1. School of Electronics and Information, Northwestern Polytechnical University, 1 Dongxiang Road, Chang’an District, Xi’an, Shaanxi 710129, P. R. China
2. Henan Provincial People’s Hospital, Henan Province No. 7 Weiwu, Henan 450000, P. R. China
3. The First Affiliated Hospital of Xi’an Jiaotong University, Xi’an, Shaanxi 710000, P. R. China
4. College of Engineering, Brunel University, Kingston Lane, Uxbridge, Middlesex, London, UB8 3PH, UK