1. Department of Radiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
2. Osteoporosis Research Group, Department of Medicine, University of California San Francisco, San Francisco, California, USA
3. Department of Cell Biology and Anatomy, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
4. Center for Chronic Disease Outcomes Research, Minneapolis Veterans Administration Medical Center and Division of Epidemiology, University of Minneapolis, Minneapolis, Minnesota, USA
5. Department of Radiology, University of California San Francisco, San Francisco, California, USA