1. Department of Ultrasound Chongqing General Hospital Chongqing University Chongqing 401147 P. R. China
2. State Key Laboratory of Molecular Engineering of Polymers Department of Macromolecule Science Fudan University Shanghai 200438 P. R. China
3. State Key Laboratory of Ultrasound in Medicine and Engineering Chongqing Medical University Chongqing 400146 P. R. China
4. Department of Materials Science and Engineering University of Maryland College Park 20742 USA
5. Department of Radiology Yan'an Hospital Affiliated to Kunming Medical University Kunming 650051 P. R. China
6. Department of ultrasound Children's Hospital of Chongqing Medical University National Clinical Research Center for Child Health and Disorders Ministry of Education Key Laboratory of Child Development and Disorders Chongqing Key Laboratory of Child Rare Diseases in Infection and Immunity Chongqing 400015 P. R. China