How does PET work
Last Modified: April 18, 2002
This information was provided by an unrestricted educational grant from Integral PET Associates, LLC.
Clinically, a PET Scan can locate metabolic defects in the human body often before they have caused structural damage. It can do this with high sensitivity and reliability. This is a great advantage in deciding treatment courses and in diagnosing various conditions.
Since PET accurately and sensitively measures function or physiology in the human body it can detect problems before they cause irreversible damage to tissues. It may also detect response to treatment earlier than many other techniques, such as CT or MRI scans. The areas in which PET is making critical contributions are cancer, heart disease, and neurology.
PET and Cancer
PET can detect active tumors in the body with very high sensitivity. Active tumors have a high metabolism and therefore high demand for glucose. In this way malignant tumors may be distinguished from benign tumors and hidden tumors may be found. Also the response of tumors to treatment (surgery, chemotherapy, radiotherapy, immunotherapy or gene-therapy) may be seen and measured earlier by PET than many other techniques. Successfully treated tumors are destroyed physiologically often long before there is significant shrinkage of tumor volume. In this way stressful treatments can be assessed and completed earlier than might otherwise be possible.
PET and Heart Disease
Blood flow and glucose metabolism in the muscles of the heart may be accurately measured by PET. These measurements are made by imaging the distribution of intravenously injected radiolabeled ammonia (blood flow) and glucose (metabolism). Areas of low blood flow but normal metabolism in the heart muscle indicate heart muscle that may be repaired by restoring blood flow (repairing the appropriate coronary artery), while areas of matched low blood flow and metabolism may already be irreversibly damaged and so require other treatments. In addition blood flow in the heart may be measured at rest and after exercise to detect partly obstructed arteries in the heart responsible for angina.
PET and Seizures
Seizures or epilepsy often start from a single focus of abnormal tissue in the brain. When the frequency and intensity of seizures do not respond well to medication, surgery may provide permanent relief. In any event, injection of a tiny amount of radiolabeled glucose is used to image the metabolism of the brain by PET. If you were to have a seizure around the time of glucose injection the seizure focus would be an area of intense metabolism (and uptake). Between seizures the focus shows up as an area of decreased metabolism in the brain.
PET and Brain Injury
Brain trauma often results in subtle changes in brain anatomy and physiology, which may have marked effects on cognition and emotion. The physiological changes underlying these longer term effects of closed head or brain injury can frequently be demonstrated with PET scans of the brain.