Myocardial kinetics of 99Tcm hexakis-(2-methoxy-isobutyl-isonitrile) (HMIBI) in patients with coronary heart disease: a comparative study versus 201Tl with SPECT.

In 15 patients with coronary heart disease, 74 MBq 201Tl (A) and 240 MBq 99Tcm HMIBI (B) were injected during exercise on separate days and SPECT imaging was applied. In (B) a consecutive second injection was given with an identical dose 3 h later (at rest) and net rest distribution was obtained from a subtraction technique. From polar, target-like ROIs, data were computed to compare regional vitality, wash-out and wash-out corrected redistribution. Myocardial wash-out, in contrast to 201Tl, was found to be 20% for 99Tcm independent of the regional myocardial state. Since no considerable redistribution occurred, myocardial distribution of 99Tcm HMIBI remained rather constant for 3 h, resulting in a maximum myocardium to lung ration of about 5. After the second injection, redistribution revealed the same results as in the 201Tl targets. From regional exercise to rest ratios a 'perfusion reserve' was determined which was 2.1 in normal and 1.3 in myocardial areas with defects. Myocardial defect uptake and defect size were nearly identical, yielding agreement in 97% of the myocardial segments. We conclude that 99Tcm HMIBI is a most powerful myocardial imaging agent. The final routine protocol, however, is as yet not established.