Apparent Diffusion Coefficient (ADC) Measurements in Pancreatic Adenocarcinoma: A Preliminary Study of the Effect of Region of Interest on ADC Values and Interobserver Variability

Purpose: To assess the influence of region of interest (ROI) on tumor apparent diffusion coefficient (ADC) measurements and interobserver variability in pancreatic ductal adenocarcinoma (PDAC). Materials and Methods: Twenty-two patients recruited with pathology-proven PDAC underwent diffusion-weighted imaging (DWI, 3.0T) prior to the surgical resection. Two independent readers measured tumor ADCs according to three ROI methods: whole-volume, single-slice, and small solid sample of tumor. Minimum and mean ADCs were obtained. The interobserver variability for each of the three methods was analyzed using interclass correlation coefficient (ICC) and Bland-Altman analysis. The minimum and mean ADCs among the ROI methods were compared using nonparametric tests. Results: The single-slice ROI method showed the best reproducibility in the minimum ADC measurements (mean difference+/-limits of agreement between two readers were 0.025+/-0.25 x 10(-3) mm(2)/s; ICC, 0.92) among the three ROI methods. For the solid tumor sample ROI, both minimum ADC and mean ADC measurements reproducibility were the worst, with limits of agreement up to +/-0.50 x 10(-3) mm(2)/s and +/-0.32 x 10(-3) mm(2)/s, respectively (ICCs, 0.41/0.58). Both the minimum and mean ADCs demonstrated significant differences among the three ROI methods (both P<0.001). The post-hoc analyses results showed no significant difference with regard to the mean ADCs between whole-volume and single-slice ROI methods (P=0.14). Conclusion: The ROI method had a considerable influence on both the minimum and mean ADC values and the interobserver variability in PDAC. The worst interobserver variability was observed for both the minimum and mean ADCs derived from small solid-sample ROI.