A Fluorodeoxyglucose-Positron Emission Tomography (FDG-PET) scan is a specialized medical imaging technique that provides detailed insights into the metabolic activity within the body’s tissues and organs. It differs from traditional imaging methods, which primarily show anatomical structures, by revealing how cells are functioning. This non-invasive procedure involves injecting a small amount of a radioactive substance, known as a radiotracer, into the bloodstream. The PET scanner then detects the energy emitted by this tracer, creating images that highlight areas of unusual metabolic activity.
The Science Behind FDG-PET
FDG-PET scans utilize a sugar analog called fluorodeoxyglucose (FDG) as their primary radiotracer. FDG is chemically similar to glucose, the body’s main energy source, allowing cells to absorb it as they would regular sugar. However, unlike glucose, FDG cannot be fully metabolized by the cells, causing it to accumulate inside them. This accumulation is particularly pronounced in cells with higher metabolic rates, such as many cancer cells, which consume glucose at an accelerated pace.
Once injected, the FDG emits positrons, which are tiny, positively charged particles. These positrons quickly collide with electrons in the body, resulting in an “annihilation” event that produces two gamma rays. These gamma rays travel in opposite directions and are detected by the PET scanner’s ring of sensors. A computer then uses the timing and location of these detected gamma rays to reconstruct a three-dimensional image, illustrating the distribution of FDG and, consequently, the metabolic activity across different tissues.
What FDG-PET Detects
FDG-PET scans provide unique functional information by visualizing metabolic activity, allowing healthcare providers to identify areas of abnormally active cells, which can indicate disease processes. The scan is frequently used in oncology to detect cancerous tumors, assess their spread (staging), and monitor how well treatments are working. It can often detect cellular changes that precede visible anatomical changes on other scans.
Beyond cancer, FDG-PET helps evaluate various neurological conditions, such as identifying areas of abnormal glucose metabolism in the brain that might be associated with epilepsy or certain dementias. In cardiology, it can assess blood flow to the heart muscle and identify damaged heart tissue.
The Patient Experience
Undergoing an FDG-PET scan involves several steps designed to ensure accurate results. Patients typically receive instructions to fast for at least 6 hours before the appointment and to avoid strenuous physical activity for 24-48 hours prior, as these can influence tracer uptake. Upon arrival, a healthcare professional will check blood glucose levels and place an intravenous line, usually in the arm. The FDG radiotracer is then injected through this IV line.
Following the injection, patients usually rest quietly for about 45 to 90 minutes to allow the FDG to distribute throughout the body and be absorbed by tissues. During this “uptake” phase, movement, talking, and chewing gum are often discouraged to prevent FDG uptake in muscles that are not being examined. After the waiting period, the patient lies on a scanning bed that moves slowly through the PET scanner, which typically takes 20-40 minutes. The process is generally painless, and patients are monitored throughout the scan.
Safety and Important Considerations
FDG-PET scans involve exposure to a small amount of radiation from the injected radiotracer and often from an accompanying CT scan. Healthcare providers carefully weigh the benefits against the risks.
Certain considerations are important for patient safety and scan accuracy. Patients are advised to hydrate well before the scan to help clear the tracer from the bladder. Pregnancy and breastfeeding are generally contraindications or require special precautions due to radiation exposure. For individuals with diabetes, strict blood glucose control is important, as high blood sugar levels can interfere with FDG uptake and affect scan quality.