A miniature phoswich detector for gamma-ray localization and beta imaging

A combined γ-ray probe/β^± imaging detector was created by modification of a beta imaging intra-operative probe. This phoswich detector consists of a thin CaF₂(Eu) β^± imaging disk, coupled through a light diffuser to 7 or 19 parallelepiped high-Z scintillation crystals arranged hexagonally in columns. These elements are either 2×2×10 mm ³ or 4×4×10 mm³ LSO, GSO or EGO crystals, and act as both light guides for the imaging light and as intrinsic γ detectors. The coincidence between the CaF₂(Eu) and phoswich scintillators identifies β⁺ or true β^- events and suppresses accompanying annihilation or background γ events. The phoswich crystals are in turn coupled through optical fibers to a multi-channel PMT with positioning and discrimination electronics. Various characteristics of this novel imaging phoswich detector are investigated and presented for each of the phoswich combinations including: detector anisotropy, effects of time blocking and energy windows on phoswich imaging, intrinsic singles and phoswich spectral and spatial resolution characteristics, and phoswich imaging ability within γ background environments. The performance characteristics of the assembled prototype devices demonstrate that in surgery, this device can be used three ways: (1) rapid localization of γ emitting radionuclides with the modestly directional, self-collimated phoswich crystals; (2) high resolution β^maging or coarse (annihilation background corrupted) β⁺ imaging in singles mode; or (3) β⁺ imaging in coincidence mode with reduced γ background contamination