LAYERED THREE-DIMENSIONAL RADIATION POSITION DETECTOR

Abstract

A layered three-dimensional radiation position detector includes two-dimensional scintillator arrays that are pixelated by optically discontinuous surfaces and stacked on a light receiving surface of a light receiving element, responses of scintillator elements detecting radiations being made identifiable on the light receiving surface to obtain a three-dimensional radiation detection position. A scintillator array lying on a radiation incident surface side has a pixel pitch smaller than that of a scintillator array lying on a light receiving element side so that the scintillator array on the radiation incident surface side has increased resolution. A layered three-dimensional radiation position detector achieving both low cost and high resolution can thus be provided.

Claims

1. A layered three-dimensional radiation position detector comprising: a light receiving element having a light receiving surface; and two-dimensional scintillator arrays that are pixelated by optically discontinuous surfaces and stacked on the light receiving surface of the light receiving element, responses of scintillator elements detecting radiations being made identifiable on the light receiving surface to obtain a three-dimensional radiation detection position, wherein a scintillator array lying on a radiation incident surface side has a pixel pitch smaller than that of a scintillator array lying on a light receiving element side so that the scintillator array on the radiation incident surface side has increased resolution.

2. The layered three-dimensional radiation position detector according to claim 1, wherein the scintillator array having the smaller pixel pitch is arranged on a first layer on the radiation incident surface side.

3. The layered three-dimensional radiation position detector according to claim 1, wherein the scintillator array is stacked 3 or more layers.

4. The layered three-dimensional radiation position detector according to claim 3, wherein the scintillator array on the light receiving element side includes a plurality of scintillator arrays having a same pixel pitch.

5. The layered three-dimensional radiation position detector according to claim 3, wherein four layers of the scintillator arrays are stacked, and a first layer of the four layers on the radiation incident surface side has a pixel pitch smaller than that of the three layers of the scintillator arrays on the light receiving element side.

6. The layered three-dimensional radiation position detector according to claim 5, wherein the scintillator array of the first layer on the radiation incident surface side is an array of 16×16 scintillator elements, and an optical reflective material is inserted for every 4×4 scintillator elements.

7. The layered three-dimensional radiation position detector according to claim 6, wherein the scintillator arrays of the second to fourth layers are configured by a stack of three layers of arrays of 8×8 scintillator elements having a size twice that of the scintillator elements of the first layer.

8. The layered three-dimensional radiation position detector according to claim 1, wherein a light guide is inserted between the scintillator arrays between which the pixel pitch changes, so that scintillation light from a scintillator array having a different pixel pitch spreads through the scintillator elements of the adjoining lower layer.

9. The layered three-dimensional radiation position detector according to claim 2, wherein the scintillator array on the radiation incident surface side has a pixel pitch 1/n (n is a natural number of 2 or greater) of that of the scintillator array on the light receiving element side in a longitudinal direction and/or a lateral direction.

10. The layered three-dimensional radiation position detector according to claim 1, wherein a radiation incident position on the scintillator array having the smaller pixel pitch is made identifiable on the light receiving surface by a layout pattern of an air gap and/or an optical adhesion layer.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0031] The preferred embodiments will be described with reference to the drawings, wherein like elements have been denoted throughout the figures with like reference numerals, and wherein;

[0032] FIG. 1 is a diagram showing a crystal identification method by a typical PET detector and barycenter calculation;

[0033] FIG. 2 is a sectional view showing a state in which annihilation radiations are detected by a PET device;

[0034] FIG. 3 is a diagram showing an example of a structure and a crystal discrimination method of a conventional layered three-dimensional radiation position detector;

[0035] FIGS. 4A and 4B are diagrams showing a structural example of a layered three-dimensional radiation position detector according to the present invention;

[0036] FIG. 5 is a diagram showing by comparison the effects of a conventional example and an embodiment of the present invention;

[0037] FIG. 6 is a diagram showing predicted spatial resolution of the conventional example and the method of the present invention;

[0038] FIGS. 7A to 7E are diagrams showing an embodiment of the present invention;

[0039] FIGS. 8A and 8B are diagrams showing an effect of an interlayer light guide; and

[0040] FIGS. 9A to 9C are diagrams showing barycentric maps obtained by the embodiment.

DESCRIPTION OF EMBODIMENTS

[0041] Embodiments of the present invention will be described below in detail with reference to the drawings. It should be noted that the present invention is not limited to the contents described in the following embodiments and practical examples. The components of the embodiments and practical examples described below may include ones easily conceivable by those skilled in the art, substantially identical ones, and ones within the range of equivalency. The components disclosed in the embodiments and practical examples described below may be combined as appropriate, and may be selected and used as appropriate.

