Myocardial kinetics of technetium-99m-hexakis-2-methoxy-2-methylpropyl-isonitrile.

Abstract

To study the potential usefulness of technetium-99m hexakis-2-methoxy-2-methylpropyl-isonitrile (Tc-MIBI) as a cardiac perfusion imaging agent, the left circumflex coronary arteries of 12 dogs were partially occluded. Eight additional control dogs had no coronary artery stenosis. Myocardial Tc-MIBI activities in the left circumflex and left anterior descending zones were continuously monitored by miniature implantable radiation detectors for 4 hr after administration of the isotope. The dogs were then killed. Serial gamma camera images were also acquired during the study. Heart rate, arterial blood pressure, pressure distal to the stenosis, and cardiac output did not change significantly during the experiment. Microsphere-determined regional myocardial blood flow was significantly reduced in the left circumflex distribution in the 12 dogs with coronary artery stenoses. In the 12 dogs with left circumflex coronary artery stenoses, the 4 hr fractional Tc-MIBI clearances from the normal and ischemic zones were minimal and equivalent (0.15 + 0.05 SD vs 0.15 ± 0.07). In the eight control dogs, 4 hr fractional Tc-MIBI clearances from the left anterior descending and left circumflex artery zones were minimal and equivalent (0.11 ± 0.06 vs 0.10 + 0.07). Four hour fractional Tc-MIBI clearance from the blood was 0.98 ± 0.03 for the dogs with stenosis and 0.97 + 0.02 for the dogs without stenosis. One additional dog had complete occlusion of the left circumflex coronary artery followed by administration of Tc-MIBI and scandium-46-labeled microspheres. This heart was immediately sectioned and counted to determine the relationship of regional blood flow to Tc-MIBI distribution (r = .92). Furthermore, the final technetium activity ratio (ischemic divided by normal zone = 0.53 + 0.19) measured in a well counter for the 12 dogs with stenosis was not significantly different from the initial flow ratio at the time of Tc-MIBI administration (0.47 ± 0.20), confirming the absence of redistribution. Gamma camera images were of excellent quality for as l-ong as 4 hr after isotope administration. Thus its linear relationship to regional myocardial blood flow, the minimal myocardial washout and redistribution, and the 140 keV gamma photon make Tc-MIBI a promising new cardiac perfusion imaging agent. Circulation 77, No. 2, 491-498, 1988. THALLIUM -201 has been widely used for the assessment of myocardial perfusion and the diagnosis of coronary artery disease. Unfortunately, its physical properties are not ideal for gamma camera imaging,' and myocardial image quality has sometimes suffered from external or self attenuation. This has resulted in considerable interobserver variability in interpretation of thallium images. Technetium-99m (99mTc) is much better suited for gamma camera imaging because of its 140 keV gamma photon. Previous attempts to link

Assessment of Myocardial Perfusion with Single Photon Emission Tomography

“…Redistribution of T1-201 can potentially occur during the 35 minutes that pass between injection and completion of SPECT sequence 15 whereas Tc-MIBI has minimal redistribution. 1,16 Defect intensity is the same on SPECT of either agent. 17 The size of defect was not considered a parameter for comparison in this study and thus it is not an issue for argument.…”

“…3 Compared to T1-201, Tc-MIBI showed some advantages such as better image quality for high photon flux, good myocardial uptake, and availability. 1,3 The potential applicability of a one-day imaging protocol with Tc-MIB 4,5 has added a further advantage over T1-201. Tc-MIBI was shown valuable when it was used to estimate areas of myocardium at risk due to severe ischemia 6 and to assess the response to thrombolytic therapy in myocardial infarction (MI).…”

Abnormal myocardial perfusion in the absence of anatomically significant coronary artery disease: Implications and clinical significance

“…There is also a nonlinear relationship between myocardial blood flow and tracer uptake, especially at higher flow rates. 25 Despite these setbacks, there is considerable interest in developing novel algorithms for quantifying MBF with SPECT.…”

Single-day combined evaluation of regional myocardial perfusion and function at rest and peak exercise with99mTc-MIBI in patients with coronary artery disease

“…At the same time, perfusional studies can be carried out, as the isotope is coupled with a molecule that is 65% taken up on first pass by myocites, mainly by simple diffusion, and does not redistribute significantly over time [3][4][5][6].…”