How to Read a PET Scan Report

## What a PET Scan Measures A PET (Positron Emission Tomography) scan measures **metabolic activity** — how actively cells are using glucose. Cancer cells typically consume glucose at much higher rates than normal cells, so they show up as "hot spots" on a PET scan. PET scans are usually combined with CT scans (PET/CT) to give both functional information (PET) and anatomical information (CT) together. ## Key Terms in a PET Scan Report ### SUV (Standardized Uptake Value) The most important number in a PET report. SUV measures how much radioactive tracer is taken up by a specific area compared to the rest of the body. - **SUV < 2.5:** Generally considered low — may be normal or benign - **SUV 2.5–5:** Borderline — may or may not be malignant; context matters - **SUV > 5:** Elevated — more concerning for malignancy - **SUV > 10:** Highly suspicious for cancer **Important:** SUV thresholds are not absolute. The same value can mean different things in different contexts. Your oncologist interprets SUVs in context. ### FDG-Avid Means the area took up FDG (fluorodeoxyglucose — the radioactive tracer). Highly FDG-avid lesions are metabolically very active, which is concerning for cancer. Not all cancers are FDG-avid — some slow-growing cancers (certain thyroid cancers, some prostate cancers) show little FDG uptake. ### Hypermetabolic Increased metabolic activity. Essentially the same as saying FDG-avid. Used to describe lesions with elevated glucose uptake. ### Lesion A general term for any area of abnormality — a mass, nodule, lymph node, or area of uptake. A lesion on a PET scan is not automatically cancer. ### Lymphadenopathy Enlarged lymph nodes. Can be caused by cancer spread, infection, or inflammatory conditions. ### Lytic / Sclerotic (bone lesions) - **Lytic:** Areas where bone is being broken down — common in certain cancers (multiple myeloma, breast, lung) - **Sclerotic:** Areas where bone has hardened or become denser — can be normal healing after treatment or certain cancer types ### Deauville Score (for lymphoma) A 1–5 scale used to interpret PET scans in lymphoma: - 1–2: No significant uptake — complete response - 3: Slight uptake, but less than liver - 4–5: Significant uptake — may indicate residual disease ## What "Compared to Prior Study" Means PET scan reports almost always compare to previous scans. Key phrases: - **"Decreased in size and activity"** — responding to treatment - **"Stable"** — no significant change - **"Increased in size and/or activity"** — possible progression - **"New lesion"** — a new area of concern that wasn't there before ## When to Ask Questions After receiving a PET scan report, ask your oncologist: - Does this scan show a response to treatment? - Are there any new areas of concern? - How does this change my treatment plan? - What does the overall picture tell us?