JP2003222676A - Radiation inspection apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiation inspection apparatus by which both a 3D-PET inspection having a wider inspection range and a local PET inspection using a local part in a specimen or an object are executed. <P>SOLUTION: The radiation inspection apparatus 1 is provided with an imaging device 2 and a specimen holding device 10. The imaging device 2 is provided with a gantry 13 in which many radiation detectors 3 are arranged cylindrically and a collimator aggregate 5. The collimator aggregate 5 comprises a cylinder part 7 and a plurality of ring-shaped collimators 6 so as to be taken in and out of the gantry 13. In the collimator aggregate 5, six ring-shaped collimators 6 are arranged in its axial direction so as to form a common focus region 30. The collimator aggregate 5 is pulled out from the gantry 13, and the 3D-PET inspection with reference to the whole body of a subject 19 is executed. When a cancer is detected, the collimator aggregate 5 is inserted into the gantry 13. An affected part by the cancer is aligned with the focus region 30, and the local PET inspection is executed. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation inspection apparatus, and more particularly to a positron emission computed tomography (Positron Emission Computed Tomograp) utilizing a positron emitting nuclide.
hy), hereinafter referred to as PET), to a radiation inspection apparatus suitable for application to the apparatus.

[0002]

2. Description of the Related Art An inspection technique utilizing radiation can inspect the inside of a subject nondestructively. Especially, X-ray CT equipment, PET equipment, SP
There is an ECT (single photon emission type CT) device and the like. Each of these technologies is a technology that measures the physical quantity of the detection target as an integrated value in the direction of flight of the radiation and calculates the physical quantity of each voxel in the subject by backprojecting the integrated value to form a tomographic image. is there. These technologies need to process a huge amount of data, and with the recent rapid development of computer technology, it has become possible to provide high-speed and high-definition images.

In particular, the PET apparatus is a method capable of detecting functions and metabolism at the level of molecular biology that cannot be obtained by X-ray CT, and can provide functional images of the body.
PET is a method in which a radioactive drug labeled with a positron-emitting nuclide such as ¹⁸ F, ¹⁵ O, and ¹¹ C (referred to as PET drug) is administered into the body, and its distribution is measured and imaged. As an example of a PET drug, fluorodeoxyglucose (2- [F-18] fluoro-2-deoxy-
D-glucose; ¹⁸ FDG). ¹⁸ FDG is used for the identification of a tumor site by utilizing its high accumulation in tumor tissues by glucose metabolism. The radionuclide incorporated into the body decays and emits positron (β ⁺ ). The emitted positrons emit a pair of γ rays (γ ray pair) having an energy of 511 keV when they combine with the electrons and disappear. Since this γ-ray pair is radiated in almost opposite directions (180 ± 0.6 °), both γ-rays of the γ-ray pair are simultaneously detected by the radiation detector arranged so as to surround the subject. Radial direction data can be accumulated to obtain projection data. This projection data is used for IEEE Transaction on Nuclear Science (IEEE Transaction on
Nuclear Science) NS-21, page 21, Filtered Back Projection Method (FBP method)
The γ-ray pair generation density can be obtained by back-projecting using, for example. The γ ray pair generation density distribution shows the accumulation position of the radionuclide, and the position of the tumor etc. can be identified by imaging.

In recent years, the PET inspection of the whole body has come to be carried out as the performance of the PET apparatus is improved. PE of whole body
In order to perform T inspection, high-speed inspection is essential, and the PET device is a two-dimensional PET (called 2D-PET).
It has evolved from a device to a three-dimensional PET (called 3D-PET) device. A configuration in which a plurality of radiation detectors are annularly arranged so as to surround the subject in a line is referred to as one radiation detector ring. The 2D-PET apparatus performs PET inspection on a two-dimensional cross section created by one radiation detector. 3D-P
The ET device forms a cylindrical radiation detector group by arranging a plurality of radiation detector rings in the body axis direction, and inspects the volume of a subject surrounded by the cylindrical radiation detector group at a time.

The 2D-PET apparatus is equipped with collimators (consisting of radiation shielding materials) on the subject side on both sides of one radiation detector ring. This collimator prevents measurement of γ-rays in scattered events and contingencies, so 2D-P
The ET device can obtain a high-quality two-dimensional image with less noise. Gamma rays in scattered and random events are blocked by the collimator. However, in the 2D-PET apparatus, since the solid angle of the radiation detector annular row that looks into the subject is small, the amount of data obtained is small and the examination time is long. On the other hand, the 3D-PET device can measure a large volume at high speed, but it detects γ-rays of γ-ray scattering events and random events, so the image quality of the obtained tomographic image is lower than that of the 2D-PET device. To do. A contingent event is an event in which γ-rays emitted from different radiation sources in the body are accidentally measured by a radiation detector, and a scattering event is an event in which γ-rays scattered in the body are measured. The angle information of the event becomes inaccurate.

[0006] 3D-PET can detect a candidate for a lesion such as a tumor by conducting a PET examination of the whole body, but since the image obtained is a little low in image quality, skill is required to diagnose a specific site. .

The PET device shown in FIG. 2 of JP-A-5-264736 has a cylindrical radiation detector group in which four radiation detector rings are arranged in the body axis direction. this
In the PET apparatus, a ring-shaped slice collimator is arranged between each radiation detector ring, and a ring-shaped slice collimator is also arranged outside each of the radiation detector rings at both ends. With this structure, gamma rays in the scattering event can be eliminated by the slice collimator. However, since the resolution in the body axis direction is reduced, in FIG. 1 of Japanese Patent Laid-Open No. 5-264736, it is proposed to arrange one slice collimator for every two radiation detector rings, without reducing the image resolution. The sensitivity is being improved.

