JP4366218B2 - Gamma ray detection camera device - Google Patents

Description

  The present invention relates to a γ-ray detection camera device such as a PET (Positron Emission Tomography) device.

One of the cancer diagnostic apparatuses is a PET apparatus. Cancer cells that constitute malignant tumors are highly active and therefore have the property of metabolizing more glucose than surrounding tissues. Therefore, when a substance added with a radiation source that emits positrons such as ¹⁸ F is added to glucose, it concentrates on malignant tumors and emits more radiation than healthy tissue. For example, as schematically shown in FIG. 11, a positron emitting nuclide 61 as a radiation source accumulated in a malignant tumor emits a positron 62, and this positron 62 annihilates a large number of electrons 63 in the surrounding area to annihilate 511 keV. Are emitted in directions opposite to each other by 180 °. The two γ rays 64 and 65 are captured by, for example, two NaI (Tl) scintillation detectors that are arranged opposite to each other with a radiation source as a center and are formed by stacking a plurality of NaI (Tl) scintillator elements, for example. Thus, the position of the radiation source 61 in the body, that is, the position of the malignant tumor can be specified. In FIG. 11, 61a and 61b are protons and neutrons, respectively.

The PET apparatus has a very high detection sensitivity for malignant tumors, but the position resolution is extremely inferior to that of an X-ray CT image, so the position of the malignant tumor cannot be accurately identified. Conventionally, diagnosis is sometimes performed using X-ray CT together. For this reason, there existed a possibility of causing the increase in the radiation exposure dose with respect to a patient.
Special table 2001-512840 gazette

  By the way, the position resolution of the PET apparatus is limited to the size of the radiation detector used in the apparatus. And since the radiation detected by PET is γ-rays with a high energy of 511 keV, it cannot be downsized at present.

  That is, in the prior art, as shown in FIG. 12, two γ rays 64 and 65 emitted from a radiation source 61 are detected by a radiation detector 66 formed by arranging a large number of scintillator elements 66a in parallel. However, the γ rays 64 and 65 sometimes pass through the scintillator element 66a as indicated by arrows. In order to prevent such passing of γ-rays, it is necessary to increase the volume of the radiation detector 66. However, the radiation detector 66 thus configured has a disadvantage in that the image definition is lowered.

Therefore, recently, the use of BGO (Bi ₄ Ge ₃ O ₁₂ ; bismuth germanate) instead of NaI (Tl) as a radiation detector for detecting the γ-ray has been studied. This BGO has a fluorescence efficiency as low as 10% compared to NaI (Tl), but has the advantage that the density is double and the detection efficiency is high. However, the radiation detector using BGO as a scintillator element has drawbacks that it is more expensive and has only 3 mm of position resolution than those using NaI (Tl) as a scintillator element. Further, the BGO is mixed with radioactive impurities caused by Bi, and it is difficult to lower the background and increase the sensitivity. In order to reduce the radiation exposure accompanying medical diagnosis, NaI (Tl), which can policy high-purity crystals at low cost, is optimal.

  The present invention has been made in consideration of the above-mentioned matters, and an object of the present invention is to provide a γ-ray detection camera device that is inexpensive and has high positional resolution and can detect γ-rays with high accuracy. is there.

To achieve the above object, the present invention is a γ ray generated based on the radiation source, the γ ray detecting camera device for detecting the scintillation detector comprising a NaI scintillator elements of several adjacent arrangement, the NaI scintillator the thickness in the adjacent direction of the element, Ri thin Citea a γ ray generated based on the radiation source to the extent that in the adjacent direction can be detected by the NaI scintillator elements, NaI scintillator elements, one plane is mirror-polished A crystal base material is provided in close contact with the reflective film, and a frame body is disposed on the reflective film so as to surround the crystal base material, and an optical adhesive is disposed between the frame body and the crystal base material. Fill and fix the crystal base material to the reflective film and the frame, and cut the other surface of the crystal base material together with the frame in the fixed state. Cutting has been surface is characterized by being produced by mirror polishing (claim 1). Here, the NaI scintillator element refers to an element made of NaI or NaI (Tl).

The scintillation detectors are arranged to face each other with the radiation source as a center .

  Moreover, the thickness in the adjacent direction of a NaI scintillator element is 1.0 mm or less (Claim 3).

