1. School of Biological Science and Medical Engineering, Beihang University, Beijing, 100083, P. R. China
2. Beijing Advanced Innovation Center for Biomedical Engineering, Beihang University, Beijing, 100083, P. R. China
3. State Key Laboratory of Virtual Reality Technology and System, Beihang University, Beijing, 100083, P. R. China
4. College of Computer Science, Sichuan Normal University, Chengdu, 610101, P. R. China