High resolution position sensitive avalanche photodiode gamma ray imaging

Single photon emission computed tomography (SPECT) is a widely used medical imaging technique, both for clinical (human) and preclinical (small animal) use to obtain in vivo functional information. Recently, effort has been devoted to the development of solid state detectors for scintillation cameras because they are lighter, smaller, and more reliable than the photomultiplier tubes (PMTs) commonly used. However, a significant disadvantage of most solid state detectors is that they require pixellization to produce position resolution, which greatly increases the number of amplifier channels and the cost of a detector with a large enough area for medical imaging. New position sensitive avalanche photodiodes (PSAPDs) can produce submillimeter position resolution over a relatively wide area with a small number of amplifier channels and therefore have the potential to replace PMTs in scintillator based gamma-ray detectors for medical imaging. PSAPDs have recently demonstrated good properties for clinical SPECT applications however submillimeter spatial resolution is desirable for preclinical use. We therefore have built and tested a detector constructed with a finely segmented cesium-iodide scintillator coupled to a PSAPD. The PSAPD detector uses only five amplifier channels and yet demonstrated 0.74 mm spatial resolution over a 64 mm² active area, with good efficiency, for ^99mTc imaging. These measurements indicate that PSAPDs coupled to segmented scintillators offer excellent performance for preclinical SPECT applications.