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The potential of proton therapy to improve the conformity of the delivered dose to the tumor volume is currently limited by range uncertainties. Injectable superheated nanodroplets have recently been proposed for ultrasound-based in vivo range verification, as these vaporize into echogenic microbubbles on proton irradiation. In previous studies, offline ultrasound images of phantoms with dispersed nanodroplets were acquired after irradiation, relating the induced vaporization profiles to the proton range. However, the aforementioned method did not enable the counting of individual vaporization events, and offline imaging cannot provide real-time feedback. In this study, we overcame these limitations using high-frame-rate ultrasound imaging with a linear array during proton irradiation of phantoms with dispersed perfluorobutane nanodroplets at 37°C and 50°C. Differential image analysis of subsequent frames allowed us to count individual vaporization events and to localize them with a resolution beyond the ultrasound diffraction limit, enabling spatial and temporal quantification of the interaction between ionizing radiation and nanodroplets. Vaporization maps were found to accurately correlate with the stopping distribution of protons (at 50°C) or secondary particles (at both temperatures). Furthermore, a linear relationship between the vaporization count and the number of incoming protons was observed. These results indicate the potential of real-time high-frame-rate contrast-enhanced ultrasound imaging for proton range verification and dosimetry. © 2021 The Authors

Purpose: Despite the physical benefits of protons over conventional photon radiation in cancer treatment, range uncertainties impede the ability to harness the full potential of proton therapy. While monitoring the proton range in vivo could reduce the currently adopted safety margins, a routinely applicable range verification technique is still lacking. Recently, phase-change nanodroplets were proposed for proton range verification, demonstrating a reproducible relationship between the proton range and generated ultrasound contrast after radiation-induced vaporization at 25°C. In this study, previous findings are extended with proton irradiations at different temperatures, including the physiological temperature of 37°C, for a novel nanodroplet formulation. Moreover, the potential to modulate the linear energy transfer (LET) threshold for vaporization by varying the degree of superheat is investigated, where the aim is to demonstrate vaporization of nanodroplets directly by primary protons. Methods: Perfluorobutane nanodroplets with a shell made of polyvinyl alcohol (PVA-PFB) or 10,12-pentacosadyinoic acid (PCDA-PFB) were dispersed in polyacrylamide hydrogels and irradiated with 62 MeV passively scattered protons at temperatures of 37°C and 50°C. Nanodroplet transition into echogenic microbubbles was assessed using ultrasound imaging (gray value and attenuation analysis) and optical images. The proton range was measured independently and compared to the generated contrast. Results: Nanodroplet design proved crucial to ensure thermal stability, as PVA-shelled nanodroplets dramatically outperformed their PCDA-shelled counterpart. At body temperature, a uniform radiation response proximal to the Bragg peak is attributed to nuclear reaction products interacting with PVA-PFB nanodroplets, with the 50% drop in ultrasound contrast being 0.17 mm ± 0.20 mm (mean ± standard deviation) in front of the proton range. Also at 50°C, highly reproducible ultrasound contrast profile

The EACVI/ASE/Industry Task Force to standardize deformation imaging prepared this consensus document to standardize definitions and techniques for using two-dimensional (2D) speckle tracking echocardiography (STE) to assess left atrial, right ventricular, and right atrial myocardial deformation. This document is intended for both the technical engineering community and the clinical community at large to provide guidance on selecting the functional parameters to measure and how to measure them using 2D STE.This document aims to represent a significant step forward in the collaboration between the scientific societies and the industry since technical specifications of the software packages designed to post-process echocardiographic datasets have been agreed and shared before their actual development. Hopefully, this will lead to more clinically oriented software packages which will be better tailored to clinical needs and will allow industry to save time and resources in their development

Quantitative assessment of mitral valve (MV) morphology is important for diagnosing MV pathology and for planning of reparative procedures. Although this is typically done using 3D transesophageal echocardiography (TEE), recent advances in the spatiotemporal resolution of 3D transthoracic echocardiography (TTE) have enabled the use of this more patient friendly modality. However, manual data analysis is time consuming and operator dependent. In this study, a fully automatic method for MV segmentation and tracking in 3D TTE is proposed and validated. The proposed framework takes advantage of a previously proposed left ventricle (LV) segmentation framework to localize the MV and performs segmentation based on the B-spline Explicit Active Surfaces (BEAS) framework. The orientation of the MV is obtained and the MV surface is cropped to the mitral annulus (MA) and divided into posterior and anterior leaflets. The segmented MV at end diastole (ED) is propagated to end systole (ES) using localized anatomical affine optical flow (lAAOF). Because the orientation and leaflet division is known, relevant clinical parameters can then be extracted from the mesh at any time point. The proposed framework shows excellent segmentation results with a mean absolute distance (MAD) and Hausdorff distance (HD) of 1.19+0.25 ext{mm} and 5.79pm 1.25 ext{mm} at ED and 1.39pm 0.32 ext{mm} and 6.70pm 1.97 ext{mm} at ES against manual analysis. In conclusion, an automatic method for MV segmentation is proposed which could provide valuable clinical information in a more patient-friendly manner.

