Method of manufacturing radiation tomography apparatus

A method of manufacturing radiation tomography apparatus in this invention includes a step of fixing a detector array to a holding member by adjusting relative positions of the detector array and the holding member the base by spacing a scintillator apart from a base through contact of the scintillator of the detector array to a supporting device. Such configuration may realize provision of radiation tomography apparatus with higher spatial resolution by manufacturing a group of detectors having the scintillators of suppressed deviation in arrangement and being arranged regularly upon arranging radiation detectors for forming the group of detectors.

TECHNICAL FIELD

This invention relates to radiation tomography apparatus that images radiation. Particularly, this invention relates to radiation tomography apparatus having block, radiation detectors arranged in a ring shape.

BACKGROUND ART

In medical fields, radiation emission computed tomography (ECT: Emission Computed Tomography) apparatus is used that detects an annihilation radiation pair (for example, gamma rays) emitted from radiopharmaceutical that is administered to a subject and is localized to a site of interest for obtaining sectional images of the site of interest in the subject showing radiopharmaceutical distributions. Typical ECT apparatus includes, for example, a PET (Positron Emission Tomography) device and an SPECT (Single Photon Emission Computed Tomography) device.

A PET device will be described by way of example. The PET device has a group of detectors having block radiation detectors arranged in a ring shape. The group of detectors is provided, for surrounding a subject, and allows detection of an annihilation radiation pair that is transmitted through the subject.

First, description will be given of a configuration of a conventional PET device. As shown inFIG. 18, a conventional PET device50includes a gantry51with an introducing hole that introduces a subject, a group of detectors53having block radiation detectors52for detecting radiation being arranged inside the gantry51so as to surround the introducing hole, and a holding member54provided so as to surround the group of detectors53. Each of the radiation detectors52has a bleeder unit55with a bleeder circuit in a position between the holding member54and thereof for connecting the holding member54and the radiation detector52. The bleeder unit55is coupled to a light detector62, mentioned later, in the radiation detector52.

Such radiation detector arranged in the group of detectors of the PET device is often equipped that allows position discrimination in a depth direction of a scintillator provided in the radiation detector for improved resolution. Next, description will be given of a construction of the radiation detector52. As shown inFIG. 19, the conventional radiation detector52includes a scintillator61that converts radiation into fluorescence, and a photomultiplier tube (hereinafter referred to as a light detector)62that detects fluorescence. The scintillator61has scintillation counter crystals63of rectangular solid that are arranged in a two-dimensional array. The light detector62allows discrimination about which scintillation counter crystal63emits fluorescence. That is, the radiation detector52may discriminate an incidence position of radiation in the scintillator61. A light guide64is provided between the scintillator61and the light detector62for receiving fluorescence.

Here in the PET device50, the radiation detectors52in the group of detectors53have to be arranged precisely. The PET device50acquires a sectional image based on an incidence direction of radiation. Accordingly, when a deviation occurs in arrangement of the radiation detectors52in the group of detectors53, the deviation also influences the sectional image acquired with the PET device50. Specifically, where the radiation detectors52in the group of detectors53are not positioned as they are by an original setting, the incidence position of radiation determined with the group of detectors53deviates from an actual incidence position thereof even when localization of radiopharmaceutical in the subject is identified from data that is outputted from the group of detectors53. Thus, the conventional PET device50has a configuration in which the holding member54is divided into split sections, and the radiation detectors are loaded therein in order that the radiation detectors52are regularly arranged to the extent possible (see, for example, Patent Literature 1.)

PATENT LITERATURE 1

DISCLOSURE OF THE INVENTION

Problem to be Solved by the Invention

However, the conventional radiation tomography apparatus has the following drawbacks. That is, according to the conventional configuration, when the radiation detectors52are arranged, positioning thereof is performed with reference to the bleeder unit55. Taking into consideration that, in the radiation detector52, the incidence position of radiation is identified by discrimination about which scintillation counter crystal63emits fluorescence, not the bleeder unit55but the scintillator61of the elements in the group of detectors53needs to be arranged regularly. The light detector62having the radiation detectors52is coupled to the holding member54via the bleeder unit55. Consequently, the light detector62and the bleeder unit55must not deviate in its coupling position for regular arrangement of the radiation detectors52.

In addition, according to the conventional radiation tomography apparatus, the scintillator61constituting the radiation detector52and the light detector62must not deviate in its coupling position. Although the light detectors62are regularly arranged in the group of detectors53, where the light detector62and the scintillator61deviate in its coupling position in each of the radiation detectors52, arrangement of the scintillators61will deviate accordingly. According to the foregoing configuration as noted above, upon arrangement of the radiation detectors52in the group of detectors53, each of the adjacent scintillators61is not ensured to be arranged regularly in the radiation detector52since the radiation detector52is not positioned with reference to the scintillator61.

On the other hand, however, when the scintillator61is accurately coupled to the light detector62, the scintillator61and the holding member54are supported on the light detector62and the bleeder unit55, which leads to further deviation in the coupling position of each member. That is, it is not easy to form the group of detectors53of the conventional, configuration with the scintillators62being arranged regularly.

