TY - JOUR T1 - A Monte Carlo approach to estimating the system matrix for quantitative human cardiac SPECT JF - Journal of Nuclear Medicine JO - J Nucl Med SP - 1500 LP - 1500 VL - 50 IS - supplement 2 AU - Anne Sauve AU - Bryan Reutter AU - Grant Gullberg Y1 - 2009/05/01 UR - http://jnm.snmjournals.org/content/50/supplement_2/1500.abstract N2 - 1500 Objectives We develop here a method for correcting for attenuation and scatter to obtain quantitative myocardial imaging in humans using SPECT/CT with parallel-hole collimators. Methods The method was first evaluated in computer simulations before application to human data. A study was performed using the computer -generated MOBY rat phantom that returns a high resolution transmission map. Monte Carlo system matrices were estimated using SIMSET for the reconstruction of 6 heart slices from projections of 6 detector rows. The system matrices also modeled spillover to account for the scatter outside the heart slices. Simset estimated projections were reconstructed using the spillover estimated matrices and 50 iterations of the ML-EM algorithm. The same Monte Carlo method was used to specify the system matrix for human imaging. Projections from a human study were reconstructed using the spillover estimated system matrices and 50 iterations of the ML-EM algorithm. Results At 140 keV there was a 20% increase of average intensity over the rat's heart region with attenuation correction compared to without and a 3.5% decrease from the attenuation corrected result after scatter+attenuation correction. Attenuation correction reconstruction alone, overestimated the original by 3.3%. We expect these results to be even more dramatic for human studies. Conclusions Correction for both attenuation and scatter is important to adequately quantify the uptake of radiopharmaceuticals in the myocardium at 140 keV. Monte Carlo methods using CT transmission maps and SPECT distributions provide an accurate method for estimating the scatter and attenuation in myocardial perfusion SPECT imaging. Research Support NIH R01-EB00121 and R01-HL50663 and U.S. Department of Energy Contract DE-AC03-76SF00098. ER -