A Positron Emission Tomography (PET) scan is a medical imaging technique that helps visualize the metabolic and biochemical functions within the body’s tissues and organs. It uses a small amount of a radioactive substance, known as a radiotracer, to highlight areas of activity. A common concern for many individuals undergoing this procedure is how long they remain radioactive afterward. The radioactivity from a PET scan is temporary and quickly diminishes.
The Radiotracer
The radioactivity in a patient after a PET scan comes from a special pharmaceutical called a radiotracer. This substance consists of a radioactive isotope attached to a biological molecule. The biological molecule targets specific processes or areas in the body, such as glucose metabolism or blood flow. For instance, cancer cells often exhibit increased metabolic activity and absorb glucose at a higher rate than healthy cells.
The most frequently used radiotracer in PET scans is Fluorodeoxyglucose (FDG). FDG is a glucose analog, chemically similar to glucose. When injected, FDG is taken up by cells actively using glucose, allowing medical professionals to identify areas of increased metabolic activity, which can indicate disease. Once inside these active cells, FDG becomes trapped, enabling the PET scanner to detect emitted radiation and create detailed images.
How the Body Clears Radioactivity
The radioactivity from a PET scan dissipates through two primary mechanisms: radioactive decay and biological elimination. Radioactive decay is a natural process where unstable atoms of the radiotracer transform into more stable forms. This process is measured by “half-life,” the time it takes for half of the radioactive material to decay.
For FDG, the radioactive isotope is Fluorine-18, which has a half-life of approximately 110 minutes (just under two hours). This means that every 110 minutes, the amount of radioactivity in the body is reduced by half. After about 10 half-lives, the radioactivity is considered negligible.
The body also eliminates the radiotracer through biological processes. The kidneys play a significant role, as a portion of the radiotracer is excreted in the urine. Drinking plenty of fluids after the scan can help accelerate this elimination, flushing the remaining radiotracer from the system more quickly. Combining both radioactive decay and biological clearance, radioactivity significantly decreases within a few hours and becomes almost entirely undetectable by the following day.
Safety Precautions After Your Scan
After a PET scan, take precautions to minimize radiation exposure to others. These measures are generally recommended for a few hours following the procedure.
Limit prolonged close contact with pregnant women, infants, and young children for about 6 to 12 hours after the scan. This is a precautionary measure, as these groups are more sensitive to radiation exposure. Maintaining a greater distance from others during this period can help reduce their exposure.
Hygiene practices aid in eliminating the radiotracer. Drinking extra fluids, such as water, helps flush the radiotracer through the urinary system. Urinating frequently and flushing the toilet twice after each use can further reduce residual radioactivity in the environment. Your medical team will provide specific instructions tailored to your scan and the type of radiotracer used.