1. Department of Ultrasonography, The First Affiliated Hospital of Hainan Medical University, Haikou, Hainan 570102, P.R. China
2. Department of Radiology, Changsha Central Hospital, Changsha, Hunan 410004, P.R. China
3. Department of Radiology, Haikou People's Hospital, Haikou, Hainan 570208, P.R. China
4. Department of Radiology, The Seventh People's Hospital of Chongqing, Chongqing 400054, P.R. China