JP2014095592A - Radiation detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiation detector that normally operates even in an electric field and is ensured in safety without affecting an MRI device.SOLUTION: A metal member composing a radiation detector 1 according to the invention comprises a plate insulated in a planer direction by a combination of metal members electrically insulated from one another. In this way, even if the radiation detector 1 according to the present invention is exposed to a change in magnetic field, the generation of a magnetic field derived from an eddy current from the metal members is restricted and the detector 1 can operate normally. Additionally, even in a case where an MRI device is installed near the radiation detector 1, the MRI device is prevented from catching a magnetic field generated from the metal members of the radiation detector 1. Since generation of force with which the radiation detector 1 is moved is also prevented by restriction of eddy current, safety for radiation detector 1 is also ensured.

Description

  The present invention relates to a radiation detector that detects an annihilation radiation pair, and more particularly to a radiation detector that is assumed to be placed in the vicinity of an MRI apparatus.

  A specific configuration of a conventional positron emission tomography apparatus (PET) for imaging the distribution of radiopharmaceuticals will be described. A conventional PET apparatus is provided with a detector ring in which radiation detectors for detecting radiation are arranged in an annular shape. The detector ring detects a pair of radiations (an annihilation radiation pair) emitted from the radiopharmaceutical in the subject and having opposite directions.

  The configuration of the radiation detector 51 will be described. As shown in FIG. 23, the radiation detector 51 includes a scintillator 52 in which scintillator crystals are arranged three-dimensionally, and a photodetector 53 that detects fluorescence emitted from the radiation absorbed by the scintillator 52. . The light detector 53 includes a detection surface in which a large number of light detection elements are arranged on a matrix. The detection surface of the photodetector 53 and one surface of the scintillator 52 are optically connected.

  The radiation detector 51 includes a case 56 and a support member 58 that supports the photodetector 53 so as to cover the scintillator 52 as shown in FIG. The case 56 is made of metal for the purpose of surely blocking stray light incident on the scintillator 52 from the outside of the apparatus, and the support member 58 is robust enough to reliably support the main part of the radiation detector 51 having a large weight. It is made of metal because it is required. The plurality of radiation detectors 51 are arranged in a ring to form a detector ring. This detector ring is a sensor for detecting radiation in the PET apparatus.

  Such a PET apparatus may be used in combination with an MRI (Magnetic Resonance Imaging) apparatus. The PET image obtained by the PET apparatus is a functional image showing the distribution of the radiopharmaceutical in the subject, whereas the MRI image obtained by the MRI apparatus is a structure image in the subject. Therefore, if these images having different properties are superimposed, the diagnosis can be made more accurate. An apparatus combining such a PET apparatus and an MRI apparatus is devised so that a PET image and an MRI image can be taken without moving the subject as much as possible. This is because it is necessary to suppress as much as possible the positional deviation of the subject when the two images are superimposed. Therefore, such an apparatus employs a configuration in which a PET apparatus configured by arranging the radiation detectors 51 in the immediate vicinity of the magnetic field generating coil of the MRI apparatus is provided (see, for example, Patent Document 1).

Special table 2008-525161

  However, the conventional radiation detector has the following problems. That is, the conventional radiation detector is not sufficiently considered for a strong magnetic field.

  Conventional radiation detectors have metal parts. These parts are affected by the magnetic field generated by MRI. That is, the metal is magnetized, or a secondary magnetic field is generated due to the eddy current generated in the metal. That is, the magnetic field generated when the MRI apparatus acquires a tomographic image is disturbed by the secondary magnetic field generated by the radiation detector of the PET apparatus.

  Then, the MRI apparatus catches more noise than when the radiation detector of the PET apparatus is not provided. The true nature of the noise captured by the MRI apparatus is a secondary magnetic field generated by a metal member of the radiation detector under the influence of the magnetic field generated by the MRI apparatus.

  Therefore, it is desirable that the radiation detector provided in the vicinity of the MRI apparatus is configured without using metal as much as possible. However, there is a circumstance that it is inevitable to use metal parts for the radiation detector because of the need to ensure the function as a member.

  In addition, if the metal parts of the radiation detector are magnetized or generate a secondary magnetic field derived from eddy current, the PET image acquired by the PET apparatus is also affected. An electronic circuit is mounted on the radiation detector. If such an electronic circuit is affected by a secondary magnetic field emitted from a metal part of the radiation detector, the radiation detector cannot accurately detect the radiation.

  Furthermore, when attaching a PET apparatus to an MRI apparatus generating a strong static magnetic field, or when trying to remove the PET apparatus, the metal member constituting the radiation detector of the PET apparatus is a static magnetic field. The eddy current is generated under the influence of. Then, a magnetic force is generated in a direction in which the PET apparatus moves away from or approaches the MRI apparatus, and an unexpected force for moving the PET apparatus is applied. When such a force is generated, there is a possibility that an MRI apparatus and a PET apparatus collide with each other, or an accident in which an operator collides with the PET apparatus may occur.

  The present invention has been made in view of such circumstances, and its purpose is to provide a radiation detector that operates normally even in a magnetic field, does not affect the MRI apparatus, and ensures safety. It is in.

The present invention has the following configuration in order to solve the above-described problems.
That is, a radiation detector according to the present invention includes a scintillator that converts radiation into fluorescence, a photodetector that detects fluorescence and is optically connected to the scintillator, and (A1) covers the scintillator to provide a photodetector. A case for preventing stray light from entering, and (B1) the case is made of a plate having a plane divided by a plurality of conductors by combining a plurality of metal members that are electrically insulated from each other. It is characterized by being comprised.

