SPECT breast imaging combining horizontal and vertical axes of rotation

Vertical axis of rotation (VAOR) geometries in which the patient lies prone with one pendulous breast, and a gamma camera orbits the breast have been proposed for SPECT breast imaging. Dedicated VAOR systems are advantageous for several reasons. They allow for minimal radius of rotation around the breast, which improved resolution-sensitivity trade-offs, but the torso is not yet viewed at enough angles to estimate torso activity. Also, VAOR geometries may involve a tilt to scan for tumors near the chest wall. These tilted VAOR projections may be insufficient to establish even breast activity alone. The authors investigated the utility of designing VAOR systems to function inside some general-purpose horizontal axis of rotation (HAOR) scanner, with the HAOR scanner orbiting a 192° angular range posteriorly, alleviating the insufficient-data problems. The authors simulated the expected projection data from 6 lesions in the breast and axilla, considering the contribution from background activity in the torso. The data were then reconstructed considering HAOR only, VAOR-only and combined HAOR-VAOR orbits and compared with the known activity concentration distribution. Substantial improvement in the noise-vs-bias curve was observed in the chest wall near the breast, an important and otherwise difficult region to image