Background: The apparent diffusion coefficient (ADC), as determined by whole-body diffusion-weighted MRI, may be useful as an outcome measure for monitoring response to treatment in chronic non-bacterial osteitis.

Purpose: To test and demonstrate the feasibility of ADC-measurement methods for use as outcome measure in chronic non-bacterial osteitis.

Materials and Methods: Using data from a randomized pilot study, feasibility of change-score ADC between baseline and second MRI (ΔADC12) and third MRI (ΔADC13) as outcome measure was assessed in three settings: "whole-lesion," "single-slice per lesion," and "index-lesion per patient". Bone marrow edema lesions were depicted on short tau inversion recovery sequence at baseline and copied to ADC maps at the three time-points. Correlations between the three settings were measured as were analysis of variances. Discriminant validity was assessed as inter- and intra-observer reproducibility and smallest detectable change.

Results: 12 subjects were enrolled, and MRI was performed at baseline and weeks 12 and 36. Pearson correlation was high (r > 0.86; p ≤ 0.01) for ΔADC between single-slice-whole-lesion and whole-lesion-index-lesion and tended to be significant for single-slice-index-lesion settings (p = 0.06). For ΔADC12 and ΔADC13, Bland-Altman plots showed small differences (0.02, 0.03) and narrow 95% limits-of-agreement (-0.13-0.09, -0.07-0.05 μm2/s) between whole-lesion and single-slice ROI settings. Inter-observer reproducibility measured by intra-class correlation coefficient was poor-to-fair (range: 0.09-0.31), whereas intra-observer reproducibility was good-to-excellent (range: 0.67-0.90). Smallest detectable changes were between 0.21-0.28 μm2/s.

Conclusion: ADC change-score as outcome measure was feasible, and the single-slice per lesion ROI setting performed almost equally to whole-lesion setting resulting in reduced assessment time.