Phase change contrast agents for ultrasound (US) imaging consist of nanodroplets (NDs) with a perfluorocarbon (PFC) liquid core stabilized with a lipid or a polymer shell. Liquid → gas transition, occurring in the core, can be triggered by US to produce acoustically active microbubbles (MBs) in a process named acoustic droplet vaporization (ADV). MB shells containing polymerized diacetylene moiety were considered as a good trade off between the lipid MBs, showing optimal attenuation, and the polymeric ones, displaying enhanced stability. This work reports on novel perfluoropentane and perfluorobutane NDs stabilized with a monolayer of an amphiphilic fatty acid, i.e. 10,12-pentacosadiynoic acid (PCDA), cured with ultraviolet (UV) irradiation. The photopolymerization of the diacetylene groups, evidenced by the appearance of a blue color due to the conjugation of ene-yne sequences, exhibits a chromatic transition from the nonfluorescent blue color to a fluorescent red color when the NDs are heated or the pH of the suspension is basic. An estimate of the molecular weights reached by the polymerized PCDA in the shell, poly(PCDA), has been obtained using gel permeation chromatography and MALDI-TOF mass spectrometry. The poly(PCDA)/PFC NDs show good biocompatibility with fibroblast cells. ADV efficiency and acoustic properties before and after the transition were tested using a 1 MHz probe, revealing a resonance frequency between 1 and 2 MHz similar to other lipidic MBs. The surface of PCDA shelled NDs can be easily modified without influencing the stability and the acoustic performances of droplets. As a proof of concept we report on the conjugation of cyclic RGD and PEG chains of the particles to support targeting ability toward endothelial cells.

Aims Speckle tracking echocardiography has already demonstrated its clinical potential. However, its use in routine practice is jeopardized by recent reports on high inter-vendor variability of the measurements. As such, the European Association of CardioVascular Imaging (EACVI) and the American Society of Echocardiography (ASE) set up a standardization task force, which was joined by all manufacturers of echocardiographic equipment as well as by companies offering software solutions only, with the ambition to tackle this problem by standardization and quality assurance (QA). Methods and results In this study, a first step towards QA of all commercially available tracking solutions based on computer-generated ultrasound images is presented. The accuracy of the products was acceptable with relative errors below 10% and intra-vendor reproducibility within 5%. Conclusion Whether these results can be extrapolated to the clinical setting is the topic of an ongoing study of the EACVI/ASE/ Industry Task Force to standardize deformation imaging. This study was an important first step in the development of generally accepted tools for QA of speckle tracking echocardiography.

Patient-specific biomechanical modelling can improve preoperative surgical planning. This requires patient-specific geometry as well as patient-specific material properties as input. The latter are, however, still quite challenging to estimate in vivo. This study focuses on the estimation of the mechanical properties of the arterial wall. Firstly, in vivo pressure, diameter and thickness of the arterial wall were acquired for sheep common carotid arteries. Next, the animals were sacrificed and the tissue was stored for mechanical testing. Planar biaxial tests were performed to obtain experimental stress-stretch curves. Finally, parameters for the hyperelastic Mooney–Rivlin and Gasser–Ogden–Holzapfel (GOH) material model were estimated based on the in vivo obtained pressure-diameter data as well as on the ex situ experimental stress-stretch curves. Both material models were able to capture the in vivo behaviour of the tissue. However, in the ex situ case only the GOH model provided satisfactory results. When comparing different fitting approaches, in vivo vs. ex situ, each of them showed its own advantages and disadvantages. The in vivo approach estimates the properties of the tissue in its physiological state while the ex situ approach allows to apply different loadings to properly capture the anisotropy of the tissue. Both of them could be further enhanced by improving the estimation of the stress-free state, i.e. by adding residual circumferential stresses in vivo and by accounting for the flattening effect of the tested samples ex vivo., QC 20180516

The figures in the published paper belong to an older version of the manuscript and had been re-submitted by mistake. Below are all figures in their final version which also correspond to text and figure legends. These have also been updated in the paper. Figure 1 wasmissing the description of the time intervals in the lower part of the image which is now corrected. Figure 2 is re-worked in layout and has now a clearer indication of the motion of the transducer. Figure 3 has been completely redrawn and shows now the landmarks and segmentation of the RV as described in the text of the consensus document. Figure 4 is provided in higher resolution.

