What does a PET-CT scan show?

PET images map uptake of FDG, a glucose-like radiotracer. CT images show the body's structure, such as the size and position of a nodule, lymph node or organ change. Together they can show whether an active area corresponds with a visible structural finding and whether activity appears in more than one region.

The appearance is descriptive, not a final diagnosis. Inflammation and infection may be active, while some cancers have limited FDG uptake. Recent treatment, blood glucose and movement can influence the result. The radiologist or nuclear medicine physician compares the images with your history, examination, pathology and previous scans.

Wait for the formal report and the clinician's explanation before drawing conclusions from colours or brightness. Ask which findings are new, which are stable and which need confirmation. A follow-up scan, MRI, ultrasound or biopsy may be suggested because each test answers a different question. Keep copies of reports for future comparisons.

For practical details, see [PET-CT Scan](/treatments/diagnostics-and-staging/pet-ct-scan/), [FDG Radiotracer](/materials/fdg-radiotracer/) and [PET-CT Scanner](/technology/pet-ct-scanner/).

During the visit, tell staff promptly about severe discomfort, swelling at the injection site, faintness, breathing difficulty or a rapidly spreading rash. Afterward, seek urgent help for throat swelling, collapse or serious breathing problems. A report that needs clarification can usually be discussed at the planned appointment, unless your clinician gives different instructions.

Which finding is the main focus of the report? Does it match what was seen on CT? What non-cancer causes could explain the activity? What test will confirm the interpretation, and when should we review the next step?