Effect of region of interest size on ADC measurements in pancreatic adenocarcinoma

BACKGROUND To investigate the influence of region of interest (ROI) size on tumor apparent diffusion coefficient (ADC) measurements in pancreatic cancer. METHODS The study population consisted of 64 patients with pathologically proved pancreatic ductal adenocarcinomas (PDACs), who underwent preoperative magnetic resonance imaging (MRI) examinations including diffusion-weighted imaging (DWI). The tumor ADCs were measured by two independent readers using six round ROIs with sizes ranging from 20 to 214 mm2 (9 to 97 pixels) in both the six separate measurements. The intra- and inter-observer variabilities were analyzed by using the coefficient of variance (CV), the interclass correlation coefficient (ICC) and Bland-Altman analysis. The mean ADCs measured with the 6 different-sized ROIs were compared using one-way repeated analysis of variance. The sample sizes were calculated by using 80% power and a 5% significance level to detect 10 to 25% changes in ADC measurements. RESULTS The largest ROI (ROI214) yielded the best intra-observer repeatability (CV, 6.3%; ICC, 0.93) and inter-observer reproducibility (CV, 10.1%; ICC, 0.84). The mean differences in ADC measurements ± limits of agreement between the two readers were (0.06 ± 0.47) × 10-3 mm2 for ROI20, (0.08 ± 0.46) × 10-3 mm2 for ROI46, (0.05 ± 0.37) × 10-3 mm2 for ROI82, (0.07 ± 0.42) × 10-3 mm2 for ROI115, (0.05 ± 0.43) × 10-3 mm2 for ROI152 and (-0.02 ± 0.29) × 10-3 mm2 for ROI214. CONCLUSIONS ROI size had a considerable influence on the ADC measurements of PDACs.