[1] Univ Calif San Francisco, Dept Radiol, San Francisco, CA 94143 USA
[2] Univ Calif San Francisco, Dept Med, San Francisco, CA 94143 USA
[3] Chinese Univ Hong Kong, Dept Diagnost Radiol & Organ Imaging, Hong Kong, Hong Kong, Peoples R China
[4] Univ Erlangen Nurnberg, Inst Med Phys, Erlangen, Germany