JP2009031132A - Radiation detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiation detector having a structure capable of specifying a light emission position in the longitudinal direction even with one scintillator crystal. <P>SOLUTION: In the radiation detector 100, radiation RR enters one end of the scintillator crystal 110 being in an elongated form, thereby emitting fluorescence FR inside the scintillator crystal 110. This fluorescence FR propagates through the inside of the scintillator crystal 110 and is detected by a photodetector 130 disposed at the other end. Such the fluorescence FR, however, propagating through the inside of the scintillator crystal 110 is attenuated in intensity by optical attenuating sections 111-113 being partially positioned on the outside surface. Therefore, the intensity of the fluorescence FR detected by the photodetector 130 is varied gradually in accordance with the number of the optical attenuating sections 111-113 positioned in an area from the emitting position of the fluorescence FR to the position of the photodetector 130. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a radiation detector having a scintillator crystal and a photodetector, and more particularly to a radiation detector capable of specifying a light emission position in the longitudinal direction of the scintillator crystal.

  When a positron emitting isotope (RI) -labeled drug is administered to the subject, annihilation γ rays are emitted. Nuclear medicine imaging apparatuses such as PET (Positron Emission Tomography), SPECT (Single Photon Emission Computed Tomography), and gamma cameras are apparatuses for obtaining a distribution image of RI in a subject by detecting this radiation.

  In such a nuclear medicine imaging apparatus, the spatial resolution in the cross section deteriorates in the peripheral region of the effective field of view of the apparatus due to the finite length (depth) of the scintillator crystal of the radiation detector.

  Further, in the three-dimensional data collection of a large solid angle / high sensitivity device having a large effective field of view, the axial resolution is deteriorated for the same reason. Therefore, in order to further improve the spatial resolution, it is necessary to recognize the reaction position in the detector depth direction.

  As a radiation three-dimensional position detector used in the nuclear medicine imaging apparatus as described above, a scintillator unit is configured by laminating a plurality of scintillator crystals on a photodetector while sandwiching transparent plates having different refractive indexes. There is a proposal to identify scintillator crystals that emit fluorescence when radiation is incident on the basis of the difference in the amount of light received by the photodetectors by varying the transmittance of light reaching the detector for each stage of scintillator crystals. Yes (see, for example, Patent Document 1).

  In addition, a plurality of scintillator crystals are stacked on the optical position detector so that the center position is deviated in a direction parallel to the light receiving surface of the optical position detector, and the center of gravity of the spatial distribution of the output light from the optical position detector There is also a proposal for identifying a scintillator crystal that emits fluorescence when radiation is incident on the basis of the center-of-gravity position calculation by making the position different for each stacked scintillator crystal (see, for example, Patent Document 2).

  In addition, a scintillator unit is configured by laminating a plurality of scintillator crystals with different fluorescence decay time constants on a photodetector, and waveform discrimination is performed based on different fluorescence decay time constants of signals detected by a common light receiving element in each layer. There is also a proposal for identifying a scintillator crystal that emits fluorescence when radiation is incident thereon (see, for example, Patent Document 3).

Furthermore, there is a radiation detector that identifies which scintillator crystal emits light by stacking a plurality of scintillator crystals and a plurality of cut filters having different cutoff wavelengths and detecting the fluorescence wavelength with a common photodetector. (For example, see Patent Documents 4 and 5).
JP 63-047686 A Japanese Unexamined Patent Publication No. 01-229995 JP 2003-021682 A JP 2005-043062 A Japanese Patent Laying-Open No. 2005-043104

  However, all of the above-mentioned Patent Documents 1 to 5 have a plurality of scintillator crystals arranged in multiple stages in the longitudinal direction. For this reason, the number of scintillator crystals increases, and a structure in which a plurality of scintillator crystals are arranged in multiple stages is also required.

  Therefore, the structure of the radiation detector is complicated, and its productivity is reduced. Moreover, the technique described in Patent Document 1 is susceptible to subtle variations in the optical properties of the scintillator crystal.

  In the technique described in Patent Document 2, the arrangement of the barycentric positions of the spatial distribution of output light from the optical position detector by each scintillator crystal becomes denser as the scintillator crystals are multilayered. This makes it difficult to identify the position of the center of gravity, which may make it difficult to accurately identify the scintillator crystal that emits fluorescence upon incidence of radiation.

  In the technique described in Patent Document 3, different types of scintillator crystals having different light emission time constants are stacked, and an element that emits light is identified by waveform discrimination. However, in this case, it is necessary to form and arrange a plurality of types of scintillator crystals.

