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Thallium-201 Myocardial Imaging: Characterization of the ECG-Synchronized Images

Veterans Administration Hospital and University of Washington, Seattle, Washington

Correspondence: For reprints contact: Glen W. Hamilton, Chief, Nuclear Medicine Section (115), Veterans Administration Hospital, 4435 Beacon Ave. So., Seattle, WA 98108.

ABSTRACT

Electrocardiographic synchronization of Tl-201 myocardial scintigrams provides images free of blurring due to the motion artifact induced by myocardial contraction. The current study was performed to characterize the qualities and technique of synchronized thallium imaging. Twenty-five studies were performed in 18 patients. Initially, standard nonsynchronized images were obtained with a high-resolution collimator in the anterior, left anterior oblique (30°, 45°, and 60°), and left lateral positions. Next, a 30-min ECG-synchronized image was acquired with a high-sensitivity collimator in the 45° left anterior oblique view. Fifty-millisecond images of the cardiac cycle can be viewed in cine mode, or end-diastolic and end-systolic images can be constructed using predefined criteria and/or a region-of-interest analysis to detect motion. With the 30-min imaging time, motion-free images with adequate counts were routinely obtained. The synchronized motion-free images resolved the myocardium more clearly and defects were more readily apparent than with the standard nonsynchronized images. Systolic myocardial thickening and wall motion could be appreciated by visual inspection or by computer analysis. This study demonstrates that image quality is enhanced by synchronized imaging and that wall motion can be assessed. Due to the longer imaging time required for synchronized imaging, it is not possible to obtain the multiple views usually obtained with standard imaging. The data presented demonstrate, however, that motion-free pictures of end-diastole alone could be obtained in much less time. It remains undetermined whether fewer ECG-synchronized views, rather than more views without synchronization, would improve lesion detectability.