Implementation and initial characterization of acquisition orbits about a pendulous breast using the ASET system

The goal of the Application Specific Emission Tomography (ASET) system is to image small (/spl les/1 cm diameter) lesions and lesions of low activity uptake in a pendulous breast reference frame with high contrast and signal-to-noise ratio (SNR). While contemporary clinical SPECT scanners are limited to a horizontal axis of rotation about the patient, the compact ASET system overcomes physical proximity limitations of clinical scanners and allows for fully 3D movement in an inverted hemisphere about the breast through combined variable radius of rotation (ROR), polar and azimuthal angular positioning. With these three degrees of freedom, the ASET can traverse orbits that satisfy Orlov's sampling criterion while maintaining a small ROR, necessary to minimize resolution degradation. One class of orbits consisting of combinations of simple circular orbits and up to 60/spl deg/ arcs that can be implemented for the ASET system includes tilted parallel beam (TPB), circle-plus-arc, incomplete moustache, incomplete circular orbit, and spiral-plus-arcs. Each collects sufficient or nearly sufficient data for activity reconstruction of the pendant breast volume. Initial ordered subsets expectation maximization reconstructed ASET data acquired with the TPB orbit at various tilt angles yields insufficiently sampled images, since TPB at polar tilt angles >0/spl deg/ does not satisfy Orlov's criteria. Artifacts present in these images are partly due to cardiac and hepatic contamination and also incomplete sampling, which the more complete orbits are designed to overcome. Each orbit is evaluated for image quality, including sampling and resolution characterization with cold disk and cold rod phantoms, and quantitated SNR and contrast of small lesions located in a breast with additional torso backgrounds.