How does a PET-CT scan work?

Before the scan, a small amount of [FDG Radiotracer](/materials/fdg-radiotracer/) may be given through a vein. Cells that use more glucose can collect more of this tracer. After a quiet waiting period, a [PET-CT Scanner](/technology/pet-ct-scanner/) detects signals from the tracer, while CT uses x-rays to show anatomy. Software combines the images so an area of altered activity can be located within the body. Increased tracer activity is not specific to cancer: inflammation and infection can also affect the picture. The result must be interpreted with symptoms, examination and other tests.

Follow the centre’s instructions about fasting, drinking water and medicines. Tell staff about diabetes, pregnancy or breastfeeding, allergies and recent illness. Wear comfortable clothing and remove metal items when asked. Plan time for the tracer injection, resting quietly and the scan itself. Drink fluids afterward if your team recommends this, and follow their instructions about contact with other people.

Tell staff immediately if you feel faint, develop pain or have difficulty breathing after the injection. Once home, seek urgent help for severe breathing difficulty, facial swelling or collapse. Contact the imaging team if redness, swelling or increasing pain develops at the injection site. A PET-CT finding needs clinical interpretation; it does not by itself confirm or exclude cancer.

Ask why PET-CT is preferred, whether fasting or medicine changes apply, what the tracer appointment will involve, and when results will be discussed. If the primary site is unclear, ask how the scan may guide the next investigation.