Advantages using pulse shape discrimination to assign the depth of interaction information (DOI) from a multi layer phoswich detector

Recently new high resolution brain PET and PET/SPECT tomographs have been discussed using phoswich detectors. The detector design is based on two layers of scintillation crystals in the z-axis with different physical properties, such as light decay time or light yield. This makes it feasible to assign the depth of interaction (DOI) information in order to be able to correct for spatial degradation in PET or to operate the detector in PET or SPECT mode. The pixel DOI detectors are cost effectively arranged in a block design [1]. In this work we discuss the possibility of separating events from the two different layers in the time domain using pulse shape discrimination or in the energy domain using pulse height discrimination. Furthermore, we have investigated the feasibility of interdetector scatter suppression using pulse shape discrimination. The measurements have been done using a LSO/LSO high resolution PET detector, a LSO and GSO crystal in coincidence and a NaT(Tl)/LSO combined PET/SPECT detector. The investigations show, that che pulse shape discrimination technique has a significant higher identification probability compared to the pulse height discrimination and does make a interdetector scatter detection feasible.