AVALANCHE PHOTODIODES FOR POSITRON EMISSION TOMOGRAPHY

POSITRON EMISSION TOMOGRAPHY IS A NONINVASIVE NUCLEAR IMAGING TECHNIQUE WHICH IS BECOMING AN IMPORTANT FUNDAMENTAL TOOL FOR BOTH CLINICAL DIAGNOSIS AND MEDICAL RESEARCH. THE HEART OF THIS INSTRUMENT IS A LARGE ARRAY OF SCINTILLATOR-PHOTOMULTIPLIER TUBE DETECTORS. THE AVAILABILITY OF A COMPACT SOLID STATE SENSOR TO REPLACE THE VACUUM TUBE DETECTORS IN THIS ARRAY WOULD SIGNIFICANTLY REDUCE THE SIZE AND COMPLEXITY OF PET CAMERAS. A SENSOR WHICH HAS THE POTENTIAL TO MEET THE DEMANDING REQUIREMENTS OF POSITRON EMISSION TOMOGRAPHY IS THE AVALANCHE PHOTODIODE. THIS UNIQUE DEVICE HAS A HIGH INTERNAL GAIN WHICH, WHEN COUPLED TO A SCINTILLATOR CRYSTAL, CAN RESULT IN A SENSITIVE AND SMALL DETECTOR. HOWEVER, PRESENT AVALANCHE DEVICES ARE NOT SUITABLE BECAUSE OF EXCESSIVE NOISE AND LOW QUANTUM EFFICIENCY AT WAVELENGTHS EMITTED BY THE BISMUTH GERMANATE SCINTILLATOR CRYSTALS TYPICALLY USED IN PET CAMERAS. THIS PROGRAM WILL INVESTIGATE WAYS TO REDUCE THE NOISE AND INCREASE THE DEVICE SENSITIVITY. THE RESULTS WILL BE A COMPACT DEVICE SUITABLE FOR USE IN POSITRON TOMOGRAPHY.