Single photon emission imaging by position sensitive PMT

Position Sensitive Photo Multiplier Tube (PSPMT) represents a strong technological improvement for Nuclear Medicine imaging. Over the last 10 years Hamamatsu has developed a number of PSPMTs with different shapes and sizes, from 1 in. square up to more recent prototype of 8 in. diameter. The position is continuously detected by centroid method and spatial resolution represents its statistical uncertainty. By coupling PSPMTs to scintillating arrays it was possible to push PMTs near their intrinsic limit. A number of scintillating crystals arranged in a matrix were tested such as: YAP : Ce, NaI(Tl), CsI(Tl) and CsI(Na) with different pixel size (from 0.3×0.3 mm2 to 2×2 mm2) with overall dimension from 4×4 cm2 up to 11 cm diameter. A number of applications in Nuclear Medicine were performed, such as miniature gamma cameras for radiopharmaceutical investigations on little animals where sub-millimeter spatial resolution values were carried out. More recently, the first prototype of dedicated gamma camera for scintimammography has been developed for small cancer detection in the breast.