Preliminary tests of a high performance LaBr$_{3}$ gamma imager for small animals .

A novel medical gamma ray imager comprised of an array of four Hamamatsu H9500 position sensitive photomultiplier tubes (PSPMT) coupled directly to a single slab of LaBr$_{3}$ scintillator has been designed and tested. The phototube-scintillator array, fabricated by Bicron-St. Gobain Inc (France), is the first such device made. A special resistive readout array designed here permits signals from the 256 anode pads in each PSPMT to be read out on only 16 data lines. Preliminary tests of uniformity, sensitivity and resolution will be described along with initial images of mice obtained with this new device.