New generation position-sensitive PMT for nuclear medicine imaging

Recently, Hamamatsu has developed a new dynode structure in a position-sensitive photomultiplier tube (PSPMT) based on metal channel technology, producing a very focused charge distribution. Hamamatsu R5900-C8 is the first metal channel dynode PSPMT with a crossed wire anode. The outline dimension is 28 × 28 × 20 mm3 with an active area of 21 × 22 mm2 and four wire anodes (4X + 4Y). A weighted summing device was realised to calculate the charge distribution centroid where each anode was directly connected to a preamplifier and amplifier. Tests of position linearity, energy response and spatial resolution were carried out coupling the PSPMT to an NaI(Tl) planar crystal and to a YAP:Ce scintillation array. To test the influence of charge spread on position linearity, the photocathode was irradiated by a light spot with 1 mm of aperture size. Position non-linearity resulted when a scintillating array with 1 × 1 mm2 pixel size was coupled to PSPMT. On the contrary, increasing the spread of charge distribution by a planar scintillation crystal, a good linearity response was obtained. Impressive spatial resolution values were obtained from the YAP:Ce scintillating array. They ranged between 0.5 and 0.2 mm irradiating the crystals by 57Co and 137Cs source, respectively.