TECHNETIUM-99M-TETROFOSMIN TO ASSESS MYOCARDIAL BLOOD-FLOW - EXPERIMENTAL VALIDATION IN AN INTACT CANINE MODEL OF ISCHEMIA

Technetium-99m-tetrofosmin is a Tc-99m-labeled perfusion tracer demons trating promise for myocardial perfusion imaging. To determine if Tc-9 9m-tetrofosmin tracks myocardial flow over a pathophysiologic range, t he initial myocardial uptake and clearance of Tc-99m-tetrofosmin relat ive to microsphere flow were evaluated in a canine model of ischemia d uring pharmacological vasodilatation. Methods: Six open-chest dogs wer e subjected to complete left anterior descending coronary artery occlu sion. Dogs were injected with Tc-99m-tetrofosmin and radiolabeled micr ospheres during pharmacological stress. Coincident with radiotracer in jection, dynamic planar imaging and arterial sampling were performed t o assess Tc-99m-tetrofosmin clearance from blood, myocardium, lung and liver. Fifteen minutes after injection, hearts were excised for well counting of myocardial Tc-99m-tetrofosmin activity and flow. Results: Myocardial Tc-99m-tetrofosmin activity correlated linearly with micros phere flow (r = 0.84). Relative Tc-99m-tetrofosmin activity underestim ated flow at higher flow ranges (>2.0 ml/min/g) and overestimated flow in low flow ranges (<0.2 ml/min/g). Technetium-99m-tetrofosmin cleare d rapidly from the blood and was retained in the myocardium. Resting t arget-to-background activity ratios (heart:lung = 3.57 +/- 1.01; heart :liver = 0.58 +/- 0.04) were acceptable 10 min after injection. Conclu sion: Our experimental data support both the validity of Tc-99m-tetrof osmin as a myocardial perfusion tracer and the use of early poststress Tc-99m-tetrofosmin imaging for the assessment of myocardial perfusion in man.