In the PET device disclosed in Japanese Patent Publication No. 11-508048, regular 20-face pairs are formed around a subject, and a radiation detector and a collimator are installed in each face. Each collimator is formed so as to focus on one point of the subject, and the image resolution is improved by selectively detecting only the information from the main focus.

[0009]

[Patent Document 1] Japanese Patent Application Laid-Open No. 5-26473
According to Japanese Patent Laid-Open No. 6-Gazette, the sensitivity is improved (speed of measurement) without degrading the image resolution at first glance, but the prior art (2D-PET) using a ring-shaped slice collimator is used.
However, the sensitivity can be improved only 1.5 times.

In Japanese Patent Publication No. 11-508048, the focus portion of the collimator is a minute area corresponding to each pixel of the image and the image resolution and the image quality can be improved. This is effective when measuring for a long time. However, this configuration cannot be applied to the examination of the human body because the volume of the subject is limited. Moreover, the high speed required for the inspection of the human body cannot be realized.

An object of the present invention is to provide a 3D having a wider inspection range.
-To provide a radiation inspection apparatus capable of performing both a PET inspection and a local-PET inspection targeting a local site of a subject.

[0012]

A feature of the present invention that achieves the above object is that an imaging device has a tubular gantry and an annular shape that is installed in the gantry so that it can be taken in and out, and a plurality of collimator members. And a collimator, the gantry, a plurality of radiation detectors arranged in a ring, a plurality of radiation detectors for detecting the radiation from the subject, an annular radiation detector array having a plurality of rows in the axial direction, the collimator, The plurality of collimator members that form a plurality of radiation passages facing the common focal region are arranged in the axial direction.

Since a collimator having a plurality of radiation passages facing a common focal region formed by a plurality of collimator members is provided so as to be able to be taken in and out of the gantry, one radiation inspection apparatus can cover a wider area of the subject. Both the 3D-PET inspection for the target and the local-PET inspection for the local region of the subject narrower than the target range of the 3D-PET inspection can be performed.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The above-mentioned contingent event and scattered event will be described a little further with reference to FIG. The detection event (C) of the γ-ray pair may include a true event (T) indicating the true emission direction of the γ-ray pair, and a random event (R) and a scattering event (S) that are false events ( (See formula (1)). Both the random event (R) and the scattered event (S) are false events or noise components. C = T + R + S (1) The key to improving the image quality of a tomographic image is to keep the measured value of γ-rays in these events low. Further, by increasing the true event measurement rate, the measurement time can be shortened (high-speed measurement). That is, what is important for improving the performance of the PET apparatus (high-speed, high-definition inspection) is to suppress false events and measure only true events at a high rate. An embodiment of the present invention in consideration of the above matters will be described below.

(Embodiment 1) A radiation inspection apparatus according to Embodiment 1, which is a preferred embodiment of the present invention, will be described with reference to FIGS. 1 and 2. The radiation inspection apparatus of this embodiment is a PET apparatus.

The radiation inspection apparatus 1 of this embodiment comprises an imaging device 2 and a subject holding device 10. Subject holding device 1
0 has a support member 11, a bed 12 provided at the upper end of the support member 11, and a drive device (not shown) for moving the bed 12 in the longitudinal direction of the bed 12. The subject holding device 10 has another driving device (not shown) that moves the bed 12 in the height direction and also in the horizontal direction orthogonal to the longitudinal direction.

The image pickup device 2 includes a casing (not shown),
A plurality of radiation detectors 3 installed inside an annular radiation detector holder 4 and a collimator assembly 5 are provided. The radiation detector holder 4 is installed on a support member 8 installed on the floor. Radiation detector 3, radiation detector holder 4
The support member 8 is provided inside the casing. The support member 8 is connected to the support member 11. The plurality of radiation detectors 3 and the radiation detector holder 4 surround a hole 9 provided in the casing. These radiation detectors 3
Is installed inside the radiation detector holder 4. A row of annular radiation detector arrays surrounding the hole 9 is called a radiation detector ring. A plurality of radiation detectors 3 are also installed in the axial direction of the hole 9. That is, a plurality of radiation detector rings are arranged in the axial direction of the hole 9. The radiation detector 3 has 5
A semiconductor radiation detector of mm cube is used, and the semiconductor element part is made of gadium tellurium (CdTe). A portion in which the plurality of radiation detectors 3 are arranged in a cylindrical shape is called a gantry. The collimator assembly 5 has a cylindrical portion 7 that is a tubular body, and a plurality of annular collimators 6. Cylindrical part 7
Is made of a plastic member (acryl, vinyl chloride, etc.) that is transparent to γ-rays (passes with almost no reaction) and is located inside the gantry 13. The annular collimator 6 includes six annular collimators 6 as shown in FIG.
A to 6F are used. The annular collimators 6A to 6F, which are collimator members, are attached to the inner surface of the cylindrical portion 7 with screws or the like. The annular collimators 6A to 6F are made of tungsten and shield γ rays. The collimator assembly 5 is
Five annular gamma ray passages 3 formed by using two adjacent annular collimators of the annular collimators 6A to 6F.
7A to 37E. The annular γ-ray passage 37C is oriented in a direction orthogonal to the central axis of the collimator assembly 5.
The focal region 30 is formed at a position intersecting the extension line of the annular γ-ray passage 37C and the central axis of the collimator assembly 5.
Other annular gamma ray passages 37A, 37B, 37D and 37
E is formed to be inclined so as to face the focal region 30.
In a state where the collimator assembly 5 is inserted into the gantry 13, the annular collimators 6A to 6F move to the gantry 1.
3 is divided into five radiation detection regions 14 to 18 in the axial direction. The radiation detection areas 14 to 18 are annular independent areas. Within one radiation detection area,
A plurality of radiation detectors 3 in the axial direction of the gantry 13
(Eg, 4) is included.

