Methods: Aortic wall deformation assessment by ultrafast ultrasound imaging: Application to bicuspid aortic valve associated aortopathy.

Purpose: Aortic maximal rate of systolic distention (MRSD) is a prognosis factor of ascending aorta dilatation with magnetic resonance imaging. Its calculation requires precise continuous tracking of the aortic diameter over the cardiac cycle, which is not feasible by focused ultrasound. We aimed to develop an automatic aortic acquisition using ultrafast ultrasound imaging (UUI) to provide access to the aortic MRSD. Methods: A phased array probe and developed sequences at 2000 frames/s were used. A created interface automatically tracked the anterior and posterior aortic walls over the cardiac cycle. Tissue Doppler allowed a precise estimation of the walls' movements. MRSD was the maximum derivative of the aortic diameter curve over time. To assess its feasibility, 34 patients with bicuspid aortic valve (BAV) and 31 controls were consecutively included to evaluate the BAV-associated aortopathy at the sinus of Valsalva, the tubular ascending aorta, and the aortic arch. Results: UUI acquisitions and the dedicated interface allow tracking of the aortic diameter and calculating the MRSD for the BAV patients and controls (mean age of 34 vs. 43 years, p = 0.120). A trend toward lower deformation in the different aortic segments was observed, as expected. Still, only the MRSD with UUI was significantly different at the sinus of Valsalva in this small series: (0.61 .103.s-1 [0.37-0.72] for BAV patients vs. 0.92 .103.s-1 [0.72-1.02] for controls, p = 0.025). Conclusion: Aortic deformation evaluated with UUI deserves attention with a simple and automated measurement technique that could assess the segmental aortic injury associated with BAV.

Quantitative stiffness assessment of cardiac grafts using ultrasound in a porcine model: A tissue biomarker for heart transplantation.

BACKGROUND: Heart transplantation is the definitive treatment for many cardiovascular diseases. However, no ideal approach is established to evaluate heart grafts and it mostly relies on qualitative interpretation of surgeon based on the organ aspect including anatomy, color and manual palpation. In this study we propose to assess quantitatively the Shear Wave Velocity (SWV) using ultrasound as a biomarker of cardiac viability on a porcine model. METHODS: The SWV was assessed quantitatively using a clinical ultrasound elastography device (Aixplorer, Supersonics Imagine, France) linked to a robotic motorized arm (UR3, Universal Robots, Denmark) and the elastic anisotropy was obtained using a custom ultrasound research system. SWV was evaluated as function of time in two porcine heart model during 20h at controlled temperature (4°C). One control group (N = 8) with the heart removed and arrested by cold cardioplegia and immerged in a preservation solution. One ischemic group (N = 6) with the organ harvested after 30 min of in situ warm ischemia, to mimic a donation after cardiac death. Hearts graft were revived at two preservation times, at 4 h (N = 11) and 20 h (N = 10) and the parameters of the cardiac function evaluated. FINDINGS: On control hearts, SWV remained unchanged during the 4h of preservation. SWV increased significantly between 4 and 20h. For the ischemic group, SWV was found higher after 4h (3.04 +/- 0.69 vs 1.69+/-0.19 m/s, p = 0.007) and 20h (4.77+/-1.22 m/s vs 3.40+/-0.75 m/s, p = 0.034) of preservation with significant differences. A good correlation between SWV and cardiac function index was found (r2=0.88) and manual palpation score (r2=0.81). INTERPRETATION: Myocardial stiffness increase was quantified as a function of preservation time and harvesting conditions. The correlation between SWV and cardiac function index suggests that SWV could be used as a marker of graft viability. This technique may be transposed to clinical transplantation for assessing the graft viability during transplantation process. FUNDING: FRM PME20170637799, Agence Biomédecine AOR Greffe 2017, ANR-18-CE18-0015.

Smart Ultrasound Device for Non-Invasive Real-Time Myocardial Stiffness Quantification of the Human Heart.

