How to read your PET/CT report (and what SUV actually means)

A PET/CT report is written for your treating doctor, not for you. That is appropriate — it needs to be precise — but it leaves patients reading a page of unfamiliar terms during the most anxious week of their year. Here is a translation.

Read the last section first

Every report ends with an Impression or Conclusion. That is the radiologist's actual answer: a short summary of what was found and what it means.

The long section above it — the Findings — is the evidence. It describes every organ, including all the normal ones, because "the liver is normal" is a finding worth recording.

If you read nothing else, read the impression.

The phrases that appear in every report

FDG-avid — takes up the tracer. Effectively, "this is metabolically active". It is not a synonym for cancer.

Metabolically active — the same idea, in other words.

Physiological uptake — normal, expected activity. Your brain, heart, liver, kidneys, bladder and bowel all take up FDG in the ordinary course of being alive. When the report says physiological, it is explicitly ruling out disease.

No abnormal FDG uptake — nothing lit up that shouldn't have. This is good news.

Hypermetabolic — brighter than surrounding tissue.

Hypometabolic / photopenic — darker than surrounding tissue. In the brain this can be the significant finding; elsewhere it often means a cyst, necrosis or scar.

Non-FDG-avid — did not light up. In a known lesion this is usually reassuring, though some slow-growing cancers are genuinely not FDG-avid, which is why context matters.

Sub-centimetre / too small to characterise — the lesion is below the resolution at which activity can be reliably measured. Honest uncertainty, not evasion. This category shrinks considerably on a digital scanner.

Interval change — what has changed since the previous scan. This is the phrase your oncologist cares about most.

SUV, and why not to fixate on it

SUV stands for standardised uptake value. It is a number expressing how much tracer accumulated in a region, corrected for the injected dose and your body weight. SUVmax is the highest value inside a given lesion.

Roughly: liver sits around 2 to 3, and many centres treat an SUVmax above about 2.5 as suspicious in a lung nodule. But that threshold is a convention, not a law, and it varies by organ and by cancer type.

Three cautions that genuinely matter:

A high SUV does not prove cancer. Active tuberculosis, sarcoidosis, abscesses, healing surgical wounds and inflamed joints all produce high values. In India, where tuberculosis is common, this is not a theoretical concern.

A low SUV does not exclude cancer. Several tumour types are inherently poorly FDG-avid — some prostate cancers, mucinous adenocarcinomas, low-grade neuroendocrine tumours, well-differentiated hepatocellular carcinoma. This is precisely why targeted tracers such as PSMA, DOTA and FAPI exist.

SUVs from different machines are not directly comparable. Values depend on the scanner, the reconstruction settings, the time between injection and scan, and your blood sugar. Comparing an SUV of 6.2 from one centre with 5.4 from another and concluding there has been improvement is unsound. Comparison is meaningful when the scans were performed under comparable conditions — one more reason to have follow-up scans at the same centre where practical.

Response criteria in the impression

If this is a follow-up scan, you may see one of these labels:

• Complete metabolic response (CMR) — no abnormal activity left. The best possible result.
• Partial metabolic response (PMR) — significantly reduced. Treatment is working.
• Stable metabolic disease (SMD) — little meaningful change.
• Progressive metabolic disease (PMD) — increased activity, or new lesions. Usually prompts a change of treatment.

For lymphoma you may instead see a Deauville score from 1 to 5, comparing residual uptake against the blood pool and liver. Scores of 1 to 3 are generally considered a good response; 4 and 5 indicate residual disease.

Things that commonly frighten people unnecessarily

"Mild uptake in the bowel." Extremely common and almost always normal. Bowel is metabolically busy.

"Brown fat uptake." Symmetrical activity in the neck and shoulders — the body generating heat in cold weather. Entirely benign.

"Uptake in the vocal cords." Usually because someone was talking during the uptake period.

"Diffuse marrow and splenic uptake." Nearly always a reaction to G-CSF injections or recent chemotherapy, not disease.

"Reactive lymph nodes." Nodes responding to infection or inflammation rather than tumour. The pattern, shape and clinical context distinguish them.

"Post-treatment inflammatory change." Radiotherapy and surgery leave inflammation that lights up for weeks to months. This is one of the reasons scans are timed rather than done immediately after treatment.

Comparison is everything

The most valuable sentence in a follow-up PET report is the one describing change over time. It cannot be written without the previous images.

Bring your old scans as DICOM files on a CD or a download link, not as printed film and not only as a report. A radiologist can measure the same lesion in the same plane on both studies only if both studies are actually available.

If you do not understand your report

Ask. Bring it back to us and we will open the images and go through them with you and your family — where the finding is, what it means, and what it does not mean.

And please do not spend the evening searching individual phrases from your report online. The internet does not know your history, your treatment, your previous scans or your grade, and it will reliably offer you the worst interpretation available. Your treating doctor has all of that context. Ask them.