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A high resolution BGO block detector has been developed for a positron emission tomography (PET) system. The detector consists of a newly developed compact position-sensitive photomultiplier tube (PS-PMT) and an 8(X) x 4(Y) BGO array of which element size is 2.8 mm x 6.8 mm x 30 mm. The PS-PMT has ten stages of metal channel dynodes and crossed-wire anodes in a 28 mm square x 20 mm high metal package. The performance of the PS-PMT and the block detector was evaluated in terms of applicability to PET. The coincidence timing resolution was 4.4 ns FWHM and 9.5 ns FWTM, and the energy resolution was about 30% for 511 keV [Gamma]-rays, with the PS-PMTs coupled to single BGO segments. The spatial resolution of the block detector was evaluated by measuring the detector response functions (DRFs) for each BGO segment. The average FWHM values of the DRFs were 3.0 mm in the X direction, and 6.8 mm in the Y direction. Count rate performance of the block detector was measured at different activity levels, when no distinct mispositioning in crystal coding was seen at count rates up to 100 kcps. A compact 3D-PET system dedicated to animal studies was designed by adopting the position-sensitive detectors.

In spectroscopic analysis, radiation detection, and medical application fields, portable instruments requiring high accuracy and high sensitivity are being developed. Since conventional photomultiplier tube(PMT) envelopes are made of glass and are large in size, it is difficult to downsize instruments. PMTs are mainly used for high accuracy instruments, while solid state detectors are employed for general purpose, or compact instruments. Hamamatsu recently developed the compact PMT R5600 series, which is downsized to the same dimensions as a solid state detector while maintaining the same performance, high sensitivity and high speed as the conventional PMTs.