In other words, according to the conventional configuration, even when the scintillation counter crystals63are arranged with high accuracy to form the scintillators61, the arrangement of the scintillators61deviate when seen the group of detectors53in its entirety. As a result, high position discrimination function of radiation in the single radiation detector52is useless without being efficiently employed in the PET device.

This invention has been made regarding the state of the art noted above, and its object is to provide radiation tomography apparatus having higher spatial resolution by suppressing deviation in arrangement of scintillators and manufacturing a group of detectors with the scintillators being arranged regularly upon arranging radiation detectors for forming the group of detectors.

Means for Solving the Problem

This invention is constituted as stated below to achieve the above object. A method of manufacturing radiation tomography apparatus according to this invention includes a group of detectors in an annular shape, the group of detectors having detector arrays in a ring shape with each of radiation detectors arranged in series in which a scintillator that converts radiation into fluorescence, a light guide that receives fluorescence, and a light detector that detects fluorescence are laminated in a height direction. The method includes a detector array formation step of forming a detector array having two or more radiation detectors integrated with one another; a first holding member fixation step of fixing a sub member of a holding member having a main member and the sub member that extends from the main member to a base of a first jig having the base, a branch portion that extends from the base, and a supporting device; a detector array placement step of inserting the detecting array into a position between the branch portion and the main member for placing the detector array on the first jig; a second holding member fixation step of fixing the detector array to the holding member by adjusting a relative position of the detector array and the holding member in a direction where the scintillator and the base are spaced through contact of the scintillator of the detector array to the supporting device; and a group of detectors formation step of forming the group of detectors by fixing the sub member to a base member plate to arrange the detector arrays at least in a circular shape.

Operation and Effect

According to this invention, the first jig positions a relative position of the detector array and the holding member. The first jig has the support device provided thereon for supporting the scintillator and determining a clearance between the scintillator and the base. Taking into consideration that the sub member is placed on the base, one clearance is certainly determined between the sub member and the scintillator. Consequently, the detector arrays are also to be arranged accurately merely by arranging the sub members annularly to fix them to the base member, thereby fanning the group of detectors. According to the radiation tomography apparatus manufactured with the configuration of this invention, the radiation detectors in the group of detectors may be arranged more regularly. Therefore, decrease in spatial resolution may be suppressed as much as possible that occurs from arrangement deviation of the radiation detectors in the group of detectors upon counting the number of annihilation radiation pairs for determination of the radiation intensity distribution.

Moreover, the following is more desirable. That is, the above base of the first jig and the sub member have a first positioning device provided therein. A relative position is determined of the holding member with respect to the first jig in a given direction via the first positioning device in the first holding member fixation step. The branch portion of the first jig and the scintillator have a second positioning device. A relative position is determined of the detector array with respect to the first jig in a given direction via the second positioning device in the second holding member fixation step. A relative positional relationship between the holding member and the detector array in a given direction is determined via the first

Operation and Effect

The foregoing configuration may realize not only adjustment in position of the sub member and the scintillator in a spacing direction but also determination, for example, of the relative position in a given direction perpendicular thereto. Upon placement of the holding member on the first jig, the first jig and the holding member are positioned based on the first positioning device provided in the base of the first jig and the sub member. Accordingly, a positional relationship may reliably be established between the holding member and the branch portion of the first jig in a given direction. Moreover, in the second holding member fixation step, a relative position is determined, of the detector array with respect to the first jig in a given direction via the second positioning device. At this time, a positional relationship is determined between the detector array and the first jig in a given direction. Accordingly, a positional relationship is determined between the detector array and the holding member in a given direction via the first jig. The radiation tomography apparatus manufactured with the foregoing configuration may realize more regular arrangement of the radiation detectors in the group of detectors.

Moreover, it is more preferable that the foregoing configuration includes a second jig placement step of placing the holding member on a bottom by contacting the scintillator of the detector array to a stem of a second jig having the bottom and the stem extending therefrom, thereby adjusting, a relative position of the second jig and the detector array in a direction where the scintillator and the stem contact to each other; and a plate fixation step of fixing a plate to the sub member while adjusting the relative position in a given direction of the detector array with respect to the stem with a third positioning device provided in the stem of the second jig and the scintillator. It is more preferable that, in the group of detectors formation step, the detector arrays with respect to the base member are adjusted in position based on a position of the plate, and are arranged at least circularly.

Operation and Effect

The foregoing configuration may ensure a given relative position of the detector array and the holding member. According to the foregoing configuration, even when the relative position of the detector array and the holding member deviates not only in (A) a direction where the sub member and the scintillator are spaced and (B) a given direction but also (C) a direction where the scintillator contacts the stem, the deviation may be corrected with the plate. According to the foregoing configuration, the scintillator of the detector array contacts the stem of the second jig, which results in adjustment in position of the second jig and the detector array. Thereafter, the plate is adjusted in position based on the position of the stein of the second jig for fixation to the sub member. Consequently, the position of the detector array and the plate may reliably be ensured with no influence on deviation in relative position of the detector array and the holding member. Thus, annular arrangement of the detector arrays based on the position of the plate may realize more regular arrangement of the radiation detectors in the group of detectors.

