1 Stanford University , Departments of Bioengineering and Radiology , 443 Via Ortega , Stanford, California 94305, United States.
2 University of Washington , Departments of Radiology, Bioengineering, and Physics , 1959 NE Pacific Street, RR215 , Seattle, Washington 98195, United States.
3 National Institutes of Health , National Institute of Biomedical Imaging and Bioengineering , 31 Center Drive , Bethesda, Maryland 20814, United States.