Scintillation Photon Detection and Event Selection in High Resolution Positron Emission Tomography

The scintillation photon detection and event selection subsystem for the high spatial resolution Donner 600-channel positron emission tomograph is described. The tomograph spatial resolution of better than 3.0 mm, FWHM, is obtained by using 600 closely-packed bismuth germanate 3 mm thick scintillation detectors. Each detector has its own 13.5 mm diameter photomultiplier and event selection channel, consisting of two fast pulse amplifiers, a charge integrator, a differential pulse height discriminator and precision time delay for event strobing. The event selection channel is capable of starting a timing cycle from the first photoelectron emitted from the photocathode. It is also capable of discriminating between true events and noise and of eliminating events occurring simultaneously in two adjacent channels. Adjustments of the event strobing time and two discriminator levels are performed by a computer.