Quantitative assessment of myocardial stiffness is crucial to understand and evaluate cardiac biomechanics and function. Despite the recent progresses of ultrasonic shear wave elastography, quantitative evaluation of myocardial stiffness still remains a challenge because of strong elastic anisotropy. In this paper we introduce a smart ultrasound approach for non-invasive real-time quantification of shear wave velocity (SWV) and elastic fractional anisotropy (FA) in locally transverse isotropic elastic medium such as the myocardium. The approach relies on a simultaneous multidirectional evaluation of the SWV without a prior knowledge of the fiber orientation. We demonstrated that it can quantify accurately SWV in the range of 1.5 to 6 m/s in transverse isotropic medium (FA < 0.7) using numerical simulations. Experimental validation was performed on calibrated phantoms and anisotropic ex vivo tissues. A mean absolute error of 0.22 m/s was found when compared to gold standard measurements. Finally, in vivo feasibility of myocardial anisotropic stiffness assessment was evaluated in four healthy volunteers on the antero-septo basal segment and on anterior free wall of the right ventricle (RV) in end-diastole. A mean longitudinal SWV of 1.08 ± 0.20 m/s was measured on the RV wall and 1.74 ± 0.51 m/s on the septal wall with a good intra-volunteer reproducibility (±0.18 m/s). This approach has the potential to become a clinical tool for the quantitative evaluation of myocardial stiffness and diastolic function.

Carotid Plaque Vulnerability Assessed by Combined Shear Wave Elastography and Ultrafast Doppler Compared to Histology.

Ultrafast ultrasound imaging (UUI) provides an estimation of carotid plaque stiffness by shear wave elastography (SWE) and the quantification of wall shear stress (WSS) by ultrafast Doppler. We aimed to evaluate the combined criteria of plaque stiffness and WSS applied on the plaque as potential biomarkers of plaque vulnerability assessed by histology. We included patients for whom carotid endarterectomy had been decided by a multidisciplinary team. UUI was performed within 48 h before surgery, and acquisitions were obtained on a carotid longitudinal view. After endarterectomy, gross examination and histological analysis were performed on each removed plaque. Forty-six plaques with SWE data and 29 with WSS data were analyzed. Histological analysis revealed 29 vulnerable and 17 stable plaques. Gray-scale median analysis by B-mode, mean, and standard deviation of stiffness by SWE did not differ between vulnerable and stable plaques. SWE analysis revealed that the percentage of stiffness range of 3-5 m/s was significantly increased in vulnerable plaques (p = 0.048). WSS alone showed no difference between stable and vulnerable plaques regardless of the segment of the plaque which was analyzed. A multiparametric score using maximal WSS at the peak of the plaque associated with SWE texture analysis parameters was calculated by stepwise regression, leading to a score with a sensitivity of 80% and a specificity of 78%. Area under the receiver operating characteristics curve was 0.85. A multiparameter scoring system including plaque stiffness and flow analysis using UUI allows to effectively identify histologically vulnerable carotid plaques. ClinicalTrials.gov Identifier: NCT03234257.

Dealiasing High-Frame-Rate Color Doppler Using Dual-Wavelength Processing.

Doppler ultrasound is the premier modality to analyze blood flow dynamics in clinical practice. With conventional systems, Doppler can either provide a time-resolved quantification of the flow dynamics in sample volumes (spectral Doppler) or an average Doppler velocity/power [color flow imaging (CFI)] in a wide field of view (FOV) but with a limited frame rate. The recent development of ultrafast parallel systems made it possible to evaluate simultaneously color, power, and spectral Doppler in a wide FOV and at high-frame rates but at the expense of signal-to-noise ratio (SNR). However, like conventional Doppler, ultrafast Doppler is subject to aliasing for large velocities and/or large depths. In a recent study, staggered multi-pulse repetition frequency (PRF) sequences were investigated to dealias color-Doppler images. In this work, we exploit the broadband nature of pulse-echo ultrasound and propose a dual-wavelength approach for CFI dealiasing with a constant PRF. We tested the dual-wavelength bandpass processing, in silico, in laminar flow phantom and validated it in vivo in human carotid arteries ( n = 25 ). The in silico results showed that the Nyquist velocity could be extended up to four times the theoretical limit. In vivo, dealiased CFI were highly consistent with unfolded Spectral Doppler ( r2=0.83 , y=1.1x+0.1 , N=25 ) and provided consistent vector flow images. Our results demonstrate that dual-wavelength processing is an efficient method for high-velocity CFI.

Wall Shear Stress Measurement by Ultrafast Vector Flow Imaging for Atherosclerotic Carotid Stenosis.

