Oversaturation of color may obscure small intraluminal partial occlusions in color Doppler imaging

Color Doppler imaging has been reported to have a low degree of accuracy in diagnosing nonocclusive deep venous thrombosis. In this modality the color saturation while diagnosing deep vein thrombosis depends on the blood flow velocity and the sensitivity setting of the color image. To determine the effect of color saturation on the detection of thrombi, an in vitro experiment was performed using a closed-loop tube circulation system with a simulated small intraluminal partial occlusion. Heparinized blood was circulated at three different velocities (2, 5.5, and 9 cm/sec) and the vessels were scanned longitudinally and transversely with color Doppler imaging at three color sensitivity settings (low, medium, and high sensitivity). In appropriate color sensitivity settings (i.e., the low, medium, and high sensitivity for the velocity of 9,5.5 and 2 cm/sec, respectively), the color was saturated adequately in the tube lumen so that the partial occlusion was delineated as a color filling defect in the color field. In undersaturated color conditions, the partial occlusion was depicted owing to its echogenicity, but not as a color filling defect. In over-saturated color conditions, such as the high color sensitivity at the high velocity, the partial occlusion was obscured by the excessive amount of color. The over saturation of color may be one of the reasons color Doppler imaging fails to detect deep vein thrombosis, particularly small intraluminal thrombi.