C9 and frontotemporal dementia: At the same statistical threshold, areas of increased RD were detected in each FTD group: orbitofrontal and forceps minor predominant changes in bvFTD, left superior temporal and insular WM alterations in svPPA and extensive multilobar WM degeneration in nfvPPA, ALS‐FTD‐C9+ and ALS‐FTD‐C9‐.