1. Department of Biomedical Engineering, Michigan Technological University, Houghton, MI 49931
2. Department of Neurosurgery, Changhai Hospital, Second Military Medical University, Shanghai 200433, China
3. Department of Radiology, School of Medicine and Public Health, University of Wisconsin, Madison, WI 53705
4. Department of Biomedical Engineering, Michigan Technological University, Houghton, MI 49931 e-mail: