1. Section of Cardiovascular Medicine, University of Wisconsin, 600 Highland Avenue, Madison, WI 53792, USA
2. Section of Cardiology, Middleton Veterans Administration Hospital, Madison, WI, USA
3. Department of Radiology, University of Wisconsin, 600 Highland Avenue, Madison, WI 53792, USA
4. Section of Vascular Surgery, University of Tennessee, Knoxville, TN, USA
5. Biostatistics, General Clinical Research Center, University of Wisconsin, 600 Highland Avenue, Madison, WI 53792, USA