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 keV, and the spatial resolution is approximately 1.5 mm FWHM. The system is equipped with a single-pinhole collimator with a 1mm 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.