Background: Gated myocardial perfusion single-photon emission computed tomographic (SPECT) imaging is currently performed by step-and-shoot detector rotation, resulting in acquisition dead time and lengthened study duration compared with nongated SPECT imaging with continuous or pseudocontinuous rotation. Dead time is particularly undesirable in new fast-gated SPECT imaging protocols with inotropic pharmacologic stress.
Methods and results: This article evaluated the influence of projections' angular spacing on quantitative measurements of left ventricular ejection fraction (LVEF) and perfusion from postexercise 99mTc-labeled sestamibi images. Gated 60-projection data sets from 30 patients were compacted into 30- and 15-projection sets. The three sets (corresponding to 3-, 6-, and 12-degree spacing over 180 degrees) were reconstructed into gated and ungated short-axis image sets. LVEFs were measured from the gated images according to a previously described automatic algorithm, whereas perfusion was assessed from the ungated images by a 20-segment division of their maximal pixel polar maps. LVEF values were essentially unchanged between 60- and 30-projection images (y = 0.37 + 0.996x; r = 0.999; standard error of the estimate = 0.56) and 60- and 15-projection images (y = 1.35 + 0.987x; r = 0.999; standard error of the estimate = 0.77) in the 30 patients. Overall, 30- and 15-projection polar maps differed by 1.87% +/- 1.24% and 4.38% +/- 2.25% from the 60-projection polar maps, respectively. Segmental perfusion score agreement between 60- and 30-projection images and between 60- and 15-projection images was 93% (kappa = 0.92; p < 0.001) and 83% (kappa = 0.81; p < 0.001), respectively. Sixty- and 30-projection images were visually undistinguishable, whereas loss of image resolution was noticed in many 15-projection gated and ungated images.
Conclusions: Thirty-projection gated SPECT imaging is a practical, accurate, and time-saving approach in standard gated protocols and, potentially, fast-gated protocols. Fifteen-projection gated SPECT imaging is not generally recommended and should be considered only for LVEF assessment in conjunction with fast-gated protocols.