Moreover, it is more desirable that a fourth positioning device is provided in the bottom of the second jig and the plate, and a relative position of the plate with respect to the sub member in the plate fixation step is determined via the fourth positioning device.

Operation and Effect

According to the foregoing configuration, the relative position of the plate with respect to the sub member may reliably be determined based on the position of the stem of the second jig. The relative position is determined of the plate with respect to the sub member via the fourth positioning device provided in the plate and the bottom of the second jig. That is, the position of the plate with respect to the holding member is determined via the fourth positioning device with no influence on positional relationship between the second jig and the sub member. In other words, with the foregoing configuration, the relative position of the plate with respect to the sub member may reliably be determined based on the detector array.

Moreover, the following is desirable. That is, a fifth positioning device is provided in the base member and the plate, and a relative position of the detector array with respect to the base member in the group of detectors formation step is determined via the fifth positioning device.

Operation and Effect

According to the foregoing configuration, the detector arrays are annularly arranged based on the position of the plate. That is because the relative position of the detector array with respect to the bottom member is determined via the fifth positioning device. The relative position of the plate with respect to the holding member is determined based on the detector array. As a result, when the plate is merely arranged accurately on the bottom member, the detector arrays may be arranged accurately in an annular shape. There is no particular difficulty in arranging the plate on the base member. It is just need to determine the relative position of the plate on the base member via the fifth positioning device.

This invention may also adopt a configuration where the second jig is omitted. That is, a sixth positioning device may be provided in the base of the first jig and the sub member, and a seventh positioning device may be provided in the base member and the sub member. The relative position of the detector array with respect to the holding member in the second holding member fixation step may be determined through contact of the scintillator of the detector array to the branch portion and the supporting device and via the sixth positioning device. The relative position of the detector array with respect to the base member in the group of detectors formation step may be determined via the seventh positioning device.

Operation and Effect

According to the foregoing configuration, a configuration may be provided without the foregoing second jig being always required. That is, the first jig and the sub member have the sixth positioning device provided therein. The relative position of the holding member and the first jig is determined via the sixth positioning device. Consequently, the relative position of a detector array and a holding member may reliably be determined. Moreover, the base member and the sub member have the seventh positioning device provided therein. The relative position of the detector array with respect to the base member in the group of detectors formation step is determined via the seventh positioning device. Such configuration may ensure annular arrangement of the holding members via the seventh positioning device. Taking into consideration that the relative position of the detector array and the holding member is reliably determined, accurate arrangement of the holding members may ensure secure arrangement of the detector arrays in an annular shape. As noted above, the radiation tomography apparatus may be provided having minimized deviation in position of the radiation detectors.

Effect of the Invention

According to this invention, the first jig determines the relative position of the detector array and the holding member. That is because the first jig has the supporting device provided therein for supporting the scintillator so as to ensure a given clearance between the sub member and the scintillator. Moreover, a given positional relationship may be achieved not only in a direction where the sub member and the scintillator are spaced but also in a given direction perpendicular thereto. That is because the first positioning device determines the positional relationship between the first jig and the holding member in a given direction.

The detector array and the holding member in this invention are adjusted in relative positional relationship with three positioning methods that are independent to one another. Specifically, the positioning methods are those using the supporting device, the first and second positioning devices, and the plate. Such configuration may realize assignment of these positioning methods to three directions, respectively, that are perpendicular to one another. In other words, the relative positional relationship between the detector array and the holding member in this invention may be adjusted in three directions that are perpendicularly to one another. Consequently, no direction exists where the detector array and the holding member may deviate upon arranging of the holding members annularly to form the group of detectors.

DESCRIPTION OF REFERENCES

S2. . . first holding member fixation step

S4. . . second holding member fixation step

S8. . . group of detectors formation step

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of radiation tomography apparatus according to this invention will be described hereinafter with reference to the drawings,

Firstly, prior to explanation of a method of manufacturing radiation tomography apparatus according to Embodiment 1, description will be given of a configuration of a radiation detector1according to Embodiment 1.FIG. 1is a perspective view of the radiation detector according to Embodiment 1. As shown inFIG. 1, the radiation detector according to Embodiment 1 includes a scintillator2that is formed of scintillation counter crystal layers each laminated in order of a scintillation counter crystal layer2D, a scintillation counter crystal layer2C, a scintillation counter crystal layer2B, and a scintillation counter crystal layer2A, in turn, in a z-direction, a photomultiplier tube (hereinafter referred to as a light detector)3having a function of position discrimination that is provided on an undersurface of the scintillator2for detecting fluorescence emitted from the scintillator1r, and a light guide4interposed between the scintillator2and the light detector3. Consequently, each of the scintillation counter crystal layers is laminated in a direction toward the light detector3. In other words, the scintillator2has scintillation counter crystals arranged in a three-dimensional array. Here, the z-direction corresponds to a height direction in this invention.

