What Should You Know About PET Scanner Images?

PET scanner images show areas of increased or reduced tracer activity alongside body structures, but a bright area is not by itself proof of cancer. The scan helps a clinical team see how tissues are behaving and where an abnormal finding sits in the body. The appearance must be compared with your symptoms, examination, other scans and sometimes a tissue sample.

A PET image maps the distribution of a radioactive tracer. Many cancer cells use glucose quickly, so an FDG radiotracer may collect more strongly in some tumours. Infection, inflammation, healing tissue and certain normal organs can also show increased activity. Areas with little visible activity can have several explanations, including tissue that uses less tracer or a finding below the scan's ability to detect it.

The CT part supplies detailed anatomical information, while the PET part adds information about activity. Clinicians review the combined images rather than judging colour alone. They may assess the location, shape, pattern and comparison with earlier imaging. A report may describe a finding as suspicious, indeterminate or likely benign; those terms guide the next step but do not replace a diagnosis.

Ask for the written report and arrange a review with the clinician who requested the scan. Bring earlier scans or reports if they were performed elsewhere, because change over time can help clarify a finding. Do not try to diagnose yourself from an online image or from the colour intensity on a screen. Depending on the result, your team may recommend observation, another imaging test, blood tests or a biopsy.

Preparation instructions can affect image quality: follow the fasting and medication guidance you were given, tell the imaging team about diabetes or pregnancy, and mention any difficulty staying still. Learn more about the [PET-CT Scan](/treatments/diagnostics-and-staging/pet-ct-scan/) and the [PET-CT Scanner](/technology/pet-ct-scanner/).

Contact your care team promptly if the report asks for urgent follow-up, recommends a biopsy, or identifies a finding that needs a near-term review. Seek urgent medical help for severe breathing difficulty, chest pain, sudden weakness, confusion, heavy bleeding or a rapidly worsening allergic reaction after the appointment. These symptoms need assessment on their own and cannot be judged from the scan image.

If you are waiting for results, ask when and how they will be shared. A delay in viewing images does not reveal what they mean. Your clinician can explain whether a finding needs attention now, routine follow-up or comparison with previous imaging.

Useful questions include: What area on the image are you explaining? Does it have a matching change on CT? Could infection or inflammation affect this result? Do I need comparison with an older scan? What follow-up is recommended, and when should I expect it? Would a biopsy or another test change the treatment plan?

The tracer used for many oncology PET scans is [FDG Radiotracer](/materials/fdg-radiotracer/). PET imaging can support evaluation of conditions such as [Lymphoma](/conditions/lymphoma/) and [Cancer of Unknown Primary](/conditions/cancer-of-unknown-primary/), but the meaning of an image depends on the individual clinical context.