CHAPTER 7 Nuclear Cardiology
Non-invasive images of the myocardium that reflect myocardial perfusion can be obtained either by using conventional nuclear medicine radiopharmaceuticals and cameras or by positron emission tomography (PET). Myocardial perfusion scintigraphy (MPS) with thallium-201 and/or technetium (Tc)-99m-labelled sestamibi and tetrofosmin, in combination with single photon emission computed tomography (SPECT), is a robust and well validated technique for the identification of myocardial ischaemia and infarction with high sensitivity and specificity. 99mTc-labelled myocardial perfusion agents have a high-count density which enables acquisition of electrocardiogram-gated images. Spatial and temporal changes in activity during the cardiac cycle reflect regional myocardial motion and thickening and this technique allows left ventricular volume, ejection fraction, and myocardial motion and thickening to be measured in addition to the information on perfusion. Since the main feature of an acute coronary syndrome is reduced myocardial perfusion, MPS can provide important diagnostic and prognostic information in the emergency department and allows patient stratification in the post-infarction phase. PET provides absolute measurement of myocardial blood flow and has enabled the demonstration of coronary microvascular dysfunction. This has highlighted the potential contribution of the microcirculation to myocardial ischaemia in patients with angiographically normal coronary arteries. Both SPECT and PET are invaluable tools for the identification of viable myocardium in patients with coronary artery disease and congestive heart failure. The constant technological developments of non-invasive cardiac imaging over the past years, including the advent of hybrid nuclear and computer tomography (CT) scanners now allow image fusion of CT coronary angiography and nuclear imaging which can be achieved by using hybrid scanners or software fusion of data sets obtained from stand-alone scanners. Although the potential of such comprehensive non-invasive coronary artery disease assessment appears great, the clinical impact of this tool remains to be established.
Chapter 28)
