1. Department of Ultrasound, Qingdao Municipal Hospital (Group), Qingdao, Shandong 266011, P.R. China
2. Department of Physical Diagnostics, Qingdao Ninth People’s Hospital, Qingdao Municipal Hospital (Group), Qingdao, Shandong 266002, P.R. China
3. Department of Ultrasound, The People's Hospital of Zhangqiu Area, Jinan, Shandong 250200, P.R. China