1. Department of Ultrasound, Xinqiao Hospital, The Third Military Medical University, 183 Xinqiao Street, Chongqing 400037, China
2. Department of Ultrasound, Southwest Hospital, The Third Military Medical University, Chongqing 400038, China
3. Department of Ultrasound, Sichuan Provincial Hospital for Women and Children, Chengdu, Sichuan 610000, China