1. Department of Radiology, Xijing Hospital, Fourth Military Medical University, Xi'an, Shaanxi 710032, P.R. China
2. Department of Radiology, Second Affiliated Hospital of Xi'an Medical Collage, Xi'an, Shaanxi 710038, P.R. China
3. Department of Radiology, Ninth Hospital of Xi'an City, Xi'an, Shaanxi 710068, P.R. China