Am I Radioactive After a PET Scan? Precautions for Family and Pets

Quick answer: yes, but only slightly and only for a few hours. The tracer used in most PET scans (FDG) contains fluorine-18, which loses half of its radioactivity about every 110 minutes, and your body also clears some of it in urine. After about 9 hours, roughly 97% has decayed. The usual advice is simple: drink water, use the toilet often and wash your hands, and avoid prolonged close contact with babies, young children and pregnant women for the period your center recommends, usually somewhere between 6 and 12 hours. Other adults and pets need no special precautions beyond common sense.

«Can I hug my grandchildren?» is probably the question I hear most after a PET scan. The honest answer: yes, but wait until this evening or tomorrow morning for long cuddles. Here is why.

How long does the radioactivity last?

Fluorine-18 has a physical half-life of about 110 minutes: every 110 minutes, half of what is left decays into a stable, non-radioactive form. On top of that, part of the tracer leaves your body in urine within the first couple of hours.

Time after the injection	Radioactivity remaining (physical decay only)
About 2 hours	About 50%
About 6 hours	About 10%
About 9 hours	About 3%
About 12 hours	About 1%
24 hours	Practically none

Because you also clear tracer through urine, the real amount in your body is even lower than the table shows. By the next morning, there is nothing to worry about.

This is very different from radioactive iodine or other radionuclide treatments, which use much larger doses and have much stricter, longer precautions. See [link: Radioactive Iodine Therapy: What to Expect and Precautions].

Who needs precautions, and for how long?

Babies, young children and unborn babies are more sensitive to radiation, so precautions focus on them.

Person	Typical advice after an FDG PET scan
Other adults at home	No special precautions
Pregnant women	Avoid prolonged close contact (for example sitting side by side for a long time) for the period your center recommends, often 6 to 12 hours
Babies and young children	Avoid prolonged close contact, such as holding them on your lap, carrying them or sharing a bed, for the same period. Brief contact is not a concern
Pets	No specific precautions are usually needed; avoid long cuddles in the first hours, as for people

Recommendations differ between organizations and hospitals. For example, Australian guidance considers contact restrictions not strictly required after FDG but suggests at least 4 hours as a prudent measure; one U.S. hospital advises avoiding prolonged contact with young children and pregnant women for 8 hours; other centers advise up to 10 or 12 hours. Follow the instructions your center gives you.

The point is distance and time: radiation falls quickly with distance, so being in the same house or room is fine. What matters is long, close contact.

From the scanner room: [TU EXPERIENCIA: qué indicaciones das tú al salir del PET, cuántas horas, y cómo respondes a la pregunta de los nietos o las mascotas.]

Practical tips for the rest of the day

Drink plenty of water and empty your bladder often: much of the tracer leaves in urine.
Wash your hands well after using the toilet, and flush. Men can sit down to avoid splashes.
Plan ahead: arrange for someone else to look after babies or toddlers for the rest of the day if possible.
Avoid long journeys sitting close to a pregnant woman or young child in the first hours, such as a long car ride with a baby on the back seat next to you.
Sleep: if you share a bed with a young child or a pregnant partner, your center may suggest sleeping separately the first night.

Breastfeeding

Very little FDG passes into breast milk. Most international radiation safety organizations say no interruption of breastfeeding is strictly necessary, but advice varies:

Some guidelines recommend pausing for 1 to 4 hours.
The FDA-approved drug label advises pumping and discarding milk and avoiding close breast contact with the baby for at least 9 hours after the injection.
Several experts suggest someone else bottle-feeds the baby with expressed milk for several hours, because the main exposure comes from close contact with the breast, not from the milk itself.

Talk to your nuclear medicine team before the scan, and consider pumping and storing milk in advance. See [link: Radioactive Tracers Explained: Are They Safe?].

Going back to work

In most jobs you can return to work the same day or the next day. If you work closely with young children or pregnant women, for example in a nursery, ask your center whether to take the rest of the day off.

Airports and radiation detectors

Sensitive radiation detectors at some airports, border crossings and buildings can pick up traces of radioactivity for a short time after nuclear medicine tests. After an FDG PET scan, this is only likely on the same day. If you travel soon after your scan, ask the center for a letter describing the test.

Tips from the technologist

[TU EXPERIENCIA: 2-3 consejos propios. Ideas: pedir la cita por la mañana si hay niños pequeños en casa, llevar una botella de agua, no venir acompañado de embarazadas o bebés a la cita.]

Frequently asked questions

Can I hug my children after a PET scan?

A quick hug is fine. Avoid long, close contact such as holding a baby on your lap for the period your center recommends, usually 6 to 12 hours.

Can I sleep in the same bed as my partner?

If your partner is an adult and not pregnant, yes. If your partner is pregnant, your center may suggest sleeping apart the first night.

Is my urine radioactive?

For a few hours, slightly. Flush the toilet and wash your hands well.

Can I be around my dog or cat?

Yes. Normal contact is fine; just avoid long cuddles in the first hours.

Can I go to the grocery store after a PET scan?

Yes. Brief contact with other people in public is not a concern.

Is a PSMA or DOTATATE PET scan different?

The tracers are different, but these diagnostic scans also use short-lived tracers, and precautions are usually similar. Follow your center’s instructions. See [link: PSMA PET Scan for Prostate Cancer: A Patient Guide].

For the full scan day, see [link: PET Scan: What to Expect From Start to Finish].

This article is for general information and does not replace the instructions given by your nuclear medicine team.