US Velocimetry in Participants with Aortoiliac Occlusive Disease

Abstract

Background:The accurate quantification of blood flow in aortoiliac arteries is challenging but clinically relevant because local flow patterns can influence atherosclerotic disease.Purpose: To investigate the feasibility and clinical application of two-dimensional blood flow quantification using high-frame-rate contrast-enhanced US (HFR-CEUS) and particle image velocimetry (PIV), or US velocimetry, in participants with aortoiliac stenosis. Materials and Methods:In this prospective study, participants with a recently diagnosed aortoiliac stenosis underwent HFR-CEUS measurements of the pre-and poststenotic vessel segments (August 2018 to July 2019). Two-dimensional quantification of blood flow was achieved by performing PIV analysis, which was based on pairwise cross-correlation of the HFR-CEUS images. Visual inspection of the entire data set was performed by five observers to evaluate the ability of the technique to enable adequate visualization of blood flow. The contrast-tobackground ratio and average vector correlation were calculated. In two participants who showed flow disturbances, the flow complexity and vorticity were calculated.Results: 35 participants (median age, 67 years; age range, 56-84 years; 22 men) were included. Visual scoring showed that flow quantification was achieved in 41 of 42 locations. In 25 locations, one or multiple issues occurred that limited optimal flow quantification, including loss of correlation during systole (n = 12), shadow regions (n = 8), a short vessel segment in the image plane (n = 7), and loss of contrast during diastole (n = 5). In the remaining 16 locations, optimal quantification was achieved.The contrast-to-background ratio was higher during systole than during diastole (11.0 6 2.9 vs 6.9 6 3.4, respectively; p < 0.001), whereas the vector correlation was lower (0.58 6 0.21 vs 0.47 6 0.13; p < 0.001). Flow complexity and vorticity were high in regions with disturbed flow. Conclusion: Blood flow quantification with US velocimetry is feasible in patients withan aortoiliac stenosis, but several challenges must be overcome before implementation into clinical practice.

Blood Flow Quantification with High-Frame-Rate, Contrast-Enhanced Ultrasound Velocimetry in Stented Aortoiliac Arteries: In Vivo Feasibility

“…Some of these issues, such as calcifications and out-ofplane blood flow, affect US imaging in general, while others apply only to echoPIV. However, it is important to note that none of these limiting issues were related to the stent, as the same limiting issues were already found and discussed in our study in untreated patients with aortoiliac occlusive disease (Engelhard et al 2021). These limiting issues can be overcome with further improvement of the echoPIV technique, including microbubble stability, 3-D imaging and near-instantaneous data processing.…”

“…All patients provided written inform consent prior to enrollment. The measurement protocol and data analysis were similar to those in an earlier feasibility study in untreated patients with aortoiliac occlusive disease (Engelhard et al 2021).…”

“…These data could be used to accurately quantify local arterial flow disturbances, using echoPIV-derived flow parameters such as vector complexity and vorticity. In an earlier study, it had been reported that these flow parameters can be used to distinguish disturbed blood flow from undisturbed blood flow in areas without an increased peak systolic velocity that would typically not be identified as problematic with DUS (Engelhard et al 2021). Another study by Hansen et al (2019) found that these parameters are better suited for the assessment of stenosis severity than the conventional peak systolic velocity ratio obtained with DUS.…”

“…H., E.G.J., J.V., M.M.P.J.R. ), with a final score based on consensus, using a previously described methodology (Engelhard et al 2021). For each location, the best measurement was selected from the different MIs and contrast dosages and used to assess feasibility, in three categories:…”

“…Recent echoPIV methods use planewave and diverging-wave ultrasound imaging to obtain several thousands of images per second. This highframe-rate echoPIV technique has been successfully used to quantify high-velocity (»1 m/s) blood flow in animal studies of the aorta and heart (Leow et al 2015;Toulemonde et al 2017) A recent study reported that 2-D blood flow quantification with echoPIV in the aortoiliac tract is feasible in patients with untreated aortoiliac occlusive disease (Engelhard et al 2021). However, echoPIV in patients with stents is more challenging because of possible attenuation artifacts caused by the metal stent struts.…”