Hello, we are interested in comparing results from deterministic and probabilistic tractography. In order to do this, we need to do the fiber tracking in dti space, but we would like to maintain compatibility with results in MNI space which are more efficient. We have a single spherical seed ROI in MNI space. We thought that  we could transform the centroid of the sphere to diffusion space, then construct a sphere of the same dimension in each subject around it and the result should be almost identical to the MNI tractography result, at least with probtrackx. Is this a correct assumption?

The second question I have in this vein is this. Deterministic tractography differs in at least two respects from probtrackx results: 1) the probabilistic nature of the tractography and 2) the fact that probtrackx recognizes a secondary fiber. Is it possible to alter probtrackx to recognize only the principal fiber?

Are you aware of any systematic work that has compared deterministic and probabilistic tractography in clinical populations?