Here, the scintillation counter crystal layer2A corresponds to an incident surface of radiation in the scintillator2. Each of the scintillation counter crystal layers2A,2B,2C, and2D is optically coupled, and includes a transparent material t of cured thermosetting resin between each of the layers. A thermosetting resin composed of a silicone resin may be used for the transparent material t. The scintillation counter crystal layer2A corresponds to a receiver of the gamma rays emitted from a radioactive source. The scintillation counter crystals in a block shape are arranged in a two-dimensional array with thirty-two numbers of the scintillation counter crystals in an x-direction and thirty-two numbers of the scintillation counter crystals in a y-direction relative to a scintillation counter crystal a (1, 1). That is, the scintillation counter crystals from a (1, 1) to (1, 32) are arranged in the y-direction to form a scintillator crystal array. Thirty-two numbers of the scintillator crystal arrays are arranged in the x-direction to form a scintillation counter crystal layer2A. Here, as for the scintillation counter crystal layers2B,2C, and2D, thirty-two numbers of the scintillator counter crystals are also arranged in the x-direction and the y-direction in a matrix in a two-dimensional array relative to a scintillation counter crystal b (1, 1), c (1, 1), and d (1, 1), respectively. In each of the scintillation counter crystal layers2A,2B,2C, and2D, the transparent material t is also provided between the scintillation counter crystals adjacent to each other. Consequently, each of the scintillation counter crystals is to be enclosed with the transparent material t. The transparent material t has a thickness around 25 μm. A gamma ray corresponds to radiation in this invention.

First reflectors r that extend in the x-direction and second reflectors s that extend in the y-direction are provided in the scintillation counter crystal layers2A,2B,2C, and2D provided in the scintillator2. Both reflectors r and s are inserted in a gap between the arranged scintillation counter crystals.

The scintillator2has scintillation counter crystals suitable for detection of gamma rays in a three-dimensional array. That is, the scintillation counter crystal is composed of Ce-doped Lu2(i-X)Y2XSiO5(hereinafter referred to as LYSO.) Each of the scintillation counter crystals is, for example, a rectangular solid having a length of 1.45 mm in the x-direction, a width of 1.45 mm in the y-direction, and a height of 4.5 mm regardless of the scintillation counter crystal layer. The scintillator2has four side end faces that are covered with a reflective film not shown. The light detector3is multi-anode type, and allows position discrimination of incident fluorescence in the x and y-directions.

The light guide4is provided for guiding fluorescence emitted in the scintillation2into the light detector3. Consequently, the light guide4is optically coupled to the scintillator2and the light detector3. The light detector has two or more connection terminals3pprovided on a bottom face opposed to the scintillator2. These connection terminals3pare connected to a bleeder unit18, mentioned later.

Next, description will be given of a configuration of radiation tomography apparatus10according to Embodiment 1.FIG. 2is a sectional cut-away view showing a configuration of the radiation tomography apparatus according to Embodiment 1. As shown inFIG. 2, the radiation tomography apparatus10according to Embodiment 1 has a gantry11having an opening for introducing a subject, and a group of detectors (detector ring)12in a circular ring shape that is provided inside the gantry11so as to contain the opening of the gantry11. Gamma rays emitted from the subject enter into the group of detectors12. The group of detectors12in the radiation tomography apparatus10determines intensity, an incident period of time, and an incident position of incident gamma rays. Description will be give hereinafter of a method of manufacturing such radiation tomography apparatus.

FIG. 3is a flow chart showing a method of manufacturing the radiation tomography apparatus according to Embodiment 1. As shown inFIG. 3, a method of manufacturing the radiation tomography apparatus10according to Embodiment 1 includes a detector array formation step S1for forming a detector array16having three radiation detectors1coupled in series for integration; a holding member fixation step S2for placing a holding member17on a first jig21; a detector array placement step S3for placing the detector array16on the first jig21; a second holding member fixation step S4for fixing both members16,17through determination of a relative position of the detector array16and the holding member17by use of the first jig21; a second jig placement step S5for removing a detector unit19manufactured in previous steps from the first jig21, and then fixing it to a second jig22; a plate fixation step S6for fixing a plate24to a sub member17bof the holding member17; a second jig removal step S7for removing the holding member17from the second jig22; and a group of detectors formation step S8for contacting the sub member17bof the holding member17to a circular plate26, thereby arranging the detector arrays16in an annular shape. These manufacturing steps will be described hereinafter in order.