Recognizing the critical need for standardization in strain imaging, in 2010, the European Association of Echocardiography (now the European Association of Cardiovascular Imaging, EACVI) and the American Society of Echocardiography (ASE) invited technical representatives from all interested vendors to participate in a concerted effort to reduce intervendor variability of strain measurement. As an initial product of the work of the EACVI/ASE/Industry initiative to standardize deformation imaging, we prepared this technical document which is intended to provide definitions, names, abbreviations, formulas, and procedures for calculation of physical quantities derived from speckle tracking echocardiography and thus create a common standard.

Recognizing the critical need for standardization in strain imaging, in 2010, the European Association of Echocardiography (now the European Association of Cardiovascular Imaging, EACVI) and the American Society of Echocardiography (ASE) invited technical representatives from all interested vendors to participate in a concerted effort to reduce intervendor variability of strain measurement. As an initial product of the work of the EACVI/ASE/Industry initiative to standardize deformation imaging, we prepared this technical document which is intended to provide definitions, names, abbreviations, formulas, and procedures for calculation of physical quantities derived from speckle tracking echocardiography and thus create a common standard.

Introduction: In inverse potential mapping, local epicardial potentials are computed from recorded body surface potentials (BSP). When BSP are recorded with only a limited number of electrodes, in general biophysical a priori models are applied to facilitate the inverse computation. This study investigated the possibility of deriving epicardial potential information using only 62 torso electrodes in the absence of an a priori model. Methods: Computer simulations were used to determine the optimal in vivo positioning of 62 torso electrodes. Subsequently, three different electrode configurations, i.e., surrounding the thorax, concentrated precordial (30 mm inter-electrode distance) and super-concentrated precordial (20 mm inter-electrode distance) were used to record BSP from three healthy volunteers. Magnetic resonance imaging (MRI) was performed to register the electrode positions with respect to the anatomy of the patient. Epicardial potentials were inversely computed from the recorded BSP. In order to determine the reconstruction quality, the super-concentrated electrode configuration was applied in four patients with an implanted MRI-conditional pacemaker system. The distance between the position of the ventricular lead tip on MRI and the inversely reconstructed pacing site was determined. Results: The epicardial potential distribution reconstructed using the super-concentrated electrode configuration demonstrated the highest correlation (R = 0.98; p < 0.01) with the original epicardial source model. A mean localization error of 5.3 mm was found in the pacemaker patients. Conclusion: This study demonstrated the feasibility of deriving detailed anterior epicardial potential information using only 62 torso electrodes without the use of an a priori model.

Background: Integration of whole-heart activation simulations and inverse potential mapping (IPM) could benefit the guidance and planning of electrophysiological procedures. Routine clinical application requires a fast and adaptable workflow. These requirements limit clinical translation of existing simulation models. This study proposes a comprehensive finite element model (FEM) based whole-heart computational workflow suitable for IPM and simulations. Methods: Three volunteers and eight patients with premature ventricular contractions underwent body surface potential (BSP) acquisition followed by a cardiac MRI (CMR) scan. The cardiac volumes were segmented from the CMR images using custom written software. The feasibility to integrate tissue-characteristics was assessed by generating meshes with virtual edema and scar. Isochronal activation maps were constructed by identifying the fastest route through the cardiac volume using the Möller-Trumbore and Floyd-Warshall algorithms. IPM's were reconstructed from the BSP's. Results: Whole-heart computational meshes were generated within seconds. The first point of atrial activation on IPM was located near the crista terminalis of the superior vena cave into the right atrium. The IPM demonstrated the ventricular epicardial breakthrough at the attachment of the moderator band with the right ventricular free wall. Simulations of sinus rhythm were successfully performed. The conduction through the virtual edema and scar meshes demonstrated delayed activation or a complete conductional block respectively. Conclusion: The proposed FEM based whole-heart computational workflow offers an integrated platform for cardiac electrical assessment using simulations and IPM. This workflow can incorporate patient-specific electrical parameters, perform whole-heart cardiac activation simulations and accurately reconstruct cardiac activation sequences from BSP's.

