Effect of Time on Liver Clearance of Technetium-99m-Tetrofosmin in Patients with Acute Chest Pain: When Should Imaging Begin?

Abstract

Objective: Due to stable myocardial retention and technetium imaging characteristics, ^99mTc-tetrofosmin has been considered potentially useful for acute chest pain imaging. Tetrofosmin also has favorable biokinetics with reported rapid liver clearance, 5 min poststress and 30–45 min postrest injection. Since comparable data are not available, the effect of time on liver clearance was evaluated in patients with acute chest pain.

Methods: One hundred six patients received an intravenous injection of 25–30 mCi ^99mTc-tetrofosmin to evaluate acute chest pain. SPECT imaging was performed 15–120 min after injection of the tracer. Patient images were grouped according to the time of acquisition after acute injection: 15–30 min, 31–45 min, 46–60 min, 61–90 min and >90 min. Quantitative analysis was performed on a similar anterior projection for each patient consisting of a 6 × 6-pixel region of interest over the myocardium and adjacent liver. Average counts per pixel were determined and a heart/liver (H/Li) ratio was calculated.

Results: The mean H/Li ratio was < 1.0 for patient images acquired 15–45 min after injection, and > 1.0 for patient images acquired after 45 min. The difference was statistically significant (p < 0.05).

Conclusion: Quantitative analysis suggests that the optimal imaging time should be at least 45 min after the injection of ^99mTc-tetrofosmin to allow adequate liver clearance before image acquisition of acute chest pain syndromes.