Department of Radiology, Wake Forest School of Medicine, Winston-Salem, North Carolina, United States of America , School of Mathematical Science, Beijing Normal University, Beijing, P. R. China.|Department of Radiology, Wake Forest School of Medicine, Winston-Salem, North Carolina, United States of America , School of Mathematical Science, Beijing Normal University, Beijing, P. R. China.|Department of Radiology, Wake Forest School of Medicine, Winston-Salem, North Carolina, United States of America , School of Mathematical Science, Beijing Normal University, Beijing, P. R. China.|Department of Radiology, Wake Forest School of Medicine, Winston-Salem, North Carolina, United States of America , School of Mathematical Science, Beijing Normal University, Beijing, P. R. China.|Department of Radiology, Wake Forest School of Medicine, Winston-Salem, North Carolina, United States of America , School of Mathematical Science, Beijing Normal University, Beijing, P. R. China.|Department of Radiology, Wake Forest School of Medicine, Winston-Salem, North Carolina, United States of America , School of Mathematical Science, Beijing Normal University, Beijing, P. R. China.