[1] VA Palo Alto Hlth Care Syst, Palo Alto, CA 94304 USA
[2] Stanford Sch Med, Dept Med, Stanford, CA USA
[3] Indiana Univ, Dept Radiol, Indianapolis, IN 46204 USA
[4] Univ Iowa, Carver Coll Med, Dept Cardiothorac Surg, Iowa City, IA USA
[5] Mayo Clin & Mayo Fdn, Mayo Med Sch, Dept Med, Rochester, MN 55905 USA
[6] NYU, Med Ctr, Dept Radiol, New York, NY 10016 USA
[7] NYU, Med Ctr, Dept Med, New York, NY 10016 USA