Hi Francesco - If this registration is done with bbregister, which is the default option in tracula, then it uses the lh.white and rh.white surfaces from the freesrufer reconstruction of the structural. The low-b diffusion images are aligned to those surfaces by optimizing the contrast of the registered low-b image across the grey-white matter boundary.

Hope this helps, a.y

On Wed, 12 Mar 2014, Francesco Baldacchini wrote:

Hi everybody,

I would like to ask a question about trac-preproc, because I'm new to Tracula and I'm studying how the entire trac-all process works. I want to know which is the specific structural image (I mean the name of the file) that is registered to the dwi volume during trac-preproc, and at which point of the process this is done. I'm doing this because I want to track down all the movements of the files used by Tracula. Thanks,

Francesco Baldacchini