Received: 21 May 2018
Accepted: 23 October 2018
First Online: 1 November 2018
Ethics approval and consent to participate
: The study was approved by the Ethics Committee of the First Affiliated Hospital, Xi’an Jiaotong University. Since this is a retrospective study, a written consent is waived by the Ethics Committee and is deemed unnecessary.
: Not applicable
: The authors declare no competing financial interests.
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