Detector Identification with Four BGO Crystals on a Dual PMT

The current trend towards higher resolution positron emission tomography (PET) requires the development of small but efficient detectors. This paper presents the initial characterization of a detector composed of four equally spaced, 4.5mm wide bismuth germanate (BGO) crystals coupled to the face of a Hamamatsu R1548 dual photomultiplier tube (PMT). The intrinsic optical cross talk between the two segments of the dual PMT exhibits a spatial dependence that has been exploited for crystal identification. Misidentification of crystals due to the combined effects of compton scattering of gamma rays between crystals, crystal penetration of gamma rays, and the imperfection of the optical cross talk identification scheme has been studied under various conditions. The detector pair spatial resolution on axis was measured to be 2.9mm full width at half maximum (FWHM), and the intrinsic peak efficiency was found to be higher than that of the larger detectors currently in use in the Montreal Neurological Institute's (MNI) Positome III camera.