A Positron Emission Tomography (PET) scan is a medical imaging test that provides detailed pictures of organs and tissues at work, often used to detect early signs of diseases like cancer, heart conditions, and brain disorders. Patients frequently express concern about radioactivity after this procedure. Understanding how the radioactive material works and how quickly it leaves the body can help alleviate these concerns.
Understanding the Radiotracer
A PET scan involves the administration of a radiotracer, which is a small, safe amount of radioactive material. This substance is typically linked to a sugar molecule, such as fluorodeoxyglucose (FDG), and is injected intravenously. The radiotracer highlights metabolic activity or specific areas within the body that may indicate a health problem. For example, rapidly growing cancer cells often absorb more FDG due to increased metabolic activity and a higher demand for glucose. The PET scanner then detects the radiation emitted by the tracer, producing images that show where it has accumulated.
How Long Radioactivity Lasts
The radioactivity from a PET scan diminishes quickly due to “half-life” and natural bodily elimination. Half-life refers to the time it takes for half of the radioactive material to decay into a more stable, non-radioactive form. For Fluorine-18 (F-18 FDG), the most commonly used radiotracer, its physical half-life is approximately 109.7 to 110 minutes, or just under two hours.
The body also actively eliminates the radiotracer, primarily through urine. Within a few hours after the scan, a significant portion of the tracer is excreted. While the physical half-life is constant, biological elimination further reduces the effective time you remain radioactive. Most radioactivity is practically negligible within 6 to 12 hours after the injection, with less than 1% of the initial dose remaining after 24 hours. Hydration can influence the speed at which the tracer is eliminated from your system.
Safety Measures After Your Scan
After a PET scan, some precautions are recommended to minimize incidental exposure to others. Staying well-hydrated by drinking plenty of fluids helps your body excrete the radiotracer more quickly. Flushing the toilet twice after each use for the first few hours can also help reduce residual radioactivity in the bathroom.
It is advised to limit prolonged close contact with vulnerable individuals such as pregnant women, infants, and young children for about six hours following the scan. Brief interactions with these groups usually pose minimal risk. You can resume most normal activities shortly after the procedure, including returning home without special transportation requirements. If you plan to travel within 24 to 48 hours after your scan, it is advisable to request a note from your medical provider explaining your recent procedure, as sensitive radiation detectors at security checkpoints might be activated by even small amounts of radiation.