Unfortunately you cannot model crossing fibers with only 12 directions and
thus the tractography results will be suspect. Also, I believe it was
shown that to get unbiased tensor modeling (for FA, etc) you need at least
30 unique directions. If instead of 12 x 6 directions you had 72 unique
directions x one average, you would have been fine. Six years ago (2007)
people were only beginning to realize the need for unique directions over
averaging, so it wasn't uncommon to acquire data like you have.
Sorry,
Matt.
On 8/3/13 2:12 AM, "Paul Chou" <[log in to unmask]> wrote:
>Dear all FSL experts
>
>I have a DTI dataset which was acquired six years ago (patient vs control
>study). The acquisition parameter for this DTI dataset were as follows :
>b value = 1000; 13 directions; NEX=6 and voxel size= 2*2*2.2 mm. I
>performed the TBSS analysis and probabilistic tractography for this
>study. After long time of journal review, I got the feedback from one
>reviewer and he/she said the acquisition parameter for DTI direction is
>"extremely outdated" (only 13 directions in this dataset) and reject my
>research. Based on these "extremely outdated acquisition scheme" for DTI,
>he also suggested me to exclude any results and discussion of the
>tractography part which I performed in this study. Do any experts have
>any suggestion or recommendation on the minimal required number of
>diffusion direction for tractrography study? I wish I could still publish
>these results (especially for tractrography part) without further
>technical problem in other journal.
>
>
>Best
>
>Paul
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