The annular collimators 6A-6F form a common focal area 30. Therefore, the annular collimators 6A, 6
B, 6E and 6F have both surfaces in the axial direction of the gantry 13 inclined with respect to the central axis of the gantry 13 (the central axis of the hole 9). The annular collimator 6C and the annular collimator 6D have vertical surfaces 23 and 24 facing each other, and are inclined surfaces 2 inclined with respect to the central axis of the gantry 13.
Has 2,25. The inclination angles of the inclined surface 19 of the annular collimator 6A and the inclined surface 27 of the annular collimator 6E are equal,
The inclined surface 19 is located on an extension of the inclined surface 27. The inclination angles of the inclined surface 20 of the annular collimator 6B and the inclined surface 28 of the annular collimator 6F are equal, and the inclined surface 20 is located on the extension line of the inclined surface 28. Inclined surface 21 of annular collimator 6B
And the inclination angles of the inclined surfaces 25 of the annular collimator 6D are equal, and the inclined surfaces 21 are located on the extension lines of the inclined surfaces 25. Inclined surface 22 of annular collimator 6C and annular collimator 6E
The inclination angles of the inclined surfaces 26 of the
Located on an extension of 6. The focal region 30 is a local examination region of the subject, and is, for example, a spherical region having a diameter of 15 cm.

The collimator assembly 5 has such a structure that it can be put in and taken out from the hole portion 9, that is, the gantry 13.
On the outer surface of the cylindrical portion 7, a rack (not shown) is provided over the entire length in the axial direction, and the gantry 13 of the collimator assembly 5 is provided.
It is provided so that it does not interfere with putting in and out.
The rack meshes with the pinion 29 shown in FIG. The pinion 29 is connected to a motor (not shown) via a speed reduction mechanism (not shown). The deceleration mechanism and the motor are attached to the radiation detector holder 4. Pinion 29,
The reduction mechanism and the motor constitute a collimator assembly moving device. In order to support the collimator assembly 5 so as not to fall when the collimator assembly 5 is pulled out from the gantry 13, the end of the radiation detector holding portion 4 on the pinion 29 side is a collimator support portion 44 which is a collimator support device. Becomes The collimator support portion 44 projects toward the pinion 29 side from the end surface of the gantry 13, and the inner diameter of the collimator support portion 44 is equal to the inner diameter of the gantry 13.

Each radiation detector 3 is connected to a corresponding γ-ray signal discriminating device 32 by a wiring 31. The γ-ray discrimination device 32 is provided for each radiation detector 3. All the gamma ray discriminating devices 32 are connected to the coincidence counting device 33. The coincidence counting device 33 is connected to the computer 34. Storage device 35
And the display device 36 is connected to the computer 34. The computer 34 is a tomographic image creating device.

The collimator assembly used in the present embodiment was devised from the results of the following study by the inventors of the simultaneous counting rate. The results of this examination will be described below. For simplicity, it is assumed that the radiation source (the part of the body where PET drug is collected) is a point source located on the central axis of the gantry. In addition, the radioactivity of the radiation source is N (B
q). Part of the gamma rays emitted from the radiation source are absorbed in the body, so the gamma rays that actually reach the radiation detector
The amount of lines is reduced. The rate of passage of this γ ray in the body is represented by A.
Also, γ rays are emitted at a solid angle of 4π radians,
It is measured by the radiation detector within the solid angle (Ω) of the gantry. The ratio of γ-rays measured within the range is represented by the geometrical incident rate B (= Ω / (4π)). Also,
It is assumed that the γ-rays incident on the radiation detector are also detected by the ratio of the sensitivity S determined by the characteristics of the radiation detector. Using the above parameters, the counting rate α of a single γ ray measured by the radiation detector (Count / sec or less CP
S) is given by (2).

Α = 2NABS (2) The coefficient “2” in the equation (2) means that 2N γ rays (single) are emitted with respect to the emission of N positrons. Also, the simultaneous coefficient rate (CPS) of the γ-ray pair is (3)
Given by the formula.

C = NB (AS) ² (3) In the equation (3), the geometrical incident rate B is determined by the γ-ray pair, so that it contributes by the first power, and the internal passage rate A and the radiation detector sensitivity S are Since there is a contribution from single gamma rays (for two rays), they are summed by the square.

Single gamma within the coincidence counting window length h (s)
The counted rate R of the line is given by the equation (4) because the random event has the Poisson distribution.

R = 1-exp (−αh) (4) When a single γ-ray is detected (one or more) at the same time as detecting the γ-ray pair (within the coincidence counting time window length h), this γ-ray The pair becomes invalid. Therefore, the coincidence counting rate C (Count / Sec (hereinafter, CPS)) considering the random event is obtained by subtracting this invalid component from the equation (3) and is given by the equation (5).

[0026]

[Equation 5] From the equation (5), the relationship between the coincidence counting rate C and the activity level N (generation rate of positron) is shown in FIG. Nmax and Cmax described in FIG. 3 are (6), respectively.
Equation (7) and equation (7) are given.

[0027]

[Equation 6]

[Equation 7] The state quantity that is affected by the size of the gantry is only the geometrical incident rate B, and the variables A, S, and h are not affected by it. For example, 2D-PET geometric incidence B ₀
The geometrical incident rate B of 3D-PET is 5 times (B =
5B ₀ ), 3D-PET is obtained from the equation (6).
Nmax is 1/5. However, from equation (7), Cma
The value of x does not change. That is, even if the gantry size is increased, the radioactivity level that gives the maximum value of the coincidence counting rate becomes smaller, but the maximum value does not change. Since the inspection time is inversely proportional to the coincidence counting rate,
It can be seen that simply increasing the gantry cannot reduce the measurement time. The reason why the coincidence counting rate saturates with increasing radioactivity level and has the maximum value is
This is because the number of single γ-rays increases and counting is lost from the consideration of equation (5).

