Nuclear cardiology

Myocardiology perfusion scintigraphy (MPS) is the most common nuclear cardiology investigation, though equilibrium radionuclide ventriculography is sometimes performed. MPS involves the comparison of myocardial perfusion during cardiac stress with that at rest. A radiopharmaceutical (thallium-201, technetium-99m-sestamibi, or technetium-99m-tetrofosmin) is injected that is delivered to and taken up by the myocardium in relation to its blood supply. Imaging involves single-photon emission computed tomography, and stress and rest acquisitions are compared. Perfusion defects appear as areas of relatively reduced radioactive counts, and may be ‘fixed’ (present at stress and rest, representing infarction) or ‘reversible’ (present at stress only, representing ischaemia). Left ventricular function can be assessed by gating image acquisition to the patient’s electrocardiogram. MPS is most commonly used in the diagnostic assessment of patients with suspected coronary disease for whom the exercise electrocardiogram is likely to be unreliable. For the detection of angiographic coronary stenoses, the sensitivity and normalcy rate of MPS are both about 90%. More importantly, MPS provides prognostic information that is independent of clinical, exercise, and even angiographic data, and a normal study is associated with an annual rate of cardiac death or non-fatal myocardial infarction of approximately 0.6%.