MR compatible brain PET using tileable GAPD arrays

The aim of this study is to develop a MR compatible PET that is insertable to MRI and allows simultaneous PET and MR imaging of human brain. The brain PET having 72 detector modules arranged in a ring of 330 mm diameter was designed. Each PET module composed of 4 ? 4 matrix of 3 mm ? 3 mm ? 20 mm LYSO crystals coupled to a tileable 4 ? 4 array Geigermode avalanche photodiode (GAPD) and designed to locate between RF and gradient coils. Signals of the each module were transferred to preamplifiers using flexible flat cable of 3 m long, and then sent to a position decoder circuit (PDC), which outputs digital address and an analog pulse of the one interacted channel from preamplifier signals. The PDC outputs were fed into FPGA-embedded DAQ boards. The analog signal was digitized, and arrival time and energy of the signal were calculated and stored. All electronics were located outside MR bore to minimize signal interference between PET and MR. Basic performance of the PET components and cross-compatibilities of the PET module and MR were evaluated. Imaging performance of the designed brain PET was investigated using Monte Carlo simulation and experimental measurement. The degradation of PET performance caused by the 3 m long cable and the PDC was negligibly small. No obvious differences of the PET module performance measured inside/outside MR bore were observed. The SNR of various MR sequence phantom images acquired with/without the PET module were also similar. Activity distribution patterns of hot-rod phantoms were well imaged without distortion, and rods down to a diameter of 3.5 mm were resolved in both simulation and experiment. Grayand white matter of the Hoffman brain phantom was also well imaged. Preliminary experimental results demonstrate that MR compatible high quality PET imaging is feasible using the GAPD arrays, electronics, signal processing method and MR insertable PET design schemes developed in this study.