[Mrtrix-discussion] First voxel of track is not a seed voxel

[Michael Schirner]

Hi Donald et al,

we encounter some strange behaviour: streamtrack produces very nice
tracks, but it is often the case, that the first voxel of a track is not
one of the specified seed voxel but right next to one (despite using the
'unidirectional' flag).

We run streamtrack using this command:
streamtrack SD_PROB CSD8.mif -seed seedmask.mif -include targetmask.mif
-mask mask.mif -nomaskinterp -unidirectional -num 1000 tracks.tck

The dwi data was read in from a DICOM directory, no further processing
except as specified in the mrtrix documentation. All masks were generated
from freesurfer segmentations, stored as NIFTI and converted to mif-format
using mrconvert. After tracking we convert the tck files to vtk files
using one of the mask-files as '-voxel' image. We tried it with and
without adding +1 to each coordinate dimension, in order to get
matrix-cube indices.

Strangely, when we use masks that contain only a single seed voxel,
everything works just fine, but as soon if we use a larger ROI we
encounter this problem.

Any help is much appreciated. Thanks!

Michael