A full-body PET scan involves exposure to a certain amount of radiation, primarily from the radioactive tracer injected into the body and sometimes combined with a CT scan for detailed anatomical imaging. The radiation dose from a PET scan alone typically ranges from about **5 to 7 millisieverts (mSv)**. When combined with a CT scan (a PET/CT scan), the total radiation dose can be higher, generally up to around **25 mSv or less**, depending on the CT settings and the body area scanned.
To understand this better, it helps to know what a PET scan is and how it works. PET stands for Positron Emission Tomography. It uses a radioactive substance called a radiotracer, most commonly fluorodeoxyglucose labeled with fluorine-18 (18F-FDG). This tracer is injected into the bloodstream, where it travels through the body and accumulates in tissues that use a lot of glucose, such as cancer cells or areas of inflammation. The PET scanner detects the gamma rays emitted as the radioactive tracer decays, creating images that show metabolic activity inside the body.
The radioactive tracer used in PET scans has a relatively short half-life—about 110 minutes for 18F-FDG. This means the radioactivity decreases quickly, losing half its strength roughly every two hours. Within about 24 hours, the radioactivity from the tracer has decayed to a tiny fraction of the original dose, making it safe for the patient and those around them after this period. Patients are usually advised to avoid close contact with very sensitive individuals, like infants or pregnant women, for about 12 hours after the scan to minimize any radiation exposure to others.
The radiation dose from the PET scan itself is comparable to or slightly higher than some other medical imaging procedures but is generally considered safe when used appropriately. For context, the average person receives about 3 mSv of radiation annually from natural background sources. A PET scan’s dose is roughly equivalent to a few years’ worth of natural background radiation.
When PET is combined with CT (PET/CT), the CT component adds additional radiation because it uses X-rays to provide detailed anatomical images that complement the metabolic information from the PET scan. The CT dose varies depending on the scan protocol but can range from about 2 to 10 mSv or more. Together, the PET and CT doses typically total up to around 25 mSv or less for a full-body scan.
Recent advances in PET technology have focused on reducing radiation exposure while maintaining image quality. Newer total-body PET scanners and improved detector sensitivity allow for lower doses of the radioactive tracer to be used. Studies have shown that radiation doses can be reduced by up to 90% in some cases without compromising the accuracy of the scan, which is especially beneficial for patients who require multiple scans, such as those undergoing cancer treatment or children.
In summary, a full-body PET scan involves a radiation dose generally between 5 and 7 mSv from the PET tracer alone, with the total dose increasing if combined with a CT scan. This level of radiation is carefully managed and justified by the valuable diagnostic information PET scans provide, particularly in oncology, neurology, and cardiology. The radioactive tracer decays quickly, minimizing long-term radiation exposure, and ongoing technological improvements continue to reduce the radiation burden on patients.
