Reading a PET report: what the common terms mean

A PET report can be unsettling to read before anyone has explained it. It is written by specialists for other doctors, so it is dense with terms such as "FDG-avid", "SUVmax" and "no abnormal uptake". Some people see the written report before they have spoken to anyone about it. This page explains the most common words in plain language, using FDG PET-CT in cancer as the example, and says what a report can and cannot tell you.

This is a vocabulary guide, not a way to interpret your own result. Only the specialists who have your scan and history can do that. For background on why PET is used this way, see PET in cancer care.

Who writes the report, and who explains it

A radiologist or a doctor trained in nuclear medicine interprets the images and sends a report to the physician who requested the scan, according to RadiologyInfo.org (RadiologyInfo.org). That referring doctor then discusses the findings with you in the context of everything else that is known. PET-CT reading draws on two bodies of knowledge, nuclear medicine and radiology, and one review of reading practice describes the combined interpretation as something that transcends each field alone (Hofman and Hicks, Cancer Imaging, 2016).

The same authors describe a typical report as short and structured: clinical notes, technique, comparative studies, findings, and a conclusion. Knowing that layout helps. The conclusion answers the question the doctor asked, while the findings section lists what was seen and where.

What SUV is, and what it cannot do

SUV stands for standardised uptake value. European guidelines define it as a measurement of the uptake in a tumour normalised on the basis of a distribution volume. In everyday terms, it is a way of expressing how much tracer has gathered in a spot, adjusted so scans of different people can be compared more fairly. You will often see SUVmax, which the guideline describes as the value of the single voxel (a tiny block of the 3D image) with the highest uptake within a lesion (Boellaard and colleagues, EANM procedure guidelines, 2014).

Because it is a single number, SUV looks more precise than it is. The same guideline notes that some factors alter quantification, for example metal implants, which prevent proper quantification at and near the implant, and contrast agents or truncated CT images, which can cause artefacts. A lesion with an SUVmax of 6 on one scanner on one day is not exactly comparable with a lesion of 6 on another scanner months later, and different centres may use different conventions.

Hofman and Hicks make a point that is useful for any reader. They describe one centre's labels, with SUV below 5 as low intensity, 5 to 10 as moderate, 10 to 15 as intense and above 15 as very intense, and say that putting the actual value in the report helps avoid ambiguity because words are interpreted differently by different readers. Treat those bands as one group's convention. A high number does not prove cancer and a low number does not prove its absence. Some benign conditions, such as infection and inflammation, take up FDG, and some tumours take up very little.

Common report terms at a glance

Frequently used PET report wording and what it generally means

Term	Plain-language meaning	Worth remembering
Uptake	How much tracer has collected in a tissue.	Uptake shows activity, not the cause of that activity.
Avid (FDG-avid)	A tissue takes up the tracer strongly enough to stand out.	Lymphoma staging guidance, for example, applies to FDG-avid subtypes.
Non-avid	Little or no tracer uptake above surroundings.	Some lesions, including certain tumours, are not FDG-avid, so a non-avid finding is not proof of benign tissue.
Hypermetabolic	Higher sugar use than expected for that tissue, so more FDG gathers.	Descriptive wording. It does not name the cause, which could be tumour, inflammation or another process.
Background	The normal level of tracer in surrounding tissue, used for comparison.	Findings are described relative to it. A PSMA guideline reports uptake as absent, low, intermediate or high compared with background.
Physiological uptake	Normal tracer collection in organs that handle it, such as the liver.	Some uptake is expected and not a concern.
Lesion	Any area of abnormality on the images.	The word means "an abnormal area", not "a tumour".
SUV, SUVmax	A standardised measure of uptake; SUVmax is the highest voxel value in a lesion.	A supporting measurement, affected by technical factors.
Deauville score	A 1 to 5 visual scale used in lymphoma to compare uptake with reference tissues such as the liver.	One example of a disease-specific system. It is not used for all cancers.
No abnormal uptake	No areas of uptake beyond the expected normal pattern.	Can mean nothing suspicious was seen. It does not rule out disease too small or too faint to detect.
Incidental finding	Something found that was not the reason for the scan.	Many do not need further tests.

Scoring systems as examples

In lymphoma, specialists use the Deauville five-point scale. A 2022 review lists it as score 1 for no uptake, 2 for uptake at or below the mediastinum (the area in the centre of the chest), 3 for above the mediastinum but at or below the liver, 4 for moderately increased uptake compared with the liver, and 5 for markedly increased uptake compared with the liver, or new lesions. There is also an X category for new uptake unlikely to be related to lymphoma (Yoo, Blood Research, 2022). The scale uses the patient's own liver and chest as the yardstick, which makes it a comparison, not an absolute number.

Other cancers have their own frameworks. Prostate imaging with PSMA tracers, for instance, has several standardised reporting systems that use five-point scales for the likelihood a finding is benign or malignant (Fendler and colleagues, EJNMMI, 2023). If your report quotes a score, ask your doctor which system it belongs to, because a "3" means different things in different systems.

"No abnormal uptake" and incidental findings

The same PSMA guideline states that the overall impression of a scan should be clearly reported as normal or abnormal, and that uptake in incidental findings unrelated to the main question should also be reported. This is why reports sometimes mention things you did not expect, such as an unrelated nodule. Hofman and Hicks note that many of the common pitfalls on FDG scans do not require further investigation. An incidental line on a report is a prompt for your doctor to judge, not a diagnosis.

The reverse also deserves honesty. "No abnormal uptake" describes what the scan could show. Small deposits and tumours that take up little FDG can be missed, as discussed on the cancer care page. Tracer choice also changes how uptake is read; see PET radiotracers explained.

Why comparison with earlier scans matters

Many reports include a comparison section, and it often carries the main message. Hofman and Hicks write that for oncologic FDG PET-CT, comparison with prior studies is critical to answer the clinical question, and that comparing only with the latest scan can mislead. A spot described as "unchanged" or "reduced" is usually a statement about change over time. If no earlier scan was available, the report should say so, and the PSMA guideline specifically asks for a statement in that case. A first scan has no baseline to measure against, which is one reason wording can be more cautious.

When reading the report, look for the clinical question stated at the top and the conclusion at the bottom, then bring questions to the doctor who ordered it. Questions about the scan day are in what to expect on scan day.

The short version

A PET report is a specialist's description of where a tracer gathered, compared with background, with earlier scans and with CT or MRI. SUV and words such as avid or hypermetabolic describe activity, not a diagnosis. The referring doctor is the person to explain what your report means for you.