  The present invention has been made in view of the above-described problems. A radiation detector capable of specifying a light emission position in the longitudinal direction even with a single scintillator crystal, a radiation detection apparatus having the radiation detector, and a position detection apparatus. , Provide.

  A radiation detector according to the present invention is a radiation detector having a scintillator crystal that generates fluorescence inside when radiation is incident thereon, and a photodetector that detects the incidence of radiation by detecting fluorescence, and has an elongated shape. A scintillator crystal in which radiation is incident on one end, a photodetector for detecting the intensity of fluorescence disposed on the other end of the scintillator crystal, and a part located on the outer surface of the scintillator crystal A light reduction unit that reduces the intensity of the fluorescent light that propagates.

  Therefore, in the radiation detector of the present invention, when radiation enters the elongated scintillator crystal from one end, fluorescence is generated inside the scintillator crystal. This fluorescence propagates through the scintillator crystal and is detected by the photodetector at the other end. However, the intensity of the fluorescence propagating through the scintillator crystal is reduced by the light reducing portion located partially on the outer surface. For this reason, the intensity of the fluorescence detected by the photodetector varies stepwise depending on the number of light reducing portions existing from the position where the fluorescence is generated to the position of the photodetector.

  In the radiation detector of the present invention, the light reduction portions may be arranged at a plurality of positions in the longitudinal direction of the outer surface of the scintillator crystal.

  In the radiation detector of the present invention, the scintillator crystal may reflect the fluorescence incident on the outer surface from the inside, and the light reduction unit may radiate the fluorescence incident from the inside of the scintillator crystal to the outside.

  In the radiation detector of the present invention, the scintillator crystal may reflect the fluorescence incident on the outer surface from the inside, and the light reduction unit may absorb the fluorescence incident from the inside of the scintillator crystal.

  In the radiation detector of the present invention, the scintillator crystal may reflect the fluorescence incident on the outer surface from the inside, and the light reduction unit may scatter the fluorescence incident from the inside of the scintillator crystal.

  In the radiation detector of the present invention, the light reduction portion may be a rough surface that is partially formed on the smooth outer surface of the scintillator crystal.

  Moreover, in the radiation detector of the present invention, the light reduction part may be formed of a recess partly formed on the outer surface of the scintillator crystal.

  Further, the radiation detector of the present invention further includes a light reflecting material that is formed on the outer surface of the scintillator crystal and reflects fluorescence, and the light reducing portion is a portion from which the light reflecting material is partially excluded. May be.

  In the radiation detector of the present invention, the light reduction part may be made of a light absorbing material partially formed on the outer surface of the scintillator crystal.

  In the radiation detector of the present invention, the scintillator crystal may be made of a LuAG crystal.

  In the radiation detector of the present invention, the scintillator crystal may be made of a LuAG crystal doped with praseodymium.

In the radiation detector of the present invention, the scintillator crystal may be made of a LuAG (Pr: Lu ₃ Al ₅ O ₁₂ ) crystal.

  The radiation detection apparatus of the present invention includes the radiation detector of the present invention, and a light emission specifying unit that specifies the light emission position in the longitudinal direction of the scintillator crystal based on the intensity of the signal output from the photodetector of the radiation detector.

  The position detection device of the present invention includes a plurality of radiation detectors of the present invention arranged in a two-dimensional manner, and the longitudinal direction of each scintillator crystal depending on the intensity of the signal output individually by the photodetector of the radiation detector. A light emission specifying unit for specifying the light emission position, and a radiation specifying unit for specifying a three-dimensional position where radiation is emitted from the light emission positions of the plurality of radiation detectors specified by the light emission specifying unit.

  The various components of the present invention need only be formed so as to realize the function. For example, dedicated hardware that exhibits a predetermined function, radiation detection in which a predetermined function is given by a computer program And a predetermined function realized in the radiation detector by a computer program, an arbitrary combination thereof, and the like.

  The various components of the present invention do not necessarily have to be independent of each other. A plurality of components are formed as a single member, and a single component is formed of a plurality of members. It may be that a certain component is a part of another component, a part of a certain component overlaps with a part of another component, or the like.

  In the radiation detector of the present invention, the intensity of fluorescence generated by the incidence of radiation and propagating through the inside of the scintillator crystal is reduced by the light reducing unit located partially on the outer surface of the scintillator crystal. For this reason, the intensity of the fluorescence detected by the photodetector varies stepwise depending on the number of light reducing portions existing from the position where the fluorescence is generated to the position of the photodetector. Therefore, by detecting the intensity of the fluorescence with the photodetector, the generation position of the fluorescence can be specified as a relative relationship with the position of the light reduction unit.

