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Purpose: To evaluate if there are any differences in duplex ultrasound velocity measurements between native and stented carotid arteries using duplex ultrasound in an animal model., Methods: The common carotid artery of 5 pigs was exposed bilaterally (10 arteries). Diameters and velocities were measured by ultrasound in the proximal, mid, and distal native artery at the intended site of stent implantation. Measurements were repeated after bilateral stent placement (Wallstent versus Precise) under angiographic control. Outcomes of native versus stented arteries and Wallstent versus Precise were statistically compared., Results: Angiographic measurements matched well with duplex-measured diameters. The mean proximal stent diameter (3.5+/-0.5 mm) was significantly smaller than the native proximal artery diameter (4.2+/-0.4 mm, p = 0.004), mostly due to narrowing of the Wallstent diameter to 3.2+/-0.5 mm (p = 0.009). Proximal, mid, and distal segments of the Wallstents were narrower than those of the Precise stent, and associated peak systolic velocities (PSV) were higher at the 3 locations versus the Precise stent, although the differences were not statistically significant. Wallstent PSVs were higher than in the native artery at the proximal, mid, and distal segments, respectively; again, the differences were not statistically significant., Conclusion: Stent placement caused anatomical and hemodynamic alterations. Narrowings and associated increased velocities were noted. Such alterations, however, were stent-type dependent and did not justify a general approach to new velocity criteria indiscriminately applied to all stents.