Fixel-based analysis using connectivity-based fixel enhancement and non-parametric permutation testing
fixelcfestats [ options ] in_fixel_directory subjects design contrast tracks out_fixel_directory
- in_fixel_directory: the fixel directory containing the data files for each subject (after obtaining fixel correspondence
- subjects: a text file listing the subject identifiers (one per line). This should correspond with the filenames in the fixel directory (including the file extension), and be listed in the same order as the rows of the design matrix.
- design: the design matrix. Note that a column of 1’s will need to be added for correlations.
- contrast: the contrast vector, specified as a single row of weights
- tracks: the tracks used to determine fixel-fixel connectivity
- out_fixel_directory: the output directory where results will be saved. Will be created if it does not exist
Note that if the -mask option is used, the output fixel directory will still contain the same set of fixels as that present in the input fixel template, in order to retain fixel correspondence. However a consequence of this is that all fixels in the template will be initialy visible when the output fixel directory is loaded in mrview. Those fixels outside the processing mask will immediately disappear from view as soon as any data-file-based fixel colouring or thresholding is applied.
Options for permutation testing¶
- -notest don’t perform permutation testing and only output population statistics (effect size, stdev etc)
- -nperms num the number of permutations (Default: 5000)
- -permutations file manually define the permutations (relabelling). The input should be a text file defining a m x n matrix, where each relabelling is defined as a column vector of size m, and the number of columns, n, defines the number of permutations. Can be generated with the palm_quickperms function in PALM (http://fsl.fmrib.ox.ac.uk/fsl/fslwiki/PALM). Overrides the nperms option.
- -nonstationary perform non-stationarity correction
- -nperms_nonstationary num the number of permutations used when precomputing the empirical statistic image for nonstationary correction (Default: 5000)
- -permutations_nonstationary file manually define the permutations (relabelling) for computing the emprical statistic image for nonstationary correction. The input should be a text file defining a m x n matrix, where each relabelling is defined as a column vector of size m, and the number of columns, n, defines the number of permutations. Can be generated with the palm_quickperms function in PALM (http://fsl.fmrib.ox.ac.uk/fsl/fslwiki/PALM) Overrides the nperms_nonstationary option.
Parameters for the Connectivity-based Fixel Enhancement algorithm¶
- -cfe_dh value the height increment used in the cfe integration (default: 0.1)
- -cfe_e value cfe extent exponent (default: 2)
- -cfe_h value cfe height exponent (default: 3)
- -cfe_c value cfe connectivity exponent (default: 0.5)
Additional options for fixelcfestats¶
- -negative automatically test the negative (opposite) contrast. By computing the opposite contrast simultaneously the computation time is reduced.
- -smooth FWHM smooth the fixel value along the fibre tracts using a Gaussian kernel with the supplied FWHM (default: 10mm)
- -connectivity threshold a threshold to define the required fraction of shared connections to be included in the neighbourhood (default: 0.01)
- -angle value the max angle threshold for assigning streamline tangents to fixels (Default: 45 degrees)
- -mask file provide a fixel data file containing a mask of those fixels to be used during processing
- -info display information messages.
- -quiet do not display information messages or progress status; alternatively, this can be achieved by setting the MRTRIX_QUIET environment variable to a non-empty string.
- -debug display debugging messages.
- -force force overwrite of output files (caution: using the same file as input and output might cause unexpected behaviour).
- -nthreads number use this number of threads in multi-threaded applications (set to 0 to disable multi-threading).
- -config key value (multiple uses permitted) temporarily set the value of an MRtrix config file entry.
- -help display this information page and exit.
- -version display version information and exit.
Raffelt, D.; Smith, RE.; Ridgway, GR.; Tournier, JD.; Vaughan, DN.; Rose, S.; Henderson, R.; Connelly, A.Connectivity-based fixel enhancement: Whole-brain statistical analysis of diffusion MRI measures in the presence of crossing fibres. Neuroimage, 2015, 15(117):40-55
- If using the -nonstationary option: Salimi-Khorshidi, G. Smith, S.M. Nichols, T.E. Adjusting the effect of nonstationarity in cluster-based and TFCE inference. NeuroImage, 2011, 54(3), 2006-19
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