  An embodiment of the present invention will be described below with reference to the drawings. The radiation detection apparatus 1000 of this Embodiment has the radiation detector 100 and the light emission specific circuit 200, as shown in FIG.

  As shown in FIGS. 1 and 2, the radiation detector 100 includes a scintillator crystal 110 that generates fluorescence FR when radiation RR enters, and light detection that detects the incidence of radiation RR by detecting fluorescence FR. Device 130.

  The scintillator crystal 110 as described above is formed in an elongated shape, and the radiation RR enters one end. The photodetector 130 is disposed at the other end of the scintillator crystal 110 and detects the intensity of the fluorescence FR.

  However, the radiation detector 100 according to the present embodiment includes light reduction units 111 to 113 that are partially located on the outer surface of the scintillator crystal 110 and reduce the intensity of the fluorescent FR that propagates inside.

  Therefore, the light emission specifying circuit 200 of the radiation detection apparatus 1000 specifies the light emission position in the longitudinal direction of the scintillator crystal 110 based on the intensity of the signal output from the photodetector 130 of the radiation detector 100 as described above.

More specifically, in the radiation detector 100 of the present embodiment, the scintillator crystal 110 is made of a LuAG (Pr: Lu ₃ Al ₅ O ₁₂ ) crystal that is a LuAG crystal doped with praseodymium, and has an elongated shape. It is formed in a certain rectangular parallelepiped shape.

  The light reduction parts 111 to 113 are arranged at equal intervals at three positions which are a plurality of positions in the longitudinal direction of the outer surface of the scintillator crystal 110. For this reason, the scintillator crystal 110 is divided into four portions 121 to 124 having the same length by the three light reduction units 111 to 113.

  The scintillator crystal 110 has a smooth outer surface, and the outer surface is covered with a light reflecting material 140. For this reason, when the outer surface of the scintillator crystal 110 is observed from the inside, it is a mirror surface that substantially totally reflects the fluorescence FR.

  However, the light reduction portions 111 to 113 are formed as concave portions having a rough surface by machining such as precision cutting. Therefore, in the light reduction units 111 to 113, the light reflecting material 140 is excluded. For this reason, the light reduction units 111 to 113 of the scintillator crystal 110 do not totally reflect the fluorescence FR incident from the inside, but reduce it by radiation, scattering, absorption, or the like.

  The photodetector 130 outputs a signal having a peak value corresponding to the intensity of incident fluorescence, for example. As such a photodetector 130, a photoelectric converter using a CCD (Charge Coupled Device) element, a photomultiplier tube, an avalanche photodiode, a silicon photomultiplier, a photodiode, or the like can be used.

  The light emission specifying circuit 200 includes, for example, a wave height analysis circuit (not shown), and compares the wave height values of the output signal of the photodetector 130 with a plurality of threshold values, so that the four portions 121 of the scintillator crystal 110 are obtained. To which of -124 the fluorescence is generated is specified.

  In the configuration as described above, in the radiation detector 100 of the present embodiment, the radiation RR is incident on one end of the elongated scintillator crystal 110 from one end as in the conventional apparatus, so that fluorescence is generated inside the scintillator crystal 110. FR occurs. The fluorescence FR propagates through the scintillator crystal 110 and is detected by the photodetector 130 at the other end.

  However, in the radiation detector 100 of the present embodiment, unlike the conventional apparatus, the intensity of the fluorescence FR generated by the incidence of the radiation RR and propagating through the scintillator crystal 110 is the outer surface of the scintillator crystal 110. Are reduced by the light reduction units 111 to 113 partially located in the area.

  For this reason, the intensity of the fluorescent light FR detected by the light detector 130 varies stepwise depending on the number of the light reduction units 111 to 113 existing from the position where the fluorescent light FR is generated to the position of the light detector 130. It will be.

  Therefore, the radiation detection apparatus 1000 according to the present embodiment detects the intensity of the fluorescence FR by the photodetector 130 of the radiation detector 100, and thereby changes the generation position of the fluorescence FR from the positions of the light reduction units 111 to 113. It can be specified as a relative relationship.

  Nevertheless, in the radiation detector 100 of the present embodiment, the light emission position in the longitudinal direction can be specified by one scintillator crystal 110. For this reason, it is not necessary to connect a plurality of scintillator crystals in multiple stages in the longitudinal direction.