In the γ-ray detection camera device according to the first aspect, since the scintillator element is extremely thin and so-called ultra-thin, γ-rays generated based on radiation can be detected by the NaI scintillator elements from each other in the adjacent direction. it can. In particular, as described in claim 3, when the thickness in the adjacent direction of the NaI scintillator element is 1.0 mm or less, the position resolution is improved and the detection sensitivity is greatly improved. This improvement in position resolution and detection sensitivity brings about the following effects. For example, when the γ-ray detection camera device is a PET device for diagnosing cancer or the like, it is possible to detect even very small cancer cells due to improved position resolution, and so-called early detection of cancer. it can. Moreover, since the radioactive impurity contained in NaI (Tl) can be used at the highest level of several ppt, the background is extremely small. Therefore, the dose of a substance obtained by adding a radiation source that emits positrons such as ¹⁸ F to glucose can be reduced, and the influence on the human body can be suppressed as small as possible.

Further, when the NaI scintillator element is manufactured by the method described in claims 1 and 2 , the other rough surface of the crystal base material can be easily cut by a cutter. That is, when cutting with the cutter of the rough surface, not only the crystal base material, but also the frame disposed concentrically with the crystal base material is cut, so the following advantages There is. That is, the crystal base material is fixed to the frame body with the optical adhesive and is fixed so that the crystal base material and the frame body are in close contact with one of the support bases. There is almost no shock, and in particular, the shock at the peripheral edge of the crystal base material can be eliminated, so that the crystal base material to be cut does not break during cutting, and the desired thickness, for example, 0.5 mm Can be cut into a very thin state. Therefore, since the NaI scintillator element having a desired thickness can be manufactured with good yield, the manufacturing cost of the γ-ray detection camera device can be reduced.

  Therefore, according to the present invention, a gamma ray detection camera device capable of reliably detecting a desired gamma ray can be obtained at a low cost. It can be used for academic experiment equipment.

  1 to 3 show an embodiment of the present invention, and schematically show a PET apparatus as an example of a γ-ray detection camera apparatus of the present invention. In these drawings, reference numeral 1 denotes an annular scintillation detector in which a plurality of NaI scintillator elements 2 (the specific configuration and manufacturing method will be described later) are arranged adjacent to each other on the same circumference without any gap. The scintillation detection unit 1 is formed so as to have an inner diameter that allows a human body 3 lying on a horizontal holding table (not shown) to pass through the center of the human body 3 with a margin. As described in FIGS. 11 and 12, the plurality of NaI scintillator elements 2 are arranged in a direction corresponding to 180 ° of γ rays (positron annihilation radiation) 15a, 15b (see FIG. 3) generated in the human body 3, in this embodiment. Then, a pair of NaI scintillator elements 2 (for example, indicated by reference numerals 2a and 2b in FIG. 3) positioned in the diameter direction are configured to detect.

  Reference numerals 4 and 5 denote amplifiers for amplifying signals (scintillator signals) based on scintillation light in the plurality of NaI scintillator elements 2 divided in two in the diameter direction. Each NaI scintillator element 2 is connected to signal transmission paths 6 and 7. Connected through. The outputs of the amplifiers 4 and 5 are inputted to the coincidence counting circuit 10 through the signal cables 8 and 9. Reference numeral 11 denotes a CPU that performs various calculations such as image analysis based on a signal input to the coincidence circuit 10, and reference numeral 12 denotes a display device that displays an image as a result of the calculation in a color state, for example.

  The NaI scintillator elements 2 are juxtaposed in a state adjacent to each other (laminated) with no gap in the direction indicated by the adjacent direction (stacking direction) 13 as shown in FIG. In order to be able to detect the γ rays 15a and 15b generated based on the cancer cells 14 as the radiation source, the thickness is, for example, 0.5 mm or less. The NaI scintillator element 2 is formed.

  The NaI scintillator element 2 has, for example, a square shape in plan view, and has reflection films 17a and 17b on both upper and lower surfaces of the NaI crystal portion 16 as the scintillator element body, as shown in FIG. Reference numerals 23a, 25, and 26 denote a frame and an optical adhesive used when the NaI scintillator element 2 is formed into a predetermined shape as shown in FIGS. 6 to 10, and of these, the frame 23a and the optical adhesive are used. The adhesive 25 functions as a transmission path for the scintillator signal generated in the NaI crystal portion 16 in the state formed in the state shown in FIG.

  As described above, in the present invention, the γ-rays 15a and 15b generated based on the radiation source 14 are disposed opposite to each other with the radiation source 14 as the center, and a plurality of NaI scintillator elements 2 are disposed adjacent to each other. 1, the thickness of the NaI scintillator element 2 in the adjacent direction 13 is made thin enough to detect the γ rays 15 a and 15 b by the adjacent NaI scintillator elements 2.

