Capron, Charles

Accurate assessment of arterial wall mechanics is essential for detecting vascular pathologies. The technique described herein incorporates a commercially available ultrasound system and applanation tonometry to noninvasively evaluate the local mechanical properties of the common carotid artery (CCA). Pressure waveforms were acquired using a tonometer combined with ultrasound-based diameter of the CCA. The signals were temporally aligned, converted to physical units using brachial systolic and diastolic pressure, and interpolated over uniform strain increments. Hoop stress was estimated using thick-wall assumptions, and hoop strain was derived from mid-wall circumferential stretch. Incremental elastic modulus was computed from local linear fits to the stress–strain data, and the area of the resulting hysteresis loop was used as a surrogate for viscoelastic energy loss, quantified by the energy dissipation ratio (EDR). The method was applied to healthy subjects (HS) and those with cardiovascular risk or confirmed atherosclerosis. In HS, pressure–strain elastic modulus (Ep) ranged from 50–55 kPa and EDR from 2%–6%, while non-healthy subjects showed higher EDR values (10%–20%), reflecting increased arterial viscoelasticity. Results revealed nonlinear pressure–diameter relationships with clear hysteresis, reflecting viscoelastic effects. The technique offers potential as a diagnostic tool for evaluating early, localized vascular alterations.

Increased arterial stiffness is an early indicator of various cardiovascular diseases (CVD). Arterial Dispersion Ultrasound Vibrometry (ADUV) employs acoustic radiation force to induce arterial wall motion, enabling estimation of arterial wave velocity (i.e., phase velocity). This study investigates the correlation between ADUV-derived wave velocity and traditional arterial stiffness metrics, including distensibility, compliance, and stiffness index in the right and left common carotid arteries (CCAs). In a cohort of 59 subjects, categorized as (a) confirmed CVD (n = 27), (b) individuals with cardiovascular risk factors (n = 20), and (c) healthy controls (n = 12), we assessed arterial wave velocity across the cardiac cycle, split into 10 stages, to capture variations in mechanical properties. Univariate analysis demonstrated a statistically significant inverse linear relationship between ADUV-derivedwave velocity and distensibility for the right CCA during the systolic phase (cardiac stages 3–5) and diastolic phase (cardiac stages 7–9) (−0.35 < ρ < −0.50, p < 0.02). The wave velocity showed associations with compliance in some of these phases. No significant correlations were observed between wave velocity and the stiffness index. Our findings provide insights into the clinical relevance of ADUV-derived wave velocity as a biomarker for arterial stiffness and its potential to complement or enhance traditional stiffness assessments.

Ultrasound wave-based elastography has emerged as a promising technique for measuring the mechanical properties of blood vessels in vivo. It is well known that blood flow modulates the velocity of the symmetric natural pulse wave, but little has been reported about how it may affect the velocity of induced waves using acoustic radiation force (ARF). We used a fluid–structure interaction model in FEBio to study the effect of flow in elastic tubes after applying a simulated ARF. We varied the vessel wall Young’s modulus (E = 200, 400, and 600 kPa) and wall thickness (WT = 0.5, 1.0, and 1.5 mm) and applied mean flow rates of ±500, 1000, and 1500 mm/s with either parabolic or plug flow using an inviscid fluid model. Analysis of the phase velocities reveals a flow dependence which diminishes with frequency. Plug flow produced greater changes in dispersion curves than parabolic flow. Thinner tubes are more sensitive to flow than thicker tubes. Increasing E tends to increase sensitivity to flow slightly. These results indicate that flow rate may be an important variable to consider when estimating vascular properties from wave-based acquisitions.

Arterial stiffness predicts cardiovascular disease, the leading cause of death worldwide. Ultrasound elastography methods that measure wave velocity have promise for evaluating the stiffness of blood vessels in vivo. However, vessel geometry modulates wave velocity by inducing geometric dispersion. Here, we compare Young's modulus E estimates obtained using in vivo wave velocity measurements and techniques that either do or do not consider geometry to ex vivo reference E values from mechanical testing . An acoustic radiation force was applied to generate propagating waves in the right common carotid artery (N = 9) and external jugular vein (N = 10) of anesthetized pigs. Vessels were imaged with ultrafast ultrasound to measure wave motion. Group velocity cg was estimated from wave motion using a Radon transform. E was estimated from cg using a bulk media assumption which neglects geometry, as well as the Moens–Korteweg equation and a semi-analytical finite element model, which consider geometry. Pigs were euthanized and vessels were excised. Ring-shaped samples were extracted and tested in a uniaxial tension setup to obtain reference E values for comparison with E values obtained from wave-based techniques. Techniques considering geometry exhibited higher correlation with reference E values, underscoring the need to incorporate geometry for accurate vascular elastography assessments.

