1. Photon Physics Group, National Institute for Standards and Technology, Gaithersburg, Maryland 20899‐8410
2. Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742
3. Department of Electrical and Computer Engineering, Cornell University, Ithaca, New York 14853
4. Weill Medical College, Cornell University, New York, New York 10065
5. Department of Radiology, University of Maryland Medical Center, Baltimore, Maryland 21201‐1595
6. Mathematical and Computational Science Division, National Institute for Standards and Technology, Boulder, Colorado 80305‐3328
7. Polymers Division, National Institute for Standards and Technology, Gaithersburg, Maryland 20899‐8453