Funding for this research was provided by:
University of Tsukuba
Received: 4 October 2019
Accepted: 7 December 2019
First Online: 19 December 2019
Ethics approval and consent to participate
: This study was approved by the Institutional Review Board of Nippon Medical University Chiba Hokusoh Hospital (Approval No. 590). Because of the anonymous nature of data, the need for informed consent was waived.
: Not applicable.
: The authors declare that they have no competing interests.