  As the NaI scintillator element 2 is made ultrathin, the signal transmission lines 6 and 7 are made of optical fibers. In the conventional PET apparatus, since the thickness of the NaI scintillator element 2 was about 5 mm, each NaI scintillator element 2 was provided with a photomultiplier tube (photomultiplier) corresponding thereto. Since the thickness of the NaI scintillator element 2 is 1/10 or less of the conventional one, an optical fiber is provided so as to correspond to each NaI scintillator element 2, thereby causing γ rays 15 a and 15 b in the NaI scintillator element 2. The optical signal generated is derived.

  In the PET apparatus having the above-described configuration, a plurality of NaI scintillator elements 2 are arranged on the same circumference, and the γ rays 15a and 15b are detected by the coincidence circuit 10, so that the spatial resolving power is within the measurement region. Therefore, it is not necessary to correct the absorption of the γ rays 15a and 15b, and a desired image analysis can be performed quantitatively.

  In the above-described embodiment, since a plurality of NaI scintillator elements 2 are fixedly provided on the same circumference without gaps as the scintillation detection unit 1, a large number of NaI scintillator elements 2 are necessary. Since the position resolution in the detection accuracy is high and there is no mechanical rotating portion, there are advantages that the control at the time of measurement is simple.

  On the other hand, as shown in FIG. 5, two scintillation detectors 1A and 1B made up of a plurality of NaI scintillator elements 2 are placed at 180 ° target positions on an annular guide rail 18 having a predetermined diameter. It is also possible to detect γ rays by rotating these two scintillation detectors 1A and 1B along the guide rail 18 while maintaining their relative positional relationship. According to this configuration, the number of NaI scintillator elements 2 to be used is small. In FIG. 5, reference numeral 19 denotes a horizontal holding table on which the human body 3 is placed.

  Next, an example of a method for manufacturing the NaI scintillator element 2 (hereinafter referred to as an element manufacturing method) will be described with reference to FIGS. First, FIG. 6 schematically shows the previous stage of the device manufacturing method. In FIG. 6A, reference numeral 20 denotes an ingot-shaped NaI single crystal base material, for example, a crystal using the Bridgeman Stock Burger method. Manufactured in a growth furnace. And this NaI single-crystal base material 20 is cut out, for example to the plate shape of about 50 mm square and thickness 4mm, as shown to the same figure (B). Actually, it is cut out slightly to see the polishing allowance. The cut-out plate-like crystal base material 21 is a rough surface having fine irregularities on the entire outer peripheral surface, but as shown in FIG. 3C, the side surface (four peripheral surfaces) 21a in the thickness direction and Either one of the upper and lower surfaces 21b, 21c (for example, the lower surface) 21b is polished in a nitrogen gas atmosphere in a drying box (not shown) whose humidity and temperature are adjusted to appropriate values, for example. It is mirror-polished using polishing sand and formed into a size of 4 mm × 50 mm square.

  7 to 9 show an example of a step of cutting the plate-like crystal base material 21 whose predetermined surface is mirror-polished to a predetermined thickness, for example, 0.5 mm, as described above. . First, in FIGS. 7 and 8A, 17a is a reflective film, and 23 is a frame 23. The reflective film 17a is made of, for example, a material having a high reflection characteristic that reflects aluminum almost 100% by depositing aluminum on a film made of polyester, fluorine resin, carbon resin, or the like. The frame body 23 includes, for example, a first frame 23a and a second frame 23b. The first frame 23a has a height of 1.0 mm × 60 mm square, and the second frame 23b has a height of 3.0 mm. × 60 mm square, both 23a and 23b are squares of the same size in plan view, only the height is different. The first frame 23a is made of a material having high mechanical hardness such as acrylic resin, and the second frame 23b is made of a material having low mechanical hardness such as nylon resin. Therefore, the height of the frame body 23 composed of the first frame 23a and the second frame 23b in this embodiment is 4 mm. The reflective film 17a has a thickness of 65 μm and is formed in a square slightly larger than the frame body 23.

  Then, the crystal base material 21 is placed on the upper surface of the reflective film 17a so that the mirror-polished lower surface 17b is close, and the first frame 23a is placed on the upper surface of the reflective film 17a so as to surround the crystal base material 21. The second frame 23b is placed on the upper surface of the first frame 23a. In this case, the position is adjusted so that the crystal base material 21 is positioned at the center of the frame body 23 including the first frame 23a and the second frame 23b.

