Chapter 3

Myocardial perfusion single photon emission computed tomography (SPECT) is a nuclear medicine imaging technique that uses a radioactive perfusion tracer to detect ischemia. Myocardial SPECT can detect, localize, and quantify the degree of ischemic myocardium. The result of a myocardial perfusion SPECT is related to the prognostic outcome of cardiac events (ie, myocardial infarction and death). Therefore, myocardial perfusion SPECT is used to guide treatment in patients with stable angina and after acute coronary syndrome. Myocardial perfusion SPECT is a mature technique, one of the most commonly used cardiac imaging techniques, and part of the international guidelines for treatment of patients with ischemic heart disease.1-3 There are international guidelines on how to perform,4 how to report,5 and when to use6 myocardial perfusion SPECT. Myocardial positron emission tomography (PET) is a newer nuclear medicine imaging technique that has rapidly become routine in cancer patients. The use in cardiology is also increasing because PET has inherent advantages compared to SPECT (eg, better image resolution and the possibility for absolute quantification of blood flow). However, the limited availability of the technique and especially of the PET perfusion tracers and higher costs are influencing the choice of method, and SPECT has kept its role as the main workhorse for cardiac patients.

Myocardial ischemia is defined as a mismatch between the demand and supply of oxygen to the myocytes, and this is mainly dependent on an adequate myocardial perfusion in various physiologic conditions. The inotropic and chronotropic states determine the myocardial demand, and during physical exercise, the heart rate increases and the force of the myocardium increases to raise the stroke volume and the left ventricular systolic pressure. At normal conditions, the arterioles can dilate during exercise, and perfusion can thus increase from a resting value of 1 mL/min/g to 3 mL/min/g. The maximal vasodilatation of the coronary arteries is even larger; over 5 mL/min/g has been measured, for example, during reactive hyperemia7 or pharmacologic vasodilatation. Coronary artery disease (or ischemic heart disease) affects myocardial perfusion by coronary artery stenoses that increase the resistance of the larger coronary arteries, and thus, the flow is limited. The heart will compensate for this increased resistance by dilatation of the arterioles at rest, thereby preventing a flow decrease. However, this means that part of the flow vasodilator reserve that is supposed to be used at stress is already being used at rest. This explains why patients who have stress-induced ischemia commonly have normal perfusion at rest.

Myocardial perfusion is depicted at rest and exercise using an intravenous injection of a radioactive perfusion tracer in a peripheral vein. The most commonly used perfusion tracers are technetium 99m (99mTc)–labeled tetrofosmin (Myoview; GE Healthcare, Little Chalfont, United Kingdom) or sestamibi (Cardiolite; Bristol-Myers Squibb, New York, NY). The formerly most used tracer, thallium, is an elementary compound with similar physiologic properties as potassium and provides a good linear relationship between blood flow and tracer uptake into ...

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