P3B-4 In Vitro Investigation of Blood-Flow Velocity Patterns Near a Fine Mesh

Recently there have been advances in endovascular therapy to reduce stroke risk. These advances include: clinical trials of stent-assisted carotid angioplasty for treatment of atheroscerlosis, and self- or balloon-expanding stents that produce a more gradual reduction in carotid stenosis. Unfortunately, past in vivo studies have indicated that the introduction of a stent into the carotid bifurcation alters the Doppler blood-velocity measurements within the stent. These situations may benefit from quantitative measurements of Doppler velocity spectra near (or through) fine mesh structures. In this study, we compared Doppler velocity-based diagnosis of stenosis severity, with and without the presence of a stent using an in vitro system with controlled model geometry of a 50% eccentric stenosis, controlled flow and controlled Doppler parameters. Our hypothesis is that Doppler ultrasound properties are affected by the introduction of a stent and therefore have an effect on Doppler velocity measurements. We have performed an in vitro investigation using a rigid Teflon phantom of a 50% eccentric carotid artery stenosis. A Cordis PRECISE self-expanding Nitinol carotid stent was used in this study to determine the affect of a stent implant on Doppler velocity measurements. A 4-MHz Doppler probe was used to acquire velocity spectra within a 1-mm sample volume. The Doppler parameters were set as follows: 60deg Doppler angle, 50 Hz wall filter, 18519 Hz pulse repetition frequency, 100% power, and 78% gain. We acquired Doppler velocity data over 10 cardiac cycles at 1024 sample points within a centrally located transverse plane of the phantom, with and without a stent implant. All data was digitized at 44.1 kHz for off-line analysis. Doppler velocity spectra were extracted and peak velocity, mean velocity and turbulence intensity (TI) were calculated. Our results indicate that the introduction of a self-expanding carotid stent did not have a significant effect on the measuremen- - ts of peak and mean velocities when geometry, flow rate, and Doppler parameters were maintained. We also found that the stent was able to conform to the complex curvature of a diseased 50% eccentric carotid stenosis. Finally, measurements of TI were found to be significantly increased within the internal carotid artery (p < 0.05) and external carotid artery (p < 0.0001) when comparing normal and stented phantoms