Design and experimental validation of a quantitative myocardial 201Tl SPECT system

We have developed a quantitative SPECT system, and evaluated its potential for quantitative assessment of biophysiological functions, in the myocardium particularly, with ²⁰¹Tl. Our approach included the development of a transmission system that provides accurate attenuation μ maps, and the implementation of ordered-subset EM reconstruction with transmission data-based attenuation correction in addition to scatter correction using the transmission-dependent convolution subtraction (TDCS) technique. The transmission system was designed using Monte Carlo simulation to minimize the scatter in the transmission projection data while keeping sensitivity loss to a minimum, and was attached to an opposing two-head gamma camera fitted with parallel beam collimators. Observed μ values agreed with the theoretical expected values in both phantoms and a human thorax. Phantom experiments with ²⁰¹Tl also demonstrated that, with corrections for both attenuation and scatter, the observed images were directly proportional to the actual radioactivity distribution for various phantom geometries. Attenuation correction without scatter correction improved images in deep structure, but resulted in significant artifacts in the chest phantom in addition to dependency of observed radioactivity concentrations on the diameter of cylindrical phantoms. Absolute quantitation of biophysiological functions, which is well established in PET, is shown to be feasible using SPECT, if both quantitative attenuation and scatter corrections are employed