1. Department of Ultrasound in Medicine, Shanghai East Hospital, Tongji University School of Medicine, No. 150 Jimo Rd., Shanghai 200120, P. R. China
2. Department of Computer Science, School of Information Science and Engineering, Xiamen University, Fujian, Xiamen 361005, P. R. China
3. Faculty of Mathematics and Computer Science, Quanzhou Normal University, Fujian, Quanzhou 362000, P. R. China