In vitro performance of echoPIV for assessment of laminar flow profiles in a carotid artery stent

Abstract

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.

Keywords: carotid; high-frame-rate ultrasound; in vitro; particle image velocimetry; stent.

Fig. 1

Schematic representation of the experimental flow setup.

Fig. 2

Time-averaged SVD-filtered B-mode frame of reference measurement 1 (R1) showing the ROIs of the nonstented region (blue) and stented region (orange) for contrast analysis. The stented area is from lateral position 0 mm to the right border of the image. The black arrow indicates the start of the stent.

Fig. 3

Boxplots of the contrast in all measurements. The different subcategories are clustered. Statistical differences within subcategories are indicated with lines above specific measurements. $p\ll 0.001$ applies for all comparisons, unless $p$-values are noted above the lines.

Fig. 4

Boxplots of the contrast in the reference measurements. The line above R1 to R5 shows the statistically significant difference between these two measurements ($p=0.006$).

Fig. 5

Time-averaged velocity vectors (yellow arrows) of reference measurement 1 in nonstented area (blue) and stented area (orange). The velocity vectors are projected on a single SVD filtered frame.

Fig. 6

Boxplots of reference measurements showing (a) mean velocities, (b) maximum velocities, and (c) correlation coefficients for nonstented and stented regions. The horizontal lines above the boxplots indicate no significant difference ($p>0.05$).

Fig. 7

Scatterplot of contrast values in dB per measurement. Each circle represents a contrast measurement of one frame. The color scale ranges from red [timepoint 1 (= 0 s)] to yellow [latest timepoint (=0.17 s)].