THE DESIGN OF AN ANIMAL PET - FLEXIBLE GEOMETRY FOR ACHIEVING OPTIMALSPATIAL-RESOLUTION OR HIGH-SENSITIVITY

We present the design of a positron emission tomograph (PET) with flex ible geometry dedicated to in who studies of small animals (TierPET). The scanner uses two pairs of detectors, Each detector consists of 400 small individual yttrium aluminum perovskite (PAP) scintillator cryst als of dimensions 2x2x15 mm(3), optically isolated and glued together, which are coupled to position-sensitive photomultiplier tubes (PSPMT' s). The detector modules can be moved in a radial direction so that th e detector-to-detector spacing can be varied, Special hardware has bee n built for coincidence detection, position detection, and real-time d ata acquisition, which is performed by a PC. The single-event data are transferred to workstations where the radioactivity distribution is r econstructed. The dimensions of the crystals and the detector layout a re the result of extensive simulations which are described in this rep ort, taking into account sensitivity, spatial resolution and additiona l parameters like parallax error or scatter effects, For the three-dim ensional (3-D) reconstruction a genuine 3-D expectation-maximization ( EM)-algorithm which can include the characteristics of the detector sy stem has been implemented, The reconstruction software is flexible and matches the different detector configurations, The main advantage of the proposed animal PET scanner is its high flexibility, allowing the realization of various detector-system configurations. By changing the detector-to-detector spacing, the system is capable of either providi ng good spatial resolution or high sensitivity for dynamic studies of pharmacokinetics.