Measurement of 32/spl times/8/spl times/4 LYSO crystal responses of DOI detector for jPET-RD

jPET-RD is designed to achieve high sensitivity as well as high spatial resolution by the use of four-layer depth of interaction (DOI) information of the detector. We have previously proposed the DOI encoding method that enables four layers DOI identification using only single kind crystal elements. The basic idea was tested by using Gd₂SiO₅, and the first prototype detector was developed using Lu_2(1-x)Y_2xSiO₅ (LYSO). In this work, we prepared a pair of jPET-RD prototype detectors composed of four layers of a 32 (transaxial)times8 (axial) LYSO (Lu: 98%, Y: 2%) crystal block and a 256-channel flat panel position sensitive photomultiplier tube (256ch FP-PMT). The size of each crystal element is 1.46 mmtimes1.46 mmtimes4.5 mm. The crystal block (46.5 mmtimes11.6 mmtimes18.0 mm) is placed on the central area of a 256ch FP-PMT (49 mmtimes49 mm useful area) and coupled with silicone rubber. First, we evaluated performance of the prototype DOI detector by uniform gamma ray irradiation. Then response functions of the prototype DOI detector were measured with collimated single gamma rays and finally coincidence responses are estimated with a pair of prototype DOI detectors in the experimental setup which simulates jPET-RD system. In the performance evaluation, the energy resolution of all events was 14.7% and the time resolution was found to be 0.66 ns. The response functions were 1.56 mm FWHM and 4.51 mm FWHM in average in transaxial and depth direction, respectively. The FWHMs of coincidence responses were 5.4 mm (non-DOI) and 3.7 mm (averaged DOI). It is confirmed that the spatial resolution is improved by using DOI information