  [Operation / Effect] The radiation detector of the present invention is provided with a case for preventing stray light from entering the photodetector. Since this case is made of metal, stray light can be reliably blocked. Furthermore, the present invention is configured to operate without problems even if a strong magnetic field is applied to the radiation detector by devising the case. That is, the case is formed of a plate having a plane divided by a plurality of conductors by combining a plurality of metal members that are electrically insulated from each other. By doing so, no strong eddy current is generated even when the case is exposed to changes in the external magnetic field. Therefore, according to the radiation detector of the present invention, even when exposed to a change in the external magnetic field, the generation of a secondary magnetic field derived from the eddy current from the case is suppressed, and it can operate normally. Further, even if the MRI apparatus is installed near the radiation detector of the present invention, the secondary magnetic field generated by the MRI apparatus from the case of the radiation detector is not regarded as noise.

  In addition, when attempting to attach the radiation detector of the present invention to an MRI apparatus that generates a strong static magnetic field, or when attempting to remove it, the metallic member constituting the radiation detector is a vortex. Does not generate current. Then, the magnetic force which moves a radiation detector is not generated, but the accident resulting from this magnetic force is suppressed. By adopting such a configuration, the safety of the radiation detector is ensured. As a specific example in which such a radiation detector is attached to or detached from the MIR apparatus, there is a case where the PET apparatus is attached to or detached from the MRI apparatus.

  A radiation detector according to the present invention includes a scintillator that converts radiation into fluorescence, a photodetector that detects fluorescence and is optically connected to the scintillator, and (A2) a support member that supports the photodetector. (B2) The support member is composed of a plate having a plane divided by a plurality of conductors by combining a plurality of metal members that are electrically insulated from each other. Is.

  [Operation / Effect] The radiation detector of the present invention is provided with a support member for supporting the photodetector. Since the support member is made of metal, the robustness is sufficient and the photodetector is reliably supported. Furthermore, the present invention is configured to operate without problems even if a strong magnetic field is applied to the radiation detector by devising the support member. That is, the support member is composed of a plate having a plane divided by a plurality of conductors by combining a plurality of metal members that are electrically insulated from each other. By doing so, no strong eddy current is generated even when the support member is exposed to a change in the external magnetic field. Therefore, according to the radiation detector of the present invention, even if it is exposed to a change in the external magnetic field, generation of a secondary magnetic field derived from eddy current from the support member is suppressed, and it can operate normally. Further, even if the MRI apparatus is installed near the radiation detector of the present invention, the secondary magnetic field generated by the MRI apparatus from the support member of the radiation detector is not regarded as noise.

  In the above-described radiation detector, it is more desirable that the metal member is made of a nonmagnetic metal.

  [Operation / Effect] The above-described configuration more specifically represents the radiation detector of the present invention. If the metal member is made of a nonmagnetic metal, the member will not be magnetized even if the radiation detector is exposed to a strong magnetic field. Therefore, according to the radiation detector of the present invention, even if it is exposed to a strong magnetic field, the generation of a magnetic field derived from the magnetization of the metal member is suppressed, and it can operate normally. Even if the MRI apparatus is installed near the radiation detector of the present invention, the MRI apparatus does not catch the magnetic field generated from the metal member of the radiation detector as noise.

  In the above-described radiation detector, the plate is formed by laminating a metal layer composed of a plurality of metal pieces, an insulating intermediate layer that blocks stray light, and a metal layer composed of a plurality of metal pieces in this order. If it becomes a laminated body, it is more desirable.

  [Operation / Effect] The above-described configuration more specifically represents the radiation detector of the present invention. For example, if the plate is a laminated body in which a metal layer composed of a plurality of metal pieces, an insulating intermediate layer that blocks stray light, and a metal layer composed of a plurality of metal pieces are laminated in this order. Even if stray light passes through the metal layer, it is absorbed by the intermediate layer, so that the light shielding property of the case is improved. Since the case of the present invention is manufactured by combining a plurality of metal pieces, a clearance may occur between adjacent metal pieces. If it is set as the structure provided with an intermediate | middle layer, even if stray light passes through this clearance, stray light can be interrupted | blocked reliably.

  The radiation detector of the present invention is configured to operate without problems even when a strong magnetic field is applied to the radiation detector by devising a metal member. That is, the metal member constituting the radiation detector is composed of a plate having a plane divided by a plurality of conductors by combining a plurality of metal members electrically insulated from each other. is there. In this way, even when the radiation detector of the present invention is exposed to a change in the external magnetic field, the generation of secondary magnetic fields derived from eddy currents from the metal member is suppressed, and the radiation detector operates normally. Can do. Moreover, even if the MRI apparatus is installed near the radiation detector of the present invention, the MRI apparatus does not catch the secondary magnetic field emitted from the metal member of the radiation detector as noise. And if eddy current is suppressed, since the force which moves the radiation detector 1 will not generate | occur | produce, the safety | security of the radiation detector 1 is also ensured.

