Comparison of correction techniques for simultaneous 201Tl/99mTC myocardial perfusion SPECT imaging:: a dog study

We compared two correction methods for simultaneous Tl-201/Tc-99m dual-isotope single-photon emission computed tomography (SPECT). Both approaches use the information from the third energy window placed between the photopeak windows of the Tl-201 and Tc-99m. The first approach, described by Moore et al, corrects only for the contribution of the Tc-99m to the Tl-201 primary 70 keV window. We developed the three-window transformation dual-isotope correction method, which is a simultaneous cross-talk correction. The two correction methods were compared in a simultaneous Tl-201/Tc-99m sestamibi cardiac dog study. Three separate acquisitions were performed in this dog study: two single-isotope and one dual-isotope acquisition. The Tl-201 single-isotope images were used as references. The total number of counts, and the contrast between the left ventricular cavity (LVC) and the myocardium, were used in 70 keV short-axis slices as parameters for evaluating the results of the dual-isotope correction methods. Three consecutive short-axis slices were used to calculate averaged contrast and the averaged total number of counts. The total number of the counts was 667 000 +/- 500 and 414 500 +/- 400 counts for the dual-isotope (Tl-201 + Tc-99m) and single-isotope (Tl-201-only) 70 keV images, respectively. The corrected dual-isotope images had 514 700 +/- 700 and 368 000 +/- 600 counts for Moore's correction and our approach, respectively. Moore's method improved contrast in the dual-isotope 70 keV image to 0.14 +/- 0.03 from 0.11 +/- 0.02, which was the value in the 70 keV non-corrected dual-isotope image. Our method improved the same contrast to 0.22 +/- 0.03. The contrast in the Tl-201 single-isotope 70 keV image was 0.28 +/- 0.02. Both methods improved the 70 keV dual-isotope images. However, our approach provided slightly better images than Moore's correction when compared with Tl-201-only 70 keV images.