Radiation tomography apparatus

Radiation tomography apparatus of this invention has a shield that shields entering of radiation flying from outside of the gantry. The shield is formed of shielding pieces. Consequently, there is no need for manufacturing the shield in a large and expensive furnace. Accordingly, the radiation tomography apparatus may be provided that is easily manufactured and achieves suppressed cost. Moreover, with the radiation tomography apparatus of this invention, maintenance may be performed through removal of the shielding pieces without removing the entire shield.

TECHNICAL FIELD

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

BACKGROUND ART

In medical fields, emission computed tomography (ECT: Emission Computed Tomography) apparatus is used that detects radiation (such as 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 radiation detectors having block radiation detectors arranged in an arc shape. The group of radiation detectors is provided for surrounding a subject, and allows detection of radiation that is transmitted through the subject.

Among PET devices, a PET-Mammography device (hereinafter, referred to as a PET-Mammo device) for conducting a breast cancer physical examination has a characteristic that more doses of radiation fly from outside of a gantry toward the apparatus in comparison with typical PET devices. Accordingly, the PET-Mammo device has a shield that shields entering of radiation flying from outside of the gantry. Description will be given of a configuration of a conventional PET-Mammo device. As shown inFIG. 14, the conventional PET-Mammo device50has a gantry51with an opening for introducing a site of interest B of a subject M, a group of radiation detectors52that is provided so as to surround the opening of the gantry51on an outer periphery thereof and detects radiation, and a ring-shaped shield53on one end of the group of radiation detectors52that is adjacent to the subject M.

It should be noted that, in the PET-Mammo device50, a whole body of the subject M is not introduced into the opening of the gantry51. Radiopharmaceutical is administered to the subject M by injection in advance for conducting diagnosis with the PET-Mammo device50. The radiopharmaceutical is to be distributed over the whole body of the subject M. Specifically, radiation is emitted from the whole body of the subject M, and flies toward the group of radiation detectors52from not only the site of interest B inside the gantry but also a site other than the breast of the subject M. Radiation54derived from outside of the gantry is obstructive to imaging of radiopharmaceutical distributions in the site of interest B. Accordingly, in order to obtain a sectional image more suitable for diagnosis, the conventional mammo-PET apparatus50has a ring-shaped shield53on one end of the group of radiation52adjacent to the subject M that prevents radiation54derived from outside of the gantry from entering into the group of radiation detectors52(see, for example, Patent Literature 1.)

Patent Literature 1

DISCLOSURE OF THE INVENTION

Problem to be Solved by the Invention

However, the conventional PET-Mammo device has the following problems. Specifically, one problem is that the conventional shield53is difficult for manufacturing. The shield53is composed of Tungsten, etc., with a high effective atomic number. The shield53is a sintered metal that is formed by heating powder up to a temperature close to a melting point. The Tungsten is a hard-to process material of high melting point and high hardness. Consequently, a large and expensive furnace is needed for forming the shield53, which leads to difficulty in manufacturing the conventional shield53.

Another problem is that the conventional shield53has a difficulty in assembling the PET-Mammo device50. Since Tungsten is a metal of high density, the shield53has a considerable weight. Accordingly, a process of attaching the shield53inside the gantry is to be complicated upon manufacturing of the PET-Mammo device50.

A further problem is that the configuration of the conventional shield53has a difficulty in maintenance of the PET-Mammo device50. In the PET-Mammo device, it is necessary to replace a radiation detector that constitutes the group of radiation detectors52due to aged deterioration and the like. Here, an operation is required of removing the shield53once from the group of radiation detectors52. Since the shield53is a member having a considerable weight as mentioned above, this operation is to be complicated. Accordingly, the conventional PET-Mammo device50needs high cost for maintenance.

This invention has been made regarding the state of the art noted above, and provides radiation tomography apparatus of low cost and easy maintainability that has divided shields for shielding radiation derived from outside of a gantry.

