In recent years it has been shown that PET is capable of obtaining in vivo metabolic images of small animals. These serve as models to study the development and progress of diseases within humans. Imaging small animals requires not only image resolution better than 2mm, but also high sensitivity in order to image ligands with low specific activity or radiochemical yields. Towards achieving these goals, we have developed a discrete 2 /spl times/ 2 /spl times/ 10mm/sup 3/ GSO Anger-logic detector for use in a high resolution, high sensitivity, and high count-rate animal PET scanner. This detector uses relatively large 19mm diameter photomultiplier tubes (PMT), but nevertheless achieves good crystal separation and energy resolution. The scanner (A-PET) has a port diameter of 21 cm, transverse field-of-view of 12.8 cm, axial length of 12.8 cm, and operates in 3D volume imaging mode. The absolute coincidence sensitivity is expected to be 2.3% for a point source. Due to the use of large PMTs in an Anger design, the encoding ratio (number of crystals/PMT) is high, which reduces the complexity and leads to a cost-effective scanner. Simulation results show that this scanner can achieve NEC rates significantly higher than many of the current generation of animal scanners for small cylindrical phantoms due to its high sensitivity and reduced deadtime. The scanner construction was recently completed and initial calibrations are currently in progress.