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Hi Mahinda, The mode characterises directly the tensor shape. A negative mode indicates an oblate profile (i.e. l1 roughly equal to l2, both much larger than l3) and a positive mode a prolate profile (l1 much larger than both l2 and l3), where l's are the tensor eigenvalues. Therefore, you can interpret directly changes in the mode to changes in the relative relationship between the tensor eigenvalues. It has been empirically observed that voxels with two crossing fibres tend to have an oblate tensor shape (and this approximation improves as the crossing becomes more perpendicular, the fibres more similar and the volume fractions more identical). That's why a negative mode value may indirectly suggest a fibre crossing. Cheers, Stam On 23 Jun 2010, at 17:33, Mahinda Y wrote: > Dear All, > > I have seen some recent and papers using the mode of anisotropy to distinguish between where changes in FA are due to changes in voxels containing 2 fibre bundles to 1 fibre bundle (causing an increase in the mode to more positive values) - is this interpretation only valid in areas where one knows there are crossing fibres - how does one interpret such changes in the mode in areas where crossing fibres are less likely ? > > Thanks. > > Mahinda >