Development of Large area Gamma-ray Camera with GSO(Ce) Scintillator Arrays and PSPMTs

We have developed a position-sensitive scintillation camera with a large area absorber for use as an advanced Compton gamma-ray camera. At first we tested GSO(Ce) crystals. We compared light output from the GSO(Ce) crystals under various conditions: the method of surface polishing, the concentration of Ce, and co-doping Zr. As a result, we chose the GSO(Ce) crystals doped with only 0.5 mol% Ce, and its surface polished by chemical etching as the scintillator of our camera. We also made a 16$\times$16 cm$^2$ scintillation camera which consisted of 9 position-sensitive PMTs (PSPMTs Hamamatsu flat-panel H8500), the each of which had 8$\times$8 anodes with a pitch of 6 mm and coupled to 8$\times$8 arrays of pixelated 6$\times6\times$13 mm$^3$ GSO(Ce) scintillators. For the readout system of the 576 anodes of the PMTs, we used chained resistors to reduce the number of readout channels down to 48 to reduce power consumption. The camera has a position resolution of less than 6mm and a typical energy resolution of 10.5% (FWHM) at 662 keV at each pixel in a large area of 16$\times$16 cm$^2$. %to choose the best scintillator for our project. Furthermore we constructed a 16$\times$16 array of 3$\times3\times$13 mm$^3$ pixelated GSO(Ce) scintillators, and glued it to a PMT H8500. This camera had the position resolution of less than 3mm, over an area of 5$\times$5 cm$^2$, except for some of the edge pixels; the energy resolution was typically 13% (FWHM) at 662 keV.Comment: Proceedings of PSD7 appear in NIM

DOI detection capability of 3D crystal array standing over two pmts.

第４回日韓合同医学物理学

A DOI PET Detector Having Extended X\u27tal Cube Structure

We developed a new PET depth-of-interaction (DOI) detector in which the scintillation crystal array is extended in one direction. It can be utilized as a PET detector having, for instance, long axial direction. The detector has the "crystal cube (X\u27tal cube)" structure and the extension was enabled by the feature of the X\u27tal cube that some MPPCs are always placed close to an originating position of the scintillation photons. X\u27tal cube is a DOI PET detector we have developed and it can provide isotropic spatial resolution. X\u27tal cube consists of a scintillation crystal block segmented into cubes and multi-pixel photon counters (MPPCs). A number of MPPCs are coupled on all six sides of the crystal block to detect scintillation photons near their originating position. In a preliminary experiment previously carried out, we confirmed sufficient detector performance of X\u27tal cube using a prototype composed of a 6 x 6 x 6 array of Lu2xGd2(1-x)SiO5:Ce (LGSO, x=0.9) crystals with dimensions of 3.0 x 3.0 x 3.0 mm3 and MPPCs of 3.0 x 3.0 mm2 active area. In this study, the crystal block was extended in one direction from 6 crystals to 14 crystals. The results of performance evaluation proved that the 6 x 6 x 14 crystals could be identified with the structure. Although MPPCs were coupled on all sides of the crystal block in the extended X\u27tal cube, at the central part, the detected radiation position would be calculated with mainly the signals of close MPPCs on the four surfaces. That means the detector can be long as considered appropriate for a system while keeping the isotropic spatial resolution.The 2010 Nuclear Science Symposium and Medical Imaging Conferenc

Application of Scintillation Crystals Cut As A Triangular Prism for A PET Detector

A depth-of interaction (DOI) PET detector is a detector which provides a detected radiation location 3-dimensionally. The DOI information is important to ensure the PET scanner has both high resolution and high sensitivity. We have successfully developed a 4-layer DOI detector which is composed of four layers of scintillation crystal arrays optically coupled to a position sensitive photomultiplier tube. Scintillation light spread in the crystal arrays is utilized for the crystal identification in the 4-layer DOI crystal arrays. As a new trial in our further investigation about scintillation light spread in a crystal array, we used scintillation crystals cut as a triangular prism (triangular crystal) with the expectation that the crystal shape would cause different light behavior compared with rectangular crystals generally used for a PET detector. As an application of the triangular crystals, we developed a 3-layer DOI detector with Lu(2x)Gd(2(1-x))SiO(5) (LGSO) crystals in dimensions of an equilateral triangle of 3.0 mm one side in cross section and 10.0 mm long. The detector performance evaluation showed sufficient crystal identification performance and energy resolution of 9 - 12% was also obtained.第5回日韓医学物理会

