Standardized uptake rate (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 (e.g. in units kBq/ml) at time T, CPET(T) and injected dose (e.g. in units MBq) at the time of injection divided by body weight (e.g. in units kg).
SUVbw = CPET(T) / (Injected dose / Patient's weight)
Instead of body weight, the injected dose may also be corrected by the lean body mass, or body surface area (BSA) (Kim et al., 1994). Verbraecken et al. (2006) review the different formulas for calculating the BSA.
SUVbsa= CPET(T) / (Injected dose / BSA)
If the above mentioned units are used, the unit of SUV will be g/ml.
Cancer treatment responce is usually assessed with FDG PET by calculating the SUV on the highest image pixel in the tumour regions (SUVmax). 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%).
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).
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 blood sampling is 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. FUR and SUV are proportional, related by plasma clearance rate and a dimensionless initial distribution volume (Thie, 1995). Although SUV and Ki may correlate well over the patient population, they may provide even opposite conclusios 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).
- Calculation of SUV image
- Calculation of regional SUV
- Fractional uptake rate (FUR)
- Multiple-time graphical analysis for irreversible tracer uptake (Gjedde-Patlak plot)