Performance characteristics of a compact position-sensitive LSO detector module

We assembled a compact detector module comprised of an array of small, indi vidual crystals of lutetium oxyorthosilicate:Ce (LSO) coupled directly to a miniature, metal-can, position-sensitive photomultiplier tube (PSPMT). We exposed this module to sources of 511-keV annihilation radiation and beams of 30- and 140-keV photons and measured spatial linearity; spatial variatio ns in module gain, energy resolution, and event positioning; coincidence ti ming; the accuracy and sensitivity of identifying the crystal-of-first-inte raction at 511 keV; and the effects of intercrystal scatter and LSO backgro und radioactivity. The results suggest that this scintillator/phototube com bination should be highly effective in the coincidence mode and can be used , with some limitations, to image relatively low-energy single photon emitt ers. Photons that are completely absorbed on their first interaction at 511 keV are positioned by the module at the center of a crystal. Intercrystal scatt er events, even those that lead to total absorption of the incident photon, are placed by the module in a regular "connect-the-dot" pattern that joins crystal centers, As a result, the accuracy of event positioning can be mad e to exceed 90%, though at significantly reduced sensitivity, by retaining only events that occur within small regions-of-interest around each crystal center and rejecting events that occur outside these regions in the connec t-the-dot pattern.