Means for Solving the Problem

This invention is configured as stated below in order to achieve the above object. Radiation tomography apparatus according to this invention includes a group of radiation detectors with radiation detectors for detecting radiation arranged at least in an arc shape, and a shield for shielding radiation that is provided so as to cover one plane side end of the group of radiation detectors, in which the shield is formed of two or more shielding pieces that are combined with one another, and the shielding pieces comprises a first shielding piece having a cut-out on a given side thereof; and a second shielding piece having a projection that contacts the first shielding piece and projects toward the cut-out, and the first shielding piece contacts the second shielding piece by fitting the cut-out and the projection.

With the configuration of this invention, the shield for shielding radiation is formed of two or more shielding pieces that are combined with one another. Consequently, the shield of this invention is easily manufactured. The shield of this invention is, for example, a sintered metal that is formed by heating powder with Tungsten as a main component up to a temperature close to a melting point. The configuration of this invention may be realized through manufacturing of the shielding pieces individually, and thereafter combining of them with one another. Consequently, there is no need for manufacturing the shield in a large and expensive furnace. Accordingly, the radiation tomography apparatus may be provided that is easily manufactured and achieves suppressed cost.

The foregoing configuration may ensure contact of the first shielding piece and the second shielding piece adjacent to each other that constitute the shielding pieces for forming the shield. The cut-out of the first shielding piece and the projection of the second shielding piece fit with each other. Consequently, both shielding pieces contact, which avoids occurrence of a gap therebetween. Accordingly, radiation derived from outside of the gantry may surely be prevented from entering into the group of radiation detectors.

Moreover, this invention may realize easy assembly of the radiation tomography apparatus. The shield has a considerable weight. According to this invention, however, the shielding pieces may individually be incorporated into the radiation tomography apparatus, which results in easy assembly of the radiation tomography apparatus. Furthermore, this invention may realize easy maintenance to the radiation tomography apparatus. Specifically, with the configuration of this invention, maintenance may be performed through removal of the shielding pieces without removing the entire shield. Accordingly, there is no need for removing the shield of a considerable weight upon maintenance, which results in easy maintenance to the radiation tomography apparatus of this invention.

Moreover, it is more desirable that an adjacent radiation detector of with the foregoing group of radiation detectors that is arranged adjacent to the shield has the same number as the shielding piece, and that each of the shielding pieces is arranged so as to cover each of the adjacent radiation detectors, thereby forming the shield.

The foregoing configuration may further realize easy maintenance to the radiation tomography apparatus. Specifically, in the foregoing configuration, an adjacent radiation detector in the group of radiation detectors that is arranged adjacent to the shield has the same number as the shielding piece. Accordingly, upon pulling out of one of the radiation detectors of the group of radiation detectors, the shielding piece that covers the radiation detector may be removed. As a result, the shielding pieces are to be removed at the minimum upon maintenance to the radiation tomography apparatus, which results in easier maintenance to the radiation tomography apparatus.

Moreover, it is more desirable that a bottom plate is provide on the other side end opposite to one side end in the foregoing group of radiation detectors for supporting each of the radiation detectors that constitute the group of radiation detectors, the bottom plate has two or more struts provided thereon that extend towards the one side end of the group of radiation detectors, and each of the shielding pieces is fixedly supported on the struts.

With the foregoing configuration, the shielding pieces may be integrally fixed. Specifically, the shielding pieces are fixed on the bottom plate via two or more struts. As a result, with the foregoing configuration, each shielding piece is integrally fixed, which may realize formation of a more rugged shield.

Moreover, it is more desirable that the foregoing strut removably fixes each of the shielding pieces, and that, when the strut releases fixation of a third shielding piece, the third shielding piece may move in a direction away from a center of curvature of an arc portion in the group of radiation detectors and the third shielding piece may move forward and backward along a given direction, whereby removal and fitting of the third shielding piece from and with the shield, respectively, may be performed reversibly.

The foregoing configuration may realize easier maintenance to the radiation tomography apparatus. Specifically, upon releasing of fixation of the struts to the third shielding piece, the third shielding piece may move in the direction away from the center of curvature of the arc portion in the group of radiation detectors. Accordingly, the third shielding piece may move in a given direction to be removed from the shield. In addition, the third shielding piece may also move in a direction opposite to the given direction to fit with the shield. That is, the foregoing configuration may complete maintenance merely by insertion and pulling out of the third shielding piece. Consequently, easy maintenance may be realized to the radiation tomography apparatus.

