What should you know about a PET-CT scan?

“PET city scan” is commonly a mistaken or shortened way of saying PET-CT scan. The PET part detects where a radiotracer is active; the CT part shows the location and shape of organs and tissues. Combining the images can help a specialist compare function with anatomy.

This examination may be used for staging, treatment planning, or checking a response. It may also help investigate cancer found in a lymph node or another site when the original source is uncertain, as in [Cancer of Unknown Primary](/conditions/cancer-of-unknown-primary/). Increased tracer activity has several possible causes and must be interpreted alongside symptoms, examination, and other tests.

Before attending, read the centre's instructions about food, fluids, exercise, medicines, and arrival time. Tell the team about diabetes, pregnancy, breastfeeding, allergies, recent infections, and any trouble lying flat. A tracer injection is followed by quiet rest, then you lie on a table that moves through the scanner.

Keep still and breathe as instructed. The CT portion is brief, while the full appointment includes preparation and the uptake wait. Drink according to the team's advice afterwards. For more detail, see [PET-CT Scan](/treatments/diagnostics-and-staging/pet-ct-scan/), [FDG Radiotracer](/materials/fdg-radiotracer/), and [PET-CT Scanner](/technology/pet-ct-scanner/).

Tell the imaging staff at once about wheezing, facial swelling, widespread itching, severe dizziness, or feeling faint after the injection. Get urgent help for major breathing difficulty, collapse, or rapidly worsening symptoms. If you feel unwell later, contact the centre or your treating team and mention the tracer and scan time.

Ask whether your appointment is a PET-CT, which regions will be covered, and whether contrast is planned. Confirm fasting and diabetes instructions, how long to allow for the visit, when results will be discussed, and whether an abnormal finding would need another scan or biopsy.