1. Department of Radiology, University of Washington Medical Center, Seattle, WA 98195‐7115, USA
2. Department of Physiology & Biophysics, University of Washington Medical Center, Seattle, WA 98195‐7115, USA
3. Department of Bioengineering, University of Washington Medical Center, Seattle, WA 98195‐7115, USA
4. Department of Rehabilitation Medicine, University of Washington Medical Center, Seattle, WA 98195‐7115, USA