The standard uptake value (SUV) is a simple way of determining activity in PET imaging, most commonly used in fluorodeoxyglucose (FDG) imaging. It is also known as the dose uptake ratio (DUR). As the name suggests it is a mathematically derived ratio of tissue radioactivity concentration at a point in time C(T) and the injected dose of radioactivity per kilogram of the patient's body weight:
SUV = C(T)/[injection dose (MBq)/patient's weight (kg)]
It is used to measure response of cancers to treatment and is considered a semi-quantitative value as it is vulnerable to other sources of variabilities. The most reliable method of measuring activity levels would be to use fractional uptake rate (FUR) which is measured from blood samples. As the FUR and SUV are proportional, related to plasma clearance rate and a dimentionless initial distribution volume, careful usage of SUV is widely used over blood sampling.
SUV may be influenced by image noise, low image resolution and variable user-biased region of interest (ROI) selection. The cut off between benign and malignant lesion/nodule is in the SUV range of 2.0-2.5. PET sensitivity and specificity decreases with lesions smaller than 7mm. Thus, continued follow-up is recommended.
It is important to note that many infectious and inflammatory processes will also have high SUV.
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