1 is a perspective view illustrating an overall configuration of a radiation detector according to Embodiment 1. FIG. 3 is a cross-sectional view illustrating a configuration of a radiation detector according to Embodiment 1. FIG. FIG. 3 is a plan view illustrating the configuration of the photodetector according to the first embodiment. FIG. 3 is a plan view for explaining a configuration of a case according to Embodiment 1. 3 is a cross-sectional view illustrating a configuration of a case according to Example 1. FIG. 3 is a cross-sectional view illustrating a configuration of a case according to Example 1. FIG. It is a schematic diagram explaining the effect which the structure of the case which concerns on Example 1 has. It is a schematic diagram explaining the effect which the structure of the case which concerns on Example 1 has. It is a schematic diagram explaining the effect which the structure of the case which concerns on Example 1 has. 6 is a plan view for explaining a case manufacturing method according to Embodiment 1. FIG. 6 is a perspective view for explaining a manufacturing method of the case according to Embodiment 1. FIG. 6 is a cross-sectional view illustrating a configuration of a radiation detector according to Embodiment 2. FIG. 6 is a plan view illustrating a configuration of a radiation detector according to Embodiment 2. FIG. 6 is a cross-sectional view illustrating a configuration of a radiation detector according to Embodiment 2. FIG. 6 is an exploded perspective view illustrating a configuration of a support member according to Embodiment 2. FIG. 6 is a cross-sectional view illustrating a configuration of a support member according to Example 2. FIG. It is sectional drawing explaining one modification of this invention. It is sectional drawing explaining one modification of this invention. It is sectional drawing explaining one modification of this invention. It is sectional drawing explaining one modification of this invention. It is sectional drawing explaining one modification of this invention. It is sectional drawing explaining one modification of this invention. It is sectional drawing explaining the radiation detector of a conventional structure.

<Overall configuration of radiation detector>
First, the overall configuration of the radiation detector will be described. As shown in FIG. 1, the radiation detector 1 according to the first embodiment is provided with a scintillator 2 configured by arranging scintillator crystals C vertically and horizontally, and a lower surface of the scintillator 2, and detects fluorescence emitted from the scintillator 2. The light detector 3 and the light guide 4 arrange | positioned in the position interposed between the scintillator 2 and the light detector 3 are provided. Each of the scintillator crystals C is composed of Lu _{2 (1-X)} Y _2X SiO ₅ (hereinafter referred to as LYSO ₎ in which Ce is diffused. When radiation enters the scintillator 2, the radiation is converted into fluorescence.

  The photodetector 3 detects the fluorescence generated by the scintillator 2. The photodetector 3 has a position discriminating function, and can discriminate which scintillator crystal C the fluorescence generated in the scintillator 2 is derived from. The light guide 4 is provided to guide the fluorescence generated in the scintillator 2 to the photodetector 3. Therefore, the light guide 4 is optically coupled to the scintillator 2 and the photodetector 3. The photodetector 3 is optically connected to the scintillator 2 through the light guide 4.

  The photodetector 3 has a detection surface 3a on which fluorescence is incident. The detection surface 3a is directly connected to the light guide 4 as shown in FIG. FIG. 3 schematically shows the detection surface 3a. The detection surface 3a is configured by two-dimensionally arranging detection elements 3b that detect fluorescence. The detection element 3b is composed of a semiconductor element provided with an avalanche diode. The semiconductor element can faithfully detect fluorescence without being affected by a relatively strong magnetic field.

  The reflective film 5 shown in FIG. 2 is a member that covers the scintillator 2 and has a function of preventing the loss of fluorescence by reflecting the fluorescence generated in the scintillator 2. The fluorescence generated in the scintillator 2 cannot be emitted toward the outside of the scintillator 2 by being blocked by the reflective film 5. Therefore, the fluorescence can only be emitted from the side surface of the scintillator 2 where the light guide 4 is provided. The fluorescence guided to the light guide 4 in this way is directed to the photodetector 3 where it is detected. By providing the reflection film 5 in this manner, the fluorescence generated in the scintillator 2 is surely collected in the photodetector 3.

  The photodetector 3 has a sensitivity that is high enough to detect slight fluorescence emitted from the scintillator 2. Therefore, when the radiation detector 1 detects the annihilation radiation pair, when light such as illumination light from the examination room enters the scintillator 2 of the radiation detector 1, the light travels toward the photodetector 3 through the scintillator 2, and the light The detector 3 detects this. Such incident light from the outside of the radiation detector 1 toward the scintillator 2 is stray light, which causes the detection accuracy to be hindered when the radiation detector 1 detects radiation. That is, when such a stray light is detected by the photodetector 3, the radiation detector 1 operates as if the fluorescence is incident although the fluorescence is not actually incident. Many estimates are made. Although the scintillator 2 is provided with a reflective film 5, the reflective film 5 is insufficient to completely block stray light.

  FIG. 2 illustrates a case 6 that prevents stray light from entering the scintillator 2 from the outside of the radiation detector 1. The case 6 is a box configured to include the main part of the radiation detector 1 including the scintillator 2, the optical detector 3, the light guide 4, and the reflection film 5 that covers the scintillator 2 that are optically connected. It is a mold member. The case 6 prevents stray light from entering the photodetector 3 by covering the main part of the scintillator 2 and the like. The case 6 has a rectangular parallelepiped shape following the shape of the main part described above. Since the case 6 is configured not to pass stray light, stray light does not enter the scintillator 2 from the outside. The case 6 is composed of a nonmagnetic metal such as aluminum and a light shielding film that does not transmit light. The configuration of the case 6 is the most characteristic part of the present invention, and details thereof will be described later. A gap is provided between the case 6 and the reflective film 5.

  The case 6 also serves as an electromagnetic shield that protects the main part of the radiation detector 1 from an electric field and a magnetic field generated outside the radiation detector 1. Even if the radiation detector 1 is placed in a strong magnetic field, since the main part of the radiation detector 1 is protected by this case 6, the radiation detector 1 can accurately detect radiation without being affected by the external magnetic field. Can be detected.