Therefore, the effect of the collimator assembly 5 of this embodiment will be considered based on the characteristics of FIG. By inserting the collimator assembly into the gantry 13, γ
Five radiation detection regions 14 to 18 capable of detecting lines are formed. Each radiation detection area is 1/6 of the solid angle of the entire gantry 13. The 3D-PET curve shown in FIG. 4 shows the simultaneous counting rate in the entire gantry 13 when the collimator assembly 5 is not inserted in the gantry 13. The 2D-PET curve shows the simultaneous counting rate of one radiation detection region (radiation detection region 16) when the collimator assembly 5 is inserted in the gantry 13. From the above consideration, the maximum value of the simultaneous counting rate of both curves and the radioactivity level which gives the maximum value are given by the equations (8) and (9), respectively.

Cmax (3D) = Cmax (2D) (8) Nmax (2D) = 6 × Nmax (3D) (9) Further, the inspection of the focal region 30 when the collimator assembly 5 is inserted is performed by the collimator assembly. There is an effect of adding the inspections by the radiation detection areas divided by 5. The maximum rate Cmax (colli) of the coincidence counting rate and the radioactivity level Nmax (colli) at that time are given by the equations (10) and (11), respectively.

Cmax (colli) = 5 × Cmax (3D) (10) Nmax (colli) = 6 × Nmax (3D) (11) That is, in the local-PET inspection using the collimator assembly 5, the collimator assembly is used. It is possible to obtain a 5-fold coincidence counting rate at a 6-fold radioactivity level as compared to the case of 3D-PET examination without 5. However, in actuality, it may not be possible to inject 6 times as much radioactivity into the body from the viewpoint of radiation exposure. For example, if the PET drug can be dosed twice as much (2 × Nmax (3D)), the coincidence counting rate in this embodiment becomes about 2.5 times (2.5 × Cmax (3D)). Gamma ray measurement time can be shortened to 1/25. That is,
In this embodiment, the single gamma ray is removed by the collimator assembly 5 to increase the simultaneous counting rate saturated in 3D-PET.

Next, the PET inspection using the radiation inspection apparatus 1 of this embodiment and the processing of the measured values detected by the radiation detector 3 will be described. Before carrying out the PET examination, first, a prescribed amount of the PET drug is previously administered into the body of the subject 19 who is the subject by a method such as injection. Furthermore, the subject 19 waits until the administered PET drug diffuses into a state in which it can be imaged. After the PET drug has sufficiently diffused into the body, the subject 19 is inserted into the hole 9 while lying on the bed 12. 3D-for subject 19
When the PET inspection is required (for example, when the whole body inspection is required), the collimator assembly 5 is pulled out from the gantry 13 before inserting the bed 12 into the hole 9 as described above. That is, the motor is driven to rotate the pinion 29 to move the collimator assembly 5 to the gantry 1.
In the axial direction of 3, the object holding device 10 is moved to the opposite side and is pulled out from the gantry 13. Gantry 1
The end portion of the collimator assembly 5 pulled out from 3 is supported by the collimator support portion 44. If necessary, two rod-shaped support members may be attached to the radiation detector holder 4 (or the support member 8) so that the lower side of the pulled-out collimator assembly 5 can be supported.

In the 3D-PET examination, the number of gamma ray pairs emitted from the body due to the PET drug was about 180.
Measured by two radiation detectors 3 located in opposite directions. The energy of these γ rays is 511 keV. The 3D-PET inspection of the whole body of the subject 19 is performed by moving the bed 12 in its longitudinal direction. The γ-ray measurement signals output from the radiation detectors 3 are input to the corresponding γ-ray signal discriminating devices 32. The input measurement signal has such a shape that it first sharply falls and then exponentially approaches 0. The signal discriminating device 32 first shapes the measurement signal having the above waveform into a temporal Gaussian waveform. Then, the signal discriminating device 32 discriminates the measurement signal having the energy of the energy set value (for example, 450 keV) or more, and generates the pulse signal based on the discriminated measurement signal.

The coincidence counting device 33 includes each signal discriminating device 32.
The pulse signals output from the above are input, simultaneous counting is performed using these pulse signals, and the count value for the γ-ray measurement signal is obtained. Simultaneous counting does not mean simultaneous in time, but is based on the measurement signal of each γ ray of the γ ray pair generated at the same position in the body when one proton released from the PET drug disappears. It means counting the obtained pulse signals. Simultaneous counting of pulse signals of γ-ray pairs generated at the same position in the body when one proton released from the PET drug disappears, the simultaneous counting time window length is set to, for example, 10 ns, and 2 The pulse signals from each of the γ-ray discriminators 32 are coincidental counters 3
3, the coincidence counting device 33 determines that the pulse signals are valid and counts the pulse signals. Further, the coincidence counting device 26 has two detection points (approximately 180 ° (strictly speaking, 180 ° ± 0.6 °) directions in which the pair of γ rays are detected by the pair of pulse signals for the pair of γ rays described above. The positions of the different radiation detectors 3) are converted into data as position information for γ-ray detection.

The coincidence counting is performed by the coincidence counting device 2 as described above.
6 may be performed in real time, but may be performed by the computer 34 instead of the coincidence counting device 26. In this case, all the measured γ-rays are measured together with the measured position information and time information, transferred to the computer 34, and stored in a list of data (position information and time information in the order of detection). Is prepared and the computer 34 performs simultaneous counting by data processing after or during the measurement of γ-rays. In this case, the coincidence counting is a method in which the γ ray pairs within the coincidence counting time window length are validated from the time information of the data list and the γ ray pairs are counted.

