This project is designed as retrospective cross-sectional study. Between April 2008 and Dec 2009, a total of approximately 300 patients with chronic lower limb edema who had had bilateral iliac digital venography and surgery at our institution will be reviewed. All patients underwent surgery by one senior vascular surgeon for lower limb conditions within one month after the venographic examination. Patients who had incomplete clinical and surgical records or incomplete images will be excluded. The surgical findings of the presence, anatomical location, and size of the venous narrowing will assessed and described. Stenosis was defined as luminal narrowing of 50% or more compared to the prestenotic or poststenotic lumen.With use of surgical findings as a the standard, the investigators calculated and compared the diagnostic accuracies, sensitivities, specificities, positive predict values and negative predict values of 2D digital venography images alone, 3D rotational venography, and combined MDCT angiography/venography with volume-rendering images supplementary to 2D digital venography.