  Then, as shown in FIG. 8A, optical adhesives 25 and 26 are injected between the frame body 23 and the crystal base material 21 using an appropriate injection tool 24. More specifically, as shown in FIG. 5B, an optical adhesive 26 is interposed between the lower surface of the first frame 23a and the reflective film 17a to bond the both 23a and 17a, and the crystal base material. The optical adhesive 25 is interposed between the lower surface 21b of the substrate 21 and the reflective film 17a to join the members 21 and 17a, and the peripheral surface of the crystal base material 21 and the inner periphery of the first frame 23a and the second frame 23b. The processing target member 27 in which the first frame 23 a and the second frame 23 b and the crystal base material 21 are joined is formed by filling the optical adhesive 25 between the surfaces. In this case, the upper surface of the optical adhesive 25 filled between the peripheral surface of the crystal base material 21 and the inner peripheral surfaces of the first frame 23a and the second frame 23b is composed of the first frame 23a and the second frame 23b. It is preferable to be equal to or slightly higher than the height of the frame body 23. Each of the optical adhesives 25 and 26 is made of an epoxy resin material such as optical cement or eco-bond. For example, the optical adhesive 25 is excellent in light transmittance.

  Then, as shown in FIG. 8C, the workpiece 27 is placed so that the reflection film 17a side is in close contact with the upper flat portion 28a of the support base 28 made of a material having an appropriate mechanical strength. Then, the adhesive tape 29 is applied to the side surface of the processing target member 27 and the side portion of the support base 28 to fix the processing target member 27 to the support base 28. A recess 28a having an appropriate shape is formed in the center of the lower surface side of the support base 28, and a screw hole 28b is formed in the center of the recess 28a.

  As shown in FIG. 8C, in order to cut the workpiece 27 fixed to the support pedestal 28, the support pedestal 28 is cut as shown in FIGS. 6 and 9A. After fixing to 30 using the fixing bolt 31, in particular, as shown in FIG. 9A, using an appropriate cutter 32, the upper surface side of the workpiece 27, more specifically, the crystal base material 21 The upper surface 21c, which is a non-polished surface, is cut together with the frame body 23 and the optical adhesive 25. In FIGS. 6 and 9A, reference numeral 30a denotes a protrusion formed on the upper surface of the cutting fixing member 30, which is formed so as to fit into the concave portion 28a on the support pedestal 28 side. Is provided with a bolt insertion hole 30b.

  When the crystal base material 21 is cut from the upper surface side together with the frame body 23 and the optical adhesive 25 by the cutting, and the cutter 32 reaches the boundary between the first frame 23a and the second frame 23b in the frame body 23, the second frame Since the cutting speed is slow because 23b is hard, cutting is stopped at this point. As a result, as shown in FIG. 9B, a crystal base material 21 having a surface 21d cut on the upper surface is obtained. At this time, the thickness of the cut crystal base material 21 is equal to the length of the first frame 23a, which is 3 mm in this embodiment, and the crystal base material 21 is 1 mm thick.

  Then, in a state where the processed member 27A after cutting is fixed to the fixing member 30 for cutting, it is set in a drying box whose humidity and temperature are adjusted to appropriate values, as shown in FIG. 9C. Then, the upper surface of the crystal base material 21 after cutting, the second frame 23b, and the upper surface of the optical adhesive 25 are mirror-polished using a polishing machine 22 or polishing sand in a nitrogen gas atmosphere.

  Thereafter, as shown in FIG. 10 (A), the optical adhesive 25 is dropped on the upper surface of the polished workpiece 27A, and as shown in FIG. 10 (B), the same material as the reflective film 17a is applied on the upper surface. The reflective film 17b made of is attached, and the support tape 28 is removed by removing the adhesive tape 29, whereby the NaI scintillator element 2 as shown in FIG. 4C and FIG. 4 is obtained. And as shown to the figure (D), the circular scintillation detection part 1 as shown in FIGS. 1-3 is formed by joining NaI scintillator element 2 via an optical adhesive agent.

