1. Assistant Researcher, State Key Laboratory of Hydroscience and Engineering, Tsinghua Univ., Beijing 100084, China.
2. Professor, Dept. of Civil Engineering, Univ. of Minnesota, Minneapolis, MN 55455 (corresponding author).
3. Professor, Dept. of Radiology, Univ. Paris Diderot, Sorbonne Paris Cite, University Hospitals Paris Nord Val de Seine, Beaujon, Clichy, 92110 France.