In the detector array formation step S1, three radiation detectors1are bonded to one another with an adhesive via a spacer15for integration, whereby the detector array16(seeFIG. 4) is formed. Specifically, the spacer15is arranged between two lights detectors3and contacts one side end of the light detectors3of the radiation detector1. Moreover, a clearance between each radiation detector1is determined based on the scintillator2of the radiation detector1. Specifically, adjacent scintillators2are set to have a clearance therebetween having integer multiples of a width in an x-direction of the scintillation counter crystal (arrangement direction of the radiation detector1) that forms the scintillator2. According to the configuration of Embodiment 1, the clearance between each scintillator2is set to be twice the width of the scintillation counter crystal in the x-direction. Moreover, the scintillators2are equal to one another in position of each radiation detector1in a y-direction a short side direction of the detector array16.) Such configuration may realize positioning of the scintillation counter crystals under consideration of the entire detector array16, which results in provision of the radiation tomography apparatus10that allows mapping of incident positions of gamma rays with more accuracy. Thereafter, as shown inFIG. 4, the connection terminals3pprovided on an under surface of the detector array16are inserted into sockets provided in the bleeder unit18. Accordingly, the detector array16is to be integrated with three bleeder units18. Here, the bleeder unit18has screw holes18don a bottom face thereof that is opposed to the scintillator2, which is to be described later.

<First Holding Member Fixation Step S2>

Here, the holding member17is fixed to the first jig21independently of forming the detector array. Description will be given of a configuration of the first jig21used in this step.FIG. 5is a perspective view showing a configuration of the first jig, according to Embodiment 1. As shown inFIG. 5, the first jig21according to Embodiment 1 has a planar base21bdirected to a yz-plane and a prismatic branch portion21aperpendicular to the base21bthat extends in the x-direction. The base21bhas two screw holes21cfor fixing the holding member17, a prismatic contact portion21dfor contacting a main member17aof the holding member17that extends in the x-direction, and a prismatic support board21efor supporting the scintillator2of the detector array16that extends in the x-direction. In addition, the base21bhas a marking21kprovided therein that extends in the z-direction. Seen the first jig21in the x-direction, the base21bhas the branch portion21a, the support board21e, the contact portion21d, the screw holes21c, and the marking21karranged, in turn, in the z-direction. Here, a position in the y-direction of the marking21kis equal to a position in the y-direction of one side21hof the branch portion21athat extends in the x-direction. The support board21ecorresponds to the support device in this invention.

As shown inFIG. 6(a), in operation during the first holding member fixation step S2, the L-shaped holding member17having the plate main member17aand the sub member17bis placed on the base21bof the first jig21. At this time, the sub member17bis directed. Opposite to the foregoing branch portion21a. On the other hand, the main member17ais directed toward the branch portion21a. As shown inFIG. 6(a), the sub member17bhas two drilled holes17cthrough which screws20care inserted. Then, the screw20cis screwed into the screw hole21cprovided in the base21b. As noted above, the holding member17is fixed to the first jig21.

Description will be given in detail of a positional relationship between the holding member17and the first jig21. First, the main member17ais brought into contact with the contact portion21dprovided on the base21b. Accordingly, the relative position of the main member17awith respect to the first jig21is to be determined in the z-direction where the holding member17and the branch portion21aare opposed to each other. Simultaneously, the position of the holding member17with respect to the first jig21is adjusted such that the marking17kprovided, in the sub member17bis equal in position to the marking21kprovided in the base21bin the y-direction. Consequently, the relative position is determined of the holding member17and the branch portion21ain the y-direction. Moreover, the sub member17bhas two through holes17fand two screw holes17e, which is to be mentioned later. Here, the marking17kand21kcorrespond to the first positioning device in this invention. In addition, the y-direction corresponds to a given direction in this invention.

As shown inFIG. 6(b), the detector array16is inserted between the branch portion21aand the main member17a. A direction is selected as an insertion direction of the detector array16where a long side direction of the detector array16conforms to an extending direction of the branch portion21, and the scintillator2of the detector array16is directed toward the branch portion21a. Consequently, the main member17ais adjacent to the bottom face of the bleeder unit18of the detector array16. Clearance is also provided between the main member17aand the branch portion21ainto which the detector array16may be inserted.

Upon insertion of the detector array16, the scintillator2that constitutes the detector array16is supported by the support board21e. Accordingly, the relative position is determined of the detector array16and the base21b. In other words, the relative position may be determined of the sub member17band the detector array16in the x-direction. Here, the x-direction corresponds to the direction in this invention where the scintillator and the base are spaced from to each other.

<Second Holding Member Fixation Step S4>

Next, the second holding member fixation step S4is performed for fixing the holding member17and the detector array16. First, the detector array16is positioned and the screw20dis inserted through a long hole17dprovided in the main member17a. Specifically, the detector array16is positioned based on the branch portion21a. That is, the detector array16is positioned such that a center line2hof the detector array16in the y-direction is equal in position to one side21hof the branch portion21aextending in the x-direction. The center line2hin the detector array16actually correspond to a first reflector r. The scintillator according to Embodiment 1 has thirty-two scintillation counter crystals arranged in the y-direction. Accordingly, the center line2his a first reflector r between the sixteenth and seventeenth scintillators in the y-direction. The first reflector r is referred to as a center reflector for convenience. The center reflector is of a ribbon shape that extends in the x-direction. Taking into consideration that the detector array16has three scintillators2, the center reflector exits in each of the three scintillators2. In the second holding member fixation step S4, three center reflectors that extend in the x-direction conform to one side21hthat extends in the x-direction. Consequently, the detector array16is set to have a longitudinal direction parallel to the x-direction. Here, the center line2hcorresponds to the first reflector r in Embodiment 1. The center line2h, however, may be a transparent material t through variation in setting of the scintillator2, in addition, the center line2hand one side21hcorrespond to the second positioning device of this invention.

