1. Department of Pathology, Medical College of Yan'an University, Yan'an, Shanxi 716000, P.R. China
2. Department of Pharmacology, Medical College of Yan'an University, Yan'an, Shanxi 716000, P.R. China
3. Department of Nursing, Medical College of Yan'an University, Yan'an, Shanxi 716000, P.R. China
4. Department of Interventional Radiology, Affiliated Hospital of Yan'an University, Yan'an, Shanxi 716000, P.R. China
5. Department of Preventive Medicine, Medical College of Yan'an University, Yan'an, Shanxi 716000, P.R. China