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We developed high resolution L(Y)SO detectors for human and animal PET applications using Photomultiplier-quadrant-sharing (PQS) technology. The crystal sizes were 1.27 × 1.27 × 10 mm 3 for the animal PQS-blocks and 3.25 × 3.25 × 20 mm 3 for human ones. Polymer mirror film patterns (PMR) were placed between crystals as reflector. The blocks were assembled together using optical grease and wrapped by Teflon tape. The blocks were coupled to regular round PMT's of 19/51 mm in PQS configuration. List-mode data of Ga-68 source (511 KeV) were acquired with our high yield pileup-event recovery (HYPER) electronics and data acquisition software. The high voltage bias was 1100V. Crystal decoding maps and individual crystal energy resolutions were extracted from the data. To investigate the potential imaging resolution of the PET cameras with these blocks, we used GATE (Geant4 Application for Tomographic Emission) simulation package. GATE is a GEANT4 based software toolkit for realistic simulation of PET and SPECT systems. The packing fractions of these blocks were found to be 95.6% and 98.2%. From the decoding maps, all 196 and 225 crystals were clearly identified. The average energy resolutions were 14.0% and 15.6%. For small animal PET systems, the detector ring diameter was 16.5 cm with an axial field of view (AFOV) of 11.8 cm. The simulation data suggests that a reconstructed radial (tangential) spatial resolution of 1.24 (1.25) mm near the center is potentially achievable. For the wholebody human PET systems, the detector ring diameter was 86 cm. The simulation data suggests that a reconstructed radial (tangential) spatial resolution of 3.09(3.38) mm near the center is potentially achievable. From this study we can conclude that PQS design could achieve high spatial resolutions and excellent energy resolutions on human and animal PET systems with substantially lower production costs and inexpensive readout devices.

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We have proposed a high-yield-pileup-event--recover (HYPER) method that can process scintillation signals in very high count-rate situations where multiple-event pileups are normal, and successfully used this method in our BGO animal PET and human PET systems. In the first generation HYPER electronics, the integration and weight-sum circuits were implemented using analog signal. However, the same idea can be implemented in full digital mode. In the digital HYPER method, the input signal is digitized with a free run ADC, and then processed in a Field Programmable Gate Array (FPGA). Recent improvement in integrated circuit technology makes it possible to do digitization and real-time processing with clock frequency over 200MHz. The dead time is reduced because there's no dead-time for discharging the integration value. The analog delay line used to balance the trigger delay is removed, which will reduce the signal distortion, and in turn increase the measurement resolution. The processing in the FPGA includes digital integration, weight-sum, and dynamic pile-up correction. Simulation shows a possible working frequency of 320MHz with a low-cost FPGA, the Altera CY2C35F484C6. Energy spectrum of LSO with count rate up to 20MCPS has been studied. The energy resolution of 1, 2, 4, 8, 12, 16 and 20MCPS is 10.6%, 11.1%, 12.4%, 14.1%, 16.2%, 18.4% and 23.0%, respectively.