A comparison of Gd/Tc versus Tc/Tl simultaneous transmission and emission imaging using both single and triple detector fan-beam SPECT systems

In this study, the authors compare the accuracy of the transmission and emission maps, produced using both a Gd/Tc and a Tc/Tl transmission-emission source combination. In both cases, the transmission and emission data are acquired simultaneously. This results in contamination of the data acquired in the lower energy window by events from the higher energy isotope. The authors use standard methods to correct for this contamination when using a Gd/Tc combination and propose a new method for use with the Tc/Tl combination. The Tc/Tl combination yields more accurate transmission images than the Gd/Tc combination. However, when a single factor is used to scale the attenuation coefficients measured using the transmission source to those appropriate for the emission isotope/energy, the resulting error in the attenuation map used for attenuation correction is larger for the Tc/Tl combination than for the Gd/Tc combination. For this study, neither combination yielded emission maps which were significantly superior (in terms of reconstructed emission ratios) to the other.>