The holding member17and the detector array16are fixed by use of the screw holes18provided in the bleeder unit18. First, description will be given of a bottom face of the bleeder unit18. As shown inFIG. 7(a), the bleeder unit18has screw holes18don the bottom face thereof. The bottom face of the bleeder unit18attached on the detector array16and the holding member are adjacent to each other. That is, as shown inFIG. 7(b), the screw20dis screwed into the screw hole18dprovided in the bleeder unit18for fixation, thereby integrating the detector array16and the holding member17.FIG. 7(b) illustrates a condition where the screw20dis fixed. As shown inFIG. 7(b), the main member17acontacts the bleeder unit18, whereas a gap D is provided between the scintillator2and the branch portion21a. This is a clearance necessary for placement of the detector array16on the first jig21in the detector array placement step S3. Specifically, the gap D has a distance of around 1 mm.

Accordingly, the detector unit19as shown inFIG. 8is formed in this way. Directing attention to a positional relationship between the holding member17and the scintillator that constitute the detector unit19, the holding member17and the detector array16are fixed while the scintillator2is placed on the support board21e. Consequently, the holding member17and the scintillator2have a uniform relative position in the x-direction in every manufacture of the detector unit19.

Moreover, the holding member17and the detector array16are fixed while the detector array16is placed on the first jig21such that the center line2h(center reflector) of the scintillator2is equal in position in the y-direction to one side21hof the branch portion21a. Furthermore, the holding member17and the detector array16are fixed while the holding member17is placed on the first jig21such that the marking17kin the sub member17bis equal in position in the y-direction to the marking21kin the base21b. Considering above, the holding member17and the scintillator2have a uniform relative position in the y-direction in every manufacture of the detector unit19. The relative position of the holding member17and the scintillator2on the first jig21is determined collectively in the x and y directions. Thus, the first jig has no concern with the relative position in the z-direction of the holding member17and the scintillator2. However, even when the relative position of the holding member17and the detector array16in the detector unit19deviates in the z-direction, the deviation in the z-direction is corrected by a second jig22, mentioned later.

Each of the detector units19having deviated holding member17and detector array16in coupling position in the z-direction is fixedly placed on the second jig22sequentially for correction of the deviation. The second jig22is used in this correction. Firstly, description will be given of a configuration of the second jig22.FIG. 9is a perspective view showing a configuration of the second jig22according to Embodiment 1. As shown inFIG. 9, the second jig22has a planar bottom22b, and a prismatic stein22athat extends in the x-direction perpendicular to a plane of the bottom22b. The bottom22bis provided with screw holes22cfor fixing the detector unit19, and two jig pins22fthat extend in the x-direction.

Description will be given of operations in the second jig placement step S5.FIG. 10is a perspective view showing each process according to Embodiment 1. As shown inFIG. 10, the detector unit19is fixedly placed on the second jig22through contact of the sub member17bof the holding member17to the bottom22b. At this time, each of the jig pins22fprovided on the bottom22bis inserted into each of the through holes17eprovided in the sub member17b. Here, the through hole17fis set to have an internal diameter sufficiently larger than a diameter of the jig pin22f. Accordingly, a placement position of the detector unit19may be adjusted with respect to the second jig22. Here, the jig pin22fpasses through the sub member17b, and is exposed from a surface thereof.

Subsequently, the placement position of the detector unit19is adjusted with respect to the second jig22for fixation of the detector unit19to the second jig22. Specifically, the screw20cis inserted through the drilled hole17cprovided in the sub member17b(seeFIG. 6) and screwed into the screw hole22cprovided in the bottom22bfor fixation of the screw20cunder a state where the scintillator2of the detector unit19contacts the stem22aof the second jig22in the z-direction for determination of the relative position of the detector unit19with respect to the second jig22. As a result, the detector unit19is fixed to the second jig22. The stem22ahas a contact surface to the scintillator2with enough width and height to contact an entire incident surface of gamma rays in the scintillator2. The stem22aalso has a marking22kat a tip thereof that extends in the y-direction. The marking22kpasses just the middle of the two jig pins22, assuming that it extends in the z-direction. When the detector unit19is fixedly placed on the second jig22, the screw20cis screwed while the center line2h(center reflector) in the detector array16in the z-direction is equal in position in the y-direction to the marking22kof the stem22athat extends in the y-direction. Of course, at this time, each of the scintillators2is in contact with the stem22a. Here, the center line2hand the marking22kcorrespond to the third positioning device of this invention. In addition, the z-direction corresponds to the direction where the scintillator contacts the stem of this invention,

