1. Department of Neurosurgery, Qilu Hospital of Shandong University, Jinan, Shandong Province, P.R. China
2. Department of Neurosurgery, Dezhou People's Hospital, Dezhou, Shandong Province, P.R. China
3. Brian Science Research Institute, Shandong University, Jinan, Shandong Province, P.R. China
4. Department of Biomedicine, University of Bergen, 5009-Bergen, Norway