Standardized uptake value

The standardized uptake value (SUV) is a nuclear medicine term, used in positron emission tomography (PET) as well as in modern calibrated single photon emission tomography (SPECT) imaging for a semiquantitative analysis. Its use is particularly common in the analysis of [18F]fluorodeoxyglucose () images of cancer patients. It can also be used with other PET agents especially when no arterial input function is available for more detailed pharmacokinetic modeling. Otherwise measures like the fractional uptake rate (FUR) or parameters from more advanced pharmacokinetic modeling may be preferable. The SUV is the ratio of the image-derived radioactivity concentration cimg and the whole body concentration of the injected radioactivity cinj, While this equation looks simple, there are a number of points that need to be discussed, such as (1) the origin of cimg data, (2) the origin of cinj data, (3) time, and (4) units. The cimg data may be the pixel intensities of a calibrated PET image. Calculated SUV data can then be visualized as parametric SUV image. Alternatively, groups of such pixels may be selected e.g. by manually drawing or otherwise segmenting a region of interest (ROI) on the PET image. Then e.g. the average intensity of that ROI may be used as cimg input to calculate SUV values. The cinj value is calculated as ratio of two independent measurements: the injected radioactivity (injected dose, ID) and the body weight (BW) of the subject. The ID can be estimated e.g. as difference in the radioactivity of the syringe before and after injection, if deemed necessary with correction for physical decay between each of those measurements and the time of injection. Conventionally the time of injection is t=0. This reference concentration represents the hypothetical case of an even distribution of the injected radioactivity across the whole body. Measured SUV values in particular parts of the body thus quantify the deviation from this hypothetical even radioactivity distribution: SUV > 1 indicates radioactivity accumulation in that region above the hypothetical even radioactivity distribution.