Arterial stiffness is a predictor of cardiovascular diseases, the leading causes of death worldwide. Ultrasound-based methods that measure arterial wave propagation have promise for evaluating local stiffness in vivo. However, geometric properties of arteries cause dispersion, invalidating typical assumptions underlying the relationship between shear modulus G and group velocity cg, which clinical implementations of ultrasound shear wave elastography do not consider. Here, we examine the dependence of these estimates on geometry and evaluate alternative approaches. Wave motion in the proximal wall of an artery after application of focused acoustic radiation force is simulated with a semi-analytical finite element (SAFE) model, and cg is estimated using a time-to-peak algorithm to determine G with several methods. First, the value of G a clinical scanner would report is calculated assuming a bulk medium. Second, a pulse wave velocity (PWV)-based G estimate is calculated by taking cg = PWV and applying the Moens–Korteweg equation. Third, we develop an interpolation-based method to provide a corrected G estimate using data generated by the SAFE model. Simulation results show severe geometry-dependent bias with the bulk method, which is partially ameliorated with the PWV method and substantially improved with the interpolation approach. Results are validated using arterial phantoms.

Arterial stiffness is recognized as a highly clinically relevant and independent prognostic biomarker of cardiovascular disease. Arterial dispersion ultrasound vibrometry (ADUV) uses acoustic radiation force to generate propagating waves in the arterial wall and measures the wave motion to estimate arterial mechanical properties from fitting phase velocity dispersion curves to a waveguide model. ADUV measurements were made with a Verasonics V1 system with a L7-4 linear array transducer in 63 human subjects (27 male/36 female) from ages 50–88 years old. We made measurements at 10 time points within the cardiac cycle, termed cardiac stages. We estimated the phase velocity (median of cp from 400-600 Hz) and G determined from matching the dispersion curves with those from a waveguide model incorporating the artery diameter and wall thickness. Within the same study visit, we measured the intima-media thickness and diameter changes through the cardiac cycle with a General Electric Logiq E9 or E10 scanner. We also tonometry to determine the carotid-femoral pulse wave velocity. We report here comparisons of median phase velocity, cp, and inverted shear modulus, G, at different stages of the cardiac cycle with clinical metrics of arterial stiffness.

Abstract Objective. Measuring waves induced with acoustic radiation force (ARF) in arteries has been studied over the last decade. To date, it remains a challenge to quantitatively assess the local arterial biomechanical properties. The cylindrical shape and waveguide behavior of waves propagating in the arterial wall pose complexities to determining the mechanical properties of the artery. Approach . In this paper, an artery-mimicking tube in water is examined utilizing three-dimensional measurements. The cross-section of the tube is measured while a transducer is translated over 41 different positions along the length of the tube. Motion in the radial direction is calculated using two components of motion which are measured from the two orthogonal views of the cross-section. This enables more accurate estimation of motion along the circumference of tube. Main results . The results provide more information to categorize the motion in tube wall into two types of responses: a transient response and a steady state response. The transient response is caused by ARF application and the waves travel along the length of the tube for a relatively short period of time. This corresponds to the axial and circumferential propagating waves. The two circumferential waves travel along the circumference of tube in CW (clockwise) and CCW (counter-clockwise) direction and result in a standing wave. By using a directional filter, the two waves were successfully separated, and their propagation was more clearly visualized. As a steady state response, a circumferential mode is generated showing a symmetric motion (i.e. the proximal and distal walls move in the opposite direction) following the transient response. Significance. This study provides a more comprehensive understanding of the waves produced in an artery-mimicking tube with ARF application, which will provide opportunities for improving measurement of arterial mechanical properties.