  As described above, in the element manufacturing method, the crystal base material 21 that is formed to have a predetermined thickness and whose one surface 21b is mirror-polished is provided in close contact with the reflective film 17a, and this reflection is performed. A frame body 23 is disposed on the film 17a so as to surround the crystal base material 21, and an optical adhesive 25 is filled between the frame body 23 and the crystal base material 21 so that the crystal base material 21 is reflected on the reflective film 17a and the crystal base material 21. It adheres to the frame body 23, the other surface 21c of the crystal base material 21 is cut together with the frame body 23 in the fixed state, and then the cut surface 21d is mirror-polished to obtain a predetermined thickness. Since the desired NaI crystal part 16 is formed by mirror-polishing one surface 21a, the other rough surface 21c of the crystal base material 21 can be easily cut by the cutter 32. It can be.

  When the rough surface 21b of the crystal base material 21 is cut by the cutter 32, not only the crystal base material 21 but also the frame body 23 arranged concentrically with the crystal base material 21 is cut. ing. That is, the crystal base material 21 is fixed to the frame body 23 by the optical adhesive 25, and the crystal base material 21 and the frame body 23 are fixed to be in close contact with one of the support bases 28. There is almost no shock to the crystal base material 21 due to cutting, and in particular, the shock at the peripheral end of the crystal base material 21 can be eliminated, so that the crystal base material 21 that is the object of cutting is not cracked during cutting. It can be cut into a very thin state of a desired thickness, for example 0.5 mm.

  Further, in the embodiment described above, the frame body 23 is composed of the first frame 23a and the second frame 23b having different hardness, and the height of the crystal base material 21 to which the height of the harder first frame 23a should be left is the same. Since the second frame 23 is placed above the first frame 23a, the height of the crystal base material 21 in the state where all the relatively soft first frame 23b is cut is It is cut by leaving only a desired height (thickness). Therefore, there is an advantage that no error occurs in the cutting dimension in the cutting of the crystal base material 21. Needless to say, the frame body 23 may be formed of a single member, and the cutting dimensions of the crystal base material 21 may be strictly managed.

  In the above-described embodiment, the thickness of the crystal base material 21 after polishing was 0.5 mm. However, according to experiments by the inventors, the thickness of the crystal base material 21 is 1.0 mm or less. It has been found that unprecedented position resolution and detection sensitivity can be obtained.

1 is a perspective view schematically showing a γ-ray detection camera device of the present invention. It is a longitudinal cross-sectional view of the said gamma ray detection camera apparatus. It is the schematic block diagram which showed in detail the NaI scintillator element part especially of the said gamma ray detection camera apparatus. It is sectional drawing which shows roughly an example of the NaI scintillator element used for the said gamma ray detection camera apparatus. It is a perspective view which shows schematically the other example of the said gamma ray detection camera apparatus. The figure which shows schematically the process of the front | former stage of the manufacturing method of the NaI scintillator element integrated in the said gamma ray detection camera apparatus, and shows the process of obtaining especially a plate-shaped crystal base material from an ingot-shaped NaI single crystal base material. Yes. It is a figure which shows roughly the process of fixing a crystal base material in order to cut the said crystal base material. It is a figure which shows schematically the first half part of the said fixing process. It is a figure which shows roughly the cutting process of a crystal | crystallization base material. It is a figure which shows roughly the finishing process of the crystal | crystallization base material after the said cutting. It is a figure for demonstrating the principle of the measurement in a PET apparatus. It is a figure for demonstrating a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Scintillation detector 2 NaI scintillator element 13 Adjacent direction 15a, 15b γ-ray 17a Reflective film 21 Crystal base material 21b Mirror-polished surface 21d Cut surface 23 Frame 25 Optical adhesive

Claims (3)

The γ-rays generated based on the radiation source, a NaI scintillator elements of several in γ-ray detection camera system for detecting the scintillation detector formed by adjacently arranged, the thickness in the adjacent direction of the NaI scintillator elements, said radiation source Ri thin Citea a γ ray generated based on the degree of the adjacent directions can be detected by the NaI scintillator elements,
The NaI scintillator element is provided with a crystal base material whose one surface is mirror-polished in close contact with the reflective film, and a frame body is disposed on the reflective film so as to surround the crystal base material. An optical adhesive is filled between the crystal base material and the crystal base material is fixed to the reflective film and the frame, and the other surface of the crystal base material is cut together with the frame in the fixed state. Thereafter, the γ-ray detection camera device is manufactured by mirror polishing the cut surface . The γ-ray detection camera device according to claim 1, wherein the scintillation detectors are arranged to face each other with the radiation source as a center .   The gamma ray detection camera device according to claim 1 or 2, wherein a thickness in the adjacent direction of the NaI scintillator element is 1.0 mm or less.

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