1. Marshall College, University of California, San Diego, La Jolla, California, USA;
2. Department of Obstetrics and Gynaecology, Daping Hospital of the Third Military Medical University, Chongqing, China;
3. Department of Obstetrics and Gynaecology, Suining Central Hospital, Sichuan, China
4. State Key Laboratory of Ultrasound Engineering in Medicine Co-founded by Chongqing and the Ministry of Science and Technology, Chongqing Key Laboratory of Ultrasound in Medicine and Engineering, College of Biomedical Engineering, Chongqing Medical University, Chongqing, China;