<Plate Fixation Step S6, and Second Jig Removal Step S7>

Subsequently, a plate fixation step S6is performed for fixing the plate24to the sub member17b. Firstly, description will be given of a configuration of the plate24prior to explanation on this step. As shown inFIG. 10, the plate24has pin holes24fthrough which two jig pins22fare inserted, and two drilled holes24ethrough which screws20eare inserted for fixing the plate24to the sub member17b. As is shown inFIG. 10, each of the jig pins22fprojecting from the sub member17bin the x-direction is inserted through each of the pin holes24fprovided in the plate24. The pin hole24fhas an internal diameter approximately equal to a diameter of the jig pin22f. Accordingly, the plate24is to be accurately positioned with respect to the second jig22via the jig pins22fupon insertion of each of the jig pins22fthrough each of the pin holes24f. Thereafter, the screw20epasses through the drilled hole24eto be screwed into the screw hole17eprovided in the sub member17b. Accordingly, the plate24is to be fixed to the sub member17b. Here, the screw20emerely integrates the sub member17band the plate24, and is not screwed into the second jig22. Specifically, the tip of the screw20edoes not reach the bottom22bof the second jig22. Here, the jig pin22fand the pin hole24fcorrespond to the fourth positioning device of this invention.

FIG. 11is a plan view showing each process according to Embodiment 1. As shown inFIG. 11, the jig pin22fpasses through the sub member17b. Accordingly, the tip of the jig pin22fis exposed from the sub member17b, and inserted through the plate24. On the other hand, the screw20efixes the sub member17band the plate24.

At this time, as shown inFIG. 12, the positional relationship between the stem22aand the plate24is fixed in every manufacture of the detector unit19. The positional relationship between the stem22aand the plate24in the z-direction is fixed among the detector units19. The scintillator2contacts the stem22ain the z-direction. Consequently, the positional relationship between the plate24and the scintillator2in the z-direction is also fixed among, the detector units19. That is, even when the incident surface of gamma rays in the scintillator2and the clearance of the holding member in the z-direction deviate, a position where the plate24is fixed to the sub member17bis determined via only the jig pin22fwith no influence of the deviation. Accordingly, even when the position of the holding member17shown inFIG. 10by dotted lines and the stem22avaries in every detector unit19to be formed, each positional relationship among the bottom22b, the stem22a, the scintillator2, and the plate24is fixed among the detector units19to be formed.

In the second jig removal step S7, the screw20cis screwed out from the sub member17b(seeFIG. 10.) In so doing, the detector unit19after fixation of the plate24is removed from the second jig22. Here in comparison of each detector unit19, the relative position of the plate24and the scintillator2is uniform in the y and z directions. Specifically, the uniform relative position in the z-direction is realized through contact of each scintillator2to the stem22a. The uniform relative position in the y-direction is realized through conformity of the center reflector in the scintillator2and the marking22kin the stern22ain the y-direction.

<Group of Detectors Formation Step S8>

Finally, the detector units19are annularly arranged to form the group of detectors. Specifically, eight sub members17bof the detector units19contact a circular plate26having an octagonal opening26aand both members19and26are fixed via bolts, whereby the group of detectors12is formed. Description will be given of a configuration of the circular plate26prior to explanation on this step. As shown inFIG. 13, the circular plate26according to Embodiment 1 has an octagonal opening26aat a center thereof and eight pairs of reference pins26for total sixteen pins that extend in the x-direction so as to surround the opening26a. Upon arrangement of the detector units19on the circular plate26, the reference pins26fare inserted through the pin holes24fin the plate24for alignment of the detector units19with respect to the circular plate. In addition, eight pairs of drilled holes26cor total sixteen holes through which bolts are inserted for fixing both members19and26are also provided so as to surround the opening26a. Here, the reference pin26fand the pin hole24fprovided in the plate correspond to the fifth positioning device of this invention. Moreover, the circular plate26corresponds to the base member of this invention.

FIG. 14is a perspective view showing a group of detectors formation step according to Embodiment 1. As shown inFIG. 14, a bolt passes through the drilled hole provided in the sub member17band the drilled hole26cprovided in the circular plate26collectively while the reference pin26fpasses through the pin hole24f. Thereafter, both members19and26are fixed by screwing the bolt on the corresponding nut. Each of the reference pins26fare arranged accurately so as to surround the opening26aannularly. Accordingly, eight plates24are to be arranged on the circular plate26accurately in an annular shape. Taking into consideration that the plate24and the scintillator2are relatively arranged uniformly in each detector unit19, the scintillator2is arranged accurately on the circular plate26in an annular shape. Here inFIG. 14, a detector unit19on the most front side in the drawing is omitted. Actually, detector units19are annularly arranged.FIG. 15is a plan view showing a configuration of the group of detectors according to Embodiment 1. In this way, the group of detectors12according to Embodiment 1 is to be formed. A gantry cover is attached thereto, and the radiation tomography apparatus10according to Embodiment 1 is accomplished.

As noted above, the configuration according to Embodiment 1 may realize relative positioning of the detector array16and the holding member17via the first jig21. That is because the first jig21has a support board21efor supporting the scintillator2that ensures a given relative position of the detector array16and the holding member17in a long side direction of the detector array16. Moreover, the first jig21may simultaneously determine a relative positional relationship between the detector array16and the holding member17in a short side direction of the detector array16. As noted above, the first jig21determines the relative position of the detector array16and the holding member17collectively in the x and y directions that are perpendicular to each other.

