[1] Johns Hopkins Univ, Med Ctr, Dept Radiol, Div Vasc & Intervent Radiol,Johns Hopkins Hosp, Baltimore, MD 21287 USA
[2] Philips Res North Amer, CIITS, Briarcliff Manor, NY 10510 USA
[3] Johns Hopkins Univ, Med Ctr, Dept Surg, Baltimore, MD 21287 USA
[4] Johns Hopkins Univ, Bloomberg Sch Publ Hlth, Dept Biostat, Baltimore, MD 21287 USA