Cardiac nuclear medicine: positron emission tomography in clinical medicine.

Positron-emission tomography (PET) and radioactively labelled substrates permit metabolic studies to be carried out in vivo and in situ with few if any limitations regarding the choice of substrates as long as they can be tagged with positron-emitting radionuclides, especially those like 11C and 13N. With respect to cardiology, 13N-ammonia and 82Rb are helpful in the examination of myocardial perfusion. The evaluation of myocardial glucose and fatty acid metabolism with 18F-deoxyglucose (FDG) and 11C-palmitate has proved to be clinically useful. Thus, myocardial ischemia and hypoxia, infarct size, the transmural extent of the infarction and tissue viability after it can all be examined as can pathological biochemistry in patients with primary or secondary cardiomyopathies. Single-photon-emitting labelled substances such as 123I-labelled fatty acid analogues also provide information equivalent to that which can be gathered by PET for clinical use. Thus, one major task of PET is the validation of methods and the transformation of these methods to single-photon-emitting radiotracers for broad clinical application, in situations where the expense of PET cannot at present be justified.