Moreover, the shielding piece and strut in the foregoing configuration have a pin hole provided for determining a relative position to each other.

According to the foregoing configuration, the shielding piece and strut have the pin hole provided therein. Specifically, a pin passes through the pin hole, whereby the shielding piece and the strut may temporarily be joined to each other. Accordingly, upon fixation of the shielding piece and the strut via a crew, no shielding piece moves as the screw turns. That is, according to the foregoing configuration, the shielding piece and the strut are coupled to each other with no shift in the relative position thereof. Consequently, the shielding pieces that constitute the shield are regularly arranged, thereby forming the shield that prevents radiation derived from outside of the gantry from entering into the group of radiation detectors.

Moreover, the group of radiation detectors in the foregoing configuration may be of a C-shape.

The foregoing configuration may realize provision of the radiation tomography apparatus that ensures insertion of the site of interest in the subject into the opening of the gantry. Where this invention is applied to mammo-PET apparatus, an arm of the subject is obstructive to insertion of a breast of the subject into the opening of the gantry. According to the foregoing configuration, a recess may be formed for retracting the arm of the subject, which ensures insertion of the breast of the subject into the opening of the gantry. Consequently, the foregoing configuration may realize provision of the radiation tomography apparatus having the whole region of the breast of the subject as a field of view.

Moreover, the group of radiation detectors in the foregoing configuration may be of a circular ring shape.

The foregoing configuration may realize provision of the radiation tomography apparatus in which pair annihilation radiation emitted from the site of interest of the subject is positively detected. According to the foregoing configuration, a blind area may be reduced as much as possible where no radiation may be detected with the group of radiation detectors. Consequently, data may increase that is available for tomography in the radiation tomography apparatus.

Effect of the Invention

With the foregoing configuration, the radiation tomography apparatus may be provided having suppressed manufacturing cost. According to the configuration of this invention, the shielding pieces are individually manufactured, and thereafter, combined to constitute the shield for shielding radiation derived from outside of the gantry. Consequently, there is no need for manufacturing the shield in a large and expensive furnace. Furthermore, this invention may realize easy maintenance to the radiation tomography apparatus. Specifically, according to this invention, maintenance may be performed through removal of the shielding pieces without removing the entire shield. Accordingly, there is no need for removing the shield of a considerable weight upon maintenance, which results in easy maintenance to the radiation tomography apparatus of this invention.

DESCRIPTION OF REFERENCES

BEST MODE FOR CARRYING OUT THE INVENTION

Description will be given hereinafter of a configuration of radiation tomography apparatus according to one embodiment of this invention with reference to the drawings.

Firstly, prior to explanation of 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 detector1according 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 scintilla for2for detecting fluorescence emitted from the scintillator2, 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. 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 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 a (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(1-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.

Next, description will be given of a configuration of radiation tomography apparatus10according to Embodiment 1.FIG. 2is a partial 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 fracture ring12in a C-shape that is provided inside the gantry11so as to contain the opening of the gantry11. The fractured ring12has block radiation detectors1p,1q,1rarranged in a C-shape. Gamma rays emitted from the subject enter into the fractured ring12. The fractured ring12in the radiation tomography apparatus10determines intensity, an incidence period of time, and an incidence position of incident gamma rays. Here, the fractured ring corresponds to the group of radiation detectors in this invention. In addition, the gantry11according to Embodiment 1 has a C-shape following a contour of the fractured ring12.

Moreover, the radiation tomography apparatus10according to Embodiment 1 has a C-shaped shield13that prevents radiation derived from the outside of the gantry11from entering into the fractured ring12. The shield13is placed so as to cover one plane side end of the fractured ring12. Specifically, the shield13is provided on one side end of a pair of plane side ends of the fractured ring12that is adjacent to the opening of the radiation tomography apparatus10for introducing a site of interest of a subject M. In other words, the shield13is provided such that the fractured ring12may extend in an axial direction. That is, the ring shield13separates a site other than the site of interest B of the subject M outside the gantry11and the fracture ring12. Here, the shield13is, for example, composed of Tungsten.

