Depth encoding multicrystal detectors for PET

A detector unit having a depth encoding scheme was designed and an experimental study has been performed to test the new idea for a positron camera detector. The detector unit consists of a multistage rectangular block of scintillation crystals optically coupled at the bottom face to four photomultiplier tubes (PMTs) in a 2x2 array or to a position sensitive photomultiplier tube. Each stage of the crystal block consists of four elements in a 2x2 array. Each scintillation event is mapped in a two dimensional (2D) distribution through the relative ratio of the output signals of the PMTs. Three dimensional location in the detector unit projects into the 2D map so that four top crystals correspond to four innermost regions in the map, and the four bottom crystals facing the PMTs correspond to four outermost regions. With appropriate light control in such a crystal block of Gd2SiO5:Ce coupled to four PMTs, good positioning performance to encode the depth-of-interaction was obtained for Cs-137 consists of a multistage rectangular gamma-rays incidence.