BIOKINETICS OF TECHNETIUM-99M-TETROFOSMIN - MYOCARDIAL PERFUSION IMAGING AGENT - IMPLICATIONS FOR A ONE-DAY IMAGING PROTOCOL

Tetrofosmin is a Tc-99m-labeled myocardial perfusion imaging agent tha t has shown encouraging results in Phase I and II clinical trials. The purpose of this study was to determine the biokinetics of this agent following administration during exercise and at rest in order to deter mine an optimal imaging protocol. Twenty patients with suspected coron ary artery disease underwent symptom-limited treadmill exercise. Six t o 8 mCi of Tc-99m-tetrofosmin was injected at peak exercise and 22-24 mCi was injected 4 hr later at rest. Serial 5-min planar images were o btained in the left anterior oblique view at 5,10,15, 30, 60,120 and 1 80 min after the radiotracer injection. Regions of interest were drawn on the serial images around the entire heart and portions of liver, l ung, spleen, gallbladder and gastrointestinal tract. Average decay-cor rected counts per pixel in each organ were plotted against time. In ad dition, heart-to-adjacent organ ratios were also determined. On stress images, the heart had the highest activity at all times, with the exc eption of gallbladder in the first 15 min. On rest images, the gallbla dder, liver and gastrointestinal tract initially had higher activity t han the heart; but the activity in these organs cleared rapidly over t he subsequent 30-60 min. Heart-to-adjacent organ ratios were > 1.0 at all times in the stress images. Heart-to-organ ratios were < 1.0 in th e first 15 min on the rest images for the liver and gastrointestinal t ract. However, 30 min later, all ratios on the rest images were greate r-than-or-equal-to 1.0. Technetium-99m-tetrofosmin images were conside red to be of good to excellent quality with good myocardial delineatio n and adequate contrast between the heart and background. These These observations indicate that a convenient one-day tetrofosmin imaging pr otocol similar in duration to conventional Tl-201 imaging is feasible.