In addition, according to the configuration of Embodiment 1, positional deviation of the detector array16and the holding member17in the z-direction is corrected through fixation of the plate24by use of the second jig22upon formation of the detector unit19. Specifically, the detector array16and the holding member17are integrated with each other, and thereafter, the plate24is fixed to the holding member17that is used as a reference of a fixing position of the detector unit19to the circular plate26. The fixing position of the plate24to the holding member17is independent of the fixing position of the detector array16to the holding member17. Accordingly, even when both members16and17deviate together in the z-direction, upon arrangement of the detector unit19on the circular plate26, the detector arrays16are naturally to be arranged in an annular shape merely by arranging the plates24in an annular shape accurately. As noted above, according to the configuration of Embodiment 1, the radiation detectors1that constitute the group of detectors12may be arranged more regularly. Therefore, decrease in spatial resolution may be suppressed as much as possible that occurs from arrangement deviation of the radiation detectors1in the group of detectors12upon counting the number of annihilation gamma-ray pairs to determine the radiation intensity distribution.

The detector array16and the holding member17according to Embodiment 1 are adjusted in relative positional relationship with three positioning methods that are independent to one another. Specifically, the methods are those using the support board21e, the markings17k,21k, the center line2hand one side21hof the branch portion21a, and the plate24. Such configuration may realize assignment of these positioning methods to three directions of x, y, and z directions, respectively, that are perpendicular to one another. Specifically, the support board21eperforms adjustment in the x-direction, the markings17k,21k, the center line2hand one side21hof the branch portion in the y-direction, and the plate24in the z direction. In other words, the relative positional relationship of the detector array16and the holding member17according to Embodiment 1 may be adjusted in all of the x, y, and z directions that are perpendicularly to one another. Consequently, no direction exists where the detector array16and the holding member17may be coupled with deviating from each other.

This invention is not limited to the foregoing configurations, but may be modified as follows:

(1) The foregoing Embodiment has the second jig22, but does not need to have this. According to this modification, the plate24is not always needed. In this case, jig pins21fmay be provided on the first jig21as shown inFIG. 16(a). On the other hand, the holding member17has pin holes17pprovided therein through which the jig pins21fare directly inserted, as shown inFIG. 16(b). Such configuration may realize determination in position of the detector arrays16with respect to the holding member17in the x and y directions. In the second holding member fixation step S4, the deviation in position of the detector array16and the holding member17in the z-direction does not sometimes leads to a significant problem. That is, this modification is directed to this, and may realize provision of the method for manufacturing the radiation tomography apparatus having suppressed steps in number in which the second jig22is not always needed. Specifically, according to this modification, the steps may be omitted as for the second jig22and the plate24of the configuration in Embodiment 1. Here, the jig pin21fand the pin hole17fcorrespond to the sixth positioning device of this invention. In addition, the reference pin26fand the pin hole17fcorrespond to the seventh positioning device of this invention again.

(2) The detector ring in the foregoing Embodiment is O-shaped. A group of radiation detectors of C-shaped may be placed instead. Specifically, as shown inFIG. 17, a bottom plate may be a C-shaped fractured ring. The fractured ring12amay be provided, instead of the ring-shaped group of detectors12, having detector units16arranged circularly. AC-shaped plate26bmay be provided, instead of the circular26, along an arc of the fractured ring12a. Here, the gantry11and the circular plate according to this modification is of C-shape corresponding to the shape of the fracture ring12a.

(3) In the foregoing embodiment, the scintillation counter crystal is composed of LYSO. Alternatively, the scintillation counter crystal may be composed of another materials, such as GSO (Gd2SiO5), may be used in this invention. With this modification, the radiation tomography apparatus may be provided having suppressed manufacturing cost.

(4) In the foregoing embodiment, the scintillator2has four scintillation counter crystal layers. This invention is not limited to this embodiment. For instance, the scintillator formed of one scintillation counter crystal layer may be applied to this invention. Moreover, the scintillation counter crystal layer may be freely adjusted in number depending on applications of the radiation tomography apparatus.

(5) The fluorescence detector in the foregoing embodiment is formed of the photomultiplier tube. This invention is not limited to this embodiment. A photodiode or an avalanche photodiode, etc. may be used instead of the photomultiplier tube.

(6) In the foregoing embodiment, the holding member17and the bleeder unit18are screwed for integration. This invention is not limited to this embodiment. The holding member17and the bleeder unit18may be integrated via an adhesive.

(7) In the foregoing embodiment, the jig pin22fis provided in the second jig22, the pin hole24fin the plate24, and the reference pin26fin the circular plate26. This invention is not limited to this embodiment. The pin hole may be provided in the second jig22and the circular plate24, and the pin may be provided in the plate24.

INDUSTRIAL UTILITY

As described above, this invention is suitable for radiation tomography apparatus for case in medical fields.