1. Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA 02139 USA.
2. Department of Electrical Engineering, Stanford University, Stanford, CA 94301 USA.
3. Department of Radiology, Stanford University, Stanford, CA 94588 USA.
4. Departments of Electrical and Computer Engineering, Diagnostic Medicine, and Oden Institute, University of Texas at Austin, Austin, TX 78712 USA.
5. Departments of Radiology and Electrical Engineering, Stanford University, Stanford, CA 94305 USA.