Implementation and initial characterization of acquisition orbits with a dedicated emission mammotomograph

While contemporary clinical single photon emission computed tomography (SPECT) scanners are limited to a horizontal axis of rotation about the patient, the compact application specific emission tomography (ASET) system overcomes physical proximity limitations of clinical scanners and allows for fully three-dimensional movement in an inverted hemisphere about the pendant breast through combined variable radius of rotation (ROR) and polar and azimuthal angular positioning. With these three degrees of freedom, the ASET can provide trajectories that satisfy Orlov´s sampling criterion while maintaining a small ROR, necessary to minimize resolution degradation. One class of orbits investigated here consists of combinations of circular orbits and up to 60° arcs. Orbits are evaluated for image quality, including sampling and resolution characterization, utilizing both cold disk and cold rod emission phantoms, and quantitated contrasts and signal-to-noise ratios (SNRs) of small lesions located in a breast phantom with and without additional torso phantom backgrounds. The reconstructed cold disk and cold rod results indicate that all tested orbits in this class completely sample the volume and provide near equal resolution recovery. Furthermore, results from all orbits yielded higher contrasts and/or SNRs for the breast lesions compared with simple vertical-axis-of-rotation acquisitions, and nearly an order of magnitude better than those from uncompressed planar imaging.