High spatial resolution measurement of depth-of-interaction of a PET LSO crystal

A new type of experimental technique to investigate the depth-of-interaction (DOI) dependence in small scintillator elements designed for high-resolution animal PET is tested. An Oxford-type nuclear microprobe was used to irradiate a lutetium oxyorthosilicate (LSO) crystal (2×2×10 mm3) with a highly focused, (few micrometers diam.), 2 MeV He+ beam. Pulse height spectra from a PMT attached to one end of the LSO crystal were collected in list mode. By scanning the beam over the crystal high-resolution 2D-images are generated and thus the DOI effect in the scintillator could be investigated. The obtained results of the overall DOI dependence confirm previous findings using γ-rays. Since the present experimental setup allows obtaining data with several orders of magnitude better spatial resolution than with collimated γ-beam, the method can be applied for variety of problems where high spatial resolution is required.