Evaluation of CT time-density curves of lower-limb veins

RATIONALE AND OBJECTIVES. TO evaluate time-density curves of the lower-limb veins for optimization of CT venography. METHODS. Fifty patients referred for chest CT were randomized into five equal groups. Five anatomic levels (abdomen, pelvis, proximal thigh, knee, and midcalf) were evaluated by a dynamic acquisition during 7 minutes, Computed tomography attenuation values of the veins, arteries, and adjacent muscles were measured for each level and plotted into curves versus time, Venous enhancement was also assessed qualitatively. RESULTS. Mean peak enhancement values of the inferior vena cava and the iliac, femoral, popliteal, anterior tibial, posterior tibial, and peroneal veins were, respectively, 112 +/- 16, 103 +/- 17, 93 +/- 23, 98 +/- 30, 112 +/- 28, 137 +/- 28, and 124 +/- 29 Hounsfield units. These were reached at 93 +/- 9.5, 129 +/- 15, 135 +/- 20, 147 +/- 57, 124 +/- 32, 123 +/- 17, and 123 +/- 18 seconds. Homogeneous opacification was obtained after 210 seconds. An optimal time window for CT venography was obtained between 210 and 240 seconds for the calf level and between 180 and 300 seconds for above-knee veins. CONCLUSIONS. For sequential CT venography, a caudocranial acquisition of the lower-limb veins, starting at 210 seconds, should allow optimal clot detection.