In inverse potential mapping, local epicardial potentials are computed from recorded body surface potentials (BSP). When BSP are recorded with only a limited number of electrodes, in general biophysical a priori models are applied to facilitate the inverse computation. This study investigated the possibility of deriving epicardial potential information using only 62 torso electrodes in the absence of an a priori model. Computer simulations were used to determine the optimal in vivo positioning of 62 torso electrodes. Subsequently, three different electrode configurations, i.e., surrounding the thorax, concentrated precordial (30 mm inter-electrode distance) and super-concentrated precordial (20 mm inter-electrode distance) were used to record BSP from three healthy volunteers. Magnetic resonance imaging (MRI) was performed to register the electrode positions with respect to the anatomy of the patient. Epicardial potentials were inversely computed from the recorded BSP. In order to determine the reconstruction quality, the super-concentrated electrode configuration was applied in four patients with an implanted MRI-conditional pacemaker system. The distance between the position of the ventricular lead tip on MRI and the inversely reconstructed pacing site was determined. The epicardial potential distribution reconstructed using the super-concentrated electrode configuration demonstrated the highest correlation (R = 0.98; p < 0.01) with the original epicardial source model. A mean localization error of 5.3 mm was found in the pacemaker patients. This study demonstrated the feasibility of deriving detailed anterior epicardial potential information using only 62 torso electrodes without the use of an a priori model.

__Introduction:__ In inverse potential mapping, local epicardial potentials are computed from recorded body surface potentials (BSP). When BSP are recorded with only a limited number of electrodes, in general biophysical a priori models are applied to facilitate the inverse computation. This study investigated the possibility of deriving epicardial potential information using only 62 torso electrodes in the absence of an a priori model. __Methods:__ Computer simulations were used to determine the optimal in vivo positioning of 62 torso electrodes. Subsequently, three different electrode configurations, i.e., surrounding the thorax, concentrated precordial (30 mm inter-electrode distance) and super-concentrated precordial (20 mm inter-electrode distance) were used to record BSP from three healthy volunteers. Magnetic resonance imaging (MRI) was performed to register the electrode positions with respect to the anatomy of the patient. Epicardial potentials were inversely computed from the recorded BSP. In order to determine the reconstruction quality, the super-concentrated electrode configuration was applied in four patients with an implanted MRI-conditional pacemaker system. The distance between the position of the ventricular lead tip on MRI and the inversely reconstructed pacing site was determined. __Results:__ The epicardial potential distribution reconstructed using the super-concentrated electrode configuration demonstrated the highest correlation (R = 0.98; p < 0.01) with the original epicardial source model. A mean localization error of 5.3 mm was found in the pacemaker patients. __Conclusion:__ This study demonstrated the feasibility of deriving detailed anterior epicardial potential information using only 62 torso electrodes without the use of an a priori model.

Background With the advent of magnetic resonance imaging (MRI) conditional pacemaker systems, the possibility of performing MRI in pacemaker patients has been introduced. Besides for the detailed evaluation of atrial and ventricular volumes and function, MRI can be used in combination with body surface potential mapping (BSPM) in a non-invasive inverse potential mapping (IPM) strategy. In non-invasive IPM, epicardial potentials are reconstructed from recorded body surface potentials (BSP). In order to investigate whether an IPM method with a limited number of electrodes could be used for the purpose of non-invasive focus localization, it was applied in patients with implanted pacing devices. Ventricular paced beats were used to simulate ventricular ectopic foci. Methods Ten patients with an MRI-conditional pacemaker system and a structurally normal heart were studied. Patientspecific 3D thorax volume models were reconstructed from the MRI images. BSP were recorded during ventricular pacing. Epicardial potentials were inversely calculated from the BSP. The site of epicardial breakthrough was compared to the position of the ventricular lead tip on MRI and the distance between these points was determined. Results For all patients, the site of earliest epicardial depolarization could be identified. When the tip of the pacing lead was implanted in vicinity to the epicardium, i.e. right ventricular (RV) apex or RV outflow tract, the distance between lead tip position and epicardial breakthrough was 6.0±1.9 mm. Conclusions In conclusion, the combined MRI and IPM method is clinically applicable and can identify sites of earliest depolarization with a clinically useful accuracy.

