SCINTILLATING ARRAY GAMMA-CAMERA FOR CLINICAL USE

Dedicated gamma cameras for specific clinical application are represen ting a new trend in Nuclear Medicine. They are based on Position Sensi tive Photo Multiplier Tubes (PSPMT). The main intrinsic limitation of large area PSPMT (5 '' diameter) is the photocathode glass window. Cou pling to a planar scintillation crystal strongly affects the useful ac tive area and the intrinsic spatial resolution, To overcome this limit ation at University of Rome ''La Sapienza'' was developed the first 5 '' diameter gamma camera consisting of a Hamamatsu R3292 PSPMT coupled to 50 x 50 YAP:Ce scintillating array. The array pixel size is 2 x 2 mm(2) and the overall dimension of multi-crystal is 10 x 10 x 1 cm(3). Resistive chains were used to calculate the centroid, The scintillati ng array produces a focused light spot minimising the spread introduce d by PSPMT glass window, The intrinsic spatial resolution varied betwe en 2 and 2.7 mm. The position linearity and useful active area resulte d in good agreement with intrinsic one obtained by light spot irradiat ion. The real limitation was the poor energy resolution of an individu al crystal (40%) and the poor uniformity response of PSPMT (within +/- 15%). A correction matrix was then carried out by which a 57% of total energy resolution was obtained for the whole matrix, The camera is cu rrently operating as Single Photon Emission Mammography (SPEM) and it is producing breast functional images for malignant tumour detection u sing the same geometry as standard X-ray mammography.