The count value and the position information for γ-ray detection are input to the computer 34 and stored in the storage device 35.
The computer 34 creates a tomographic image of the subject 19 using the count value and the position information for γ-ray detection. The creation of this tomographic image is specifically performed as follows. That is, using the count value and the position information for γ-ray detection, the two corresponding radiation detectors 3 (positioned in 180 ° opposite directions)
The number of γ ray pairs generated in the body during the period is calculated. This γ-ray pair generation number is used to backproject by the FBP method (or the successive approximation method) to obtain the γ-ray pair generation density of each voxel. A tomographic image is created based on the γ ray pair generation density of each voxel. A large number of tomographic images are created for the whole body of the subject 19. The doctor diagnoses the presence or absence of cancer by looking at those tomographic images displayed on the display device 36.

If cancer, eg liver cancer, is found,
Perform a detailed examination by local-PET examination in the vicinity of the liver. The target range of the local-PET test is a local site narrower than the test range of the 3D-PET test. Local-P
Before the ET inspection, drive the motor to drive the pinion 29
Is rotated to move the collimator assembly 5 in the axial direction of the gantry 13 until the state of FIG.
Insert in 3. Bed 12 on which the subject 9 lies
Is moved in the longitudinal direction, the height direction, and the horizontal direction orthogonal to the longitudinal direction to align the affected part, that is, the liver where the cancer exists, with the focal region 30. The PET drug is administered to the subject 19.

Many γ-rays generated in the liver cancer located in the focal region 30 due to the PET drug are emitted in all directions centering on the liver cancer, and the radiation detection regions 14 to 1
It is measured by each radiation detector 3 in 8. For example,
When one γ-ray of the γ-ray pair is detected by the one radiation detector 3 in the radiation detection area 14, the other γ-ray is located in a direction substantially 180 ° opposite to that of the radiation detector 3.
The radiation is detected by the other radiation detector 3 in the radiation detection area 18. Similarly, when one γ ray of the γ ray pair is detected by one radiation detector 3 in the radiation detection region 15, the other γ ray is approximately 180 ° with respect to the radiation detector 3.
The radiation is detected by the other radiation detector 3 in the radiation detection area 17, which is located in the opposite direction. When one γ-ray of the γ-ray pair is detected by one radiation detector 3 in the radiation detection area 16, the other γ-ray is located in a direction approximately 180 ° opposite to the radiation detector 3. Same radiation detection area 1
It is detected by the other radiation detector 3 in 6.

The measurement signals output from the radiation detectors 3 in the radiation detection areas 14 to 18 are input to the corresponding γ-ray discriminators 32, and the γ-ray discriminators 32 are pulse signals as described above. Is output. Coincidence counting device 33
Inputs all pulse signals output from the γ-ray discrimination device 32 and outputs the count value of the pulse signals and the position information for γ-ray detection. Computer 34 is local-PET
A tomographic image in the vicinity of the liver of the subject 19 is created based on the count value in the examination and the position information for γ-ray detection. These tomographic images are displayed on the display device 36.

This embodiment can obtain the following respective effects. (1) Plural annular collimators (arranged in the axial direction of the collimator assembly 5) to face the focal region 30
Since the collimator assembly 5 having the line passage is formed so as to be taken in and out of the gantry 13, one radiation inspection apparatus can be used to cover a wide range (2D-P) of the subject 19.
3D targeting a wider area than the ET inspection range)
Both the PET inspection and the local PET inspection targeting the local site of the subject 19 can be performed. (2) In the 3D-PET inspection and the local-PET inspection, the gantry 13 can also be used, so the radiation inspection apparatus becomes compact. (3) Since the collimator assembly 5 in which a plurality of annular γ-ray passages facing the focal region 30 are formed by a plurality of annular collimators is used, γ-rays that are false events can be removed and the subject 19 of the subject 19 can be removed. High-definition PET inspection of local areas becomes possible. (4) Since the above collimator assembly 5 is used,
Among false events, especially contingent events can be removed, and saturation of the coincidence counting rate can be suppressed. Therefore, it is possible to perform measurement with an increased simultaneous counting rate, and it is possible to significantly shorten the PET inspection time, that is, to speed up the PET inspection. (5) A plurality of radiation detectors 3 are provided in one circular γ-ray passage.
Therefore, the sensitivity can be improved without substantially deteriorating the spatial resolution of the gantry 13 in the axial direction. (6) Since the subject holding device 10 that allows the bed 12 to move in three directions is provided, a focus of the collimator assembly 5 can be easily applied to a specific local site (for example, an affected part) of the subject 19 in a local-PET examination. It can be fitted to the region 30. Therefore, a high-definition inspection can be performed on the specific local site. (7) Even if the specific local region of the subject 19 is larger than the focal region 30, since the subject holding device 10 that can move the bed 12 in three directions is provided, the local-PET for the specific local region is provided. Inspection can be carried out. That is,
By dividing the specific local portion and shifting the divided portion in time and moving it into the focal region 30 by the subject holding device 10, the local region with respect to the entire specific local portion is moved.
PET inspection can be performed. (8) The collimator assembly 5 is attached to the gantry 1 as described above.
With a structure that allows the collimator assembly 5 to be put in and taken out of the gantry 3, it is possible to confirm the position of the specific local site to be inspected in detail by the 3D-PET inspection with the collimator assembly 5 taken out from the gantry 13. Therefore, 2D-P
The position of ET inspection can be easily set. (9) Since the semiconductor radiation detector is used as the radiation detector 3, the gantry 13 can be downsized. Therefore, the imaging device 2 is also compact.

In this embodiment, the subject 19 is moved using the subject holding device 10. The gantry 13 may be configured to be movable in the axial direction, the height direction, and the horizontal direction orthogonal to the axial direction without moving the subject 19.
As the radiation detector, other than the semiconductor radiation detector, for example, a scintillator such as BGO and a photomultiplier tube may be used.

(Embodiment 2) A radiation inspection apparatus according to Embodiment 2 which is another embodiment of the present invention will be described below with reference to FIGS. 6 and 7. The radiation inspection apparatus of this embodiment is also used for PET inspection.