Description will be given of a configuration of the fractured ring12.FIG. 3is an exploded perspective view showing a configuration of the group of radiation detectors according to Embodiment 1. As shown inFIG. 3, the fractured ring12has two or more detector units15arranged in an arc shape following the contour of the bottom plate14in the C-shape. Let a center of curvature of the arc be a center of curvature D. In the detector unit15, a detector array15ahaving three radiation detectors1p,1q, and1rarranged in series in an x-direction and an L-shaped support tool16are coupled in a d-direction away from the center of curvature D in the fractured ring12(seeFIG. 7.) Here, let a radiation detector closest to the shield13be a radiation detector1p. The radiation detector1pcorresponds to the adjacent radiation detector of this invention that is arranged adjacent to the shield.

Seen the fractured ring12in the x-direction, the scintillators2provided in the detector unit15are arranged so as to face toward inside of the bottom plate14. Accordingly, the scintillators2cover the inside of the fractured ring12. In addition, the detector unit15is fastened to the bottom plate14via a sub-plate16b, mentioned later, with a bolt and a nut. The sub plate16bhas a hole16cprovided therein through which a bolt passes. The bottom plate14has a long hole14afor every detector unit15through which the bolt passes. Here in Embodiment 1, seven detector units15are arranged in the C-shape. The fractured ring12that extends from the bottom plate14in the x-direction has a C-shaped plane at a front end thereof that forms a front surface. The front surface is formed of seven radiation detectors1p, and corresponds to one end of the group of radiation detectors of this invention.

The bottom plate14has an interior hole14bprovided in a center thereof. The interior hole14bis octagonal, and each side thereof faces toward the detector unit15. Moreover, the bottom plate14has eight first struts21and eight second struts22that extend in the x-direction for supporting the shield13. The first struts21are arranged annularly so as to surround the interior hole14bof the bottom plate14. The second struts22are arranged annularly so as to surround a circular ring of the first struts21from outside thereof. Both struts21and22are provided within a V-shaped dead space of the bottom plate14that extends between the detector units15adjacent to each other. In addition, both struts21and22has a length in the x-direction approximately equal to that of the detector unit15in the x-direction that is provided on the bottom plate14. Here, merely each one of both struts21and22is illustrated inFIG. 3. Actually, eight first struts21and eight second struts22are provided on the bottom plate14.

Description will be given of the shield13.FIG. 4is a plan view showing a configuration of the shield according to Embodiment 1. As shown inFIG. 4(a), the shield13is formed of seven shielding pieces13a,13b,13c. The shielding piece13a,13b,13cis a plate of a trapezoidal shape that is composed of Tungsten. The thickness thereof in the x-direction is set, for example, at 5 mm. In addition, a pair of shielding pieces13a,13b, and13cadjacent to one another in the shield13partially overlap one another in the x-direction to form an overlap portion13d. The shielding pieces13a,13b, and13ceach covers the front end of the single detector unit15in the x-direction, and are arranged in an arc shape seen as a whole thereof to form the C-shaped shield13. Taking into consideration that one radiation detector1pis provided on the front end of the detector unit15in the x-direction, the radiation tomography apparatus10has the shielding pieces13a,13b, and13cof the same number (seven) as that of the radiation detectors1pthat constitute the front end surface of the fractured ring12in the x-direction.

Next, description will be given of both struts21and22for supporting the shield13provided on the bottom plate14. As shown inFIG. 4(b), the first strut21has screw holes21aprovided therein for fixing the shielding pieces13a,13b, and13c. Likewise, the second strut22has screw holes22aprovided therein for fixing the shielding pieces13a,13b, and13c. As shown inFIG. 4(a), the overlap portion13dhas a screw21band a screw22bprovided therein that are used for collectively fixing a pair of shielding pieces13a,13b, and13coverlapping thereon. The screw21band screw22bare threaded into the foregoing screw hole21aand screw hole22a, respectively. Consequently, each of the side portions of the shielding pieces13a,13b, and13chaving a trapezoidal shape that are inclined to each other has a drilled hole13kprovided therein in the x-direction through which the screw21band the screw22bpass (seeFIG. 5.) Accordingly, seen one shielding piece13a,13b, and13c, four drilled holes13kare provided through which the screws21band22bpass. In this way, one shielding piece13a,13b,13cis supported with two first struts21and two second struts22.

