Unlike diagnostic X-rays and CT scans where radiation stops the millisecond the exposure ends, nuclear medicine procedures involve injecting radiopharmaceuticals that temporarily emit gamma rays from inside the patient.1
Decay Physics: F-18 (110 min) vs Tc-99m (6 hr)
- Fluorine-18 (PET/CT): With a half-life of 110 minutes, radioactivity drops to 12.5% at 6 hours and below 1% at 10–12 hours.2, 4
- Technetium-99m (Scintigraphy): With a 6-hour half-life, activity decays to 25% at 12 hours and 6.25% at 24 hours.4
Practical Contact Rules
By the Inverse Square Law, doubling distance from 1 to 2 meters cuts radiation exposure by 75%.1
- Infants & Children: Avoid prolonged close lap-holding or co-sleeping for the first 6–12 hours; sharing the same room at 1.5–2 meters is completely safe.2
- Pregnancy: Maintain a 2-meter distance during the first 12 hours.1
- Hydration: Drink 1.5–2 liters of water to accelerate urinary excretion and reduce bladder dose.2
References
- IAEA. Release of Patients After Radionuclide Therapy. Safety Reports Series No. 63, International Atomic Energy Agency, Vienna, 2014.
- SNMMI (Society of Nuclear Medicine and Molecular Imaging). Patient Information and Radiation Safety in Diagnostic Nuclear Medicine, 2021.
- EANM (European Association of Nuclear Medicine). Radiation Protection of the Patient in Nuclear Medicine. EANM Guidelines, 2020.
- ICRP. Radiation Dose to Patients from Radiopharmaceuticals. ICRP Publication 128, 2015.
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Sıkça Sorulan SorularFrequently Asked QuestionsHäufig gestellte FragenPreguntas frecuentes
Do I contaminate people around me with radiation after a PET/CT scan?
No. Radiation is not contagious like a virus. The injected radiopharmaceutical (F-18 FDG) decays rapidly and is excreted in urine. There is only low external gamma emission for the first 6-12 hours; avoiding prolonged close physical contact (such as holding children on your lap) is sufficient.
How long should I keep distance from children after a PET/CT scan?
The half-life of F-18 is 110 minutes. By 6 hours, radioactivity drops to 12.5%, and by 10-12 hours, to below 1%. Avoiding prolonged close lap-holding for the first 6-12 hours while maintaining a 1-2 meter distance in the same room is completely safe. After 12 hours, all restrictions end.