Abstract!Objectives: Measuring tumour heterogeneity by textural analysis in 18 F-fluorodeoxyglucose positron emission tomography ( 18 F-FDG PET) provides predictive and prognostic information but technical aspects of image processing can influence parameter measurements. We therefore tested effects of image smoothing, segmentation and quantisation on the precision of heterogeneity measurements.Methods: Sixty-four 18 F-FDG PET/CT scans of oesophageal cancer were processed using different Gaussian smoothing levels (2.0, 2.5, 3.0, 3.5, 4.0mm), maximum standardised uptake values (SUV max ) segmentation thresholds (45%, 50%, 55%, 60%) and quantisation (8,16, 32, 64, 128 2) Quantisation shows large effects on precision of heterogeneity parameters in 18 F-FDG PET/CT.