Hi Henrik - There's no explicit parameter in the current version, but you can run bedpostx the multi-exponential model yourself, and then let tracula use the orientation estimates from that model (as long as the output dir is called dmri.bedpostX, it'll read the files from there).
We are in the process of evaluting this with tracula, but note that I suspect that the benefits for tracula may be limited. The general benefit of the multi-exponential model in bedpostx is that it may produce fewer spurious secondary "sticks" (fiber populations) that you might get when fitting the mono-exponential model of bedpostx to multi-shell DWI data. An exploratory (local) tractography method will follow those spurious orientations and end up in the wrong place. But tracula is a global tractography method, i.e., it fits the pathway to the diffusion orientations everywhere along the pathway, rather at one voxel at a time. So spurious secondary orientations in some of those voxels may not have such a big effect on the final result, hence removing those spurious secondary orientations may not make a big difference.
Best, a.y On Wed, 14 Oct 2015, Henrik Sjöström wrote:
Hi! I have some questions regarding Tracula and multi-shell DWI. -Is it possible to activate the multi-shell model within bedpostx when running it through tracula? -does anyone have experience on running multi-shell data through Tracula (2 or 3 crossing fibers)? We are planning an experiment and discussing protocols consisting of around 32 directions with b=1000 and 64 directions at b=2500 so I'm looking for opinions on this with regard to Tracula processing. Thanks! Henrik Sjöström _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
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