PET Imaging

Cardiac positron emission tomography (PET), also known as PET perfusion, is an accurate method for assessing myocardial perfusion and metabolism in the evaluation of coronary heart disease. Cardiac disease is the leading killer of Americans and was responsible for 700,142 deaths in the United States of America during the year 2001. During that same year, the number of new cardiac disease diagnoses was approximately 23 million, which makes up 11.5% of the American population. Broken down into age groups, cardiac disease is:

• The third leading cause of death among individuals who are between the ages of 0 and 14.
• The fifth leading cause of death among individuals who are between the ages of 15 and 24.
• The second leading cause of death among individuals who are between the ages of 25 and 64.
• The leading cause of death among individuals who are over 65 years of age or older.

PET allows more exact detection of myocardial ischemia than single photon emission tomography (SPECT). Coronary perfusion is most commonly evaluated by PET with Rubidium-82 and viability with FDG (although other radiotracers can be used for either exam). In addition, PET has higher spatial resolution and allows attenuation correction and the quantification of various physiologic parameters.

In order to read a cardiac PET, fluorodeoxyglucose (FDG) is used as a tracer to measure myocardial cell glucose metabolism. An area of ischemic viable myocardial wall will show a mismatch between the blood flow and metabolism. Regions showing deficits in both perfusion and FDG uptake can be considered dead regions. An area showing a defect in blood flow but with preserved FDG uptake represents a blood flow-metabolism mismatch, and is considered still viable for revascularization.  Other less commonly used clinical applications of cardiac PET include assessment of myocardial oxygen consumption and fatty acid metabolism.

The PET scan procedure begins with the injection of pharmacological stress agents where the imaging takes place. This allows an assessment of the extent of coronary collaterals and measures absolute and extent of flow. PET has an increase in response to coronary dilator and allows optimal visualization of the inferior wall. Common clinical indications provided by PET imaging includes the assessment of functional level/prognosis in angina (CAD), evaluation of cardiac perfusion pre/post intervention, and pre surgical evaluation prior to major non-cardiac surgery.