Quarter-Trio Mapping Electronics Readout Scheme for APD Block Detector in PET

Quarter-trio mapping (QTM) is a new detector readout scheme for avalanche-photodiode (APD) block detectors in positron emission tomography (PET). This design simplifies the detector readout electronics, and more efficiently utilizes APDs in detector blocks hence reducing cost. With the QTM design, eight APDs are positioned in each detector block. The APDs are positioned in such a way that 12 times 12 crystal elements each of 2.5 mm times 2.5 mm times 20 mm can be identified. Moreover, we developed an efficient electronics readout QTM scheme in which only four output channels instead of eight are sent to main electronics to readout eight APD signals. Compared with nine APDs in a 3 times 3 array setup, initial results from eight APDs in QTM readout shows that the 12 times 12 crystal block can be well identified. The timing resolution (crystal block of 12 times 12 elements vs. single plastic scintillator) is about 2.95 ns vs. 2.84 ns from a 3 times 3 crystal array. More experiments are on going to further improve the energy and timing performance.