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Effect of Reperfusion and Hyperemia on the Myocardial Distribution of Technetium-99m t-Butylisonitrile

Departments of Radiology and Medicine, Harvard Medical School and Brigham and Women's Hospital, Boston
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts

Correspondence: For reprints contact: B. Leonard Holman, MD, Dept. of Radiology, Brigham and Women's Hospital, 75 Francis St., Boston, MA 02115.

ABSTRACT

Technetium-99m t-butylisonitrile ([^99mTc]TBI) is a promising new radiotracer for myocardial imaging. Its myocardial uptake is sufficiently high in humans to permit planar, tomographic, and gated images of excellent technical quality. We studied the behavior of [^99mTc]TBI in the dog at rest and under conditions of hyperemia and reperfusion in order to determine the relationship between [^99mTc]TBI myocardial concentration and blood flow. After permanent occlusion of the left anterior descending artery, the correlation between the relative myocardial concentration of [^99mTc]TBI and regional myocardial blood flow (RMBF) measured with radiolabeled microspheres was excellent. In a dog model of transient hyperemia, the concentration of [^99mTc]TBI was directly related to blood flow but underestimated the degree of hyperemia. Technetium-99m TBI redistributed into transiently ischemic myocardium. The myocardial concentrations of [^99mTc]TBI and thallium-201(²⁰¹Tl) in transiently ischemic myocardium were similar at 10 and 30 min following reperfusion and were significantly higher than blood flow prior to reperfusion. When [^99mTc]TBI was injected into the left anterior descending artery, the washout was slow, falling to 78% of initial activity at 120 min after injection. In conclusion, [^99mTc]TBI reflects regional myocardial blood flow accurately in ischemic and normal resting myocardium and underestimates blood flow at high flows. The rate of myocardial redistribution after reperfusion is similar for [^99mTc]TBI and ²⁰¹Tl.

FOOTNOTES

^* Present address: Div. of Cardiology, Wayne State University, School of Medicine, Harper Hospital, 3990 John R. Detroit, MI 48201.