The utilization of Tc-99m-TBI as a myocardial perfusion agent in exercise studies: Comparison with Tl-201 thallous chloride and examination of its biodistribution in humans

Twenty-four patients were studied with both ²⁰¹Tl-thallous chloride and ^99mTc-TBI scintigraphy following exercise. Comparison of the two agents in detecting segmental myocardial ischemia and scar was made in 18 patients with evidence of coronary artery disease on ²⁰¹Tl-thallous chloride scintigraphy. Agreement between the two studies was observed in 77% (125 of 162) of left ventricular segments, suggesting that ^99mTc-TBI can be used as a myocardial perfusion agent. Limitations were related to early high background activity from lungs and liver. The high lung activity and early myocardial redistribution within the 1st hour contributed to the failure of ^99mTc-TBI to detect 16 segmental defects seen in the immediate post-exercise thallous chloride scan. Persistently high liver activity additionally affected accurate interpretation in the left ventricular segments close to the diaphargm. Improvement in the accuracy of ^99mTc-TBI stress studies might be achieved with tomographic imaging to reduce the problem of background activity or by the development of ^99mTc-labeled isonitrile analogues with rapid lung and liver clearance.