Multicomponent T2 relaxometry reveals early myelin white matter changes induced by proton radiation treatment

Purpose: To investigate MRI myelin water imaging (MWI) by multicomponent T2 relaxometry as a quantitative imaging biomarker for brain radiation-induced changes and to compare it with DTI. Methods: Sixteen patients underwent fractionated proton therapy (PT) receiving dose to the healthy tissue because of direct or indirect (base skull tumors) irradiation. MWI was performed by a multi-echo sequence with 32 equally spaced echoes (10-320 ms). Decay data were processed to identify 3 T2 compartments: myelin water (Mw) below 40 ms, intra-extracellular water (IEw) between 40 and 250 ms, and free water (CSFw) above 250 ms. Both MWI and DTI scans were acquired pre (pre)-treatment and immediately at the end (end) of PT. After image registration, voxel-wise difference maps, obtained by subtracting MWI and DTI pre from those acquired at the end of PT, were compared with the corresponding biological equivalent dose (BED). Results: Mw difference showed a positive correlation and IEw difference showed a negative correlation with BED considering end–pre changes (P <.01). The changes in CSFw were not significantly correlated with the delivered BED. The changes in DTI data, considering end–pre acquisitions, showed a positive correlation between fractional anisotropy and the delivered BED. Conclusion: MWI might detect early white matter radiation-induced alterations, providing additional information to DTI, which might improve the understanding of the pathogenesis of the radiation damage.