PET imaging scan: what should you know?

Before the scan, a radiotracer is given, commonly FDG, a glucose-related material. After a quiet waiting period, the scanner detects signals from the tracer. PET highlights patterns of cellular activity; CT or another anatomical scan helps locate those patterns. Increased uptake may reflect cancer but can also occur with infection, healing or inflammation. A report therefore needs clinical context. PET-CT may be used to find active disease, clarify an uncertain finding, assess treatment response or support planning. It does not replace the full assessment by your care team.

Use the centre's instructions about fasting, water, exercise and medicines. Tell staff about diabetes, pregnancy or breastfeeding, recent illness and any difficulty staying still. Avoid strenuous activity if instructed, because muscle activity can affect tracer distribution. At the department, you may have a blood glucose check, receive the tracer, rest in a quiet room and then lie still during imaging. Bring earlier reports if requested. Learn more about the [FDG Radiotracer](/materials/fdg-radiotracer/) and the [PET-CT Scanner](/technology/pet-ct-scanner/).

Tell the imaging staff immediately if you feel unwell during the visit. After leaving, seek urgent help for severe breathlessness, chest pain, collapse, or swelling of the face or throat. Contact the service promptly for persistent vomiting, marked dizziness, a widespread rash or worsening pain at an injection site. These symptoms are not a way to interpret the scan; they are reasons to be assessed. For questions about a report, use the appointment arranged by your referring clinician rather than trying to read an isolated image.

Ask what the scan is intended to answer, whether you need to change food or medicines, how diabetes affects preparation, and when the report will be reviewed. Ask whether a [PET-CT Scan](/treatments/diagnostics-and-staging/pet-ct-scan/) is being used to assess a known condition such as [Lymphoma](/conditions/lymphoma/) or to investigate a possible [Cancer of Unknown Primary](/conditions/cancer-of-unknown-primary/).