Nuclear cardiology

1

What is nuclear cardiology?

• Nuclear cardiology is a field of cardiology that uses radioisotopes to assess myocardial perfusion and myocardial function in different clinical settings, as well as radionuclide angiography and metabolic and receptor imaging.

2

What is myocardial perfusion imaging?

• Myocardial perfusion imaging (MPI) is a noninvasive imaging method that utilizes radioisotopes to assess regional myocardial blood flow, function, and viability. MPI is used to identify ischemic or infarcted regions by detecting differences in blood flow during stress compared with rest. MPI can be performed using single-photon emission computed tomography (SPECT) or positron emission tomography (PET) imaging.

• During the stress portion of the test, exercise causes an increase in myocardial demand, or a pharmacologic agent is used to produce vasodilation in the coronary vascular bed. A normal vessel vasodilates and can increase coronary blood flow up to four times its baseline in response to stress. However, a markedly diseased or stenotic vessel cannot increase blood flow to the myocardium to the extent that a normal vessel can. The radiotracer is delivered to the myocardium via the blood vessel after stress (exercise or pharmacologic vasodilator), so the inability to vasodilate results in less relative radiotracer uptake compared to the rest of the myocardium. The areas of myocardium supplied by diseased blood vessels will therefore take up less radiotracer than the areas supplied by normal blood vessels because of relatively less blood flow. This heterogeneous radiotracer uptake is seen as a perfusion defect.

3

What are the uses of myocardial perfusion imaging?

• To diagnose coronary artery disease (CAD) in patients with intermediate risk for CAD who present with symptoms concerning for CAD.

• To localize and quantify ischemia in patients with known CAD to help guide medical decision making.

• To determine infarct size in patients with known CAD.

• For risk stratification in those with elevated coronary calcium score on computed tomography (CT) imaging.

• To determine areas of residual ischemia or areas of myocardium at risk after revascularization.

• To assess the presence of viability of myocardium after prior damage.

4