A MINIATURE PHOSWICH DETECTOR FOR GAMMA-RAY LOCALIZATION AND BETA-IMAGING

A combined gamma-ray probe/beta(+/-) imaging detector was created by m odification of a beta imaging intra-operative probe. This phoswich det ector consists of a thin CaF2(Eu) beta(+/-) imaging disk, coupled thro ugh a light diffuser to 7 or 19 parallelepiped high-Z scintillation cr ystals arranged hexagonally in columns. These elements are either 2x2x 10 mm(3) or 4x4x10 mm(3) LSO, GSO or EGO crystals, and act as both lig ht guides for the imaging light and as intrinsic gamma detectors. The coincidence between the CaF2(Eu) and phoswich scintillators identifies beta(+) or true beta(-) events and suppresses accompanying annihilati on or background gamma events. The phoswich crystals are in turn coupl ed through optical fibers to a multi-channel PMT with positioning and discrimination electronics. Various characteristics of this novel imag ing phoswich detector are investigated and presented for each of the p hoswich combinations including: detector anisotropy, effects of time b locking and energy windows on phoswich imaging, intrinsic singles and phoswich spectral and spacial resolution characteristics, and phoswich imaging ability within gamma background environments. The performance characteristics of the assembled prototype devices demonstrate that i n surgery, this device can be used three ways: (1) rapid localization of gamma emitting radionuclides with the modestly directional, self-co llimated phoswich crystals; (2) high resolution beta(-) imaging or coa rse (annihilation background corrupted) beta(+) imaging in singles mod e; or (3) beta(+) imaging in coincidence mode with reduced gamma backg round contamination.