<Case configuration>
Next, the configuration of case 6 will be described. Although the case of the conventional device is constructed by assembling aluminum plates, the case 6 of the present invention does not employ such a configuration. That is, the case 6 is composed of a plate 7 having a plane divided by a plurality of conductors by combining a plurality of metal members that are electrically insulated from each other. Specifically, the case 6 is constructed by assembling the plates 7 as shown in FIG. That is, the case 6 includes an aluminum layer L1, L2 composed of a plurality of aluminum pieces 7a, an insulating resin film 7c that blocks stray light, and an aluminum layer L1, L2 composed of a plurality of aluminum pieces 7a in this order. It is comprised from the board 7 laminated | stacked (refer FIG. 5). The plate 7 corresponds to the laminate of the present invention.

  As shown in FIG. 4, the plate 7 is configured by arranging strip-shaped aluminum pieces 7 a having a longitudinal direction and a short direction in the short direction. These aluminum pieces 7a are electrically insulated from each other. The aluminum piece 7a reliably blocks stray light. When the stray light hits the aluminum piece 7a, the stray light cannot be transmitted through the aluminum piece 7a. Accordingly, stray light cannot pass through the plate 7 or the case 6 constituted by the plate 7. The aluminum piece 7a corresponds to the metal piece of the present invention.

  FIG. 5 shows a cross section that appears when the plate 7 of FIG. 4 is cut along a straight line indicated by A. Referring to FIG. 5, it can be seen that the plate 7 is composed of a plurality of layers. That is, the plate 7 is formed by laminating an aluminum layer L1 composed of a plurality of aluminum pieces 7a, a black resin film 7c that blocks stray light, and another aluminum layer L2. The resin film 7c is made of an insulating material that does not conduct electricity. The resin film 7c corresponds to the intermediate layer of the present invention.

  FIG. 6 illustrates the function of the resin film 7c. It is assumed that stray light is incident on the seam of the aluminum piece 7a of the aluminum layer L1, as indicated by an arrow in FIG. A clearance is provided at the joint of the aluminum pieces 7a for the purpose of maintaining insulation between the adjacent aluminum pieces 7a. This clearance may include air or may be filled with an adhesive. In any case, the stray light incident on the seam of the aluminum piece 7a passes through the aluminum layer L described with reference to FIG. 5 through the clearance. However, such stray light is absorbed by the resin film 7 c and cannot pass through the plate 7.

  Thus, the resin film 7c is provided for the purpose of not transmitting stray light slightly transmitted by the aluminum layer L1. Most of the stray light incident on the plate 7 is absorbed by the aluminum piece 7a. Since the aluminum piece 7a is made of metal, it has an excellent shielding property against stray light. However, since a clearance is provided at the joint of the aluminum piece 7a, the aluminum piece 7a cannot shield all stray light. Therefore, the resin film 7c is necessary.

  The reason why the clearance is provided at the joint of the aluminum pieces 7a until the stray light shielding property is impaired in the aluminum layers L1 and L2 is to maintain the electrical insulation between the aluminum pieces 7a. The insulating property of the aluminum piece 7a is a feature of the present invention, and details of the effects obtained thereby will be described later. The aluminum layers L1 and L2 correspond to the metal layer of the present invention.

  An insulating adhesive 7b that does not conduct electricity is interposed between the aluminum piece 7a belonging to the aluminum layers L1 and L2 and the resin film 7c. The aluminum piece 7a and the resin film 7c are integrated by this adhesive to constitute the plate 7.

  The aluminum layer L2 has the same structure as the aluminum layer L1. That is, strip-shaped aluminum pieces 7a having a longitudinal direction and a short direction are arranged in the short direction. These aluminum pieces 7a are electrically insulated from each other. Moreover, the arrangement direction of the aluminum pieces 7a in the aluminum layer L2 coincides with the arrangement direction of the aluminum pieces 7a in the aluminum layer L1. The aluminum pieces 7a are arranged at the same pitch on the aluminum layers L1 and L2. However, the positions of the seams of the aluminum pieces 7a in the arrangement direction of the aluminum pieces 7a are different between the aluminum layers L1 and L2.

  By changing the position of the joint of the aluminum piece 7a between the aluminum layers L1 and L2, the stray light shielding property of the plate 7 is further enhanced. As shown in FIG. 6, it is assumed that there is stray light that enters from the clearance of the seam of the aluminum piece 7a in the aluminum layer L1. Most of such stray light is absorbed by the resin film 7c, but only a small part passes through the resin film 7c. The slight stray light that has passed through the aluminum layer L1 and the resin film 7c enters the aluminum layer L2. This stray light is reliably shielded by the aluminum layer L2. This is because stray light is incident on the center position of the aluminum piece 7a constituting the aluminum layer L2 and cannot be incident on the joint position according to FIG. Thus, by making the positions of the clearances of the aluminum layers L1 and L2 different from each other, stray light transmitted through the clearance of one aluminum layer L cannot be transmitted through the clearance of the other aluminum layer L. It is.

  A method for manufacturing such a plate 7 will be described. To manufacture the plate 7, an aluminum tape is prepared. This aluminum tape has a two-layer structure in which the front surface is made of an aluminum material and the back surface is made of an adhesive material. The plate 7 is manufactured by attaching an aluminum tape to the resin film 7c.

