Parameterization of Pb X-ray contamination in simultaneous Tl-201 and Tc-99m dual isotope SPECT

In simultaneous Tl-201 and Tc-99m dual isotope SPECT, Pb X-rays are a significant source of contamination. In order to characterize this contamination, the authors used experimentally verified Monte Carlo simulations of line sources with photon energies from 88 to 140.5 keV at various distances from the collimator. The Pb X-ray contamination response function was fitted well by a Gaussian plus an exponential function. The width of these two functions changed linearly with distance. The response was parameterized by simultaneously fitting Pb X-ray response functions at various distances with a fitting function that was determined empirically to model the distance dependence of the Gaussian and exponential components of the Pb X-ray response. The parameterized model of Pb X-rays is useful in developing methods to model Pb X-ray contamination of Tl-201 data by Tc-99m. A Pb X-ray contamination model can be used in iterative reconstruction-based cross-talk compensation for improved simultaneous Tc/Tl dual isotope imaging