Text and Data Mining valid from 2019-04-10
Received: 14 January 2019
Accepted: 31 March 2019
First Online: 10 April 2019
Compliance with ethical standards
: Drs. Shinsuke Masubuchi, Junji Okuda, Hiroki Hamamoto, Masatsugu Ishii, Wataru Osumi, Masashi Yamamoto, Yoshihiro Inoue, Keitaro Tanaka and Kazuhisa Uchiyama have no conflicts of interest or financial ties to disclose.