In the radiation inspection apparatus 1A of this embodiment, the radiation detector 3 is arranged in a hexagonal shape so as to surround the hole portion 9,
This is different from the radiation inspection apparatus 1 in that the collimator assembly 5A is composed of a plurality of movable collimators. The other configuration of the radiation inspection apparatus 1A is the same as that of the radiation inspection apparatus 1.

The radiation detector ring provided in the image pickup apparatus 2A in this embodiment has a hexagonal shape so as to surround the hole 9. Gantry 13A configured by arranging such a plurality of radiation detector rings in the axial direction of the hole 9
Is a cylinder whose longitudinal section is hexagonal. The collimator assembly 5A that can be put in and taken out from the gantry 13A also has a hexagonal longitudinal section. The collimator assembly 5A has a hexagonal tubular portion 38 which is a tubular body, and a movable collimator portion 40 which is a collimator member. A plurality of movable collimator parts 40 are arranged at a predetermined interval. One movable collimator section 40
Has six collimator plates 39A ₁ ~39A _6, six opposed thereto collimator plate 39B ₁ ~39B ₆ (only shown collimator plates 39B ₁₎ and the support plate 41, another point of view, six Movable collimator section element 42
Have. The collimator plates 39A _{1 to} 39A ₆ , the collimator plates 39B _{1 to} 39B ₆ and the support plate 41 are made of tungsten which is a γ-ray shielding material.

The detailed structure of a part of the movable collimator section element 42 will be described with reference to FIG. The collimator plate 39A ₁ and the collimator plate 39B ₁ which are opposed to each other are the support plate 4
It is attached to the rotating shafts 42A and 42B rotatably installed in the first unit. The support plate 41 is installed on one surface of the inner surface of the hexagonal tubular portion 38. A motor 43A in which a gear (not shown) provided on the rotation shaft 42A is installed on the support plate 41.
Meshes with another gear connected to the. A gear (not shown) provided on the rotary shaft 42B meshes with another gear connected to the motor 43B installed on the support plate 41.
Since the rotation shaft 42A is rotated by driving the motor 43A, the tilt angle of the collimator plate 39A ₁ with respect to the hexagonal cylinder portion 38 can be changed. The tilt angle of the collimator plate 39B ₁ with respect to the hexagonal tubular portion 38 can also be changed by rotating the rotating shaft 42B by driving the motor 43B. The other movable collimator section elements 42 each having the collimator plates 39A _{2 to} 39A ₆ have the same configuration. One movable collimator section 40 is configured such that the movable collimator section elements 42 are arranged in a line and are installed on the inner surface of the hexagonal tubular section 38 so as to surround the hole section 9. The movable collimator section elements 4 adjacent to each other in one movable collimator section 40
The second collimator plates (for example, collimator plate 39A ₁ and collimator plate 39A ₂ ) partially overlap each other like a diaphragm of a camera. With such a structure,
In the case of changing the inclination angle of the collimator plates 39A ₁ and 39A _2, collimator plates 39A ₁ and the collimator plate 3
Interference with 9A ₂ can be avoided.

The collimator assembly 5A can be put in and taken out of the gantry 13A by rotating the pinion 29 as in the first embodiment. With the six movable collimator units 40 provided in the collimator assembly 5A, as in the first embodiment,
Radiation detection areas 14-1 divided into gantry 13A
8 is formed.

The radiation inspection apparatus 1A is also 3D-P with the collimator assembly 5A pulled out from the gantry 13A.
An ET test is performed, and a local-PET test is performed with the collimator assembly 5A inserted in the gantry 13A, targeting the local site (cancer affected area) identified by the PET test. The local-PET inspection is performed by each movable collimator unit 40.
In, the tilt angle of the collimator plate (for example, the collimator plate 39A ₁ and the collimator plate 39A ₂ ) of each movable collimator section element 42 is adjusted by driving the motor,
This is performed after changing the focal region 30 facing each γ-ray passage formed between the movable collimator units 40 so as to match the position of the affected part.

Also in this embodiment, the effects (1) to (6), (8) and (9) produced in the first embodiment can be obtained. Further, the following effects (10) to (12) can be obtained. (10) Since the position of the focal region 30 can be changed by installing the movable collimator unit 40, it is not necessary to move the subject 19. Therefore, relative displacement of the subject 19 with respect to the subject holding device 10 due to movement of the subject 19 can be prevented, and high-speed and high-definition PET inspection of the local inspection site can be performed. (11) Since the size of the focal region 30 can be changed by the movable collimator section 40 according to the size of the affected area, the first embodiment
It is not necessary to move the subject 19 by the subject holding device 10 as described in (6) above, and it is possible to perform 2D once even in a large affected area.
-It can be inspected by PET inspection. Therefore, the time required for the 2D-PET inspection can be further reduced. (12) Since one movable collimator section 40 is formed in a hollow shape by the collimator plate and the support plate 41 arranged to face each other, the weight of the collimator assembly 5A can be reduced. Therefore, the capacity of the motor of the collimator assembly moving device can be reduced.

(Embodiment 3) A radiation inspection apparatus according to Embodiment 3 which is another embodiment of the present invention will be described. The radiation inspection apparatus of this embodiment has the same hardware configuration as the radiation inspection apparatus 1. In the radiation inspection apparatus of this embodiment, the data processing in the computer 34, which is a tomographic image forming apparatus, is different from the data processing performed in the computer 34 of the radiation inspection apparatus 1. Of the data processing performed by the computer 34 of the present embodiment, portions different from the data processing performed by the computer 34 of the radiation inspection apparatus 1 will be described.

