Gated TI-201 myocardial perfusion SPECT: application of energy window optimization.
OBJECTIVE
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 window to 34% centered on 77 keV. In this study, energy window optimization (EWO) was applied to gated TI-201 myocardial perfusion SPECT, and myocardial functional parameters were compared for gated TI-201 SPECT and gated Tc-99m sestamibi (Tc-99m MIBI) SPECT.


METHODS
Count statistics for standard and optimal TI-201 myocardial scintigraphy were noted in 25 patients by assessing the total counts in a mid-ventricular slice of a rest-gated TI-201 myocardial SPECT study. The feasibility of performing functional studies with the application of EWO to TI-201 was assessed using the count statistics of a mid-ventricular slice of an optimized gated TI-201 SPECT study and a gated Tc-99m MIBI SPECT study. The functional parameters (ejection fraction, wall motion, and thickening) of TI-201 with EWO and Tc-99m MIBI were compared in 60 patients who underwent rest-gated TI-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 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 gated Tc-99m MIBI SPECT (not significantly different). Overall, the image quality 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.


CONCLUSIONS
The application of EWO to TI-201 SPECT allows myocardial functional parameters to be assessed without having to increase the acquisition times or the administered dose of TI-201.
Department of Nuclear Medicine, Wollongong Hospital, New South Wales, Australia. swadhwa@ozemail.com.au
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Wadhwa
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Mansberg
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Wilkinson
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Abbati
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D015637:Gated Blood-Pool Imaging / Q000379:methods*; D006321:Heart / Q000000981:diagnostic imaging*; D006801:Humans; D007089:Image Enhancement; D008297:Male; D008875:Middle Aged; D019275:Radiopharmaceuticals; D012680:Sensitivity and Specificity; D013318:Stroke Volume; D017256:Technetium Tc 99m Sestamibi; D013794:Thallium Radioisotopes; D015899:Tomography, Emission-Computed, Single-Photon / Q000295:instrumentation / Q000379:methods*; D016277:Ventricular Function, Left
D019275:Radiopharmaceuticals; D013794:Thallium Radioisotopes; D017256:Technetium Tc 99m Sestamibi