Background: With the advent of magnetic resonance imaging (MRI) conditional pacemaker systems, the possibility of performing MRI in pacemaker patients has been introduced.

With the advent of magnetic resonance imaging (MRI) conditional pacemaker systems, the possibility of performing MRI in pacemaker patients has been introduced. Besides for the detailed evaluation of atrial and ventricular volumes and function, MRI can be used in combination with body surface potential mapping (BSPM) in a non-invasive inverse potential mapping (IPM) strategy. In non-invasive IPM, epicardial potentials are reconstructed from recorded body surface potentials (BSP). In order to investigate whether an IPM method with a limited number of electrodes could be used for the purpose of non-invasive focus localization, it was applied in patients with implanted pacing devices. Ventricular paced beats were used to simulate ventricular ectopic foci. Ten patients with an MRI-conditional pacemaker system and a structurally normal heart were studied. Patient-specific 3D thorax volume models were reconstructed from the MRI images. BSP were recorded during ventricular pacing. Epicardial potentials were inversely calculated from the BSP. The site of epicardial breakthrough was compared to the position of the ventricular lead tip on MRI and the distance between these points was determined. For all patients, the site of earliest epicardial depolarization could be identified. When the tip of the pacing lead was implanted in vicinity to the epicardium, i.e. right ventricular (RV) apex or RV outflow tract, the distance between lead tip position and epicardial breakthrough was 6.0 +/- 1.9 mm. In conclusion, the combined MRI and IPM method is clinically applicable and can identify sites of earliest depolarization with a clinically useful accuracy.

Characterization of vulnerable plaques in the carotid artery is critical for the prevention of ischemic stroke. However, ultrasound-based methods for plaque characterization used in the clinics today are limited to visual assessment and evaluation of plaque echogenicity. Shear Wave Elastography (SWE) is a new tissue characterization technique based on radiation force-induced shear wave propagation with potential use in plaque vulnerability assessment. The purpose of this study was to develop an experimental setup to test the feasibility of SWE for carotid plaque characterization. A carotid artery phantom with a soft inclusion in the wall, mimicking a vulnerable plaque, was constructed (10% polyvinyl alcohol (PVA), 3% graphite) by exposing the vessel and plaque to three and one freeze-thaw cycles (6h freeze, 6h thaw) respectively. An Aixplorer SWE system (Supersonic Imagine) was used to measure the shear wave speed (cT) in the vessel wall and plaque. The Young's modulus (E) was then calculated via the Moens-Korteweg (M-K) equation. For comparison, eight cylinders (d = 4 cm, h = 4 cm) were constructed for mechanical testing from the same PVA batch, of which four were exposed to three freeze-thaw cycles (mimicking the vessel wall) and four to one freeze-thaw cycle (mimicking the plaque). The Young's moduli for the cylinders were obtained via a displacement controlled mechanical compression test (Instron 5567) by applying 5% strain. The mean shear wave speed was 2.6 (±0.7) m/s in the vessel wall, 1.8 (±0.7) m/s in the plaque, resulting in Evessel = 11.5 (±0.5) kPa, Eplaque = 4.3 (±0.5) kPa. The compression tests resulted in E = 64.2 (±11.1) kPa in the hard cylinder and E = 9.7 (±3.1) kPa in the soft cylinder. The results showed that it was possible to distinguish between the arterial wall and the plaque. The disagreement between mechanical testing and SWE can be explained by the fact that the shear wave does not propagate monochromatically in cylindrical geometry. To ac, QC 20130910

Carotid strain imaging using ultrasound-based speckle tracking has showed potential in risk stratification of cardiovascular diseases. However, assessing strain in the artery wall and in atherosclerotic plaques is challenging because of small dimensions and low deformations in relation to the applied ultrasound wavelength. High-resolution ultrasound has potential to improve the speckle tracking performance by increasing spatial resolution. The aim of this study was to compare carotid strain estimation by speckle tracking using standard clinical ultrasound and high-resolution ultrasound in an experimental setup. Ultrasound long-axis images were obtained using a standard clinical ultrasound system (Vivid7) and a high-resolution ultrasound system (Vevo2100) in dynamic phantoms mimicking the carotid artery. Speckle tracking was performed to estimate radial and longitudinal strain whereas sonomicrometry was used as reference. The results showed a significant better performance for speckle tracking applied on images from the high-resolution system compared to the standard clinical system., QC 20130910

