High-frame-rate contrast-enhanced ultrasound particle image velocimetry in patients with a stented superficial femoral artery: a feasibility study

Abstract

Background: Local blood flow affects vascular disease and outcomes of endovascular treatment, but quantifying it is challenging, especially inside stents. We assessed the feasibility of blood flow quantification in native and stented femoral arteries, using high-frame-rate (HFR) contrast-enhanced ultrasound (CEUS) particle image velocimetry (PIV), also known as echoPIV.

Methods: Twenty-one patients with peripheral arterial disease, recently treated with a stent in the femoral artery, were included. HFR CEUS measurements were performed in the native femoral artery and at the inflow and outflow of the stent. Two-dimensional blood flow was quantified through PIV analysis. EchoPIV recordings were visually assessed by five observers and categorised as optimal, partial, or unfeasible. To evaluate image quality and tracking performance, contrast-to-tissue ratio (CTR) and vector correlation were calculated, respectively.

Results: Fifty-eight locations were measured and blood flow quantification was established in 49 of them (84%). Results were optimal for 17/58 recordings (29%) and partial for 32 recordings (55%) due to loss of correlation (5/32; 16%), short vessel segment (8/32; 25%), loss of contrast (14/32; 44%), and/or shadows (18/32; 56%). In the remaining 9/58 measurements (16%) no meaningful flow information was visualised. Overall, CTR and vector correlation were lower during diastole. CTR and vector correlation were not different between stented and native vessel segments, except for a higher native CTR at the inflow during systole (p = 0.037).

Conclusions: Blood flow quantification is feasible in untreated and stented femoral arteries using echoPIV. Limitations remain, however, none of them related to the presence of the stent.

Trial registration: ClinicalTrials.gov, NCT04934501 (retrospectively registered).

Keywords: Microbubbles; Peripheral arterial disease; Rheology; Stents; Ultrasonography.

Fig. 1

Enrolment (a) and data (b) flowchart of complete dataset considering the best measurement per location. n Number of measurements, p Number of patients, SVD Singular value decomposition

Fig. 2

Schematic representation of the femoral bifurcation indicating the locations of interest. High-frame-rate contrast-enhanced radiofrequency data was obtained at the common femoral artery (1), inflow region of the stent (2), and the outflow region of the stent (3). CFA Common femoral artery, DFA Deep femoral artery, SFA Superficial femoral artery

Fig. 3

Example indicating the stent location and regions of interest (ROIs) used for the quantitative analysis. a, b Filtered contrast-enhanced US image captured at the proximal edge of the stent (white lines) with the velocity streamlines superimposed. a ROIs used to analyse the entire imaged vessel. To calculate the contrast-to-tissue ratio (CTR), the red squares were used for contrast signal strength whereas the blue square was used for tissue signal strength. Black lines represent the delineation of the imaged vessel. All vectors inside this (masked) region were used to calculate the average vector correlation. b ROIs used to analyse the stent influence. CTR was calculated for both the red (contrast strength in native vessel segment) and grey square (contrast strength in stented vessel segment) compared to the blue square. The average vector correlation was computed over all vectors inside the red and grey square for the native and stented segment, respectively. c B-mode image used to identify the stent transition. Orange arrows indicate the proximal edge of the stent

Fig. 4

Example of each limiting issue causing partial flow quantification. Filtered contrast-enhanced US images with velocity streamlines superimposed. The vessel wall is presented in black in all examples. The presence of a stent is indicated in white. a Loss of correlation due to high velocities or complex flow phenomena, here observed distal to a stenotic lesion, indicated with the orange arrow (supplementary video 4). b Only a small part of the vessel is captured within the field of view due to the geometry of the arteries (supplementary video 5). c Loss of contrast due to microbubble destruction. During systole (top), constant replenishment of microbubbles permits sufficient bubble signal, whereas severe bubble destruction occurs during diastole (bottom) due to the prolonged insonation period in the case of lower blood flow velocities (supplementary video 6). d A shadow region possibly caused by a calcified lesion at the anterior side of the lumen, resulting in an interruption of the vector velocity field (top) and bubble intensity (bottom) (supplementary video 7)

Fig. 5

Comparison of contrast-to-tissue ratio (CTR) (a) and vector correlation (b) between systole (purple) and diastole (green) per location. Edges of the boxes indicate the 25th (Q1) and 75th (Q3) percentiles, whereas whiskers give the minimum and maximum values. Outliers are presented as crosses. The values corresponding to measurements assigned as “loss of contrast” by the observers are indicated with a diamond shape.*p < 0.05, ns Not significant, CFA Common femoral artery

Fig. 6

Comparison of contrast-to-tissue ratio (CTR) (a, b) and vector correlation (c, d) between a stented and native vessel segment. Stented segment is presented in dark blue, whereas native segment is given in light blue. Edges of the boxes indicate the 25th (Q1) and 75th (Q3) percentiles, whereas whiskers give the minimum and maximum values. Outliers are presented as crosses. *p < 0.05, ns Not significant