Gated Intracoronary Thallium201 Scintigraphy: Feasibility and Potential Clinical Advantages

Abstract

Visualization of ventricular walls with true global motion and myocardial thickening is not possible with use of present scintigraphic techniques. When thallium 201 ( ²⁰¹TI) is injected intravenously (IV), only about 5% reaches the myocardium. However, if ²⁰¹TI is injected intracoronarily, 100% reaches, and approximately 88% localizes in, the myocardium, which results in higher count rates than when given IV, permitting acceptable acquisition times for gated true wall motion studies. The authors describe a new technique using intracoronary (IC) ²⁰¹ TI to acquire high count rate, high contrast, and short acquisition time in gated true wall motion studies.

Thirteen patients were studied at rest with gated IC thallium. Six of these patients also had resting IV ²⁰¹TI myocardial studies. After routine coronary angiography, 0.75 mCi of ²⁰¹TI was injected into each coronary artery. Multiple sequential one-minute gated studies were obtained in LAO and RAO projec tions, followed by sequential five-minute images for two hours to determine ²⁰¹TI redistribution kinetics. Regions of interest over segments of left and right ven tricles and background permitted definition of temporal and spatial distribu tions. Three one-minute gated studies were summed with a total count of 2,100 K for a three-minute acquisition.

Myocardium-to-background ratios were as high as 13:1 with a mean of 11.4:1 in the IC study compared with 2.3:1 in the IV studies. Washout half-time in normal myocardium was 95 ± 5 min. The detectability and size of perfusion defects were different on gated diastolic and systolic, nongated, and IV studies. Questionable defects seen on nongated studies or after IV administration were easily noted on gated diastolic images. Apparent alterations in wall thickness during the cardiac cycle were visualized.

Short-acquisition and high-resolution myocardial perfusion images demon strating the wall motion obtained by this new technique may be a useful adjunct to the blood pool and coronary anatomy detail acquired during cardiac cathe terization. The apparent advantages of the gated perfusion study are being ap plied to experimental ^99mTc-labeled myocardial perfusion agents presently being evaluated.