Funding for this research was provided by:
Ministry of Health & Welfare, Republic of Korea (HI19C0577)
Received: 30 May 2019
Accepted: 23 December 2019
First Online: 9 January 2020
Ethics approval and consent to participate
: This study was approved by the institutional review board (IRB) of Samsung Medical Center (IRB no. 2019–04-027) and was conducted according to the principles expressed in the Declaration of Helsinki.
: Not applicable due to the nature of this study and because images are entirely unidentifiable.
: The authors declare that they have no competing interests.