def patch_cmass_output(lst, index=0):
    """
    Parameters
    ----------
    lst : list of tuples
        output of afni.CenterMass()
    index : int
        index in the list of tuples

    Returns
    -------
        tuple
            one set of center of mass coordinates
    """
    if len(lst) <= index:
        raise IndexError("lst index out of range")
    return lst[index]