Simple Steps to Clear — the Tracer Faster

There is no single measured amount that has been proven to be the correct target, and guidance varies slightly between nuclear medicine centres. The consistent recommendation across IAEA and standard nuclear medicine practice is to drink more than your usual daily amount — steadily throughout the rest of the day — rather than forcing a large volume at once. If you have a health condition that limits how much you can drink, such as a kidney problem or heart failure, tell your scan team before you leave so they can give advice that is safe for your situation.

Most of the active radioactivity reduces within a few hours. The radioactive element in FDG, fluorine-18, has a half-life of around 110 minutes according to IAEA guidance, meaning the radioactivity halves roughly every two hours. Combined with excretion through urine, the tracer is largely cleared by the end of the scan day for most people. A very small residual amount continues to decay overnight and is not considered a safety concern by the time you wake the next morning.

The dose that reaches someone sitting near you after a PET scan is very low — well below the levels associated with any health effect. The short-term precautions around young children and pregnant women are a standard conservative measure used across nuclear medicine worldwide, not a signal that the dose is harmful. IAEA nuclear medicine guidance describes them as practical good practice rather than urgent protection. If you live alone with a very young baby, mention this to your scan team before the appointment so they can give advice suited to your home situation.

A brief hug is fine. The precaution that matters is prolonged close contact — sitting a young child on your lap for a long period, or holding a baby against your body for an extended time — not a normal greeting or a short hug. As the hours pass and the tracer clears through urine and natural decay, even that restriction falls away on its own. By the next morning, standard precautions no longer apply.

Yes, for the rest of the day while the tracer is still being excreted in your urine. Double-flushing dilutes the tracer in the water and reduces exposure for others who use the same toilet. This is a simple precaution included in standard nuclear medicine aftercare instructions. By the next morning, the tracer has largely cleared and there is no need to continue the practice.

Any fluid counts. The goal is to keep your kidneys working steadily so they continue to filter and excrete the tracer. Plain water is the simplest choice, but coconut water, diluted juice or light tea all work. Very strong tea or coffee in large quantities can be mildly dehydrating in some people, so plain water is the safest default — but one or two cups of tea alongside water is not a problem.

FDG, the tracer used in most PET scans, can pass into breast milk in small amounts. Nuclear medicine centres advise interrupting breastfeeding for a period after the scan, though the specific duration depends on the tracer used and the guidance of your centre's radiation safety officer. The most important thing is to tell your scan team that you are breastfeeding before your appointment, not afterwards. They can put a plan in place for managing feeds on the scan day and tell you exactly when it is safe to resume.

Feeling mildly tired or lightheaded after a PET scan is common, mainly because most scans require several hours of fasting beforehand. The tracer itself very rarely causes symptoms. If you feel genuinely unwell — nausea, dizziness, difficulty breathing, or chest discomfort — tell the scan centre before you leave, or call your oncology team once you are home. Reactions to the tracer are uncommon, but your team needs to know if something does not feel right.