ADC Quantification of the Vertebral Bone Marrow Water Component: Removing the Confounding Effect of Residual Fat

Purpose: To remove the confounding effect of unsuppressed fat on the imaging-based apparent diffusion coefficient (ADC) of the vertebral bone marrow water component when using spectrally selective fat suppression and to compare and validate the proposed quantification strategy against diffusion-weighted magnetic resonance spectroscopy (DW-MRS). Methods: Twelve subjects underwent diffusion-weighted imaging (DWI) and DW-MRS of the vertebral bone marrow. A theoretical model was developed to take into account and correct the effects of residual fat on ADC, incorporating additional measurements for proton density fat fraction (PDFF) and water T₂ (T_2w). Uncorrected and corrected DWI-based ADC was compared with DW-MRS–based ADC using the Bland–Altman method. Results: There was a systematic bias equal to 0.118 ± 0.116 × 10⁻³ mm²/s between DWI and DW-MRS when no correction was performed. Taking into account measured PDFF and constant T_2w reduced the bias to 0.006 ± 0.128 × 10⁻³ mm²/s. Using the proposed approach with both individually measured PDFF and T_2w reduced both the bias and the limits of agreement between DWI and DW-MRS (0.018 ± 0.065 × 10⁻³ mm²/s). Conclusion: By taking into account the presence of residual fat in a modified signal model that incorporates additional individual measurements of PDFF and T_2w, good agreement of imaging-based ADC with MRS-based ADC can be achieved in vertebral bone marrow. Magn Reson Med 78:1432–1441, 2017.