  The aluminum pieces 7a constituting the plate 7 manufactured in this way are electrically insulated from each other. First, the aluminum pieces 7a adjacent to each other are kept insulative by the clearance between them. Moreover, since the aluminum piece 7a is attached to the resin film 7c via the insulating adhesive 7b, there is no opportunity for the aluminum pieces 7a to be electrically connected to each other.

<Eddy current generated by magnetic field>
The effect by comprising the case 6 with the board 7 which has the aluminum piece 7a insulated from each other is demonstrated. First, it is necessary to explain the eddy current generated by the external magnetic field. FIG. 7 illustrates the manner in which the alternating magnetic field B is applied to the metal plate. The configuration in FIG. 7 describes a case of a conventional radiation imaging apparatus, and is not the configuration of the first embodiment. An alternating magnetic field is a type of magnetic field in which the magnetic field repeatedly increases and decreases.

  Assume that an alternating magnetic field B having magnetic lines perpendicular to the metal plate is applied as shown in FIG. Since the magnetic field lines are derived from the alternating magnetic field and fluctuate, an eddy current that circulates around the magnetic field lines is generated in the metal plate. Since this eddy current is generated over the entire area of the metal plate, the current value of the entire eddy current is considerably large.

  FIG. 8 shows a cross section that appears when the metal plate of FIG. 7 is cut along a straight line indicated by A. It is assumed that the eddy current I in FIG. 8 flows in a direction that advances from the back side of the paper surface of FIG. Then, a new magnetic field B having magnetic field lines surrounding the eddy current is generated. This magnetic field B is a secondary magnetic field generated from the metal plate itself. Therefore, when a secondary magnetic field derived from eddy current is generated in the conventional case, the inside of the case is also affected by the secondary magnetic field. Certainly, the case of the radiation detector is configured so that the magnetic field from the outside does not reach the main part of the radiation detector. However, the case cannot shield a secondary magnetic field emanating from itself. Therefore, the main part of the radiation detector is affected by the secondary magnetic field emitted from the case. The influence on the main part of the radiation detector is, for example, an increase in noise for each circuit constituting the photodetector 3. As a result, the radiation detector cannot accurately detect radiation.

  Consider a case where the radiation detector is placed in the vicinity of the MRI apparatus. At this time, when the MRI apparatus generates an alternating magnetic field, the case of the radiation detector generates a secondary magnetic field derived from the eddy current. Then, the MRI apparatus captures a secondary magnetic field generated from this case. That is, the secondary magnetic field deteriorates the tomographic image of the MRI apparatus.

  Thus, when an eddy current occurs in the case of the radiation detector, it not only has an adverse effect on the detection of radiation, but is also harmful to the imaging of the MRI apparatus. But the problem doesn't stop there. Eddy currents generate a magnetic force that attempts to move the radiation detector itself. It is not desirable that an excessive force is applied to the radiation detector in this way when considering the safety of the apparatus.

  Furthermore, the MRI apparatus generates a very strong static magnetic field. Unlike an alternating magnetic field, a static magnetic field is not strong or weak, so it should not generate eddy currents even when applied to a case. However, a static magnetic field also becomes a source of eddy current. That is, when the radiation detector is moved closer to or away from the MRI apparatus, the manner in which the magnetic field is applied to the case of the radiation detector changes. In other words, the case is exposed to changes in the external magnetic field. Then, a secondary magnetic field is generated from the case. The static magnetic field of this MRI apparatus cannot be easily turned on / off. Accordingly, when the PET apparatus is attached to the MRI apparatus, the PET apparatus is brought closer to the MRI apparatus in a state where a static magnetic field is generated. Then, the static magnetic field applied to the PET apparatus gradually increases as it approaches the MRI apparatus. Then, the case of the radiation detector constituting the PET apparatus captures a change in the external magnetic field and generates an eddy current. As a result, a secondary magnetic field is generated from the case. Then, the force which tries to move a PET apparatus generate | occur | produces, and the safe attachment of a PET apparatus is prevented.

  Some PET apparatuses are configured such that the radiation detector can be moved within the apparatus for the purpose of improving image quality. The later-described modification shown in FIG. 20 specifically represents the PET apparatus. When a radiation detector in a static magnetic field is moved in such an apparatus, the magnetic field applied to the radiation detector changes. Then, the radiation detector is exposed to a change in the external magnetic field, and a secondary magnetic field is generated from the case. Since the movement of the radiation detector is performed while the PET apparatus is detecting the radiation, the detection of the radiation detector is disturbed by a secondary magnetic field derived from the case.

<Prevention of eddy current>
The plate 7 of the first embodiment is configured to prevent the above-described eddy current as much as possible. FIG. 9 illustrates a state where an AC magnetic field is applied to the plate 7. In the aluminum piece 7a, an eddy current is generated in the aluminum piece 7a under the influence of the alternating magnetic field. However, since the aluminum pieces 7a are electrically insulated from each other, no eddy current is generated across the adjacent aluminum pieces 7a. This is because the plate 7 is insulated in the plane direction, and eddy currents do not occur over a wide plane. As a result, even if an alternating magnetic field is applied to the plate 7, only a small eddy current is generated inside the aluminum piece 7a, and the current value is extremely small compared to the case of FIG. When the generation of eddy current is suppressed, the generation of the secondary magnetic field described with reference to FIG. 8 is also suppressed accordingly.

  By the way, since the resin film 7c which the board 7 has is a member extending over the entire area of the board 7, if an eddy current is generated in the resin film 7c, an eddy current having a considerably large current value should be generated. However, since the resin film 7c is made of an insulating member, it can be said that there is no room for eddy currents to be generated from the resin film 7c. Since the radiation detector 1 according to the present invention is composed of the plate 7 that does not generate eddy currents, all of the various problems derived from eddy currents are suppressed.

