Kinetics of Tc-99m hexakis t-butyl isonitrile in normal and ischemic canine myocardium.

Hexakis 99mTc-tertiary butyl isonitrile (99mTc-TBI) was studied as a cardiac perfusion imaging agent in nine dogs with partial occlusion of the LAD. Thirty min after applying the stenosis, 99mTc-TBI was injected into the right atrium (RA) in five dogs and left atrium (LA) in four dogs. Normal and ischemic zone regional myocardial 99mTc-TBI activities were monitored continuously for 4 h. Dogs with LA injections had minimal and equivalent 4 h fractional clearance from the normal and ischemic zones. Dogs with RA injections had minimal, but significantly lower 4 h fractional 99mTc clearances in the ischemic zone (0.08 +/- 0.08) compared to the normal zone (0.16 +/- 0.07, P less than 0.05). The delayed ischemic zone clearance is probably due to the high initial lung uptake observed after RA injection. Despite the differences in clearance, this minimal amount of redistribution could not be detected on gamma camera images. The minimal myocardial washout and redistribution, and the 140 keV gamma make 99mTc-TBI a promising cardiac perfusion imaging agent.