What does a PET scan actually measure?
A PET scan tracks a mildly radioactive sugar injected before imaging. Cells that burn sugar fastest light up — and fast metabolism is a hallmark of active cancer. Fused with a CT scan (PET-CT), it shows where things are and how metabolically active they are in one picture.
The numbers on the report
- SUV (standardised uptake value) — how intensely a spot takes up the sugar compared to background. Higher generally means more metabolically active. There is no universal “cancer threshold”: SUVs vary by scanner, timing and tissue, so comparisons between your own scans matter more than any single value.
- Deauville score (lymphoma) — a 1-to-5 scale comparing lymphoma activity to two internal reference points (blood pool and liver). 1–3 is generally read as good response; 5 means activity well above liver or new lesions. In lymphoma care, pre-agreed rules like “Deauville 5 → escalate treatment” are powerful protections — our published research documents how costly it is when such a written rule is not acted on.
Why a hot spot is not automatically cancer
Infection, inflammation, healing tissue, brown fat, and normal organs (brain, heart, bladder) all take up sugar. Radiologists read patterns, not just brightness — which is why the written report matters more than the colourful image.
Getting the most from your scans
- Keep every report — response is judged by change between scans.
- Try to scan on the same machine and protocol when possible.
- Ask two questions after each scan: what changed since last time? and does this change the plan?
Have a PET report you don’t fully understand? Attach it to a ticket — we will translate every line, SUVs and all.