As shown inFIG. 4(b), the second strut22has a pin hole22eprovided therein through which an alignment pin, mentioned later, passes. The shielding piece13a,13b,13chas a pin insertion hole13ethat extends in the x-direction through which the alignment pin (seeFIG. 4(a)) passes. Taking into consideration that one shielding piece13a,13b,13cis supported with two second struts22, one pin insertion hole13eis provided on each of the side portions of the shielding piece13a,13b,13chaving a trapezoidal shape that are inclined to each other. The pin insertion hole corresponds to the pin hole of this invention.

Description will be given in detail of the configuration of the shielding piece13a,13b,13c.FIG. 5is a perspective view showing the configuration of the shielding piece according to Embodiment 1. The shielding piece13a,13b, and13cthat constitutes the shield13has a first piece13a, a second piece13b, and a third piece13c, respectively. The first piece13ais located on one end side of the C-shaped shield13. As shown inFIG. 5(a), a cut-out13fis provided on one of the pair of side portions of the first piece13ain the trapezoidal shape that are inclined to each other. Specifically, the cut-out13fis provided so as to cut out an upper surface of the side portion in the first piece13a. Here, one of the foregoing side portions corresponds to the given side with the cut-out of this invention.

As shown inFIG. 5(c), the shield13has on its other end the third piece13c. A projection13gis provided on one of the pair of side portions of the third piece13cin the trapezoidal shape that are inclined to each other. Specifically, the projection13gis provided so as to cover the upper surface of the side portion in the third piece13c. Moreover, as shown inFIG. 5(b), the second piece13bin a trapezoidal shape has any of the shielding pieces13a,13b,13cadjacently placed on each of both the pair of side portions thereof inclined to each other. A cut-out13fsimilar to that in the first piece13ais provided on one of the pair of side portions of the second piece13b, whereas a projection13gsimilar to that in the third piece13cis provided on the other thereof.

FIG. 6is a plan view showing an overlap portion according to Embodiment 1. As shown inFIG. 6, the piece13pand the piece13qadjacent thereto partially overlaps each other in the x-direction to form the overlap portion13d. The overlap portion13dhas the cut-out13fprovided in the piece13pand the projection13gprojecting toward the cut-out13fprovided in the piece13pthat fit with each other (seeFIG. 5.) In this way, the piece13pand the piece13qcontact to each other. Likewise, every overlap portion13dof the shield13has the cut-out13fand the projection13gfitting with each other. Here, the piece13pand the piece13qcorrespond to the first shielding piece and the second shielding piece, respectively, in this invention.

Description will be next given of a configuration of the detector unit15.

FIG. 7is a plan view showing a configuration of the detector unit according to Embodiment 1. As shown inFIG. 7, the detector unit15has three radiation detectors arranged in series in the x-direction. Specifically, the detector unit15has an L-shaped support tool16, a bleeder unit17that is coupled to the support tool16in the d-direction by screw and provided with a bleeder circuit for supplying voltages to the radiation detector1, and the radiation detector1that is connected to the bleeder unit17so as to extend in the d-direction. More specifically, the light detector3in the radiation detector1is connected to the bleeder unit17. Such configuration allows the bleeder unit17to supply voltages directly to the light detector3. Moreover, the detector unit15has three light detectors3that are joined via a plate spacer18in the x-direction. The scintillator2inFIG. 7has nine scintillation counter crystals arranged in the x-direction. This is due to simplification of the drawing for suitable explanation. Actually, the scintillator2has thirty-two scintillation counter crystals arranged in the x-direction. Three scintillators2of the detector unit15are integrally covered with a box cover25made from aluminum, etc.

Easy maintenance may be realized to the radiation tomography apparatus10according to Embodiment 1. Next, description will be given of a maintenance method performed in the radiation tomography apparatus10when the radiation detector that constitutes the fractured ring12has to be replaced due to aged deterioration, etc.

