Hi Elijah - I suggest looking at the axial diffusivity (AD) and radial diffusivity (RD) to help you interpret these results. These are the diffusivity parallel and perpendicular to the main budnle going through a voxel, respectively. Essentially, FA tells you how different the AD and RD are from each other, and MD tells you how big AD and RD are in aggregate.
Here are just a couple of all the possible scenarios that can lead to opposite FA/MD relationships:
AD increases, RD stays the same => MD increases, FA increases AD stays the same, RD increases => MD increases, FA decreases Hope this helps, a.y On Thu, 24 Mar 2016, Elijah Mak wrote:
Hi Freesurfer Community, I recently used mri_segstats to extract FA and MD as suggested here: http://freesurfer.net/fswiki/FsTutorial/Diffusion Using the aparc+aseg and wmparc (resampled to diffusion space), I looked at some of the correlations between FA and MD in the same regions, and came across a few interesting ones. wm_lh_entorhinal FA & wm_lh_entorhinal MD: r = 0.6, p <0.001 ctx_lh_entorhinal FA & ctx_lh_entorhinal MD: r = -0.3, p < 0.020 wm_lh_precuneus FA & wm_lh_precuneus MD: r = -0.6, p <0.001 As I understand, a clear-cut interpretation especially with regards to FA changes is not so easy! But could someone discuss / speculate as to why FA and MD could be positively correlated within the entorhinal WM region? That was found separately within a group of a elderly healthy controls and a group of dementia subjects. Thank you for your time! Best Wishes, Elijah
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