Helical SPECT using axially truncated data

In this study, use of a helical orbit in performing a long object SPECT scan with parallel, cone, fan, rotated fan, varying focal-length cone, divergent, and astigmatic collimators is proposed. Sufficient-data scanning helical orbits for these collimation geometries are developed. Both a single-detector system and a multi-detector system are considered. In order to verify the authors´ orbit design requirement, the iterative ML-EM algorithm is used to reconstruct images of a long Defrise phantom. The phantom height is five times the height of the detectors. Computer simulations are performed and exact reconstructions are obtained. The proposed sufficient helical orbit pitch will facilitate performing whole body SPECT and PET scans that demand an exact reconstruction.