Gated TI-201 myocardial perfusion SPECT: application of energy window optimization.

Purpose: Tl-201 scintigraphy is plagued with poor image quality because of the low-energy photons of Tl-201 decay. Traditionally, a narrow 20% window centered on 71-72 keV has been used to improve sensitivity. Recent studies indicate that better imaging may be possible by optimizing the energy window to 34% centered on 77 keV. In this study, energy window optimization (EWO) was applied to gated Tl-201 myocardial perfusion SPECT, and myocardial functional parameters were compared for gated Tl-201 SPECT and gated Tc-99m sestamibi (Tc-99m MIBI) SPECT. Methods: Count statistics for standard and optimal Tl-201 myocardial scintigraphy were noted in 25 patients by assessing the total counts in a mid-ventricular slice of a rest-gated Tl-201 myocardial SPECT study. The feasibility of performing functional studies with the application of EWO to Tl-201 was assessed using the count statistics of a mid-ventricular slice of an optimized gated Tl-201 SPECT study and a gated Tc-99m MIBI SPECT study. The functional parameters (ejection fraction, wall motion, and thickening) of Tl-201 with EWO and Tc-99m MIBI were compared in 60 patients who underwent rest-gated Tl-201 SPECT followed by poststress gated Tc-99m MIBI SPECT. The left ventricular ejection fraction was calculated using commercially available software, whereas wall thickness and motion were assessed by the consensus of two readers. Results: The application of EWO increased available counts by more than 25%. It also resulted in sufficient counts being available to perform gated Tl-201 SPECT without increasing acquisition times or the dose of Tl-201. The average ejection fraction was 60.4% for gated Tl-201 SPECT and 59.6% for gated Tc-99m MIBI SPECT (not significantly different). Overall, the image quality was rated excellent in 12% for Tl-201 and Tc-99m MIBI and good in 50% and 62%, respectively, and poor in 38% and 26%, respectively. Conclusion: The application of EWO to Tl-201 SPECT allows myocardial functional parameters to be assessed without having to increase the acquisition times or the administered dose of Tl-201.