<Assembly of the case>
How such a plate 7 is assembled to form the case 6 will be described. FIG. 10 shows a state in which a cross-shaped portion indicated by oblique lines is cut out from the plate 7. The shape of the cross-shaped member thus obtained is a part of the developed view of the case 6. The case 6 as shown in FIG. 11 is manufactured by assembling the members. The extending direction of the aluminum piece 7a constituting the plate 7 and the extending direction of each side of the cross-shaped member do not need to be particularly matched.

  As described above, the radiation detector 1 of the present invention is provided with the case 6 that prevents stray light from entering the photodetector 3. Since the case 6 is made of metal, stray light can be reliably blocked. Furthermore, the present invention is configured to operate without any problem even if a strong magnetic field is applied to the radiation detector 1 by devising the case 6. That is, the case 6 is composed of a plate 7 having a plane divided by a plurality of conductors by combining a plurality of aluminum pieces 7a that are electrically insulated from each other. By doing so, no strong eddy current is generated even when the case 6 is exposed to a change in the external magnetic field. Therefore, according to the radiation detector 1 of the present invention, even when exposed to a change in the external magnetic field, generation of a secondary magnetic field derived from the eddy current from the case 6 is suppressed, and normal operation is possible. Even if the MRI apparatus is installed near the radiation detector 1 of the present invention, the MRI apparatus does not catch the secondary magnetic field emitted from the case 6 of the radiation detector 1 as noise.

  Further, when attaching the radiation detector 1 of the present invention to an MRI apparatus generating a strong static magnetic field, or when trying to remove it, a metal case 6 constituting the radiation detector 1 is used. Does not generate eddy currents. Then, the magnetic force which tries to move the radiation detector 1 is not generated, and the accident caused by this magnetic force is suppressed. By setting it as such a structure, the safety | security of the radiation detector 1 is ensured.

  As described above, if the metal member such as the aluminum piece 7a is made of a nonmagnetic metal, the member will not be magnetized even if the radiation detector 1 is exposed to a strong magnetic field from the outside. Therefore, according to the radiation detector 1 of the present invention, even when exposed to a strong magnetic field, the generation of a magnetic field derived from the magnetization of the metal member is suppressed, and the device can operate normally. Moreover, even if an MRI apparatus is installed near the radiation detector 1 of the present invention, the MRI apparatus does not catch the secondary magnetic field emitted from the metal member of the radiation detector 1 as noise.

  In addition, the case 6 includes aluminum layers L1 and L2 composed of a plurality of aluminum pieces 7a, an insulating resin film 7c for shielding stray light, and aluminum layers L1 and L2 composed of a plurality of aluminum pieces 7a in this order. If composed of the laminated plates 7, even if the stray light passes through the aluminum layers L1, L2, it is absorbed by the resin film 7c, so that the light shielding property of the case 6 is improved. Since the case 6 of the present invention is manufactured by combining a plurality of aluminum pieces 7a, there may be a clearance between adjacent aluminum pieces 7a. If it is set as the structure provided with the resin film 7c, even if a stray light passes through this clearance, a stray light can be interrupted | blocked reliably.

  Subsequently, a radiation detector according to the second embodiment will be described. The basic structure of the radiation detector according to the second embodiment is the same as that of the radiation detector according to the first embodiment. However, the case 6 included in the radiation detector may use the configuration of the first embodiment or a conventional configuration.

  The radiation detector according to the second embodiment includes a support member that fixes the radiation detector to the PET apparatus. The radiation detector is supported by the PET apparatus main body through this support member.

  FIG. 12 simply shows a PET apparatus 30 according to the second embodiment. The PET apparatus 30 includes a ring-shaped gantry 31 and a detector ring 32 housed inside the gantry 31.

  The gantry 31 of the PET apparatus 30 is provided with a through hole for inserting a subject, and is provided adjacent to the MRI apparatus 20. The MRI apparatus 20 includes a ring-shaped gantry 21 and a superconducting coil 22 housed inside the gantry 21. The gantry 21 of the MRI apparatus 20 is provided with a through hole for inserting a subject, and the PET apparatus 30 is provided so that the through hole of the gantry 31 extends the through hole of the gantry 21 of the MRI apparatus 20. Yes. Therefore, the central axes z of the detector ring 32 and the superconducting coil 22 are coincident with each other.

  The top plate 23 on which the subject is placed is inserted through the gantry 21, 31 so that the gantry 21, 31 can move forward and backward in the central axis z direction.

  The PET apparatus 30 is configured to be able to move back and forth in the direction of the central axis z of the gantry 21 and 31 with respect to the MRI apparatus 20. Thereby, the PET apparatus 30 can approach and separate from the MRI apparatus 20 provided on the floor surface of the examination room as shown by the arrow in FIG.

  FIG. 13 illustrates the configuration of the detector ring 32. The detector ring 32 is configured by arranging the radiation detectors 1 in an annular shape on a donut-shaped disc 32a provided with a hollow. Each of the radiation detectors 1 is arranged in an annular shape by fixing a support member 8 (described later) of the radiation detector 1 to the disc 32a.

  The detector ring 32 is provided for the purpose of detecting an annihilation radiation pair emitted from a positron emission type radiopharmaceutical previously administered to a subject.

