Note that this reference documentation is identical to the help that is displayed in MATLAB when you type “help fieldtrip2bis”.

  FIELDTRIP2BIS writes BioImage Suite .mgrid files with eletrode 
  positions in 'xyz' coordinates using a elec datatype structure and the 
  corresponding MRI volume 
 
  Use as
    fieldtrip2bis('Subject_grid.mgrid', elec, 'Subject_MR.nii')
 
  See also BIS2FIELDTRIP, FT_WRITE_SENS, WRITE_BIOIMAGE_MGRID