We proposed and tested the a block detector for a multislice, depth-of-interaction (DOI) MR-compatible positron emission tomography (PET). The detector consists of a block detector, four optical fibers and photo-multiplier tubes (PMTs). The block detector is a lutetium oxyorthosilicate (LSO) DOI detector comprising eight LSOs arranged in a 2 × 2 × 2 matrix based on the concept proposed by Murayama et al. The size of a single scintillator of a prototype block detector was 2 × 2 × 2 mm. The scintillation photons are collected from the side of the scintillator block detector and are transferred to four channels of the position-sensitive PMT (PSPMT) using four optical fibers several meters long. The outputs of the PSPMT signals are calculated to determine the position of gamma interaction in the block detector. Results show that although the light loss from using the fiber was around 90%, there were sufficient transferred scintillation photons to obtain the photo-peak and to calculate the position of gamma interaction in the block detector with reasonable separation. We also modified the block detector to improve the performance of the detector. The size of a single scintillator of the modified block detector was enlarged to be 2.5 mm (transaxial) × 3.5 mm (axial) × 3.5 mm (depth) to improve the sensitivity. Good position responses as well as time resolution of 5.6-ns full-width at half-maximum (FWHM) were obtained for the modified block detector. With these results, we conclude that a two-rings, two-layer DOI-MR-compatible PET can be realized using the proposed block detector.
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