ADC measurements of lymph nodes: Inter- and intra-observer reproducibility study and an overview of the literature

Purpose: Apparent diffusion coefficient (ADC) measurements in diffusion-weighted magnetic resonance imaging (DWI) may be of value in discriminating malignant from non-malignant lymph nodes, provided that they are reproducible. The aim of this study was to determine the inter- and intra-observer reproducibilities of ADC measurements of lymph nodes and to provide an overview of the current literature on ADC measurements in the characterization of lymph nodes. Materials and methods: Twenty healthy volunteers underwent DWI of the head and neck region and the pelvic region, at b-values of 0 and 1000 s/mm2. Two observers independently and blindly measured ADCs of lymph nodes. Inter- and intra-observer reproducibilities were assessed using the Bland-Altman method. Results: Mean ADCs of normal lymph nodes (in 10-3 mm2/s) varied between 1.15 and 1.18. Ranges of mean ADC difference ± limits of agreement (in 10-3 mm2/s) for inter-observer agreement were -0.03 to 0.02 ± 0.15 to 0.31. Ranges of mean ADC difference ± limits of agreement (in 10-3 mm2/s) for intra-observer agreement were 0.00 to 0.04 ± 0.13 to 0.32. Conclusion: In conclusion, in light of previously reported data, the results of the present study suggest that ADC measurements may not always be sufficiently reproducible to discriminate malignant from non-malignant lymph nodes. Future studies which directly compare the ADCs of different nodal pathologies/conditions are required to further investigate the inter- and intra-observer reproducibilities of ADC measurements of lymph nodes.