Performance characteristics of Positologica III: a whole-body positron emission tomograph.

A whole-body, multislice positron emission tomograph, Positologica III, has been constructed based on a sampling method "positology." The scanner consists of four continuously rotating detector rings with 192 bismuth germanate (BGO) crystals (12 X 24 X 24 mm) arranged at irregular intervals along each ring, providing seven tomographic images at 16 mm intervals simultaneously, for a total axial coverage of 12 cm. The patient aperture is 54 cm in diameter, and the field of view is 40 cm in diameter and 12 cm in depth. Newly developed dual photomultiplier tubes are used with 12 mm wide BGO crystals to provide a packing ratio of 0.894. The spatial resolution at the center of the field is 7.6 mm full width at half maximum, and 2.5 mm hot spots were delineated in the Derenzo phantom. The sensitivity for a 20 cm diameter cylindrical phantom is 34.2 and 52.2 kcps/muCi/ml for true planes and cross planes, respectively. In clinical studies the posterior papillary muscle of the heart was visualized in the myocardial scan, and the lung behind the pulmonary artery was also visualized in the pulmonary ventilation scan. These results suggest that our machine has sufficient resolution for most of the clinical studies of the body.