Absolute quantitation of myocardial activity in phantoms

The authors have developed a new technique for compensating myocardial SPECT images for partial volume errors using coregistered X-ray CT images. The CT-derived myocardial mass defines a template that can be assigned unit activity and mathematically projected with a realistic physical model of the radionuclide imaging process including non-ideal collimation and incorporating an object-specific attenuation map from CT. The template projections then are reconstructed using the SPECT reconstruction algorithm to obtain a pixel-by-pixel partial-volume correction for the myocardial SPECT image. Experiments in phantoms demonstrate that this technique substantially improves the absolute quantitation of myocardial radionuclide concentration, reducing the accuracy error from approximately 50% to less than 8%. This method also can by used for correcting background effects such as "spill-in" of background counts from uptake in the liver.