read.dti.bvec: Read b-vectors from a FSL-style bvecs file.

In freesurferformats: Read and Write 'FreeSurfer' Neuroimaging File Formats

Read b-vectors from a FSL-style bvecs file.

Description

Reads the diffusion gradient directions of a diffusion MRI dataset, i.e. the b-vectors part of the FSL bvecs/bvals format. The file contains unit vectors (or zero vectors for the b=0 volumes), stored as three rows of n values, one row per component, one column per volume.

Usage

read.dti.bvec(filepath, layout = "auto")

Arguments

filepath

character string, path to the b-vectors file, typically ending in .bvec or .bvecs, but without an extension in the HCP layout.

layout

character string, one of 'auto', 'components' or 'volumes'. components means that there are 3 lines, one per vector component (the FSL layout, and what the file name bvecs implies), volumes means one volume per line, i.e. n lines with 3 values each (the HCP layout). With 'auto' (the default), the layout is derived from the matrix dimensions and a warning is raised for a square table, which is ambiguous.

Value

a numeric matrix with n rows and 3 columns, one row per volume, the columns being the x, y and z component of the gradient direction. Note that these vectors are given with respect to the image axes, not to the scanner axes, so they are only meaningful together with the image they belong to: converting them to scanner space requires the transform of that image. Use read.dti.gradients to read b-vectors and b-values together, with consistency checks.

Note

The b-vectors are returned exactly as they are stored, i.e. they are not renormalized, and missing values (see read.dti.gradients) are not replaced here.

See Also

Other dti functions: read.dti.bval(), read.dti.grad(), read.dti.gradients(), write.dti.bval(), write.dti.bvec(), write.dti.grad()

freesurferformats documentation built on Sept. 25, 2026, 1:07 a.m.