  Therefore, the structure is simple, the number of parts can be reduced, and a structure for fixing a plurality of scintillator crystals in multiple stages is not necessary. For this reason, the productivity of the radiation detector 100 can be improved.

  In addition, in the radiation detector 100 of the present embodiment, the light reduction units 111 to 113 are arranged at a plurality of positions in the longitudinal direction of the outer surface of the scintillator crystal 110. For this reason, the light emission position can be specified from the plurality of portions 121 to 124 in the longitudinal direction of the scintillator crystal 110, and the resolution in the longitudinal direction is good.

  Further, the light reducing portions 111 to 113 are formed of a rough concave portion formed on the smooth outer surface of the scintillator crystal 110. For this reason, the light reduction parts 111-113 which reduce fluorescence by scattering, radiation | emission, and absorption can be formed easily.

Moreover, the scintillator crystal 110 is made of a LuAG (Pr: Lu ₃ Al ₅ O ₁₂ ) crystal that is a LuAG crystal doped with praseodymium. For this reason, even if it forms the light reduction parts 111-113 by precision cutting etc., it is hard to be damaged, and the scintillator crystal 110 in which the light reduction parts 111-113 are formed can be manufactured with favorable productivity.

  The radiation detector 100 as described above is actually used for a position detection device (not shown) such as a PET device. Such a position detection apparatus includes a plurality of radiation detectors 100 arranged in a two-dimensional manner, and the longitudinal direction of each scintillator crystal 110 depending on the intensity of signals individually output from the photodetectors 130 of the radiation detector 100. A light emission specifying circuit 200 for specifying a light emission position at the light emission position, a radiation specifying circuit for specifying a three-dimensional position where the radiation RR is emitted from the light emission positions of the plurality of radiation detectors 100 specified by the light emission specification circuit 200, Have

  In a position detection apparatus such as a PET apparatus, the resolution is improved by arranging an enormous number of minute radiation detectors 100 in two dimensions. Since the radiation detector 100 of the present embodiment has a simple structure and is easy to install as described above, the productivity of the position detection device can also be improved.

  Moreover, the radiation detector 100 that is simple in structure and easy to install can easily be reduced in size in the front-rear and left-right directions. For this reason, the resolution can be improved by increasing the density of the radiation detectors 100 arranged in the position detection device.

The inventor actually made a prototype of the radiation detector 100 and the radiation detection apparatus 1000 as described above, and confirmed the operation thereof. The experimental results will be briefly described below. First, a rectangular parallelepiped LuAG (Pr: Lu ₃ Al ₅ O 12) (hereinafter referred to as “Pr: LuAG”) crystal of 3 mm length × 3 mm width × 30 mm height was formed as the scintillator crystal 110.

  The outer surface of the scintillator crystal 110 was coated with a light reflecting material 140 having a thickness of 200 μm with polytetrafluoroethylene. On the outer surface of the scintillator crystal 110, three light reduction portions 111 to 113 were formed as recesses having a width of 0.5 mm and a depth of 0.6 mm at intervals of 7.5 mm. The radiation detector 100 was completed by optically coupling a photomultiplier tube as the photodetector 130 to the lower end of the scintillator crystal 110 as described above.

  Then, as shown in FIG. 3, the four parts 121 to 124 divided by the light reducing units 111 to 113 of the radiation detector 100 are irradiated with 662 keV cesium 137 radiation from the slits of the lead block. The amount of light detected by the detector 130 was measured.

(Table 1)

Position irradiated with radiation Light intensity (ch)
First part 121 126
Second part 122 162
Third part 123 224
Fourth part 124 332

  Then, as described above, it was confirmed that the detected light amount clearly differs for each of the four portions 121 to 124 divided by the light reduction units 111 to 113. Furthermore, FIG. 4 shows a wave height distribution detected when the four portions 121 to 124 divided by the light reduction units 111 to 113 are selectively irradiated with radiation.

  In FIG. 4, the peak value of the signal (the total amount of light received by the light receiving element) is taken on the horizontal axis, and the count number for each pulse peak value is shown on the vertical axis. The peak value corresponding to the sharp peak on the right side indicates the maximum light amount of the light receiving element.

  The light intensity decreases as the emission position is farther from the detector. As a result, it was confirmed that the amount of energy of light received by the light receiving element changes for each region where the radiation is incident, and the reaction position of the radiation can be clearly identified.