  FIG. 14 illustrates the support member 8 of the second embodiment. The support member 8 is a member provided outside the case 6, and the photodetector 3 is connected to the support member 8 through the case 6. The support member 8 is a member that supports the photodetector 3. The detector ring 32 is configured by fixing the support member 8 on the disc 32a. The support member 9 is composed of a plate 9 having a plane divided by a plurality of conductors by combining a plurality of metal members that are electrically insulated from each other.

  FIG. 15 illustrates the configuration of the plate 9 constituting the support member 8. As shown in FIG. 15, the plate 9 is configured by arranging strip-shaped aluminum pieces 9 a having a longitudinal direction and a short direction in the short direction. These aluminum pieces 9a are electrically insulated from each other. Referring to FIG. 15, it can be seen that the plate 9 is composed of a plurality of layers. That is, the plate 9 is configured by laminating an aluminum layer L1 composed of a plurality of aluminum pieces 9a and another aluminum layer L2. The aluminum piece 9a corresponds to the metal piece of the present invention.

  An insulating adhesive 9b that does not conduct electricity is interposed between the aluminum piece 9a belonging to the aluminum layer L1 and the aluminum piece 9a belonging to the aluminum layer L2. The aluminum piece 9a is integrated by this adhesive, and the board 9 is comprised.

  The aluminum layer L2 has the same structure as the aluminum layer L1. That is, strip-shaped aluminum pieces 9a having a longitudinal direction and a short direction are arranged in the short direction. These aluminum pieces 9a are electrically insulated from each other. Aluminum pieces 9a are arranged at the same pitch on the aluminum layers L1 and L2. Moreover, the arrangement direction of the aluminum pieces 9a in the aluminum layer L2 is orthogonal to the arrangement direction of the aluminum pieces 9a in the aluminum layer L1. The support member 8 is configured by combining a plurality of aluminum pieces 9a that are electrically insulated from each other.

  FIG. 16 shows a cross-sectional structure of the plate 9. As shown in FIG. 16, since the plate 9 is configured such that the aluminum pieces 9 a intersect each other, high strength can be realized.

  A method for manufacturing such a plate 9 will be described. To manufacture the plate 9, an aluminum tape is prepared. This aluminum tape has a two-layer structure in which the front surface is made of an aluminum material and the back surface is made of an adhesive material. The plate 9 is manufactured by attaching an aluminum tape to the array of aluminum pieces 9a.

  The aluminum pieces 9a constituting the plate 9 manufactured in this manner are electrically insulated from each other. First, the aluminum pieces 9a adjacent to each other are kept insulative by the clearance between them. Moreover, since the aluminum piece 9a is integrated with the other aluminum piece 9a via the insulating adhesive 9b, there is no opportunity for the aluminum pieces 9a to be electrically connected to each other.

  Since the support member 8 manufactured from such a plate 9 is composed of a plurality of aluminum pieces 9a that are electrically insulated from each other, even if the support member 8 is exposed to changes in the external magnetic field, the support member 8 A large eddy current is not generated in the case 2, and generation of a secondary magnetic field from the support member 8 is suppressed. As a result, both the MRI apparatus 20 and the PET apparatus 30 can acquire a tomographic image with little noise without being influenced by a secondary magnetic field.

  As described above, the radiation detector 1 of the present invention is provided with the support member 8 that supports the photodetector 3. Since the support member 8 is made of metal, the robustness is sufficient and the photodetector 3 is reliably supported. Furthermore, the present invention is configured so that the support member 8 can be operated without any problem even if a strong magnetic field is applied to the radiation detector 1 by devising the support member 8. That is, the support member 8 is composed of a plate having a plane divided by a plurality of conductors by combining a plurality of metal members that are electrically insulated from each other. By doing so, no strong eddy current is generated even when the support member 8 is exposed to a change in the external magnetic field. Therefore, according to the radiation detector 1 of the present invention, the generation of the secondary magnetic field derived from the eddy current from the support member 8 is suppressed even when exposed to a change in the external magnetic field, and can operate normally. . Even if the MRI apparatus is installed near the radiation detector 1 of the present invention, the MRI apparatus does not catch the secondary magnetic field generated from the support member 8 of the radiation detector 1 as noise.

  Further, when attaching the radiation detector 1 of the present invention to an MRI apparatus generating a strong static magnetic field, or when trying to remove it, a metal support member constituting the radiation detector 1 is used. 8 does not generate eddy current. Then, the magnetic force which tries to move the radiation detector 1 is not generated, and the accident caused by this magnetic force is suppressed. By setting it as such a structure, the safety | security of the radiation detector 1 is ensured.

  The present invention is not limited to the above-described configuration and can be modified as follows.

  (1) In the above-described embodiment, the aluminum pieces 7a and 9a are made of aluminum, but the present invention is not limited to this structure. The aluminum pieces 7a and 9a can be made of other nonmagnetic metals. By doing so, the metal member constituting the radiation detector 1 is not magnetized even if it is exposed to a strong magnetic field, and the radiation detector 1 operates normally without being influenced by the external magnetic field. Can do. Further, the MRI apparatus placed in the vicinity of the radiation detector 1 does not catch the magnetic field generated from the metal member constituting the radiation detector 1 as noise.

  (2) Although the aluminum pieces 7a and 9a are arranged at the same pitch in the aluminum layers L1 and L2 in the above-described embodiment, the arrangement pitch may be different between the aluminum layers L1 and L2.

  (3) In Example 1 described above, the plate 7 is configured to include the resin film 7c. However, the present invention is not limited to this configuration, and may be configured to omit the resin film 7c as shown in FIG. it can.

