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-requ...@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 > > > > > _______________________________________________ > Freesurfer mailing list > Freesurfer@nmr.mgh.harvard.edu > https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer > > > The information in this e-mail is intended only for the person to whom it is > addressed. If you believe this e-mail was sent to you in error and the e-mail > contains patient information, please contact the Partners Compliance HelpLine > at > http://www.partners.org/complianceline . If the e-mail was sent to you in > error > but does not contain patient information, please contact the sender and > properly > dispose of the e-mail. _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
