Use of apparent diffusion coefficient as a response biomarker in bone: effect of developing sclerosis on quantified values

To investigate the effect of sclerosis on apparent diffusion coefficient measurements in bone metastases from prostate cancer undergoing treatment. Sixteen patients underwent CT scans and MRI at baseline and 12 weeks following commencement of chemotherapy. For each patient, up to five bone metastases were selected. Hounsfield units were measured on CT and apparent diffusion coefficient (ADC) was measured on diffusion weighted MRI at both time points. Correlations between changes in apparent diffusion coefficient and Hounsfield units were investigated. Corresponding pre- and post-treatment apparent diffusion coefficient and Hounsfield units were available on 60 lesions from 16 patients. Overall, there was no significant correlation between changes in apparent diffusion coefficient with Hounsfield units. However, where changes in Hounsfield units increased by more than 50 %, there was a trend for an associated ADC rise. Increasing sclerosis of bone metastases on treatment does not significantly impede diffusion.