Echoplanar distortion correction on dti images

[m.roth]

Hi everybody,

I applied echoplanar distortion correction on my bruker dti images acquired with b values of 400 and 1500 s/mm2. I observed a problem of FOV on some corrected images. In fact, this problem appears on the volumes with the smaller SNR (for b=1500 s/mm2). On a corrected volume, some slices are OK, but other slices present zero lines in the upper and lower part of the images and the brain lenght is then shorter (like a compression in the antero-posterior direction).

Do you already see this problem ?

Sincerely yours

Muriel ROTH

[Yann Cointepas]

I have not seen that yet. The distorsion correction algorithm is based on a slice by slice registration technique. If the SNR is too low, perhaps the registration fail on some slices ?

[m.roth]

Hi Yann,

Thank you very much for your answer.
First, a remark :
-even if the SNR is low, we don't understand why the FOV is changed by the algorithm. Indeed, the FOV is stretched in the antero-posterior direction: the most anterior and posterior parts of the images are filled with zeros. If you like, we can send you some images presenting this bug.
Second, a small question :
- in the state of the software at the moment, is it possible to use the deformation field calculated on the b=400 images and apply it to the b=1500 images, for each direction ??

Thank you again for your precious help.
Muriel and Jean-Luc