1. Department of Ultrasound, The Third Affiliated Hospital of Jinzhou Medical University, Jinzhou, P.R. China
2. Department of Ultrasound, Shengjing Hospital of China Medical University, Shenyang, P.R. China
3. Department of General Surgery, The Third Affiliated Hospital of Jinzhou Medical University, Jinzhou, P.R. China
4. Department of Obstetrics, The Third Affiliated Hospital of Jinzhou Medical University, Jinzhou, P.R. China
5. Department of Anesthesiology, The Third Affiliated Hospital of Jinzhou Medical University, Jinzhou, P.R. China.