validate.dti.gradients: Validate and normalize a diffusion MRI gradient table.

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

Validate and normalize a diffusion MRI gradient table.

Description

Checks that a set of b-vectors and b-values is consistent, replaces missing values by b=0 volumes, and reports suspicious entries. This is the validation used by read.dti.gradients, but it can also be called directly on gradients from any other source.

Usage

validate.dti.gradients(bvec, bval, n_volumes = NULL)

Arguments

bvec	character string (path to a b-vectors file), or a numeric matrix with one row per volume (or one column per volume) and 3 columns.
bval	character string (path to a b-values file), or a numeric vector with one value per volume. Can be NULL if bvec identifies both files.
n_volumes	scalar numeric or integer, the number of volumes in the DWI image that the gradients belong to, used to check that the table matches the image. Typically dim(volume$data)[4]. Set to NULL (the default) to skip this check.

Value

a named list with the entries bvec (numeric matrix with n rows and 3 columns, one row per volume) and bval (numeric vector of length n).

Note

The rules for missing values match those of MRtrix3: a missing b-value in a volume with a valid direction, or a missing direction in a volume with a non-zero b-value, is an error, because such a volume cannot be interpreted. Everything else is treated as a b=0 volume. The norm of the gradient vectors is never changed, and a b-value is never rescaled, because that would silently alter the data.

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