Characterization of a Small-Animal High-Purity Germanium SPECT System

Attempts have been made to use segmented planar germanium detectors for nuclear medicine imaging since the early 1970's, but have been hindered by difficulties with detector fabrication, cumbersome electronics, and limited computing power, in addition to the need for a bulky liquid nitrogen dewar to achieve required operating temperatures. Advances in electronics in addition to compact mechanical cooling systems have made high-purity germanium (HPGe) systems appealing for biomedical applications. We are developing a small-animal single-photon emission computed tomography (SPECT) system based on an HPGe double-sided strip detector that is 90 mm in diameter, 10 mm thick, and comprised of two sets of 16 orthogonal strips that are each 4.75 mm wide with a 5 mm strip pitch. The detector's energy resolution is < 1% FWHM at 140 keY, and the spatial resolution is approximately 1.5 mm FWHM. The system is equipped with a single-pinhole collimator with a 1-mm diameter and a 70-degree opening angle with a focal length variable between 4.5 and 9 cm. Preliminary phantom images from a bench-top HPGe SPECT system and from an integrated HPGe-SPECT-CT system are shown.