[1] Stanford Univ, Stanford Prevent Res Ctr, Stanford, CA 94305 USA
[2] Stanford Univ, Sch Med, Dept Radiol, Stanford, CA 94305 USA
[3] Stanford Univ, Sch Med, Dept Hlth Res & Policy, Stanford, CA 94305 USA
[4] Kaiser Permanente No Calif, Div Res, Oakland, CA USA
[5] Univ Calif San Francisco, Dept Epidemiol, San Francisco, CA 94143 USA
[6] Univ Calif San Francisco, Dept Biostat, San Francisco, CA 94143 USA
[7] Univ Calif San Francisco, Dept Med, San Francisco, CA USA