The computer 34 in the present embodiment (hereinafter, referred to as the computer 34 in order to distinguish from the computer 34 in the first embodiment) is obtained based on the measurement value of each radiation detector 3 in the 3D-PET inspection. A tomographic image of the subject 19 is created using the counted value of the obtained pulse signal and the position information for γ-ray detection. This computer 3
4 is the γ of each voxel obtained when creating the tomographic image.
The line pair generation density (referred to as the first γ-ray pair generation density) is stored in the storage device 35. The computer 34 uses the count value of the pulse signal obtained based on the measurement value of each radiation detector 3 obtained by the local-PET inspection described in the first embodiment and the position information of γ-ray detection. Then, a tomographic image of a portion of the subject 19 including a specific local region (called a local region tomographic image)
To create.

The creation of a local region tomographic image in this embodiment will be described in detail. The computer 34 is calculated based on the count values simultaneously counted by the radiation detector 3 of number i and the radiation detector 3 of number j positioned 180 ° opposite to this in the process of creating the tomographic image of the local region. The correction coefficient K _ij for the number of generated γ-ray pairs is calculated by the equation (12) using the first γ-ray pair generation density stored in the storage device 35. As shown in FIG. 8, α _ij is the body of the subject 19 formed by connecting the radiation detector 3 of number i and the radiation detector 3 of number j to form K _ij = α _ij / β _ij (12) Is the number of γ-rays generated within the volume of the focal region 30 in the volume V. β _ij is its volume V
Is the number of γ ray pairs generated within. The number of γ ray pairs generated is
It is calculated based on the distribution of the first γ-ray pair generation density. The computer 34 uses the count value of the pulse signal obtained based on the measurement value of each radiation detector 3 obtained by the local-PET inspection and the position information of the γ ray detection to determine the γ ray pair. The number of γ ray pairs generated in the body between the detected pair of radiation detectors 3 is obtained. The computer 34 corrects the obtained number of γ-ray pair occurrences with the correction coefficient K _ij to calculate the corrected number of γ-ray pair occurrences. The computer 34 uses the corrected number of γ-ray pair generations to backproject by the FBP method (or the successive approximation method) to obtain the γ-ray pair generation density of each voxel. A local region tomographic image is created based on the γ ray pair generation density of each voxel. The local region tomographic image is displayed on the display device 36.

In this embodiment, (1) to
The effect of (9) can be obtained. Further, this embodiment is
Since the local region tomographic image is created using the corrected γ ray pair generation number calculated using the correction coefficient K _ij , the image quality of the local region tomographic image can be improved. This is because the use of the correction coefficient K _ij removes γ rays (noise) emitted from the body other than the focal region 30 and detected by the radiation detector 3.

The γ ray pair generation density of each voxel is obtained by using the corrected γ ray pair generation number corrected by using the correction coefficient K _ij , and the local region tomographic image is created as compared with the second embodiment. Can also be applied.

(Fourth Embodiment) A radiation inspection apparatus 1B according to a fourth embodiment which is another embodiment of the present invention will be described with reference to FIG. The radiation inspection apparatus 1B has the same configuration as the radiation inspection apparatus 1 except for the imaging device 2B. The image pickup device 2B is different from the image pickup device 2 in that the collimator assembly moving device is not provided. The other configuration of the imaging device 2B is the same as that of the imaging device 2. The radiation inspection apparatus 1B is the radiation inspection apparatus 1
Similar to 3D-PET inspection and local-PET inspection can be performed. The collimator assembly 5 is moved in and out of the gantry 13 in the radiation inspection apparatus 1B by using the collimator assembly moving device 45 instead of the collimator assembly moving device.

The collimator attachment / detachment device 45 includes a main body 46 that can move on the floor surface, an arm 47 inserted into a guide groove 49 provided in the main body 46, and a collimator holding portion 48. The arm 47 moves up and down in the guide groove 49.
Collimator holder 48 provided on the upper end of the arm 47
Are six annular collimators 6A to 6A of the collimator assembly 5.
It has 6 notches 50 for receiving 6F.

The operation of pulling out the collimator assembly 5 from the gantry 13 for the 3D-PET inspection will be described. The main body 46 is moved on the floor surface and the collimator holding portion 48 is inserted into the hole 9. After aligning the notches 50 with the annular collimators 6A to 6F, the main body 46
The arm drive device (not shown) provided in the above is driven to raise the arm 47 along the guide groove 49, and contact the bottom surface of each notch portion 50 and the annular collimators 6A to 6F. At the time of contact, the ascending of the arm 47 is stopped and the main body 46 is moved in a direction away from the gantry 13.
With the movement of the main body 46, the annular collimators 6A to 6F of the collimator assembly 5 are caught by the collimator holding portion 48, and the collimator assembly 5 is pulled out from the gantry 13. The collimator assembly 5 that has been pulled out is held by the collimator holding portion 48. 2 after 3D-PET inspection
Gantry 1 with collimator assembly 5 before D-PET inspection
When it is inserted into the inside of the No. 3, the collimator attachment / detachment device 45 may be used to perform the reverse operation to the above operation.

In this embodiment, the effects obtained in the first embodiment can be obtained.

[0057]

According to the present invention, 3D-PET for a wide range of an object is examined by using one radiation inspection apparatus.
Examination and local-PET targeting the local site of the subject
Both tests can be performed.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a radiation inspection apparatus that is a preferred embodiment of the present invention.

FIG. 2 is a detailed vertical sectional view of a gantry section in FIG.

FIG. 3 is a characteristic diagram showing a relationship between a radioactivity level and a coincidence counting rate.

FIG. 4 2D-PET inspection, 3D-PET inspection and FIG.
6 is a characteristic diagram showing the relationship between the radioactivity level and the coincidence counting rate in the example of FIG.

FIG. 5: γ detected by a radiation detector in PET inspection
It is explanatory drawing which shows each phenomenon of a line.

