1. Department of Vascular Surgery, Qingdao Municipal Hospital, Qingdao, Shandong 266011, P.R. China
2. Department of Ultrasound, Qingdao Municipal Hospital, Qingdao, Shandong 266011, P.R. China
3. Department of Science and Education, Qingdao Municipal Hospital, Qingdao, Shandong 266011, P.R. China