ULTRA-Fast wiener filter based crystal identification algorithm applied to the LabPETTM phoswich detectors

摘要

A Wiener filter based crystal identification (CI) algorithm achieving excellent discrimination accuracy (˜98%) was recently proposed for identifying LYSO and LGSO crystals in phoswich detectors coupled to an Avalanche Photodiode. Such detectors are used in the LabPETTM, an all-digital positron emission tomography (PET) scanner for small animal imaging recently developed in Sherbrooke. This algorithm was based on evaluating the scintillation decay constant and gain (αl and βo parameters, respectively) of events sampled at 45 MSPS and discriminating crystals by thresholding the al spectra. The input gain was not considered in the CI process even if it must be computed. We propose a 2-fold faster CI approach which also takes into consideration the input gain coefficient of each crystal. The new algorithm incorporates the DAQ chain model in the Z domain- to each individual crystal model evaluated in a Wiener filter calibration process. The identification is performed by evaluating a single parameter -compared to two parameters in previous Wiener CI algorithm-characterizing the percentage of each crystal gain contribution in the event signal. The CI algorithm demonstrated a discrimination rate accuracy 98.5% for LYSO-LGSO and 99% for LSO-GSO crystals in phoswich arrangement for 511 keV photopeak. Although a calibration is required, initial implementation of the algorithm in a 400 MHz clocked FPGA can process up to 15 Mevents/sec.