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

We have developed a method of effecting depth-of-interaction sensitivity fo r PET detectors. It exploits a significant difference in the index of refra ction between adjacent scintillator segments and the compound optically cou pling them, to induce discrete and resolved photopeak pulse heights dependi ng on the segment of interaction of gamma-rays. The approach was put to a f irst 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 comprisi ng three segments along their longitudinal axis. Measurements of their abso lute pulse height responses when irradiated by 511 keV photons are presente d and show resolved peaks for photoelectric interactions occurring in each longitudinal segment as desired. For the second of the above prototypes, th e lowest(highest) of these peaks is measured to correspond to a pulse heigh t of 335(559) photoelectrons with full-width-at-half-maximum resolution of 28%(12%). The expected performances of PET detector units comprising a plur ality of such segmented crystals is also discussed.