1. State Key Laboratory of Applied Organic Chemistry and Key Laboratory of Nonferrous Metal Chemistry and Resources Utilization of Gansu Province Lanzhou University Lanzhou 730000 P. R. China
2. College of Chemistry and Chemical Engineering Qinghai Normal University Xining 810008 China
3. Department of Magnetic Resonance Lanzhou University Second Hospital Lanzhou 730030 P. R. China
4. Gansu Province Clinical Research Center for Functional and Molecular Imaging Lanzhou University Second Hospital Lanzhou 730030 P. R. China