Variability of average SUV from several hottest voxels is lower than that of SUVmax and SUVpeak

Objectives

To assess variability of the average standard uptake value (SUV) computed by varying the number of hottest voxels within an ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG)-positive lesion. This SUV metric was compared with the maximal SUV (SUV_max: the hottest voxel) and peak SUV (SUV_peak: SUV_max and its 26 neighbouring voxels).

Methods

Twelve lung cancer patients (20 lesions) were analysed using PET dynamic acquisition involving ten successive 2.5-min frames. In each frame and lesion, average SUV obtained from the N?=?5, 10, 15, 20, 25 or 30 hottest voxels (SUV_max–N )_, SUV_max and SUV_peak were assessed. The relative standard deviations (SDrs) from ten frames were calculated for each SUV metric and lesion, yielding the mean relative SD from 20 lesions for each SUV metric (SDr _N , SDr_max and SDr_peak), and hence relative measurement error and repeatability (MEr–R).

Results

For each N, SDr _N was significantly lower than SDr_max and SDr_peak. SDr _N correlated strongly with N: 6.471?×?N ^-0.103 (r?=?0.994; P?<?0.01). MEr–R of SUV_max-30 was 8.94–12.63 % (95 % CL), versus 13.86–19.59 % and 13.41–18.95 % for SUV_max and SUV_peak respectively.

Conclusions

Variability of SUV_max–N is significantly lower than for SUV_max and SUV_peak. Further prospective studies should be performed to determine the optimal total hottest volume, as voxel volume may depend on the PET system.

Key Points

? PET imaging provides functional parameters of ¹⁸ F-FDG-positive lesions, such as SUVmax and SUVpeak. ? Averaging SUV from several hottest voxels (SUVmax- _N ) is a further SUV metric. ? Variability of SUVmax– _N is significantly lower than SUVmax and SUVpeak variability. ? SUVmax– _N should improve SUV accuracy for predicting outcome or assessing treatment response. ? An optimal total hottest volume should be determined through further prospective studies.