Purpose: Detailed blood flow studies may contribute to improvements in carotid artery stenting. High-frame-rate contrast-enhanced ultrasound followed by particle image velocimetry (PIV), also called echoPIV, is a technique to study blood flow patterns in detail. The performance of echoPIV in presence of a stent has not yet been studied extensively. We compared the performance of echoPIV in stented and nonstented regions in an in vitro flow setup.
Approach: A carotid artery stent was deployed in a vessel-mimicking phantom. High-frame-rate contrast-enhanced ultrasound images were acquired with various settings. Signal intensities of the contrast agent, velocity values, and flow profiles were calculated.
Results: The results showed decreased signal intensities and correlation coefficients inside the stent, however, PIV analysis in the stent still resulted in plausible flow vectors.
Conclusions: Velocity values and laminar flow profiles can be measured in vitro in stented arteries using echoPIV.
Introduction. Treatment choice for extracranial carotid artery widening, also called aneurysm, is difficult. Blood flow simulation and experimental visualization can be supportive in clinical decision making and patient-specific treatment prediction. This study aims to simulate and validate the effect of flow-diverting stent placement on blood flow characteristics using numerical and in vitro simulation techniques in simplified carotid artery and aneurysm models. Methods. We have developed a workflow from geometry design to flow simulations and in vitro measurements in a carotid aneurysm model. To show feasibility of the numerical simulation part of the workflow that uses an immersed boundary method, we study a model geometry of an extracranial carotid artery aneurysm and put a flow-diverting stent in the aneurysm. We use ultrasound particle image velocimetry (PIV) to visualize experimentally the flow inside the aneurysm model. Results. Feasibility of ultrasound visualization of the flow, virtual flow-diverting stent placement and numerical flow simulation are presented. Flow is resolved to scales much smaller than the cross section of individual wires of the flow-diverting stent. Numerical analysis in stented model introduced 25% reduction of the blood flow inside the aneurysm sac. Quantitative comparison of experimental and numerical results showed agreement in 1D velocity profiles. Discussion/conclusion. We find good numerical convergence of the simulations at appropriate spatial resolutions using the immersed boundary method. This allows us to quantify the changes in the flow in model geometries after deploying a flow-diverting stent. We visualized the physiological blood flow in a 1-to-1 aneurysm model, using PIV, showing a good correspondence to the numerical simulations. The novel workflow enables numerical as well as experimental flow simulations in patient-specific cases before and after flow-diverting stent placement. This may contribute to endovascular treatment prediction.
Introduction: To improve carotid artery stenting (CAS), more information about the functioning of the stent is needed. Therefore, a method that can image the flow near and around a stent is required. The aim of this study was to evaluate the performance of high-frame-rate contrast-enhanced ultrasound (HFR CEUS) in the presence of a stent. Methodology: HFR CEUS acquisitions of a carotid artery phantom, a silicone tube with diameter 8 mm, with and without a stent were acquired at transmit voltages of 2V, 4V and 10V using a Verasonics ultrasound system and C5-2 probe. Different concentrations of ultrasound contrast agent (UCA) were tested in a blood mimicking fluid (BMF). Particle image velocimetry (PIV) analysis was performed on Singular Value Decomposition (SVD) filtered images. Mean and peak velocities, and correlation coefficients were compared between stented and non-stented regions. Also, experimental results were compared with theoretical and numerical models. Results: The averaged experimental mean velocity (0.113 m/s) was significant lower than the theoretical and numerical mean velocity (0.129 m/s). The averaged experimental peak velocity (0.152 m/s) was significant lower than the theoretical and numerical peak velocity (0.259 m/s). Correlation coefficients and averaged mean velocity values were lower (difference of 0.022 m/s) in stented regions compared to non-stented regions. Conclusion: In vitro experiments showed an underestimation of mean and peak velocities in stented regions compared to non-stented regions. However, the microbubbles can be tracked efficiently and the expected laminar flow profile can be quantified using HFR CEUS near and around a stent.