Design of a depth of interaction (DOI) PET detector module

A method to determine depth of interaction (DOI) from a PET detector module is described and evaluated. The basic element of the DOI detector module is a two crystal detector unit. The hypothesis is that by controlling how light is shared between two crystals (A and B) DOI information can be extracted from the ratio of light collected using simple Anger logic [(A-B)/(A+B)]. The interface between crystals is designed so that a significant amount of light is shared when a photon interacts near the front face of a crystal and very little light is shared when an interaction occurs near the back of a crystal. The effects of surface treatment (e.g., polished, roughened) and optical coupling compounds are investigated. BGO, GSO and LSO detector units have been evaluated. A DOI uncertainty of ~6 mm was attained for the front section (~4 mm) of a 2×2×20 mm LSO detector unit. A method to decode a 64 crystal detector module (32 detector units) using a 16 channel multi-anode photomultiplier tube is described