[caret-users] ROI definition by connection distance

[John Harwell]

On Jul 11, 2007, at 10:57 AM, Alon Keren wrote:

> Hi.
>
> I have been using CARET a lot lately, and found it very powerful  
> and useful for a variety of applications. There is a feature that I  
> am interested in, and I think is not available at the moment. I am  
> interested in a sophisticated measure of distance between nodes:
> The "real" distance, or functional or connection distance between  
> two nodes is neither euclidean nor geodesic. Two nodes on opposite  
> walls of a sulcus are further away in the connectivity sense then  
> two nodes on opposite walls of a gyrus, with white matter bridging  
> the gap. In the first case a geodesic measure is suitable, whereas  
> in the second an euclidean measure is more adequate. I imagine it  
> is much more complicated to implement, but a measure of distance  
> that goes around CSF but cuts through WM would be very useful and  
> more accurate for functional purposes. For instance I would like to  
> estimate the relationship between this functional distance and co- 
> activation of nodes.
>

I understand what you are asking for, but I do not see a way to  
perform this on a surface.  Perhaps the distance measurement you are  
seeking could be performed by creating topology and coordinate files  
from the white and gray matter voxels (a uniform grid) and performing  
a geodesic search.  This probably would provide the shortest path  
through the gray and white matter opposed to the surface which is  
gray matter only.

> A question on the same topic:
> Is there an automatic way to produce a matrix of node to node  
> geodesic distances (of size #ofNodes^2)?
>

At this time, the only way to perform geodesic distance operations is  
one node at a time using the surface region of interest dialog.

> Thanks,
> Alon.
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-----------------------------------
John Harwell
john at brainmap.wustl.edu

Department of Anatomy and Neurobiology
Washington University School of Medicine
660 S. Euclid Ave   Box 8108
Saint Louis, MO 63110