Whole-body diffusion-weighted MRI of normal lymph nodes: prospective apparent diffusion coefficient histogram and nodal distribution analysis in a healthy cohort

Background Whole body DWI (WB-DWI) enables the identification of lymph nodes for disease evaluation. However, quantitative data of benign lymph nodes across the body are lacking to allow meaningful comparison of diseased states. We evaluated apparent diffusion coefficient (ADC) histogram parameters of all visible lymph nodes in healthy volunteers on WB-DWI and compared differences in nodal ADC values between anatomical regions. Methods WB-DWI was performed on a 1.5 T MR system in 20 healthy volunteers (7 female, 13 male, mean age 35 years). The b900 images were evaluated by two radiologists and all visible nodes from the neck to groin areas were segmented and individual nodal median ADC recorded. All segmented nodes in a patient were summated to generate the total nodal volume. Descriptors of the global ADC histogram, derived from individual node median ADCs, including mean, median, skewness and kurtosis were obtained for the global volume and each nodal region per patient. ADC values between nodal regions were compared using one-way ANOVA with Bonferroni post hoc tests and a p-value <= 0.05 was deemed statistically significant. Results One thousand sixty-seven lymph nodes were analyzed. The global mean and median ADC of all lymph nodes were 1.12 +/- 0.27 (10(- 3) mm(2)/s) and 1.09 (10(- 3) mm(2)/s). The average median ADC skewness was 0.25 +/- 0.02 and average median ADC kurtosis was 0.34 +/- 0.04. The ADC values of intrathoracic, portal and retroperitoneal nodes were significantly higher (1.53 x 10(- 3), 1.75 x 10(- 3) and 1.58 x 10(- 3) mm(2)/s respectively) than in other regions. Intrathoracic, portal and mesenteric nodes were relatively uncommon, accounting for only 3% of the total nodes segmented. Conclusions The global mean and median ADC of all lymph nodes were 1.12 +/- 0.27 (10(- 3) mm(2)/s) and 1.09 (10(- 3) mm(2)/s). Intrathoracic, portal and retroperitoneal nodes display significantly higher ADCs. Normal intrathoracic, portal and mesenteric nodes are infrequently visualized on WB-DWI of healthy individuals.