1. Department of Mechanical and Aerospace Engineering, Washington University, 1 Brookings Drive, Box 1185, St. Louis, MO 63130
2. Advanced Imaging Research Center, Oregon Health and Science University, 3181 S. W. Sam Jackson Park Road, Portland, OR 97239-3098
3. Department of Mechanical and Aerospace Engineering, Department of Biomedical Engineering, Washington University, 1 Brookings Drive, Box 1185, St. Louis, MO 63130