1. Department of Emergency, Chinese PLA General Hospital, Beijing 100853, P.R. China
2. Department of Critical Care Medicine, General Hospital of Jinan Command, Jinan, Shandong 250031, P.R. China
3. Department of Electrical and Computer Engineering, Purdue University, Indianapolis, IN 46202, USA
4. Department of Ultrasound, Chinese PLA General Hospital, Beijing 100853, P.R. China