def _find_confounds(confounds_raw, keywords):
    """Find confounds that contain certain keywords."""
    list_confounds = []
    for key in keywords:
        key_found = False
        for col in confounds_raw.columns:
            if key in col:
                list_confounds.append(col)
                key_found = True
        if not key_found:
            raise ValueError(f"could not find any confound with the key {key}")
    return list_confounds