Internal comparison standard for abdominal diffusion-weighted imaging.

Background Standards for abdominal diffusion-weighted imaging (DWI), apparent diffusion coefficient (ADC) measurements, and analysis are required for reproducibility. Purpose To identify optimal internal comparison standards for DWI to normalize the measured ADC for increased accuracy of differentiating malignant and benign abdominal lesions. Material and Methods We retrospectively studied 97 lesions (89 patients; age, 57 ± 13 years) with histopathologically confirmed abdominal disease. Seven normal body parts/contents (normal parenchyma, spleen, kidney, gallbladder bile, paraspinal muscle, spinal cord, and cerebrospinal fluid [CSF]) were assessed as internal references for possible use as comparison standards. Three observers performed ADC measurements. Statistical analyses included interclass correlation coefficients (ICCs), Mann-Whitney and Kruskal-Wallis tests, and coefficient of variation (CV). ROC analyses were performed to assess diagnostic accuracy of lesion ADC and normalized ADC for differentiating lesions. Pathology results were the reference standard. Results Mean and normalized ADCs were significantly lower for malignant lesions than for benign lesions ( P < 0.001). ICC was excellent for all internal references. Gallbladder had the lowest CV. Receiver operating characteristic (ROC) analyses showed that normalized ADCs obtained using normal parenchyma were better than lesion ADCs for differentiating malignant and benign abdominal lesions (area under the curve [AUC], 0.808 and 0.756, respectively). The normalized ADCs obtained using CSF shows higher accuracy than lesion ADCs (0.80 and 0.76, respectively) for differentiating between malignant and benign abdominal lesions. Conclusion The normal parenchyma from a lesion-detected organ can be used as an internal comparison standard for DWI. CSF can be used as a generalizable in plane reference standard.