[1] Univ Pittsburgh, Grad Sch Publ Hlth, Dept Epidemiol, Pittsburgh, PA 15261 USA
[2] CHS Coordinating Ctr, Seattle, WA USA
[3] Kaiser Permanente Georgia, Tucker, GA USA
[4] Johns Hopkins Radiol, Neuroradiol Div, Baltimore, MD USA
[5] NHLBI, Div Epidemiol & Clin Applicat, Bethesda, MD 20892 USA
[6] Tufts Univ New England Med Ctr, Dept Radiol, Boston, MA USA