Positron emission tomographic (PET) imaging in cardiology
Positron emission tomographic (PET) imaging in cardiology: Positron emission tomography (PET) can measure both the myocardial perfusion and metabolism. Clinically available cardiac PET tracers include perfusion tracers like rubidium-82 and 13N-ammonia as well as the metabolic tracer 18Fluoro-2-deoxyglucose (FDG). High 18FDG uptake is interpreted as myocardial inflammation. A matched metabolic and perfusion defect is taken as a scar. PET data can be acquired in dynamic mode so that it is possible to display myocardial perfusion and metabolism in absolute terms as milliliters per gram per minute of blood flow and moles per gram per minute of metabolism.
PET perfusion tracers are classified as freely diffusible and non diffusible tracers. Freely diffusible tracers accumulate and wash out from the myocardial tissue as a function of blood flow. 15O Water is a freely diffusible tracer. Non-diffusible tracers are retained in the myocardium as a function of the blood flow. Rubidium-82 and 13N-ammonia are non-diffusible tracers. Uptake of rubidium-82 across the sarcolemmal membrane reflects active sodium potassium ATPase pump as rubidium-82 has biological properties similar to potassium.
Some special subsets who are more likely to benefit from PET imaging are: obese patients, women, patients with previous non-diagnostic tests and patients with poor left ventricular function being planned for coronary revascularization . These patients groups are those who are difficult to image with conventional single photon emission computed tomography (SPECT).