SPECT breast imaging using more nearly complete orbits and combined pinhole-parallel-beam collimation
Two novel pinhole orbits for SPECT breast imaging are investigated using noise-free analytically simulated projection data. The two orbits are designed to more nearly completely sample the breast region while also maintaining close proximity of the pinhole to the breast. The two orbits involve the same trajectory but different angular orientations for the pinhole. For both orbits the pinhole traverses two half circles, which from an anterior perspective thus appear to have the shape of an "X". The orbits differ in that in one case the pinhole is tilted toward a single point throughout the orbit whereas in the other case it is untilted. It is found that both orbits remove the distortions characteristic of purely transverse, single-half-circle orbits. Also investigated is the use of parallel-beam collimators on the remaining cameras of triple-headed SPECT scanners. It is found that these additional parallel-beam measurements greatly improve estimates of torso activity. Determining whether parallel-beam measurements improve estimates of breast activity will require additional studies involving clinical levels of noise in the projection data.
