The estimation of attenuation maps for cardiac-SPECT using cone-beam imaging of high-energy photons through parallel-hole collimators

The goal of these investigations was to develop a rapid transmission imaging method for estimating truncation-free attenuation maps in cardiac SPECT without mechanical motion of the transmission sources. We conducted both theoretical and experimental investigations of cone-beam transmission imaging. The theoretical studies were conducted to evaluate the various gantry configurations and determine the axial extent of the asymmetric cone-beam region which could be reconstructed without significant artifacts. The experimental studies were performed using the two Ba-133 point sources of the Beacon scanning point-source transmission system on our Philips Medical Systems IRIX SPECT system. We obtained from the manufacturer the ability to position the point sources at any fixed location axially along the path that they move during scanning. We determined experimentally that it was necessary to separate the point sources axially so that the reconstructed attenuation maps would span the heart region axially. A dual-planar-circular-orbit cone-beam iterative reconstruction algorithm was developed and used to estimate the attenuation maps. Physical phantom experiments and volunteer acquisitions were performed to validate the theoretical predictions, and to investigate imaging parameters that affect the accuracy and axial extent of reconstruction. We determined that truncation-free attenuation maps covering an axial extent of 15.9 cm were possible with less than 2 min of acquisition time.