def _add_volumes(bold_file, bold_cut_file, skip_vols):
    """Prepend skip_vols from bold_file onto bold_cut_file."""
    import nibabel as nb
    import numpy as np
    from nipype.utils.filemanip import fname_presuffix
    if skip_vols == 0:
        return bold_cut_file
    bold_img = nb.load(bold_file)
    bold_cut_img = nb.load(bold_cut_file)
    bold_data = np.concatenate((bold_img.dataobj[(...), :skip_vols],
        bold_cut_img.dataobj), axis=3)
    out = fname_presuffix(bold_cut_file, suffix='_addnonsteady')
    bold_img.__class__(bold_data, bold_img.affine, bold_img.header
        ).to_filename(out)
    return out
