Non-uniform attenuation correction using simultaneous transmission and emission converging tomography

Photon attenuation in cardiac single photon emission computed tomography (SPECT) is a major factor contributing to the quantitative inaccuracy and the decrease in specificity of lesion detection. A measured map of the attenuation distribution was used in combination with iterative reconstruction algorithms to accurately compensate for the variable attenuation in the chest. The transmission and emission data were acquired simultaneously using a multidetector, fan-beam collimated SPECT system with a transmission line source (Tc-99m) precisely aligned at the focal line opposite one of the detectors and of a different energy than the emission source (Tl-201). The contamination of transmission data by the high-energy photopeaks of Tl-201 was removed based on measurements from emission-only acquisition detectors. An algorithm was derived to eliminate scatter of Tc-99m transmission photons into the lower-energy Tl-201 window of all three detectors. Results are given for both phantom and patient studies.