1. Department of Computer Science and Engineering, The Chinese University of Hong Kong. E-mail: {wangwm, lzhu, ypchui, pheng}@cse.cuhk.edu.hk
2. Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences. E-mail: jing.qin@siat.ac.cn
3. National-Regional Key Technology Engineering Laboratory for Medical Ultrasound, School of Medicine, Shenzhen University, Nanhai Avenue 3688, Shenzhen, Guangdong, P.R.China, 518060. E-mail: nidong@szu.edu.cn