Standardized uptake value (SUV)
Standardized uptake value, SUV, (also referred to as the dose uptake ratio, DUR) is a widely used, simple PET quantifier, calculated as a ratio of tissue radioactivity concentration (for example in units [kBq/mL]) at time T, CPET(T), and administered dose (for example in units [MBq]) at the time of injection divided by body weight (usually in units [kg]).
If the above mentioned units are used, the unit of SUV will be [g/ml]. Tissue radioactivity and dose must be decay corrected to the same time point.
Instead of the body weight, the administered dose may also be corrected by the lean body mass (LBM), or body surface area (BSA) (Kim et al., 1994); for FDG PET studies the SUVBSA is recommended.
Verbraecken et al. (2006) review the different formulas for calculating the BSA.
Calculation of SUV does not require blood sampling or dynamic imaging. The imaging must take place at a late time point, and always at the same time point, if results are to be compared (Eckelman et al., 2000). In FDG studies SUV can be corrected for plasma glucose level.
Cancer treatment responce is usually assessed with FDG PET by calculating the SUV on the highest image pixel in the tumour regions (SUVmax), because this provides lower interobserver variability than averaged SUV (SUVmean). Alternatively, tumour volume can be estimated using threshold or region growing techniques, and average SUV inside the region is reported as such or multiplied by tumour volume to calculate the total glycolytic volume, TGV (Boucek et al., 2008). Nahmias and Wahl (2008) reported that the use of SUVmax has worse reproducibility (3% ± 11%) than does the SUVmean value (1% ± 7%), and Burger et al (2012) confirmed that repeatability of SUVmean is superior to SUVmax. SUVpeak, based on a spherical volume of interest (VOI) having a volume of ~1 mL in a position that provides the maximal VOI average, avoids the noise-indused bias of SUVmax, but is less sensitive to image characteristics (Lodge et al, 2012). Combination of SUVmax and SUVpeak (Lasnon et al., 2013) should become the standard approach in multicentre FDG PET/CT studies (Boellaard, 2013).
SUV is vulnerable to several major sources of variability (Hamberg et al. 1994; Keyes 1995; Huang 2000), and the application of SUV as a quantitative index should be discouraged. The only reason for its continuous usage is that dynamic imaging and blood sampling are not necessary. If blood samples have been measured, a simple but quantitative alternative to SUV is fractional uptake rate (FUR), which is an approximation to the Gjedde-Patlak slope Ki, but does not require dynamic PET scan. FUR and SUV are proportional, related by plasma clearance rate and a dimensionless initial distribution volume (Thie, 1995). Even simpler approach in clinical settings is to calculate tissue-to-blood ratio at a late time point - this has been shown to correlate with metabolic rate of FDG in tumors (van den Hoff et al., 2013).
Although SUV and Ki may correlate well over the patient population, they may provide even opposite conclusions regarding the progression of disease (Freedman et al., 2003). Image noise, poor resolution and ROI definition affect the SUV and may hamper their use, especially in multicenter trials (Boellaard et al., 2004).
In animal studies, dissected tissue samples are weighted and radioactivity is measured. Radioactivity is divided by sample weight to calculate the concentration (Bq/g). With injected dose and animal weight the SUV could be calculated similarly as from PET data. However, in animal studies the animal weight is often not taken into account: radioactivity concentration is simply divided by injected dose and multiplied by 100, and outcome is percent of injected dose per gram of tissue (%i.d./g).
Similar calculation can be done to PET data. In PET image the radioactivity concentration is measured per tissue volume (Bq/mL) instead of mass, and therefore the outcome will be in units %i.d./mL or %i.d./L. If tissue density (g/mL) is known or assumed to be 1 g/mL, it can be converted to %i.d./g.
- Calculation of SUV image
- Calculation of regional SUV
- Retention index (RI)
- Fractional uptake rate (FUR)
- Multiple-time graphical analysis for irreversible tracer uptake (Gjedde-Patlak plot)
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Created at: 2008-11-20
Updated at: 2013-12-18
Written by: Vesa Oikonen