Funding for this research was provided by:
post-doctoral research start-up fund in Heilongjiang Province (LBH-Q16156)
Received: 11 October 2018
Accepted: 13 May 2019
First Online: 20 May 2019
Ethics approval and consent to participate
: The study protocol was approved by the ethics committee of the First Affiliated Hospital of Harbin Medical University. Due to the retrospective nature of the study, the need for informed consent was waived. Access to case data was approved by the medical record departments of the First Affiliated Hospital of Harbin Medical University and the Second Hospital of Daqing.
: Not applicable.
: The authors declare that they have no competing interests.
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