2.2. Ethical approval
The Institutional Review Board of Dongguk University Ilsan Hospital approved this study (IRB No. 2007-24). Written informed consent was obtained from all participants. All study procedures were performed in accordance with the guideline of Act on Bioethics and Sefety of South Korea. This study has been registered in Clinical Research Information Service, Republic of Korea (KCT0004135, July 11, 2019).