Blood Flow Quantification Near Stented SFA Lesions Using Ultrasound Velocimetry

Study Overview
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Brief Summary
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Peripheral arterial disease (PAD) in the lower extremity is the third leading cause of atherosclerotic cardiovascular morbidity. Endovascular treatment has become the principal surgical strategy in femoro-popliteal lesions. Stent placement induces significant changes in the arterial geometry and thereby in the hemodynamic environment. Visualization of local blood flow patterns (around stents) is challenging, but clinically relevant. Blood flow has a significant influence on the development of atherosclerosis and therefore stent patency. In vivo blood flow characterization might enable the recognition, prediction and explanation of (in-stent) restenosis. This study will therefore aim to investigate the feasibility of a novel ultrasound technique (echoPIV) to quantify spatiotemporal blood flow near stented femoral artery lesions. Furthermore, the blood flow information obtained during the echoPIV measurements will be used as patient-specific boundary conditions in a computational fluid dynamics (CFD) simulation. The tested hypothesis is that blood flow quantification using echoPIV is feasible in and around stents in the femoral artery and that it will improve CFD simulations.

Official Title
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Feasibility of Ultrasound Particle Image Velocimetry to Quantify Flow Near Stented SFA Lesions

Conditions
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Peripheral Arterial Disease

Intervention / Treatment
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* Diagnostic Test: High-frame-rate contrast-enhanced ultrasound measurements (echoPIV)
* Diagnostic Test: Computed tomography angiography (CTA) scan


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Scheduled endovascular treatment of a lesion in the SFA through placement of a bare metal or a covered stent A recently (<6 weeks) treated lesion in the SFA through placement of a bare metal or a covered stent Exclusion Criteria: Hypersensitivity to the active substance(s) or any of the excipients in SonoVue Right-to-left cardiac shunt Severe pulmonary hypertension (pulmonary artery pressure > 90mmHg) Uncontrolled systemic hypertension Adult respiratory distress syndrome Severe pulmonary disease (e.g. COPD GOLD 3/4, adult respiratory distress syndrome) Clinically unstable cardiac disease (recent or ongoing myocardial infarction, unstable angina at rest, recent percutaneous coronary intervention, clinically worsening cardiac symptoms, severe cardiac arrythmia's, endocarditis, etc.) Prosthetic valves Loss of renal function (GFR < 31 ml/min), end-stage renal disease End-stage liver disease Sepsis Hypercoagulable status, recent thrombosis Congestive heart failure (class III or IV) Hypersensitivity to iodinated contrast media Pregnancy

Ages Eligible for Study
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Minimum Age: 18 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| PAD patients<br>The entire cohort exists of patients recently treated with an endovascular stent placement in the superficial femoral artery (SFA). | Diagnostic Test: High-frame-rate contrast-enhanced ultrasound measurements (echoPIV)<br>* Patients will undergo high-frame-rate contrast-enhanced ultrasound measurements, within 6 to 8 weeks after the endovascular procedure, at the vascular center of Rijnstate hospital. Prior to these measurements a venous cannula will be placed to ensure venous access for the contrast administration.<br>Diagnostic Test: Computed tomography angiography (CTA) scan<br>* Patients will undergo a CTA scan of the lower extremities at the Radiology dept. of Rijnstate hospital the same day as the echoPIV measurements. This CTA scan serves as a reference for the vessel geometry and stent location.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Qualitative assessment vector velocity fields | Vector velocity fields derived from the echoPIV data will be used to calculate and visualize the velocity profile. In order to answer the question regarding feasibility of echoPIV the quality of the vector velocity fields will be assessed using three different metrics of which the first one is a qualitative assessment by different observers. Recordings of the contrast-enhanced ultrasound with an overlay of the vector velocity profiles will be reviewed on different topics following a scoring rubrics. | 6 to 8 weeks after the procedure (stent placement of SFA) | 
| Contrast-to-background ratio | The contrast-to-background ratio (CBR) is the second metric to assess the outcomes of the echoPIV measurements. The CBR is a quantitative measure for the contrast levels and therefore for the quality of the contrast-enhanced US image. The higher the CBR level (in dB) the higher the intensity of the contrast which is needed for sufficient PIV analysis. | 6 to 8 weeks after the procedure (stent placement of SFA) | 
| Vector correlation | The vector correlation is the third metric to assess the outcomes of the echoPIV measurements. The vector correlation demonstrates the tracking performance of the PIV algorithm. The vector correlation provides a unitless value between 0 and 1 in which 0 indicates poor tracking of the microbubble contrast and 1 indicates perfect tracking of the microbubble contrast. | 6 to 8 weeks after the procedure (stent placement of SFA) | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Vorticity | Multiple blood flow parameters will be derived from the echoPIV data. The first one is the vorticity, or the curl of the velocity. The vorticity represents the rotation of particles inside the flow field. This measure can potentially be used to define regions with disturbed blood flow, as a high value (in rad/s) indicates the occurence of a recirculation. | 6 to 8 weeks after the procedure (stent placement of SFA) | 
| Vector complexity | The second blood flow parameters derived from the echoPIV data is the vector complexity. Vector complexity is a measure of multi-directional flow, ranging from 0 till 1. a value of 1 means complex flow with all velocity vectors pointing in all directions, whereas a value of 0 means laminar flow with all velocity vectors pointing in the same direction. This measure can potentially be used to indicate regions with disturbed blood flow. | 6 to 8 weeks after the procedure (stent placement of SFA) | 
| Correlation echoPIV and CFD | Velocity profiles obtained with echoPIV will be compared to outcomes of a computational fluid dynamics (CFD) simulation model of the femoral artery. Multiple points along the imaged vessel will be selected in both the echoPIV and the CFD data to extract the temporal velocity profile. This profile will be compared point-by-point after which the correlation between both outcomes/techniques will be obtained. | 6 to 8 weeks after the procedure (stent placement of SFA) |