Experience with a High Efficiency Positron Emission Tomograph

Based on a series of experiments designed to maximize detection efficiency while maintaining adequate spatial resolution, a positron emission tomograph has been constructed. It comprises 160 Bismuth Germanate crystals 10 × 25 × 45 mm3 closely packed on a ring, 26 cm in radius. A unique feature of our design is that adjacent crystals are not separated from each other by inserts. Preliminary experiments have demonstrated that the spatial resolution is slightly degraded (of the order of 10% of the FWHM) when 2 mm thick Tungsten inserts are omitted. We suggest that thin inserts add little to the spatial performance while their omission can increase the detection efficiency by as much as 20% depending on the relative sizes of the crystals and the inserts.