Compliance with ethical standards

Guarantor
The scientific guarantor of this publication is Shaolin Li.

Conflict of interest
The authors of this manuscript declare no relationships with any companies, whose products or services may be related to the subject matter of the article.

Statistics and biometry
No complex statistical methods were necessary for this paper.

Informed consent
Written informed consent was waived by the Institutional Review Board.

Ethical approval
Institutional Review Board approval was obtained.

Methodology
• retrospective
• diagnostic or prognostic study
• performed at one institution