Experimental estimates of the absolute sensitivity of a small animal PET scanner with depth-of-interaction capability

The authors are constructing a depth-of-interaction (DOI) capable small animal PET scanner that will consist of 18 LGSO/GSO DOI modules arranged around a 11.8 cm diameter ring. These 18 modules will be grouped together electronically by 3´s forming 6 sectors. Two of these sectors; have been fabricated, placed opposite one another on the ring and operated in time coincidence with the data acquisition system to be used in the final device. Since a 2-sector partial ring provides the first opportunity to obtain experimental measurements of absolute central (¹⁸F) point source sensitivity (ACPS), an important design parameter for this system, the authors sought to measure this quantity as a function of energy window at the earliest stage of construction. Measured ACPS values extrapolated to the full, 6-sector ring decreased as window width decreased: from 1034 cps/Ci or 2.8% (no energy window) to 594 cps/Ci or 1.6% (250-650 keV energy window) to 375 cps/Ci or 1.0% (400-650 keV energy window). These early results suggest that the final system will possess an ACPS substantially higher than several recently described small animal PET scanners