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

Purpose: TI-201 scintigraphy is plagued with poor image quality because of the low-energy photons of TI-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 windo w to 34% centered on 77 keV. In this study, energy window optimization (EWO ) was applied to gated TI-201 myocardial perfusion SPECT, and myocardial fu nctional parameters were compared for gated TI-201 SPECT and gated Tc-99m s estamibi (Tc-99m MIBI) SPECT. Methods: Count statistics for standard and optimal TI-201 myocardial scinti graphy were noted in 25 patients by assessing the total counts in a mid-ven tricular slice of a rest-gated TI-201 myocardial SPECT study. The feasibili ty of performing functional studies with the application of EWO to TI-201 w as assessed using the count statistics of a mid-ventricular slice of an opt imized gated TI-201 SPECT study and a gated Tc-99m MIBI SPECT study. The fu nctional parameters (ejection fraction, wall motion, and thickening) of TI- 201 with EWO and Tc-99m MIBI were compared in 60 patients who underwent res t-gated TI-201 SPECT followed by poststress gated Tc-99m MIBI SPECT. The le ft ventricular ejection fraction was calculated using commercially availabl e software, whereas wall thickness and motion were assessed by the consensu s 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 TI -201 SPECT without increasing acquisition times or the dose of TI-201. The average ejection fraction was 60.4% for gated TI-201 SPECT and 59.6% for ga ted Tc-99m MIBI SPECT (not significantly different). Overall, the image qua lity was rated excellent in 12% for TI-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 TI-201 SPECT allows myocardial functi onal parameters to be assessed without having to increase the acquisition t imes or the administered dose of TI-201.