def _get_units(intuple):
    """
    Extract Units from metadata.

    >>> _get_units([("fmap.nii.gz", {"Units": "rad/s"})])
    'rad/s'

    >>> _get_units(("fmap.nii.gz", {"Units": "rad/s"}))
    'rad/s'

    """
    if isinstance(intuple, list):
        intuple = intuple[0]
    return intuple[1]["Units"]