Ultrasound imaging represents a well designed modality to estimate the motion of biological tissues in vivo, from which relevant clinical information can be assessed. However, the lack of ground truth constitutes a challenging issue when it comes to evaluate the accuracy of computerized methods. Indeed, quantification of the reliability of experimental results often involves manual or visual human operations, which may introduce subjectivity and variability. Nonetheless, numerical simulation of the imaged tissues allow a comparison with a known reference. For this purpose, we propose in this work a realistic kinematic multi-layer model of the common carotid artery. A set of 10 models was generated by randomly positioning scatterers, on which intensity, specular reflection, and bi-dimensional motion over the duration of one cardiac cycle were applied. Two computerized methods, namely a block-matching method and a segmentation method, were also applied on our model using identical parameter settings as those used for in vivo clinical data, in the objective to assess their accuracy. The tracking errors were 42 ± 40 μm and 12 ± 10 μm in the longitudinal and radial directions, respectively. The segmentation errors were 28±18 μm for the lumen diameter, and 15±10 μm for the intima-media thickness. We conclude from these results that our model can constitute a reliable method to quantify the accuracy of computerized algorithms., QC 20131014

Characterization of vulnerable plaques in the carotid artery is critical for the prevention of ischemic stroke. However, ultrasound-based methods for plaque characterization used in the clinics today are limited to visual assessment and evaluation of plaque echogenicity. Shear Wave Elastography (SWE) is a new tissue characterization technique based on radiation force-induced shear wave propagation with potential use in plaque vulnerability assessment. The purpose of this study was to develop an experimental setup to test the feasibility of SWE for carotid plaque characterization. A carotid artery phantom with a soft inclusion in the wall, mimicking a vulnerable plaque, was constructed (10% polyvinyl alcohol (PVA), 3% graphite) by exposing the vessel and plaque to three and one freeze-thaw cycles (6h freeze, 6h thaw) respectively. An Aixplorer SWE system (Supersonic Imagine) was used to measure the shear wave speed (cT) in the vessel wall and plaque. The Young's modulus (E) was then calculated via the Moens-Korteweg (M-K) equation. For comparison, eight cylinders (d = 4 cm, h = 4 cm) were constructed for mechanical testing from the same PVA batch, of which four were exposed to three freeze-thaw cycles (mimicking the vessel wall) and four to one freeze-thaw cycle (mimicking the plaque). The Young's moduli for the cylinders were obtained via a displacement controlled mechanical compression test (Instron 5567) by applying 5% strain. The mean shear wave speed was 2.6 (±0.7) m/s in the vessel wall, 1.8 (±0.7) m/s in the plaque, resulting in Evessel = 11.5 (±0.5) kPa, Eplaque = 4.3 (±0.5) kPa. The compression tests resulted in E = 64.2 (±11.1) kPa in the hard cylinder and E = 9.7 (±3.1) kPa in the soft cylinder. The results showed that it was possible to distinguish between the arterial wall and the plaque. The disagreement between mechanical testing and SWE can be explained by the fact that the shear wave does not propagate monochromatically in cylindrical geometry. To ac

Arterial stiffness is an important risk factor for cardiovascular disease. As such, ultrasound-based methods have been proposed to assess arterial strain as a measure of stiffness. The aim of the current study was to validate our recently proposed speckle tracking (ST) algorithm to estimate the in-plane wall strain tensor in an experimental setup. Three polyvinyl alcohol phantoms mimicking the carotid artery were constructed with different mechanical properties (2, 3 and 4 freeze-thaw cycles). The phantoms were connected to a pump, programmed to generate carotid flow profiles at peak flows of 7, 14, 21, 28 and 35 ml/s. Long and short-axis ultrasound images were obtained using a Vivid7 Dimension system. Radial, longitudinal and circumferential strains were estimated using the ST algorithm (kernel size: 2.7λx2λ, normalized cross-correlation; spline inter-polation for subsample motion estimation; 40% window overlap). Sonomicrometry was used to acquire reference values of strain in the phantoms. Good agreement was found between the estimated radial, longitudinal and circumferential strain and the acquired reference strain. The correlation between estimated mean peak strain values and reference peak strain values was r = 0.92 (p < 0.001) for radial strain, r = 0.72 (p = 0.006) for longitudinal strain and r = 0.91 (p < 0.001) for circumferential strain., QC 20140908