Upon replacement of the radiation detector that constitutes the fractured ring12, it is necessary to remove a detector unit15rof a damaged radiation detector from the fractured ring12. Prior to this, the shielding piece13a,13b,13cobstructive to this operation is removed from the shield13.FIG. 8is a plan view showing a step of removing the shielding piece according to Embodiment 1. It is assumed inFIG. 8(a) that the detector unit15rto be replaced is covered with the piece13r. Firstly, four screws21band22bthat fix the piece13r(seeFIG. 4)are threaded out and removed from the shield13. Accordingly, the piece13rmay move in the d-direction away from the center of curvature D in the fractured ring12. At this time, the piece13rmoves in the d-direction to be removed from the shield13. Upon completion of the shielding piece removal step, the detector unit15ris exposed as shown inFIG. 8(b) when seen the fractured ring12in the x-direction. Here, the piece13ris one example of the third shielding piece of this invention.

At this time, a bolt26for fixing the detector unit15rto the bottom plate14is also exposed when seen the fractured ring12in the x-direction. In the detector unit replacement step, the bolt26is released to pull out the detector unit15rin the d-direction. Instead, a new detector unit15is inserted into the fractured ring12by moving into a direction approaching to the center of curvature D in the fractured ring12. Thereafter, the new detector unit15is fixed to the bottom plate14via the bolt26. Thus, the step is to be completed.

Subsequently, the piece13ragain fit with the shield13for reattaching thereof.FIG. 9is a perspective view showing a step of fitting the shielding piece according to Embodiment 1. In this step, the piece13ris fixed to both struts21,22by screw. Prior to this, the piece13ris aligned with respect to both struts21,22. Description will be given of the alignment. Firstly, the piece13ris inserted in the direction approaching the center of curvature D in the fractured ring12(seeFIG. 8), thereby fitting with the shield13. Thereafter, as shown inFIG. 9(a), a pin23epasses through each two pin insertion holes13eprovided in the piece13r. Accordingly, a tip end of the pin23epasses through the pin insertion hole13e, and thereafter contacts the front end of the second strut22. Then, a position of the piece13rwith respect to the second strut22is adjusted, and the tip end of the pin23efits into the pin hole22e(seeFIG. 4)provided in the second strut22. In this way, the piece13ris firstly aligned with respect to both struts21,22. Moreover, taking into consideration that the piece13rhas two pin insertion holes13eprovided therein, the piece13ris temporarily joined to the second strut22via two pins23e. Accordingly, once the piece13ris aligned with respect to both struts21,22through insertion of two pins23e, the piece13rdoes not shift with respect to both struts21and22.

In addition, a proximal end of the pin23eis connected to a base23having a larger diameter than the pin insertion hole13e. Consequently, upon insertion of the pin23einto the pin insertion hole13e, the base23engages an outer periphery of the pin insertion hole13e, which avoids further insertion of the pin23einto the pin insertion hole13eany more.

Then, as shown inFIG. 9(b), the screw21band the screw22bpass through four drilled holes13kprovided in each of side portions of the trapezoidal piece13rthat are inclined to each other, thread into each of the screw holes21a,22aprovided in both struts21,22while the piece13ris temporarily joined to the second strut22via two pins23e. Consequently, the piece13ris fixed to both struts21,22. In this way, maintenance to the radiation tomography apparatus10according to Embodiment 1 is to be completed.

The foregoing explanation on the maintenance exemplifies the case where the second piece13bis to be removed. Where the first piece13aor the third piece13cis to be removed, similar maintenance as above is performed, and thus description thereof will be omitted. In addition, in the foregoing shielding piece removal step, the pins23emay once pass through two pin insertion holes13ein the piece13cprior to removal of four screws21b,22, from the piece13r. Consequently, the piece13ris temporarily joined to the second strut22via two pins23e, thereby being prevented from moving as the screws21b,22bturn.

Moreover, the piece13rmoves in the direction away from the center of curvature D in the fractured ring12(seeFIG. 8), whereby removal and fitting of the piece13rfrom and with the shield13, respectively, may be performed reversibly.