OBJECTIVE: Carotid plaque vulnerability assessment could guide the decision to perform endarterectomy. Ultrafast ultrasound imaging (UF) can evaluate local flow velocities over an entire 2D image, allowing measurement of the wall shear stress (WSS). We aimed at evaluating the feasibility of WSS measurement in a prospective series of patients with carotid stenosis. METHODS: UF acquisitions, performed with a linear probe, had an effective frame rate of 5000 Hz. The flow velocity was imaged over the entire plaque area. WSS was computed with the vector field speed using the formula: with the blood velocity and µ, the blood viscosity. The WSS measurement method was validated using a calibrated phantom. In vivo, WSS was analyzed in 5 areas of the carotid wall: common carotid artery, plaque ascent, plaque peak, plaque descent, internal carotid artery. RESULTS: Good correlation was found between in vitro measurement and the theoretical WSS values (R2 = 0.95; p < 0.001). 33 patients were prospectively evaluated, with a median carotid stenosis degree of 80 % [75-85]. The maximum WSS value over the cardiac cycle follows the shape of the plaque with an increase during the ascent, reaching its maximum value of 3.25 Pa [2.26-4.38] at the peak of the plaque, and a decrease after passing of the peak (0.93 Pa [0.80-1.19]) lower than the WSS values in the non-stenotic areas (1.47 Pa [1.12-1.77] for the common carotid artery). CONCLUSION: UF allowed local and direct evaluation of the plaque's WSS, thus better characterizing local hemodynamics to identify areas of vulnerability. KEY POINTS: · Ultrafast vector Doppler allows calculation of the wall shear stress (WSS) by measuring velocity vectors over the entire 2D image.. · The setup to measure the WSS has been validated in vitro on a linear flow phantom by comparing measurements to in silico calculations.. · Applying this method to carotid plaque allows us to better describe the hemodynamic constraints that apply along the entire length of the plaque..

Innovative Multiparametric Characterization of Carotid Plaque Vulnerability by Ultrasound.

OBJECTIVE: The degree of stenosis of a carotid plaque is a well-established risk factor for ischemic stroke. Nevertheless, the risk of ipsilateral stroke in asymptomatic carotid stenosis remains low and new imaging markers are needed to better target which patients would benefit most from endarterectomy or intensive medical therapy. Ultrafast ultrasound imaging offers parameters helping at characterizing the carotid plaque by shear wave elastography and Ultrafast Doppler (UFD). We aimed at using these techniques to characterize 3 different ultrasound biomarkers: plaque stiffness heterogeneity, wall shear stress (WSS) and intraplaque micro-flows and to correlate these biomarkers with findings on computed tomography angiography (CTA) and the pathological examination. METHODS: We present the case of a multimodal evaluation of a carotid plaque using ultrasound. Elastography has been coupled to the WSS assessment and the detection of intraplaque micro-flows by UFD. The data have been compared to CTA and to the pathology examination of the tissue after carotid endarterectomy. RESULTS: Elastography allowed at identifying stiff areas corresponding to calcifications, as well as a soft area corresponding to an intraplaque hemorrhage. The flow evaluation with UFD showed an increase of the WSS along the plaque and identified the presence of a plaque rupture, confirmed by the pathologist. CONCLUSION: Ultrafast ultrasound imaging is an innovative, easily accessible technique that provides imaging modalities on top of the conventional B-mode. Ultrafast ultrasound biomarkers such as plaque stiffness heterogeneity, WSS and intraplaque micro-flows could help to define the vulnerability of the carotid plaque in order to stratify patients that could benefit most from endarterectomy or intensive medical therapy.

Carotid Stiffness Assessment With Ultrafast Ultrasound Imaging in Case of Bicuspid Aortic Valve.

AIMS: To compare the carotid stiffness and flow parameters by ultrafast ultrasound imaging (UF), in bicuspid aortic valve (BAV) patients to first-degree relatives (controls). METHODS: BAV patients (n = 92) and controls (n = 48) were consecutively included at a reference center for BAV. Aortic valve and ascending aorta were evaluated by echocardiography. Common carotid arteries were evaluated by UF with a linear probe. A high frame rate (2,000 frames/s) was used to measure the pulse wave velocity (PWV). The arterial diameter change over the cardiac cycle was obtained by UF-Doppler imaging. This allowed us to measure the distensibility and the maximal rate of systolic distension (MRSD). The wall shear stress (WSS) was measured based on the same acquisitions, by analyzing blood flow velocities close to the carotid walls. RESULTS: BAV patients had significantly larger aortic diameters (p < 0.001) at the Valsalva sinus and at the tubular ascending aorta but no larger carotid diameters. No significant differences were found in carotid stiffness parameters (distensibility, MRSD, and PWV), even though these patients had a higher aortic stiffness. Carotid stiffness correlated linearly with age and similar slopes were obtained for BAV patients and controls. No difference in carotid WSS was found between BAV patients and controls. CONCLUSION: Our results clearly show that the carotid stiffness and flow parameters are not altered in case of BAV compared with controls.