Tracula

TRACULA is a fiber tracking and white matter segmentation tool within FreeSurfer.

Running TRACULA

1. Required data
2. Copy to local SUBJECTS_DIR
3. Edit dmrirc
4. Run processing
5. View results

Required data

T1 with FreeSurfer processing

Each subject needs T1 anatomicals that have been processing with the usual FreeSurfer analysis. Typically, these are under the SUBJECTS_DIR LinuxShare\subjects4freesurfer. I'm not sure if the FreeSurfer processing needs to be successful (sometimes it fails).

DTI and bvecs/bvals

The DTI data need to be in the format of DICOM or custom nifti files. However, the DICOM files may be unreliable, as in practice, 64-direction Siemens DTI files with extra b0's caused errors. (It is possible this was because they were on the SUBJECTS_DIR on Windows network share.) The alternative is to use the FSL-ready DTI data in LinuxShare\subjects4fsl.

The bvals and bvecs files that TRACULA needs are slightly different to those used by FSL, so new files need to be created. The difference is that FSL has data across columns/volume, whereas TRACULA requires rows/volume, so they simply need to be flipped. One way to do this is as follows:

1. Find the bvals file (e.g., V:\LinuxShare\subjects4FSL\CON302\DTI_b0corr\bvals) and open it in Excel
   • Open Excel
   • File => Open (or Ctrl^O)
   • Change type to "All Files"
   • Select bvals, click Open

• • In the Text Import Wizard

• • • Step 1 choose "Delimited" (click Next)
    • Step 2 check "Space" (click Finish)

1. The values will appear as one row. Select the row of values, and Copy
2. Go to an empty cell (next row down)

A configuration file is used to define subjects and locations.

The following commands are examples of running the preprocessing steps:

Configuration File (dmrirc)

This is a required file which is passed to the TRACULA processing steps. A reasonable place to save this is LinuxShare\tracula.

• Example

FreeSurfer Preprocessing

Make sure each subject has a successfully completed FreeSurfer preprocessing set of files.

DTI Data

Probably easiest to use an outside folder; if DICOM files are available, these will work (at least for Siemens scanners). Otherwise, the format is akin to FSL.

• Note that for Linux, spaces are a problem, so the file names must have spaces removed.

Technical Note: Issues running in a VM*

The scripts rely on symbolic links, which cannot be created on Windows shared folders. Thus, the SUBJECTS_DIR must be local, and under the usual VM setup we use, the files need to be copied locally, and the local SUBJECTS_DIR set.

An alternative that does not work is to run with the SUBJECTS_DIR on the shared folder. I did test by editing the file "track-preproc" (trac-preproc as of 2013-08-20) to change all the symbolic link creations to file-copy instead. Although the initial preprocessing step worked with this edited file, it crashed later on. Even had this worked, it may cause a problem if the "linked" files are changed.

*VM = Virtual Machine