Performance evaluation of GAPD-based brain PET

A Geiger-mode avalanche photodiode (GAPD) is actively studied silicon-based photo-detector that is a promising photo-sensor for PET because of various advantages, such as gain, compact size, fast response and magnetic field insensitivity. Previously, we have developed a brain PET employing GAPD-based PET detector block, charge signal transmission method via 4 m long cable, high density position decoder circuit (PDC) and digital signal processing with FPGA-embedded ADC boards. The purpose of this study was to evaluate the performance of the developed brain PET system. The PET consists of 18 detector blocks, each of which comprises 4 × 4 GAPDs and 4 × 4 LYSO arrays. The output signals of PET detector block were amplified by preamplifier circuits and then transferred to the PDC. The PDC was used to identify the one valid channel among 256 channels of PET detector blocks and to output digital address analog pulse corresponding to the valid channel. Three FPGA-embedded DAQ boards were used to digitize analog output signals of the PDCs. The gain uniformity, spatial resolution, sensitivity, stability and count rate performance were measured. Tomographic image of 3D Hoffman brain phantom was also acquired to evaluate imaging capability of the PET. Normalized average photo-peak positions of PET detector block were 1.0 ± 0.14 without the gain correction and 1.0 ± 0.03 with the gain correction. Spatial resolution and sensitivity in the center of field of view were 3.1 mm and 0.8%, respectively. The average scatter fraction was 0.4 with lower energy threshold of 350 keV. The maximum true count rate and maximum NECR were measured 43.3 kcps and 6.5 kcps at an activity concentration of 16.7 kBq/ml and 5.5 kBq/ml, respectively. Activity distribution patterns between white and gray matter in the Hoffman brain phantom were well imaged. These results demonstrate that the developed GAPD based brain PET system is useful for high quality brain PET imaging.