  (4) In the first embodiment described above, the position of the seam of the aluminum piece 7a constituting the plate 7 is different between the aluminum layers L1 and L2. However, the present invention is not limited to this structure, and resin If the light-shielding property of the film 7c is sufficiently ensured, as shown in FIG. 18, the position of the seam of the aluminum piece 7a constituting the plate 7 is made to coincide between the aluminum layers L1 and L2. Also good.

  (5) In the first embodiment described above, the arrangement direction of the aluminum pieces 7a in the aluminum layer L2 coincides with the arrangement direction of the aluminum pieces 7a in the aluminum layer L1, but the configuration of the present invention is not limited to this. As long as the light-shielding property of 7 is sufficiently secured, the angle between the arrangement directions can be freely changed.

  (6) In the second embodiment described above, the plate 9 is composed of the two aluminum layers L1 and L2, but this may be configured to have a plurality of aluminum layers as shown in FIG.

  (7) In Example 2 described above, the arrangement direction of the aluminum pieces 7a in the aluminum layer L2 was orthogonal to the arrangement direction of the aluminum pieces 7a in the aluminum layer L1, but the configuration of the present invention is not limited to this, and the plate As long as the strength of 9 is sufficiently secured, the angle formed by the arrangement directions can be freely changed.

  (8) The second embodiment described above has a configuration having the O-type detector ring 32. However, the present invention is not limited to this configuration, and the detector ring 32 may be a C-type as shown in FIG. Good. A specific configuration of the PET apparatus according to this modification will be described. As shown in FIG. 20, the PET apparatus 30 according to this modification includes a C-shaped detector ring 32, a support 33 that supports the detector ring 32, a support 34 that supports the support 33, and a base that supports the support 34. 35. The support column 34 can be expanded and contracted in the vertical direction as indicated by an arrow. Further, the base 35 is movable in the horizontal direction as indicated by an arrow. The moving direction of the base 35 and the direction (center axis direction) in which the detector ring 32 extends are orthogonal to each other.

  As shown in FIG. 21, the detector ring 32 includes two arc members 32p and 32q arranged on a virtual circle VA. The arc member 32p is movable along the virtual circle VA with respect to the support 33 as indicated by the arrows and dotted lines in FIG. The arc member 32q can also move along the virtual circle VA with respect to the support 33. The arc members 32p and 32q can be moved independently of each other or can be moved mirror-symmetrically. By deforming the detector ring 32 in this way, it becomes possible to detect appropriate radiation according to the inspection purpose. The arc members 32p and 32q are configured by arranging the radiation detectors 1 in an arc shape on a fan-shaped plate material such as a part of the disk 32a described in FIG.

  FIG. 22 shows a state in which the PET apparatus 30 according to this modification is attached to the MRI apparatus 20. The PET apparatus 30 is advanced and retracted in a direction orthogonal to the z direction that is the moving direction of the subject M. By making the PET apparatus 30 movable with respect to the MRI apparatus 20 in this way, the apparatus configuration can be changed according to the purpose of the examination. When an inspection is performed using the PET apparatus 30, the base 35 of the PET apparatus 30 is moved with respect to the floor surface, and the support 34 is expanded and contracted, so that the central axis of the superconducting coil 22 included in the MRI apparatus 20 is The detector ring 32 is moved to a position where the center axis of the detector ring 32 coincides. At this time, the superconducting coil 22 remains in a state of generating a static magnetic field. When the detector ring 32 moves to a desired position, the PET apparatus 30 is fixed to the floor surface of the examination room using an attached lever (not shown). As a result, the PET apparatus 30 during inspection does not move under the influence of the static magnetic field of the MRI apparatus 20.

  Further, the arc members 32p and 32q of the detector ring 32 are moved as described with reference to FIG.

  That is, the PET apparatus 30 according to the present modification is premised on moving the detector ring 32 and the radiation detector 1 constituting the detector ring 32 in a strong static magnetic field. Even in such a severe situation, the radiation detector 1 according to the present invention operates normally without being affected by the magnetic field, and can be safely moved without affecting the MRI apparatus 20.

DESCRIPTION OF SYMBOLS 1 Radiation detector 2 Scintillator 3 Photo detector 6 Case 7 Board (laminate)
7a Aluminum piece (metal piece)
7c Resin film (intermediate layer)
8 Support member 9 Plate 9a Aluminum piece (metal piece)
L1, L2 Aluminum layer (metal layer)

Claims (4)

A scintillator that converts radiation into fluorescence;
A photodetector for detecting fluorescence and optically connected to the scintillator;
(A1) including a case for preventing stray light from entering the photodetector by covering the scintillator;
(B1) The radiation detector is characterized in that the case is constituted by a plate having a plane divided by a plurality of conductors by combining a plurality of metal members electrically insulated from each other. . A scintillator that converts radiation into fluorescence;
A photodetector for detecting fluorescence and optically connected to the scintillator;
(A2) comprising a support member that supports the photodetector,
(B2) The radiation detection is characterized in that the support member is composed of a plate having a plane divided by a plurality of conductors by combining a plurality of metal members electrically insulated from each other. vessel. The radiation detector according to claim 1 or 2,
The radiation detector is characterized in that the metal member is made of a nonmagnetic metal. The radiation detector according to claim 1.
The plate is a laminate in which a metal layer composed of a plurality of metal pieces, an insulating intermediate layer that blocks stray light, and a metal layer composed of a plurality of metal pieces are laminated in this order. Characteristic radiation detector.

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