1. Department of Occupational Medicine and Toxicology, Beijing Chaoyang Hospital, Capital Medical University, Beijing 100020, P.R. China
2. Department of Radiology, Beijing Chaoyang Hospital, Capital Medical University, Beijing 100020, P.R. China
3. Shenyang Ninth People's Hospital, Shenyang, Liaoning 110024, P.R. China
4. Shanxi Second People's Hospital, Taiyuan, Shanxi 030012, P.R. China
5. Chinese Center for Disease Control and Prevention, Beijing 100050, P.R. China
6. Shandong Provincial Hospital, Jinan, Shandong 250021, P.R. China
7. Department of Neurology, Beijing Chaoyang Hospital, Capital Medical University, Beijing 100020, P.R. China