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 2×2 array or to a position sensitive photomultiplier tube. Each stage of the crystal block consists of four elements in a 2×2 array. Each scintillation event is mapped in a two dimensional (2D) distribution through the relative ratio of the output signals of the PMTs. The 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 gamma-rays incidence