docs: def volreg(dset,suffix='_volreg',base=3,tshift=3,dfile_suffix='_volreg.1D'):
      '''simple interface to 3dvolreg
  
          :suffix:        suffix to add to ``dset`` for volreg'ed file
          :base:          either a number or ``dset[#]`` of the base image to register to
          :tshift:        if a number, then tshift ignoring that many images, if ``None``
                          then don't tshift
          :dfile_suffix:  suffix to add to ``dset`` to save the motion parameters to
      '''
      cmd = ['3dvolreg','-prefix',nl.suffix(dset,suffix),'-base',base,'-dfile',nl.prefix(dset)+dfile_suffix]
      if tshift:
          cmd += ['-tshift',tshift]
      cmd += [dset]
      nl.run(cmd,products=nl.suffix(dset,suffix))