Text and Data Mining valid from 2019-02-15
Received: 19 October 2018
Accepted: 1 February 2019
First Online: 15 February 2019
Ethics approval and consent to participate
: This study was approved by the Yamagata University ethics committee and by the institutional review board of each university. Written informed consent was not necessarily required in this observational noninvasive retrospective study according to the local guidelines (the Ethical Guidelines for Medical and Health Research Involving Human Subjects by the Ministry of Health, Labour and Welfare of Japan).
: This manuscript contains no individual person’s data.
: The authors declare that they have no competing interests.
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