A practical reconstruction algorithm for multifocal cone beam SPECT

Multifocal cone-beam collimation has been proposed for cardiac SPECT (single photon emission computed tomography) imaging to increase sensitivity over the heart without truncation of activity distribution in the chest. An accurate and efficient algorithm has been derived for multifocal fan-beam SPECT reconstruction and has been extended to multifocal cone-beam SPECT reconstruction. In the multifocal fan-beam algorithm, the projection data were weighted and filtered for every discrete distance from the detector plane, and then the filtered data were interpolated for a given image point in the backprojection. Thus, the backprojection was carried out only once at a projection view. The multifocal cone-beam algorithm was evaluated using the simulated 3-D Defrise slab phantom and the 3-D Shepp-Logan head phantom. In addition, a preliminary study to evaluate the multifocal cone-beam collimator was performed, in which effects of the focal length distribution and the radius-of-rotation (ROR) on the reconstructed image quality were examined. The image quality was improved with decreased ROR