Correspondence:
Xiaopeng Li, Department of Ultrasound, the Second Affiliated Hospital of Xi’an Jiaotong University, Xi Wu Road 157, Xi’an, Shaanxi Province 710004, China.
Email: xiaopengli8@126.com
Baomin Liu, Department of Ultrasound, the Second Affiliated Hospital of Xi’an Jiaotong University, Xi Wu Road 157, Xi’an, Shaanxi Province 710004, China. Email: dr.liubm@163.com