LSO PET/CT Pico performance improvements with ultra Hi-Rez option

Abstract

Factors which may improve image quality in PET systems include spatial resolution and scatter fraction. By reducing the energy window, the size of the crystal elements and thickness, the spatial resolution and scatter fraction can be improved. The LSO PET/CT Pico system, which consists of an 8times8 crystal array per detector block, operates on an energy window of 400 to 650 keV. The new LSO PET/CT Hi-Rez system includes a 13times13 crystal array per detector block, a decrease of 20% in crystal thickness and a narrower energy window of 425 to 650 keV. Improvements in spatial resolution and in scatter fraction are therefore expected. Although a reduction in sensitivity may result, the image quality of the system should not be affected. In order to evaluate the overall performance of the new system, tests from the NEMA NU 2-2001 protocol were conducted on LSO PET/CT Pico and Hi-Rez systems, and their results were compared. The Hi-Rez system presented an improvement in spatial resolution of 27% at 1cm and 28% at 10 cm. The scatter fraction on the Pico and Hi-Rez systems indicate average values of 41% and 34% respectively, equivalent to a decrease of 17% for the Hi-Rez system. The sensitivity of the Hi-Rez system diminished by 22% and changes of less than 4% were observed for the peak NEC rate. The improvements in spatial resolution and scatter fraction obtained in our measurements may create significant advances in the physician's ability to detect small lesions in PET/CT images