Positron emission tomographic scanning, or PET scanning, is employed for two major cardiovascular applications – assessment of coronary artery disease and assessment of heart muscle viability. PET scans operate on a principle identical to that described above for SPECT scanning.
Unlike SPECT images, which employ a radiopharmaceutical label that has relatively low energy. This radiopharmaceutical, 82Rubidium emits a particle called a positron. When this positron is emitted by the radiopharmaceutical, it interacts with tissues within the patient to produce gamma ray radiation that can be detected and measured. The radiation produced is of much higher energy than the gamma ray radiation produced by SPECT imaging.
The benefit of this higher energy gamma radiation is that the radiation easily “makes it out of” the patient, regardless of patient size. 82Rb-PET provides a higher quality image and higher rate of diagnostic test accuracy for larger patients undergoing non-invasive assessment for suspected coronary artery disease than does SPECT imaging.
The other major cardiovascular application for PET scanning is the assessment of heart muscle viability, often also referred to as myocardial viability. For patients who have suffered heart attacks due to blocked coronary arteries, it is often helpful to assess the extent of heart muscle damage to determine if interventions, such as angioplasty and stent placement or coronary artery bypass grafting surgery, have the potential to improve blood flow to the area of damaged heart muscle and allow some recovery of function.
Often the heart muscle damage following a heart attack may appear more extensive than it is. Some muscle in the involved area may not be functioning well because it is not receiving enough blood flow to function properly, but not so little blood flow that it actually dies. Additionally, some muscle may transiently stop functioning all together after a heart attack, but still remain viable.
Often interventions designed to supply new blood flow to an area of heart muscle damaged by blocked coronary arteries can allow poorly functioning or non-functioning heart muscle to recover and function properly once more. PET scans (using a different radioisotope than 82Rb-PET: 18Fluorine) can show physicians that muscle that is not contracting properly is still viable and salvageable, which can make the decision to pursue revascularization therapy clear.