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 for cardiac SPECT without mechanical motion of the transmission sources. We conducted both theoretical and experimental investigations of cone-beam transmission imaging. 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 they move during scanning. We determined experimentally that it was necessary to separate the point-sources axially so that the reconstructed attenuation maps would axially span the heart region. The dual-planar-circular-orbit cone-beam iterative ML-EM reconstruction was used to estimate the attenuation maps. Physical phantom studies and one study with a volunteer have been performed to validate the reconstruction algorithm and evaluate acquisition protocols. We have determined that we can obtain truncation-free attenuation maps covering an axial extent of 16.8 cm with 2 minutes of acquisition time.