A POSITRON EMISSION TOMOGRAPH DESIGNED FOR 3 4 MM RESOLUTION/

Two factors of the design for a positron tomograph affect the magnitud e of the tomograph spatial resolution: the gamma ray detector width an d the analogue measurement of the scintillator location. in the tomogr aph design reported here the analogue measurement is eliminated and th e detector transaxial width factor is reduced to 3/4 mm, The analogue measurement is eliminated by transmitting the scintillation light from each individual scintillator through optical fibers to four photo-mul tipliers (PMT's); the identities of the PMT's then provide a digital a ddress for the scintillation location. Plastic scintillators are used to provide enough scintillation light for transmission through the opt ical fibers. Bonuses from the use of plastic scintillators are first, the reduction of the scintillator dead time to about 10 nsec, second, a large reduction of cross-talk between neighboring scintillators, thi rd, the reduction of resolution loss from off-axis gamma rays and, fou rth, the ability to sample the axial image at one-eighth the axial res olution distance of 2.5 mm. The designed tomograph incorporates 20 rin gs. Two of the 32 tomograph 20-ring modules have been constructed to m easure the resolution and other characteristics of the tomograph.