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 bio-physiological functions in the myocardium particularly with ²⁰¹Tl. Our approach included development of a transmission system that provides accurate attenuation μ maps, and 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 loss of sensitivity minimal, and was attached to an opposing 2-head gamma camera fitted with parallel beam collimators. Observed μ values agreed quantitatively well with the theoretical expected values in both phantoms and human thorax. Phantom experiments with ²⁰¹Tl also demonstrated that, with both corrections for attenuation and scatter, 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 bio-physiological functions, which is well established in PET, is shown to be feasible using SPECT, if both quantitative attenuation and scatter corrections are employed