Next, description will be given of operations of the radiation tomography apparatus10according to Embodiment 1.FIG. 10is a functional block diagram showing a configuration of the radiation tomography apparatus according to Embodiment 1. As shown inFIG. 10, the radiation tomography apparatus10according to Embodiment 1 has a gantry11, a fractured ring12in a C-shape provided inside the gantry11, a shield13in a C-shape that prevents radiation derived from outside the gantry11from entering into the fractured ring12, an external radiation source33provided on an inner surface side of the fractured ring12for emitting fan beams of gamma rays, and an external radiation source drive34for driving thereof. Here, the external radiation source34is controlled under an external radiation source controller35. The radiation tomography apparatus10further includes each unit for obtaining an sectional image on a site of interest B of a subject M. Specifically, the radiation tomography apparatus10includes a coincidence unit40to receive gamma ray detection signals showing a detection position, detection strength, and detection time of gamma rays from the fractured ring12for performing coincidence of an annihilation gamma ray-pair, a fluorescence generating position discrimination unit41to discriminate an incident position of gamma rays in the fractured ring12based on two pieces of gamma ray detection data determined to be an annihilation-gamma-rays pair in the coincidence unit40, an absorption correction unit42to perform absorption correction of gamma rays with reference to transmission data mentioned later, and an image formation unit43to form a radiation tomography image on the site of interest B.

The radiation tomography apparatus10according to Embodiment 1 further includes a main controller36to control such as the external radiation source controller35en bloc, and a display unit37to display the radiation tomography image. The main controller36is formed of a CPU, and performs execution of various programs to realize the external radiation source controller35and coincidence unit40, the fluorescence generating position discrimination unit41, the absorption correction unit42, and the image formation unit43.

Description will be given to operations of the radiation tomography apparatus according to Embodiment 1 with reference toFIG. 10. Upon conducting of examinations with the radiation tomography apparatus10according to Embodiment 1, firstly the site of interest B (breast) of the subject M is inserted into the opening of the gantry11with radiopharmaceutical being administered thereto by injection in advance. Transmission data is obtained that shows absorption distributions of gamma rays within the site of interest B. Specifically, beams of gamma rays in a fan shape are applied from the external radiation source33towards the site of interest B. The gamma ray beams will pass through the site of interest B to be detected with the fractured ring12. Such detection is performed throughout the periphery of the site of interest B while rotating the external radiation source33along an arc track on the inner surface of the fractured ring12, whereby an absorption map of gamma rays throughout the site of interest B is obtained.

Following obtaining of the transmission data as mentioned above, emission data is obtained to detect the annihilation-gamma-rays pair that is emitted from the radiopharmaceutical localized in the site of interest B. Prior to this, the external radiation source33obstructive to emission data obtaining is moved in the axis direction of the fractured ring12for storage thereof into a radiation source shield not shown.

Thereafter, emission data is obtained. Specifically, the fractured ring12detects an annihilation gamma-rays pair that is emitted from inside of the site of interest B having a traveling opposite direction. Gamma-ray detection signals detected with the fractured ring12are sent to the coincidence unit40. It is considered as one count only when two gamma ray photons are detected simultaneously in positions different to each other in the fractured ring12, and then subsequent data processing may be performed. Thereafter, such emission data is repeatedly obtained, whereby emission data may be obtained having sufficient number of counts for imaging localization of the radiopharmaceutical within the site of interest B. Finally, the site of interest B of the subject M is retracted from the opening of the gantry11. An examination is to be completed.

Next, description will be given of data processing in the radiation tomography apparatus according to Embodiment 1 with reference toFIG. 10.

Transmission detection data Tr and emission detection data Em outputted from the fractured ring12are sent to the fluorescence generating position discrimination unit41to identify which scintillation counter crystal has detected the data. Detection data sent from the multi-anode type optical detector3includes information on fluorescence intensity distributions that the optical detector3detected, and the fluorescence generating position discrimination unit41calculates a center of gravity of fluorescence from the data. Consequently, the fluorescence position is discriminated in x-, y-, and z-directions inFIG. 1. As mentioned above, transmission detection data and emission detection data including incident positions of gamma rays are formed and sent to the subsequent absorption correction unit42.

