Inter-crystal scatter identification for a depth-sensitive detector using multi-anode outputs

In conventional PET detectors, detected events are projected to a 2D position histogram using the Anger calculation for crystal identification. Inter-crystal scatter (ICS) events cause mispositioned identification of crystals because peaks projected by each crystal in the histogram are blurred. A depth-of-interaction (DOI) detector has been developed for the small animal PET scanner: jPET-RD. This DOI detector uses four-layered arrays of 32 times 32 crystals and a 256-channel multi-anode flat panel photomultiplier tube (FP-PMT). Each crystal is 1.45 mm times 1.45 mm times 4.5 mm. The FP-PMT has a large detective area and small anode pitch. We think that the FP-PMT has a good potential for tracing the scattered gamma rays in the crystals. In this study, we therefore propose a novel method for ICS event identification using the principle component analysis (PCA). The PCA is applied to multiple-anode outputs in order to discriminate photoelectric events from ICS events. The first principle component depends on the number of anode outputs deposited energy through preprocessing. Numerical simulation results show that the rate of the ICS identification by the proposed method is about 77.6 % at a 511 keV uniform irradiation. Also, by incorporating the PCA technique in our method we can identify only events which have large effect on spatial resolution in the ICS events. Our method can archive a true subtraction of ICS events from measured events.