Note that this reference documentation is identical to the help that is displayed in MATLAB when you type “help ft_volumewrite”.

  FT_VOLUMEWRITE exports anatomical or functional volume data to a Analyze
  or BrainVoyager file. The data in the resulting file(s) can be
  further analyzed and/or visualized in MRIcro, SPM, BrainVoyager,
  AFNI or similar packages.
  Use as
    ft_volumewrite(cfg, volume)
  where the input volume structure should represent an anatomical MRI
  that was for example obtained from FT_READ_MRI, the source
  reconstruction results from FT_SOURCEANALYSIS, the statistical
  results from FT_SOURCESTATISTICS or an otherwise processed anatomical
  or functional volume.
  The configuration structure should contain the following elements
    cfg.parameter     = string, describing the functional data to be processed,
                          e.g. 'pow', 'coh', 'nai' or 'anatomy'
    cfg.filename      = filename without the extension
    cfg.filetype      = 'analyze', 'nifti', 'nifti_img', 'analyze_spm', 'mgz',
                          'vmp' or 'vmr'
    cfg.vmpversion    = 1 or 2 (default) version of the vmp-format to use
  The default filetype is 'nifti', which means that a single *.nii file
  will be written using the SPM8 toolbox. The 'nifti_img' filetype uses SPM8 for
  a dual file (*.img/*.hdr) nifti-format file.
  The analyze, analyze_spm, nifti, nifti_img and mgz filetypes support a homogeneous
  transformation matrix, the other filetypes do not support a homogeneous transformation
  matrix and hence will be written in their native coordinate system.
  You can specify the datatype for the analyze_spm and analyze formats using
    cfg.datatype      = 'bit1', 'uint8', 'int16', 'int32', 'float' or 'double'
  By default, integer datatypes will be scaled to the maximum value of the
  physical or statistical parameter, floating point datatypes will not be
  scaled. This can be modified with
    cfg.scaling       = 'yes' or 'no'
  Optional configuration items are
    cfg.downsample    = integer number (default = 1, i.e. no downsampling)
    cfg.fiducial.nas  = [x y z] position of nasion
    cfg.fiducial.lpa  = [x y z] position of LPA
    cfg.fiducial.rpa  = [x y z] position of RPA
    cfg.markfiducial  = 'yes' or 'no', mark the fiducials
    cfg.markorigin    = 'yes' or 'no', mark the origin
    cfg.markcorner    = 'yes' or 'no', mark the first corner of the volume
  To facilitate data-handling and distributed computing you can use
    cfg.inputfile   =  ...
  If you specify this option the input data will be read from a *.mat
  file on disk. This mat files should contain only a single variable named 'data',
  corresponding to the input structure.