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: 60° 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 measurements 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.