HI Ed, I believe that you are referring to the RA measure of anisotropy. FA is theoretically limited to the range 0-1.
FA's greater than 1 can arise when you have negative estimates of the eigenvalues, which can arise when using linear least squares estimation of the tensor.
cheers, -MH
On Fri, 2012-02-03 at 14:21 +0100, Ed Gronenschild wrote:
Dear Antonella,
In theory, FA can be sqrt(3/2) = 1.2247449. This occurs if eigenvalues 2 and 3 are zero. You will find these high FA values (>1) mainly outside the brain.
Ed
On 3 Feb 2012, at 11:31, freesurfer-request@nmr.mgh.harvard.edu wrote:
Dear all,
I use dt_recon to process my DTI data and get my fa.nii for the individual subjects. I wonder if the FA values can be greater that one since for all my subjects I got the FA max? value graeter than one. Is something wrong with my data or this is acceptable? I saw in? most of the papers FA<1 so 0<FA<1.
Thank you.
Antonella
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