FIG. 6 is a configuration diagram of a radiation inspection apparatus which is another embodiment of the present invention.

7 is a sectional view taken along line VII-VII of FIG.

FIG. 8 is an explanatory diagram showing the concept of a correction method in a radiation inspection apparatus which is another embodiment of the present invention.

FIG. 9 is a configuration diagram of a radiation inspection apparatus that is another embodiment of the present invention.

[Explanation of symbols]

1, 1A, 1B ... Radiation inspection device, 2, 2A, 2B ... Imaging device, 3 ... Radiation detector, 4 ... Radiation detector holding unit,
5, 5A ... Collimator assembly, 6, 6A, 6B, 6C,
6D, 6E, 6F ... Annular collimator, 7 ... Cylindrical part, 10
... Subject holding device, 12 ... Bed, 13 ... Gantry,
14, 15, 16, 17, 18 ... Radiation detection region, 29
... pinion, 30 ... focal area, 32 ... gamma ray discriminating device, 3
3 ... Simultaneous counting device, 34 ... Computer, 37A, 37
B, 37C, 37D, 37E ... Ring gamma ray passage, 38
... hexagonal tube part, 40 ... movable collimator part, 42 ... movable collimator part element, 44 ... collimator support part, 45 ...
Collimator attachment / detachment device.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kensuke Amemiya             2-12-1 Omika-cho, Hitachi-shi, Ibaraki Prefecture             Ceremony Company Hitachi, Ltd. (72) Inventor Shinichi Kojima             2-12-1 Omika-cho, Hitachi-shi, Ibaraki Prefecture             Ceremony Company Hitachi, Ltd. (72) Inventor Hiroshi Kitaguchi             2-12-1 Omika-cho, Hitachi-shi, Ibaraki Prefecture             Ceremony Company Hitachi, Ltd. (72) Inventor Takashi Okazaki             2-12-1 Omika-cho, Hitachi-shi, Ibaraki Prefecture             Ceremony Company Hitachi, Ltd. (72) Inventor Kazuma Yokoi             2-12-1 Omika-cho, Hitachi-shi, Ibaraki Prefecture             Ceremony Company Hitachi, Ltd. F-term (reference) 2G088 EE01 FF07 JJ17

Claims (17)

[Claims] 1. A subject holding device for holding a subject, and an imaging device, the imaging device comprising a tubular gantry and a plurality of collimator members installed in the gantry so that the subject can be taken in and out. And an annular collimator, wherein the gantry has an annular radiation detector array in which a plurality of radiation detectors for detecting radiation from the subject are annularly arranged, and the collimator has a plurality of rows. The radiation inspection apparatus is characterized in that the plurality of collimator members that form a plurality of radiation passages facing a common focal area are arranged in the axial direction. 2. The radiation inspection apparatus according to claim 1, wherein each of the radiation passageways formed between adjacent ones of the collimator members faces the plurality of annular radiation detector arrays. 3. The radiation inspection apparatus according to claim 1, wherein the imaging device includes a collimator moving device that moves the collimator in and out of the gantry. 4. The image pickup device is provided with a collimator support device for supporting the collimator pulled out from the gantry, on the pull-out side of the collimator.
The radiation inspection apparatus according to claim 3. 5. The radiation inspection apparatus according to claim 1, wherein the collimator member is an annular collimator member. 6. The radiation inspection apparatus according to claim 1, wherein the radiation detector is a semiconductor radiation detector. 7. The radiation inspection apparatus according to claim 1, further comprising a tomographic image creating device that creates a tomographic image of the subject based on an output signal of the radiation detector. 8. The tomographic image forming apparatus uses the γ-ray pair generation information obtained based on the output signal of the radiation detector when the collimator is pulled out from the gantry, and the collimator is configured to detect the γ-ray pair generation information. Compensating the γ-ray pair generation information obtained based on the output signal of the radiation detector while being inserted into the gantry, and creating the tomographic image using the corrected γ-ray pair generation information. Item 7. The radiation inspection apparatus according to item 7. 9. An object holding device for holding an object, and an imaging device, wherein the imaging device is composed of a cylindrical gantry and a plurality of collimator members installed in the gantry so as to be removable. And an annular collimator, wherein the gantry has an annular radiation detector array in which a plurality of radiation detectors for detecting radiation from the subject are annularly arranged, and the collimator has a plurality of rows. Is configured by arranging a plurality of collimator members that form a plurality of radiation passages facing a common focal region in an axial direction, and the collimator member is a movable collimator capable of changing an inclination angle with respect to the gantry. Radiation inspection equipment. 10. The radiation inspection apparatus according to claim 9, wherein each of the radiation passageways formed between adjacent ones of the collimator members faces the plurality of annular radiation detector arrays. 11. The radiation inspection apparatus according to claim 9, wherein the imaging device includes a collimator moving device that moves the collimator in and out of the gantry. 12. The radiation inspection according to claim 9, wherein the image pickup device is provided with a collimator support device for supporting the collimator pulled out from the gantry, on the pull-out side of the collimator. apparatus. 13. The radiation inspection apparatus according to claim 9, wherein the radiation detector is a semiconductor radiation detector. 14. The gantry has a polygonal shape, the collimator member has a plurality of collimator elements arranged in the polygonal shape, and the collimator element is rotatably mounted on the support member and the support member. The radiation inspection apparatus according to claim 9, further comprising: a pair of collimator plates that can change the tilt angle and a drive device that rotates each of the collimator plates. 15. The radiation inspection apparatus according to claim 9, further comprising a tomographic image creating device that creates a tomographic image of the subject based on an output signal of the radiation detector. 16. The radiation inspection apparatus according to claim 1, wherein the collimator includes a tubular body and the plurality of collimator members installed on an inner surface of the tubular body. 17. The radiation inspection apparatus according to claim 16, wherein the tubular body is made of plastic.