[Mristudio-users] question - changes of FA and eigenvalues after Gd contrast

[Amir Zolal]

Hi,

I have tried comparing DTI images before and after Gd contrast
administration, and I have found that the FA was increased after the
contrast agent (more in the ROIs where there was contrast
enhancement), I have also (among other things) seen a significant
decrease of all eigenvalues, however the third eigenvalue decreased
the most (the difference between the change of lambda1 and lambda3 was
also significant), causing the paradoxical increase in FA. This was
not observable in the normal white matter. Because I don't believe,
that the contrast agent would in any way influence water diffusion, my
theory is, that the addition of a paramagnetic contrast agent  could
cause more local noise and the small attenuation in the (lambda3)
direction would be even less discernible, in contrast to the strong
attenuation in the (lambda1) direction. My question is, to your
knowledge, would there be anything else in the processing of the DTI
datasets that could cause the above described effect?

Thanks in advance for your ideas,

Amir