Optimization of crystal length and coating to improve the Depth Of Interaction spatial resolution in PET imaging

Recent researches in PET instrumentation tend to improve the reconstructed spatial resolution using the gamma ray Depth Of Interaction (DOI) information. This method, already introduced by Moses et al., requires reading both ends of a scintillating crystal to be efficient. The recorded charges obtained by the two photodetector such as Photomultiplier Tubes (PMT) or Avalanche PhotoDiodes (APD) are dependent on the depth gamma ray interaction. Braem et al. recently used the contrast calculated as the ratio between the difference of the recorded charges and their sum to improve the DOI spatial resolution. In this work, we investigate the optimization of the crystal length and coating to improve the depth of interaction spatial resolution in PET applications. For a 1.5 × 1.5 mm² LYSO:Ce crystal section read at both ends by PMT, we find that a length of 25 mm and a coating made with PMMA and 30% of TiO2 are appropriate to reach a DOI spatial resolution of 1 mm.