Received: 20 October 2018
Accepted: 20 March 2019
First Online: 2 April 2019
Ethics approval and consent to participate
: Ethical approval for this study was provided by the Ethic Committee (N° 054/04) of the University Hospital Bonn, Germany on February 14th, 2005 and the need for informed consent was waived.
: not applicable.
: The authors declare that they have no competing interests.
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