Okay, I understand what you did. Are you
tracking a pathway along a non-primary fiber orientation? That could cause a
negative correlation between waytotal and FA (i.e. the stronger the pathway,
the lower the FA because of crossing effects). It would help to know the
pathway as well, but if you don’t want to publically say, you could tell me off
list.
Peace,
Matt.
From:
Sent: Thursday, May 12, 2011 1:49
AM
To: [log in to unmask]
Subject: Re: [FSL] Highly
negatively correlated waytotal and average FA
Hi Matt.,
I made an error in describing how I normalized. I didn't
divide the waytotal, but divided the number of streamlines per voxel along the
pathway. But in case you got what I meant, are you suggesting to take the
average FA on a not-thresholded pathway?
Best,
HD
On 11 May 2011 18:33, Matt Glasser <[log in to unmask]>
wrote:
What happens if you don’t do this normalization.
Peace,
Matt.
From:
Sent: Wednesday, May 11, 2011 3:53
AM
To: [log in to unmask]
Subject: [FSL] Highly negatively
correlated waytotal and average FA
Dear list,
I'm working
on a study examining the relationship between a behavioral measure and a
particular white matter pathway defined using probtrackx (part of the arcuate
fasciculus), and I found:
1. The behavioral measure is negatively correlated with the waytotal for
the pathway but positively correlated with average FA along the
pathway.
2. There is a strong Negative correlation between waytotal and
average FA along
the pathway.
The above
two points seem to suggest something circular. Would this be due to a problem
of low thresholding or something related to the probabilistic algorithm?
Ps, I
divided the waytotal by the total sample sent out to normalize the
pathway and took a threshold of 5X10-6 .
Any thoughts
or experience are highly appreciated.
Best
regards,
hd