  The present invention is not limited to the present embodiment, and various modifications are allowed without departing from the scope of the present invention. For example, in the above embodiment, the composition, size, and the like of the scintillator crystal 110 are specifically exemplified, but it is needless to say that the composition, size, and the like can be variously modified.

  Moreover, although the said embodiment illustrated that the light reflecting material 140 was coat | covered by the outer surface of the scintillator crystal | crystallization 110, this does not need to be coat | covered. Further, in the above embodiment, the three light reducing portions 111 to 113 are formed on the outer surface of the scintillator crystal 110, but this may be one, two, or four or more.

  Moreover, in the said form, it illustrated that the light reduction parts 111-113 consist of a recessed part of a rough surface. However, the light reduction part may be formed only by a rough surface, and may be formed only by the recessed part.

  Further, a light reduction part may be formed by partially eliminating the light reflecting material 140, and light is absorbed by a light absorbing material (not shown) partially formed on the outer surface of the scintillator crystal 110. A reduction part may be formed.

  Needless to say, the above-described embodiment and a plurality of modifications can be combined within a range in which the contents do not conflict with each other. Further, in the above-described embodiments and modifications, the structure of each part has been specifically described, but the structure and the like can be changed in various ways within a range that satisfies the present invention.

It is a typical vertical front view which shows the internal structure of the radiation detection apparatus of embodiment of this invention. It is a typical perspective view which shows the external appearance of a radiation detector. It is a schematic diagram which shows the content of an experiment with the prototyped radiation detector. It is a characteristic view which shows the output signal of a radiation detector.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Radiation detector 110 Scintillator crystal 111-113 Light reduction part 121-124 Part 130 Photo detector 140 Light reflector 200 Light emission specific circuit 1000 Radiation detection apparatus FR Fluorescence RR Radiation

Claims (13)

A scintillator crystal that generates fluorescence when radiation is incident thereon, and a photodetector that detects the incidence of the radiation by detecting the fluorescence,
The scintillator crystal formed in an elongated shape and having the radiation incident on one end thereof;
The photodetector disposed at the other end of the scintillator crystal to detect the intensity of the fluorescence;
A light reduction part that reduces the intensity of the fluorescence that is partially located on the outer surface of the scintillator crystal and propagates inside;
A radiation detector.   The radiation detector according to claim 1, wherein the light reduction portions are arranged at a plurality of positions in the longitudinal direction of the outer surface of the scintillator crystal. The scintillator crystal reflects the fluorescence incident on the outer surface from the inside,
The radiation detector according to claim 1, wherein the light reduction unit radiates the fluorescence incident from the inside of the scintillator crystal to the outside. The scintillator crystal reflects the fluorescence incident on the outer surface from the inside,
The radiation detector according to any one of claims 1 to 3, wherein the light reduction unit absorbs the fluorescence incident from inside the scintillator crystal. The scintillator crystal reflects the fluorescence incident on the outer surface from the inside,
The radiation detector according to any one of claims 1 to 4, wherein the light reducing unit scatters the fluorescence incident from inside the scintillator crystal.   The radiation detector according to any one of claims 1 to 5, wherein the light reduction portion is formed of a rough surface partially formed on a smooth outer surface of the scintillator crystal.   The radiation detector according to any one of claims 1 to 6, wherein the light reduction portion is formed of a concave portion partially formed on an outer surface of the scintillator crystal.   The radiation detector according to any one of claims 1 to 7, wherein the light reduction portion is made of a light absorbing material partially formed on an outer surface of the scintillator crystal.   The radiation detector according to any one of claims 1 to 8, wherein the scintillator crystal is made of a LuAG crystal.   The radiation detector according to claim 9, wherein the scintillator crystal is the LuAG crystal doped with praseodymium. The radiation detector according to claim 10, wherein the scintillator crystal is made of a LuAG (Pr: Lu ₃ Al ₅ O ₁₂ ) crystal. A radiation detector according to any one of claims 1 to 11,
A light emission specifying unit for specifying a light emission position in a longitudinal direction of the scintillator crystal according to an intensity of a signal output from the light detector of the radiation detector;
A radiation detection apparatus. A plurality of radiation detectors according to any one of claims 1 to 11 arranged two-dimensionally;
A light emission specifying unit for specifying the light emission position in the longitudinal direction of each scintillator crystal according to the intensity of the signal individually output by the light detector of the radiation detector;
A radiation specifying unit for specifying a three-dimensional position where the radiation is emitted from the light emission positions of the plurality of radiation detectors specified by the light emission specifying unit;
A position detecting device.

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