Assessing response of myeloma bone disease with diffusion-weighted MRI

Objectives: To measure apparent diffusion coefficient (ADC) values in patients with active myeloma and remission and to determine whether changes differ in those responding/progressing on treatment. The relationship between changes in marrow fat and ADC was also explored. Methods: 20 patients were recruited. T-1 weighted, T-2 weighted, short tau inversion-recovery, diffusion-weighted and two-point Dixon MRI of the lumbar spine and pelvis were performed at baseline, 4-6 weeks and 20 weeks. Results: ADC values of active disease (mean 761.2 +/- 255x10(-6) mm(2) s(-1)) were significantly higher (p=0.047) than marrow in remission (mean 601.8 +/- 459x10(-6) mm(2) s(-1)). Changes in ADC in responders showed a significant increase at 4-6 weeks (p=0.005) but no significant change between baseline and 20 weeks (p=0.733). ADCs in progressing and stable patients did not change significantly between either time point. Pearson's correlation coefficient between change in fat fraction and change in the number of pixels with an ADC of <= 655x10(-6) mm(2) s(-1) was 0.924, indicating a significant correlation (p < 0.001). Conclusion: ADC values in active myeloma are significantly higher than marrow in remission, indicating the potential for diffusion-weighted MRI to quantify the transition from active disease to remission and vice versa. This study confirms significant changes in ADC in patients responding to treatment and indirect evidence from two-point Dixon MRI suggests that these changes are influenced by changes in marrow fat. Advances in knowledge: ADC of active myeloma is significantly higher than marrow in remission; the direction of ADC changes on treatment is dependent on the timing of measurements and is influenced by changes in marrow fat.