Standardized Uptake Value (SUV)It was designed to be a simplistic method to quantify uptake as opposed to true quantification through compartmental and kinetic modeling. An SUV of 2.5 or higher is generally considered to be indicative of malignant tissue; however, there has been a wide range of SUVs reported for similar diseases. Table 4-2 summarizes some of these reported values. It is important to recognize that an SUV around 2.5 can be measured in non-malignant regions. Conversely, small tumors can also exhibit maximum SUV of < 2.5.
The SUV was created to determine whether a region may be considered “tumor” or “malignant” but may have limited value for determining the edges of a tumor. SUV has a number of limitations, many of which will be mentioned but are beyond the scope of this chapter to discuss in depth. SUV is dependent on many patient-related factors including the ROI defined, the activity injected, plasma glucose levels, competition with endogenous glucose, rate of phosphorylation, body size and body composition, as well as tumor type. Technically, SUV values will vary depending on the PET scanner's signal-to-noise properties, the accuracy of the image reconstruction algorithm as well as corrections algorithms, and the time between injection and image acquisition. Not accounting for all these error sources can lead to potential errors of ≥50% in SUV calculations. While one would seldom question the interpretation of regions with very high SUVs, uncorrected errors in marginal SUVs (e.g., those in the range of 2.5) could potentially have a large impact on the interpretation of this value. Unfortunately, it is this range of 2.5 that has been proposed as a possible threshold for target localization. This value is based on the diagnostic criteria used to determine if the region of interest may be considered malignant or not. SUVs have been used in delineation of GTVs for esophageal, lung, and head and neck tumors.
For tumors within the lung, respiratory motion can be a major source of error in SUV values when combined PET-CT scanners are used and the CT images are used to perform attenuation correction on the PET images. CT acquisition of a tumor can occur in seconds, while PET emission acquisition requires a few minutes. Therefore, an incongruent tumor position during CT will bias activity estimates (i.e., SUV calculation) on PET. Using respiratory-gated CT and PET acquisitions, Erdi and colleagues have demonstrated that SUV can vary up to 30% and a tumor position can vary by up to 9 mm on the resultant CT-attenuation-corrected PET image depending on the respiratory phase.
For diagnosis, SUV has been useful for determining whether or not an area of uptake should be reported as suspicious for malignancy. However for defining the edges of a radiation target, the use of SUV is limited and uncertain. More sophisticated segmentation techniques are required if accurate and consistent targets are to be segmented from PET-CT images.
Reference:
https://www.sciencedirect.com/topics/medicine-and-dentistry/standardized-uptake-value