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 d iscussed using phoswich detectors. The detector design is based on two laye rs of scintillation crystals in the z-axis with different physical properti es, such as light decay time or light yield. This makes it feasible to assi gn the depth of interaction (DOI) information in order to be able to correc t 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 des ign [1]. In this work we discuss the possibility of separating events from the two different layers in the time domain using pulse shape discriminatio n or in the energy domain using pulse height discrimination. Furthermore, w e have investigated the feasibility of interdetector scatter suppression us ing 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 heigh t discrimination and does make a interdetector scatter detection feasible.