[1] Univ N Carolina, Dept Pediat, Div Pulmonol, Chapel Hill, NC USA
[2] Univ N Carolina, Dept Radiol, Chapel Hill, NC USA
[3] Univ N Carolina, Sch Publ Hlth, Dept Biostat, Chapel Hill, NC USA
[4] Cincinnati Childrens Hosp, Dept Radiol, Cincinnati, OH USA