion side,
The radiation generator emits the beam having a shape that looks into the radiation detector annular body from the radiation emission port at an end of the radiation detector annular body on the subject insertion side .
A transmission imaging control method in a positron emission tomography apparatus. The radiation emission port is
A pair of opposing substantially planar first and second surfaces that limit the radiation direction of the beam so that the beam does not protrude from the imaging region of the radiation detector annulus,
A substantially planar third surface provided on the subject insertion side for limiting a radiation direction of the beam so that the beam does not protrude from a detector region of the radiation detector annular body;
A curved fourth surface provided on the opposite side of the subject insertion side to limit the radiation direction of the beam so that the beam does not protrude from the detector region of the radiation detector annular body;
6. The method of controlling transmission imaging in a positron emission tomography apparatus according to claim 5, wherein the housing formed by the method is used.

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