[0042] FIGS. 7A to 7E show an embodiment of the present invention which is applied to the four-layer radiation three-dimensional position detector shown in FIG. 3.

[0043] In the present embodiment, a first-layer scintillator array 31 on a radiation incident surface side has a pixel pitch ½ that of the other three layers (second, third, and fourth layers) of scintillator arrays 32, 33, and 34 on a light receiving element 30 side of low detection efficiency in both a longitudinal direction and a lateral direction. A light guide 40 is inserted between the first-layer scintillator array 31 and the second-layer scintillator array 32. The light guide and the scintillator arrays can be optically coupled by an optical adhesive and the like.

[0044] For example, the first-layer scintillator array 31 as shown in FIG. 7B may be an array of 16×16 LYSO scintillator elements each having 1.5×1.5×5 mm.sup.3.

[0045] In the first layer of scintillator elements, an optical reflective material 36 is inserted for every 4×4 LYSO scintillator elements. The scintillator elements inside the optical reflective material 36 are optimized by an optical adhesive 38 and air gaps 37 so that their crystal responses on the light receiving surface do not overlap. Specifically, as shown in the diagram, the four center elements of the 4×4 scintillator elements are preferably bonded by the optical adhesive 38. The peripheral elements are preferably separated by air gaps 37. However, such a configuration is not restrictive.

[0046] As shown in FIGS. 7A, 7C to 7E, the second- to fourth-layer scintillator arrays 32 to 34 are a stack of three arrays of 8×8 LGSO scintillator elements each having 3×3×5 mm.sup.3. The structure of the reflective material 36 and other factors are the same as with the conventional four-layer radiation three-dimensional position detector shown in FIG. 3.

[0047] The light guide 40 is interposed between the first and second layers. The light guide 40 is preferably made of an acrylic resin, and has the same size as that of the scintillator arrays (the foregoing arrays have a size of 23×23 mm.sup.2) and a thickness of 0.5 mm. Basically, increasing the thickness of the light guide cause deterioration of overall position discrimination. Decreasing the thickness of the light guide cause deterioration of distributing effect. Inventors have tried thicknesses of 0.5 mm, 1.0 mm, 1.5 mm and 2.0 mm. All thicknesses show effect of the light guide, but 0.5 mm is best for position discrimination. However, this is not restrictive. FIGS. 8A and 8B shows an effect of the interlayer light guide 40.

[0048] FIGS. 9A to 9B show barycentric maps obtained by uniform irradiation with a .sup.22Na radiation source from above. It can be seen that the insertion of the light guide between the first and second layers improves the identification of the first layer. Under the condition, the optimum thickness of the light guide is 0.5 mm. A thickness of 1 mm tended to produce overlapping responses. On the barycentric map with the 0.5-mm-thick light guide, it is evident that the responses of the 16 elements in the first layer within the minimum segment shown enlarged in FIG. 7B and four elements in each of the second and third layers are identifiable.

[0049] In the foregoing embodiment, the scintillator arrays are pixelated by crystal division. However, the scintillator arrays may be pixelated by laser engraving to a monolithic crystal or by laser engraving to divided crystals.

[0050] In the foregoing embodiment, only the first layer on the radiation incident surface side has a pixel pitch smaller than that of the other layers. However, up to predetermined layers from the radiation incident surface may have a pixel pitch smaller than that of the rest of the layers.

[0051] In the foregoing embodiment, the first layer on the radiation incident surface side has a pixel pitch ½ that on the light receiving element side in both the longitudinal direction and the lateral direction. As shown in FIG. 4B, the pixel pitch may be reduced to ½ in either one of the longitudinal and lateral directions. The pixel pitch may be reduced to other than ½ but 1/n (n is a natural number of 3 or greater) in the longitudinal direction and/or the lateral direction.

[0052] The number of layers of scintillator arrays is not limited to four. As shown in FIG. 4A, the number of layers may be two or more.

[0053] The material of the scintillators is not limited to that of the embodiment.

[0054] According to the present invention, resolution of the order of 4 mm of an existing PET device can be improved to the order of 2 mm without much increase in cost. Head PET devices including the helmet type PET device proposed in Patent Literature 5 can thus be accommodated.

[0055] It should be apparent to those skilled in the art that the above-described embodiments are merely illustrative which represent the application of the principles of the present invention. Numerous and varied other arrangements can be readily devised by those skilled in the art without departing from the spirit and the scope of the present invention.