A comparison of Gd-153 and Co-57 as transmission sources for simultaneous TCT and Tl-201 SPECT

In this study we investigated the potential of Gd-153 and Co-57 as transmission sources. Since both of these sources have higher energy photopeaks higher than that of the predominant Tl-201 photons, they will result in contamination of the emission data. The amount of contamination and the ease of compensating for it are important factors in selecting an isotope for the transmission source. These factors were investigated and, based on these studies, we conclude that both isotopes result in a level of contamination that is significant in comparison to typical Tl-201 emission count levels. While Gd-153 results in approximately 50% more contamination of the emission data than Co-153, the object dependence of the contamination for both isotopes is such that contamination compensation will be difficult. In fact, compensation may be somewhat easier for Gd-153. As a result, selection of one of these isotopes may be based on other considerations such as cost and usability with other emission isotopes