David E Avrin1, Thomas H Urbania2. 1. Department of Radiology and Biomedical Imaging, University of California, San Francisco, 505 Parnassus Ave., Box 0628, San Francisco, CA 94143-0628. Electronic address: david.avrin@ucsf.edu. 2. Department of Radiology and Biomedical Imaging, University of California, San Francisco, 505 Parnassus Ave., Box 0628, San Francisco, CA 94143-0628.