Isotopic assessment of regional abnormalities of myocardial perfusion

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Nuclear cardiology comprises four different areas that include (1) regional myocardial perfusion with the use of potassium analogues, namely thallium-201; (2) evaluation of left ventricular function both at rest and at exercise with blood pool agents, primarily Tc-99m-labeled red blood cells and human serum albumin; (3) shunt analysis and semi-quantification with first pass bolus technique using primarily technetium preparation, (4) myocardial infarct imaging or “hot spot” imaging with Tc-99m pyrophosphate and occasionally tetracycline preparations.

There are several different tracer methods available for studying myocardial perfusion. These include labeled metabolic substrates, particulate regional blood flow, direct injection of diffusible tracers, and potassium analogues including thallium-201. The metabolic substrates include I-131-labeled fatty acids, carbon-11 tagged to palmitic acid as well as to carbon monoxide and nitrogen-13 to ammonia.

Carbon-11 and nitrogen-13 are short-lived cyclotron-produced isotopes not commercially available. They produce images by annihilation radiation that require special detecting devices. They do offer promise in the future when they become more readily available.

Particulate regional blood flow with either human albumin microspheres or macroaggregates of albumin attached to different isotopes is another method of studying myocardial perfusion. With this method, one injects two isotopes with different photon energies into the right and left coronary arteries, respectively. One is then able, by taking multiple views, to generate the isotopic geographic distribution of the territories, supplied by each of the two vessels.

The use of xenon-133, an inert gas, is another method of evaluating regional perfusion. By injecting the xenon directly into the coronary . . .



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