Ultrasound-based algorithms are commonly used to assess mechanical properties of arterial walls in studies of arterial stiffness and atherosclerosis. Speckle tracking based techniques used for estimation of myocardial strain can be applied on vessels to estimate strain of the arterial wall. Previous elastography studies in vessels have mainly focused on radial strain measurements, whereas the longitudinal strain has been more or less ignored. However, recently we showed the feasibility of speckle tracking to assess longitudinal strain of the carotid artery in-silico. The aim of this study was to test this methodology in-vivo. Ultrasound images were obtained in seven healthy subjects with no known cardiovascular disease (39 ± 14 years old) and in seven patients with coronary artery disease (CAD), (69 ± 4 years old). Speckle tracking was performed on the envelope detected data using our previous developed algorithm. Radial and longitudinal strains were estimated throughout two cardiac cycles in a region of interest (ROI) positioned in the posterior vessel wall. The mean peak systolic radial and longitudinal strain values from the two heart cycles were compared between the groups using a student's t-test. The mean peak radial strain was -39.1 ± 15.1% for the healthy group and -20.4 ± 7.5% for the diseased group (p = 0.01), whereas the mean peak longitudinal strain was 4.8 ± 1.1% and 3.2 ± 1.6% (p = 0.05) for the healthy and diseased group, respectively. Both peak radial and longitudinal strain values were thus significantly reduced in the CAD patient group. This study shows the feasibility to estimate radial and longitudinal strain in-vivo using speckle tracking and indicates that the method can detect differences between groups of healthy and diseased (CAD) subjects., QC 20111201

Ultrasound-based algorithms are commonly used to assess mechanical properties of arterial walls in studies of arterial stiffness and atherosclerosis. Speckle tracking based techniques used for estimation of myocardial strain can be applied on vessels to estimate strain of the arterial wall. Previous elastography studies in vessels have mainly focused on radial strain measurements, whereas the longitudinal strain has been more or less ignored. However, recently we showed the feasibility of speckle tracking to assess longitudinal strain of the carotid artery in-silico. The aim of this study was to test this methodology in-vivo. Ultrasound images were obtained in seven healthy subjects with no known cardiovascular disease (39 ± 14 years old) and in seven patients with coronary artery disease (CAD), (69 ± 4 years old). Speckle tracking was performed on the envelope detected data using our previous developed algorithm. Radial and longitudinal strains were estimated throughout two cardiac cycles in a region of interest (ROI) positioned in the posterior vessel wall. The mean peak systolic radial and longitudinal strain values from the two heart cycles were compared between the groups using a student's t-test. The mean peak radial strain was -39.1 ± 15.1% for the healthy group and -20.4 ± 7.5% for the diseased group (p = 0.01), whereas the mean peak longitudinal strain was 4.8 ± 1.1% and 3.2 ± 1.6% (p = 0.05) for the healthy and diseased group, respectively. Both peak radial and longitudinal strain values were thus significantly reduced in the CAD patient group. This study shows the feasibility to estimate radial and longitudinal strain in-vivo using speckle tracking and indicates that the method can detect differences between groups of healthy and diseased (CAD) subjects.

Ultrasound based estimation of arterial wall properties is commonly used to assess vessel wall stiffness in studies of vascular diseases. Recently, it was shown that the longitudinal motion of the vessel during systole can be measured using speckle tracking. However, the assessment of longitudinal strain in the vessel wall has to be further investigated. The aim of this study was to test the feasibility of simultaneous assessment of radial and longitudinal strain in the carotid artery using computer simulations. A kinematic cylindrical model of the carotid artery with realistic dimensions was constructed. The model was deformed radially according to temporal distention measured in-vivo while longitudinal deformation was the result of conservation of volume. Moreover, longitudinal motion was superimposed based on profiles obtained in-vivo. Ultrasound long axis images were simulated using a generalized convolution model (COLE) with realistic image properties. Four models with different scatterer distributions were built. For each of them, longitudinal and radial motion were estimated using normalized cross-correlation with spline interpolation to detect sub-sample motion. Radial and longitudinal strains, obtained by linear regression were compared with the ground truth from the model. The maximal systolic radial strain was estimated to be -12.77 ± 0.4% (ground truth -13.89%) while longitudinal strain was 5.21 ± 0.67% (ground truth 5.3%). This study shows the feasibility of simultaneously measuring radial and longitudinal strain in the carotid artery by making use of currently available hardware., QC 20100727