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With the recent development of positron emission tomography (PET), cross sectional functional imaging of the heart has become possible. This demonstrates quantitatively the distribution of radioactive ligands in the myocardium. PET images thus resemble in vivo autoradiographs, providing a potential non-invasive means of quantifying regional myocardial metabolism and perfusion.1
Types of PET study
There are three types of cardiac PET study: regional blood flow (which can be measured at rest and during pharmacological induced stress), substrate metabolism, and chemical recognition (including receptors and enzymes).2 Currently, the main clinical application of PET is in the diagnosis of coronary artery disease, in terms of the differentiation between infarcted and “stunned” myocardial tissue, in which complete recovery of severely ischaemic and non-contracting myocardium is possible after reperfusion.3 4 Other methods for differentiating recoverable myocardium from non-viable tissue, such as the presence of ECG Q waves, wall motion abnormalities on ultrasound, gated isotope scans, or fixed thallium-201 perfusion defects,5 all seriously underestimate viable myocardium even with delayed imaging or reinjection techniques in the last.5
A number of tracers have been developed for clinical PET studies. These include oxygen-15, nitrogen-13, carbon-11, fluorine-18, and rubidium-82, all of which may be coupled to a number of physiologically active molecules.3 N-13 ammonia, Rb-82, and O-15 water can be used to assess myocardial blood flow.1 6 7 Carbon-11 labelled fatty acids and F-18 deoxyglucose are commonly used metabolic tracers; C-11 acetate is used to assess oxidative metabolism and oxygen consumption.8 Because these tracers have very short half lives and relatively low radiation doses, it is possible to undertake sequential studies of perfusion and metabolism enabling accurate differentiation between stunned and infarcted tissue.3 9
Metabolic changes in myocardial ischaemia
Depending on plasma substrate levels, hormonal factors, and oxygen supply and demand, the heart …