Proposal of a 8-Layer DOI Detector Composed of Same Scintillation Crystal Elements

Previously, we developed a 4-layer depth of interaction (DOI) detector. It is composed of four layers of a scintillation crystal array and a position sensitive photomultiplier tube (PS-PMT) and by removing some reflectors between the crystal elements in the array, we control scintillation light distribution on the PS-PMT so that the responses of all crystal elements are discriminated. We also proposed a 2-layer DOI encoding method by using the crystal elements cut as a triangular prism and proved its capability. Combining these two methods, here we propose an 8-layer DOI encoding method. The method makes it possible that the 8-layer DOI detector is consisted of same scintillation crystal elements, that is to say, any scintillation crystals. The method was demonstrated with the Lu2xGd2(1-x)SiO5 (LGSO) crystals. The obtained results indicated the possibility of the proposed method.2009 Nuclear Science Symposium, Medical Imaging Conferenc

Improved spatial resolution of the X\u27tal cube: a 3D crystal array covered with MPPCs

The "crystal (X\u27tal) cube" is our new PET detector, which is composed of a segmented scintillation crystal block covered with Multi-Pixel Photon Counters (MPPCs). For a proof-of-concept, in the last year, we developed the first prototype detector having 3 mm isotropic resolution with 3 mm x 3 mm aperture MPPCs. In this paper, we succeeded to obtain 2 mm isotropic detector resolution (i.e., each crystal whose volume was reduced to 8/27 was identified) with the same MPPCs. In PET, it is important to get information of radiation detected location in PET detectors 3-dimensionaly to achieve both high spatial resolution and high sensitivity. A photomultiplier tube (PMT) which generally used as a photo-detector of a PET detector provides the 2-dimensional information and additional idea is always required to obtain depth of interaction (DOI) information. Fig. 1a) shows a typical structure of X\u27tal cube in which MPPCs are used instead of PMTs.. Unlike a PMT, a MPPC is small enough and will not interfere in radiation detection even if it is set on the path of the radiation. In X\u27tal cube, MPPCs are then set on the all six surfaces of the segmented crystal block and detect scintillation photons in 3-dimension. Since always some MPPCs are placed near originated position of scintillation photons, the photons can be detected before attenuation and sufficient amount of detected photons creates clear responses, which allow fine segmentation of the crystal block for high spatial resolution.In this study, we made the X\u27tal cube composed of a cubic crystal block 18.0 mm on a side and 96 MPPCs (Hamamatsu Photonics K.K., Japan, sensitive area: 3 mm x 3 mm, micro cell: 50 micrometer), 16 MPPCs on each surface of the crystal block. The crystal block consists of a 9 x 9 x 9 array of cubic Lu2xGd2(1-x)SiO5 (LGSO, x = 0.9) crystals 2 mm on a side. Fig.1b) shows the results of crystal identification performance. Each peak is crystal response. All responses were discriminated sufficiently and that means the X\u27tal cube achieved 2 mm isotropic spatial resolution.2010 World Molecular Imaging Congres

Development of Depth-of-interaction (DOI) Detector for PET and Prototype PET Scanner

INTRODUCTION:Our group has been developed a prototype PET scanner, jPET-D4. It is designed to achieve high performance by the use of depth-of-interaction (DOI) detectors. The DOI detector offers 3D radiation detected location and it is the new technique of necessity to gain sensitivity with maintaining spatial resolution in a PET system. In most proposals, DOI detectors have two scintillation crystal layers as depth information. However, we developed a 4-layer DOI detector and showed its capability of easy construction and performance reliability even in mass-production process. On the basis of the 4-layer DOI encoding technique, we further developed a simpler 4-layer DOI encoding method and recently an 8-layer encoding method. In this presentation, we will introduce the jPET-D4 scanner and our DOI detectors.「第６回放射線生物学および画像医学に関する日仏ワークショップ　The 6th Japan-France Workshop on Radiobiology and Isotopic imaging