Segmented LSO crystals for depth-of-interaction encoding in PET

We have developed a method of effecting depth-of-interaction sensitivity for PET detectors. It exploits a significant difference in the index of refraction between adjacent scintillator segments and the compound optically coupling them, to induce discrete and resolved photopeak pulse heights depending on the segment of interaction of gamma-rays. The approach was put to a first experimental test by manufacturing two prototypes with LSO crystals of dimensions 4 x 4 x 30 mm and 2.5 x 2.5 x 20 mm respectively, each comprising three segments along their longitudinal axis. Measurements of their absolute pulse height responses when irradiated by 511 keV photons are presented and show resolved peaks for photoelectric interactions occurring in each longitudinal segment as desired. For the second of the above prototypes, the lowest(highest) of these peaks is measured to correspond to a pulse height of 335(559) photoelectrons with full-width-at-half-maximum resolution of 28%(12%). The expected performances of PET detector units comprising a plurality of such segmented crystals is also discussed.