def is_same_scanner_position(*images):
    """Check that all images have the same unique scanner position.

    Parameters
    ----------
    images : sequence[MRI]

    Returns
    -------
    True if all elements of the input set have the same unique scanner
    position (which is not `None`).

    """
    uids = [img.scanner_position for img in images
            if img.scanner_position is not None]
    uids = set(uids)
    return len(uids) == 1