The absorption correction unit42performs absorption corrections to the emission detection data Em for eliminating influences of the gamma ray absorption distributions in the of interest B superimposed on the emission detection data Em while referring to the transmission detection data Tr noted above. Thus, detection data showing radiopharmaceutical distributions in the site of interest B with more accuracy is sent to the image formation unit43, and then a radiation tomography image is to be reconstructed. Finally, the display unit37displays the image.

Here, the fractured ring has a C-shape. The reason therefor is to be described. In order to obtain a sectional image more suitable for diagnosis, it is necessary to insert the site of interest B of the subject M more deeply into the opening of the gantry11. Thus, it is more desirable to contact the arm of the subject M firmly to the gantry11. Consequently, a recess for introducing the arm of the subject M is provided so as to expand the opening of the gantry11, and therefore, the gantry11has a C-shape. No detector unit15may be provided in a portion of the fractured ring12that corresponds to the recess. Therefore, the group of radiation detectors having the arranged radiation detectors in Embodiment 1 is the C-shaped fractured ring12.

As noted above, according to the configuration of Embodiment 1, the shield13for shielding radiation is formed of two or more shielding pieces13a,13b,13cthat are combined with one another. Consequently, the shield13of Embodiment 1 is easily manufactured. The shield13of Embodiment 1 is, for example, a sintered metal that is formed by heating powder with Tungsten as a main component up to a temperature close to a melting point. The configuration of Embodiment 1 may be realized through manufacturing of the shielding pieces13a,13b,13cindividually, and thereafter combining of them with one another. Consequently, there is no need for manufacturing the shield13in a large and expensive furnace. Accordingly, the radiation tomography apparatus10may be provided that is easily manufactured and achieves Suppressed cost.

Moreover, Embodiment 1 may realize easy assembly of the radiation tomography apparatus10. The shield13has a considerable weight. According to Embodiment 1, however, the shielding piece13a,13b,13cmay individually be incorporated into the radiation tomography apparatus10, which results in easy assembly of the radiation tomography apparatus10. Furthermore, Embodiment 1 may realize easy maintenance to the radiation tomography apparatus10. Specifically, according to Embodiment 1, maintenance may be performed through removal of the shielding pieces13a,13b,13cwithout removing the entire shield13. Accordingly, there is no need for removing the shield13of a considerable weight upon maintenance, which results in easy maintenance to the radiation tomography apparatus10of Embodiment 1.

This invention is not limited to the foregoing embodiments, but may be modified as follows.

(1) 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. According to this modification, a method of manufacturing a radiation detector may be provide that allows provision of a radiation detector of low price.

(2) 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 detector.

(3) 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.

(4) In the foregoing embodiment, the fracture ring has a C-shape. A group of radiation detectors in a ring shape may be mounted instead. Specifically, as shown inFIG. 13, the shield13and the bottom plate14may have an O-shape, and instead of the fractured ring12, a detector ring12may have detector units15arranged annularly. Here, the gantry11according to this modification has an O-ring shape so as to correspond to the shape of the detector ring12a.

(5) The shielding piece in the foregoing embodiment has a trapezoidal shape. This invention is not limited to this embodiment. As shown inFIG. 11, the shielding piece may have a fan shape.

(6) In the foregoing embodiment, the second piece13bhas the cut-out and the projection. This invention is not limited to this embodiment. As shown inFIG. 12(a), the cut-out13fis provided on each of side portions of the trapezoidal second piece13bthat are inclined to each other. According to the configuration, as shown inFIG. 12(b), the second adjacent pieces13bare arranged in a C-shape while selecting both faces thereof so as to have an upside-down relation with respect to each other, thereby forming the shield13.

(7) The fractured ring in the foregoing embodiment includes seven detector units. This invention is not limited to this embodiment. The detector unit that constitutes the fractured ring may be increased or decreased in number depending on applications of the radiation tomography apparatus. Accordingly, the shielding piece may also be increased or decreased in number that constitutes the shield.

INDUSTRIAL UTILITY

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