Cluster threshold when visualising fixel plots

3

Hi Giuseppe,

The concept of a “cluster” is not as simple with fixel data as it is for voxel data. There are however a couple of options:

  • Map fixels to voxels, perform a connected-component analysis, omit small components, and then take the intersection of that mask with the original fixel mask.

  • fixelfilter does not exclusively perform fixel-based data smoothing: there is also connect, which is a basic attempt at a fixel-based connected-component analysis utilising the fixel-fixel connectivity matrix. It is moreso intended for the separation of discrete isolated bundles rather than the rejection of spatially disconnected fixels (as two fixels that are two voxels apart may still possess a high fraction of connectivity to one another), but it’s nevertheless there if you want to experiment with it, and might have utility if combined with the first point above.

  • The TSF-based smoothing described in the Wiki page can potentially reduce the prevalence of disconnected statistically significant elements when visualised using streamlines rather than the fixels themselves.

Rob