[1] Univ Wisconsin, Dept Radiol, Madison, WI 53792 USA
[2] Univ Wisconsin, Dept Med Phys, Madison, WI 53792 USA
[3] Univ Wisconsin, Dept Biomed Engn, Madison, WI 53792 USA
[4] Univ Wisconsin, Dept Med, Madison, WI 53792 USA
[5] Univ Calif San Francisco, Dept Radiol, San Francisco, CA 94143 USA
[6] Univ Calif San Francisco, Dept Bioengn, San Francisco, CA 94143 USA