MYOCARDIAL PERFUSION IMAGING WITH A COMBINED X-RAY CT AND SPECT SYSTEM

We evaluated a novel combined x-ray CT and SPECT medical imaging syste m for quantitative in vivo measurements of Tc-99m-sestamibi uptake in an animal model of myocardial perfusion. Methods: Correlated emission- transmission myocardial images were obtained from 7- to 10-kg pigs. Th e x-ray CT image was used to generate an object-specific attenuation m ap that was incorporated into an iterative ML-EM algorithm for reconst ruction and attenuation correction of the coregistered SPECT images. T he pixel intensities in the SPECT images were calibrated in units of r adionuclide concentrations (MBq/g), then compared against in vitro Tc- 99m activity concentration measured from the excised myocardium. In ad dition, the coregistered x-ray CT image was used to determine anatomic al boundaries for quantitation of myocardial regions with low perfusio n, Results: The accuracy of the quantitative measurement of in vivo ac tivity concentration in the porcine myocardium was improved by object- specific attenuation correction. However, an additional correction for partial volume errors was required to retrieve the true activity conc entration from the reconstructed SPECT images. Conclusion: Accurate ab solute SPECT quantitation required object-specific correction for atte nuation and partial volume effects. Additional anatomical information from the x-ray CT image was helpful in defining regions of interest fo r quantitation oi the SPECT images.