Thanks. Also, I would say that FA has been the most popular measure of
anisotropy _within_ a voxel. If you are interested in quantifying
anisotropy (etc.) using longer-range measures then IC may indeed be
interesting but is no longer a purely within-voxel measure, and so the
gates are open to also potentially consider methods such as
tractography in your analysis.
Cheers, Steve.
On 5 Feb 2008, at 21:17, Marenco, Stefano (NIH/NIMH) [E] wrote:
> I think that this measure was originally named Lattice Index in the
> Pierpaoli paper cited. It is more stable than FA (less sensitive to
> noise), but more prone to partial volume effects. I used this in a
> recent PNAS paper (Marenco et al. 2007). Some discussion of the
> reasons to choose LI or IC instead of FA are mentioned in the
> supplementary material of the paper. Stefano Marenco
>
> From: Dianne Patterson [mailto:[log in to unmask]]
> Sent: Tuesday, February 05, 2008 3:38 PM
> To: [log in to unmask]
> Subject: [FSL] Intervoxel Coherence, anyone?
>
> Dear Group,
>
> I recently came across the following:
>
> Begre, S., Frommer, A., von Kanel, R., Kiefer, C., & Federspiel, A.
> (2007). Relation of white matter anisotropy to visual memory in 17
> healthy subjects. Brain Research, 1168, 60-66.
>
> "DTI measures diffusion-driven displacements of molecules during
> their random path along axonal fibers, expressed as fractional
> anisotropy (FA) or intervoxel coherence (IC) ranging from 0
> (isotropic medium) to 1 (fully anisotropic medium). FA is a measure
> that quantifies the degree to which diffusion differs in the three
> dimensions. IC considers the degree of collinearity between the
> diffusion tensor of the reference voxel and the adjacent voxels,
> and, in addition, guarantees a better signal-to-noise ratio than the
> commonly used FA (Pierpaoli and Basser, 1996). Hence, based on the
> determination of the similarity of orientation of adjacent voxels,
> IC reflects a measure of connectivity, expressing fiber coherence at
> the voxel level with a spatial sampling limited by voxel size."
>
> "To compute the difference of intervoxel coherence values between
> the low performer and the high performer group, a t-test was
> computed for each voxel within the 3-D white matter template. To
> identify volume-corrected regions, clusters were defined as 6 or
> more neighboring voxels (6 mm3) exceeding the t-test value of 2.9 (P
> < .01). For each cluster, IC values were averaged and tabulated and
> Talairach coordinates (Talairach and Tournoux, 1988) of the centers
> of gravity were noted. Clusters were assigned to the underlying
> white matter using 3-D anatomical data."
>
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> ======================================================================
> I can find little else on the subject, and I wondered, if IC is so
> superior to FA, why isn't it a commonplace dti measure?
> Has anyone out there used this technique, and would you care to
> comment on it?
>
> Thankyou,
>
> Dianne
>
> --
> Dianne Patterson, Ph.D.
> [log in to unmask]
> ERP Lab
> University of Arizona
> 621-3256 (Office)
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Stephen M. Smith, Professor of Biomedical Engineering
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