To compare the reproducibility and diagnostic performance of IVIM parameters derived from 3D whole-lesion (W-L ROI) and single-section (S-S ROI) delineation respectively . Forty-three patients with 46 pathologically confirmed thyroid nodules were involved. Reduced FOV DWI with 2D RF was employed to decrease the distortion. The ICC values of all IVIM parameters were higher with W-L ROI delineation than with S-S ROI delineation. The 95% limits of agreement (Bland-Altman plots) determined by W-L ROI revealed smaller absolute intra- and interobserver variability and the AUC of W-L ROI delineation was higher than S-S ROI according to ROC analysis.