1. Department of Radiology; Chinese PLA General Hospital; No. 28 Fuxing Road Beijing 100853 P. R. China
2. Key Laboratory of Colloid; Interface and Chemical Thermodynamics; Institute of Chemistry; Chinese Academy of Sciences; Bei Yi Jie 2, Zhong Guan Cun Beijing 100190 P. R. China
3. Department of Neurosurgery; Chinese PLA General Hospital; No. 28 Fuxing Road Beijing 100853 P. R. China
4. School of Chemistry and Chemical Engineering; University of Chinese Academy of Sciences; Beijing 100049 China