1. Department of Gastroenterology, Changhai Hospital, Second Military Medical University, 200433 Shanghai, P. R. China
2. State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, 200050 Shanghai, P. R. China
3. Shanghai Institute of Ultrasound in Medicine, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital, 200050 Shanghai, P. R. China