Biodistribution of Tc-99m methoxy-isobutyl-isonitrile (MIBI) in humans.

Hexakis (methoxyisobutilisonitrile) technetium(I), 99mTc-MIBI, has been proposed for myocardial perfusion studies. We have evaluated the biodistribution of this new agent in normal volunteers at rest and after stress. The biodistribution of 99mTc-MIBI is characterized by rapid blood clearance and a consequently early myocardial uptake. The initial intense hepatic activity is cleared into the gallbladder at 1 h after injection, and the best target to non target ratio is observed at 60-90 min after injection. Absorbed radiation dose calculations show that the thyroid is the critical target organ (230 mRad/mCi at rest), presumably because of 99mTc-pertechnetate generated in vivo. Our results indicate that 99mTc-MIBI is a promising tracer for myocardial perfusion imaging.