The recently discovered longitudinal displacement of the common carotid arterial wall (i.e., the motion along the same plane as the blood flow), may be associated with incident cardiovascular events and represents a novel and relevant clinical information. At present, there have only been a few studies that have been conducted to investigate this longitudinal movement. We propose here a method to assess noninvasively the wall bi-dimensional (two-dimensional [2-D], cross-sectional and longitudinal) motion and present an original approach that combines a robust speckle tracking scheme to guidance by minimal path contours segmentation. Our method is well suited to large clinical population studies as it does not necessitate strong imaging prerequisites. The aim of this study is to describe the association between the longitudinal displacement of the carotid arterial wall and cardiovascular risk factors, among which periodontal disease. Some 126 Indigenous Australians with periodontal disease, an emerging risk factor, and 27 healthy age- and sex-matched non-indigenous control subjects had high-resolution ultrasound scans of the common carotid artery. Carotid intima-media thickness and arterial wall 2-D motion were then assessed using our method in ultrasound B-mode sequences. Carotid longitudinal displacement was markedly lower in the periodontal disease group than the control group (geometric mean (IQR): 0.15 mm (0.13) vs. 0.42 mm (0.30), respectively; p < 0.0001), independent of cardiovascular risk factors, cross-sectional distensibility and carotid intima-media thickness (p < 0.0001). A multivariable model indicated that the strongest correlates of carotid longitudinal displacement in adults with periodontal disease were age (β-coefficient = −.235, p = .03), waist (β-coefficient = −.357, p = 0.001), and pulse pressure (β-coefficient = .175, p = 0.07), independent of other cardiovascular risk factors, cross-sectional distensibility and pulse wave velocity. Carotid longitudinal displacement, estimated with our approach, is impaired in the periodontal disease group, independent of established cardiovascular risk factors and other noninvasive measures of arterial stiffness, and may represent an important marker of cardiovascular risk.

Longitudinal displacement of the carotid wall and cardiovascular risk factors: associations with aging, adiposity, blood pressure and periodontal disease independent of cross-sectional distensibility and intima-media thickness.

Arterial stiffness is an independent risk factor found to correlate with a wide range of cardiovascular diseases. It has been suggested that shear wave elastography (SWE) can be used to quantitatively measure local arterial shear modulus, but an accuracy assessment of the technique for arterial applications has not yet been performed. In this study, the influence of confined geometry on shear modulus estimation, by both group and phase velocity analysis, was assessed, and the accuracy of SWE in comparison with mechanical testing was measured in nine pressurized arterial phantoms. The results indicated that group velocity with an infinite medium assumption estimated shear modulus values incorrectly in comparison with mechanical testing in arterial phantoms (6.7 ± 0.0 kPa from group velocity and 30.5 ± 0.4 kPa from mechanical testing). To the contrary, SWE measurements based on phase velocity analysis (30.6 ± 3.2 kPa) were in good agreement with mechanical testing, with a relative error between the two techniques of 8.8 ± 6.0% in the shear modulus range evaluated (40-100 kPa). SWE by phase velocity analysis was validated to accurately measure stiffness in arterial phantoms.

Arterial Stiffness Estimation by Shear Wave Elastography: Validation in Phantoms with Mechanical Testing

A versatile, computationally efficient two-dimensional (2D) speckle-tracking method based on high resolution ultrasound imaging is proposed to quantify regional myocardial dysfunction in mice. Ultrasound scans were performed on the hearts of normal and post myocardial infarction (MI) mice with a Vevo770 scanner (VisualSonics, Toronto, Canada) operating at 30 MHz frequency. Regional myocardial motion was tracked using a 2D minimum sum of absolute differences (MSAD) block-matching algorithm. Motion analyses calculated from ultrasound images were compared with gold-standard analyses performed using small animal magnetic resonance imaging (MRI). The radial and circumferential components of strain were compared between ultrasound and MRI short axis views and promising correlations were obtained (r = 0.90 and r = 0.85 for radial and circumferential strain, respectively). Therefore, ultrasound imaging, followed by 2D image tracking, provides an effective, low cost, mobile method to quantify murine cardiac function accurately and reliably.

Abstract 769: Quantification and MRI Validation of Regional Contractile Dysfunction in Mice Post Myocardial Infarction Using High Resolution Ultrasound

Elastic arteries are significantly prestretched in an axial direction. This property minimises axial deformations during pressure cycle. Ageing-induced changes in arterial biomechanics, among others, are manifested via a marked decrease in the prestretch. Although this fact is well known, little attention has been paid to the effect of decreased prestretch on mechanical response. Our study presents the results of an analytical simulation of the inflation–extension behaviour of the human abdominal aorta treated as nonlinear, anisotropic, prestrained thin-walled as well as thick-walled tube with closed ends. The constitutive parameters and geometries for 17 aortas adopted from the literature were supplemented with initial axial prestretches obtained from the statistics of 365 autopsy measurements. For each aorta, the inflation–extension response was calculated three times, with the expected value of the initial prestretch and with the upper and lower confidence limit of the initial prestretch derived from the statistics. This approach enabled age-related trends to be evaluated bearing in mind the uncertainty in the prestretch. Despite significantly decreased longitudinal prestretch with age, the biomechanical response of human abdominal aorta changes substantially depending on the initial axial stretch was used. In particular, substituting the upper limit of initial prestretch gave mechanical responses which can be characterised by (1) low variation in axial stretch and (2) high circumferential distensibility during pressurisation, in contrast to the responses obtained for their weakly prestretched counterparts. The simulation also suggested the significant effect of the axial prestretch on the variation of axial stress in the pressure cycle. Finally, the obtained results are in accordance with the hypothesis that circumferential-to-axial stiffness ratio is the quantity relatively constant within this cycle.

http://users.fs.cvut.cz/~hornyluk/files/Horny-Netusil-Vonavkova-2013-BMMB-Axial-prestretch-and-distensibility-of-aorta.pdf

Axial prestretch and circumferential distensibility in biomechanics of abdominal aorta.

A hierarchical block-matching motion tracking algorithm for strain imaging is presented. Displacements are estimated with improved robustness and precision by utilizing a Bayesian regularization algorithm and an unbiased subsample interpolation technique. A modified least-squares strain estimator is proposed to estimate strain images from a noisy displacement input while addressing the motion discontinuity at the wall-lumen boundary. Methods to track deformation over the cardiac cycle incorporate a dynamic frame skip criterion to process data frames with sufficient deformation to produce high signal-to-noise displacement and strain images. Algorithms to accumulate displacement and/or strain on particles in a region of interest over the cardiac cycle are described. New methods to visualize and characterize the deformation measured with the full 2D strain tensor are presented. Initial results from patients imaged prior to carotid endarterectomy suggest that strain imaging detects conditions that are traditionally considered high risk including soft plaque composition, unstable morphology, abnormal hemodynamics and shear of plaque against tethering tissue can be exacerbated by neoangiogenesis. For example, a maximum absolute principal strain exceeding 0.2 is observed near calcified regions adjacent to turbulent flow, protrusion of the plaque into the arterial lumen and regions of low echogenicity associated with soft plaques. Non-invasive carotid strain imaging is therefore a potentially useful tool for detecting unstable carotid plaque.

/pdf/methods-for-robust-in-vivo-strain-estimation-in-the-carotid-1wszwfg6ou.pdf

Methods for robust in vivo strain estimation in the carotid artery

Ultrasound-based estimation of arterial wall elasticity is commonly used to assess arterial stiffness. However, previous elastography studies have mostly addressed radial strain measurements, and the longitudinal strain has been more or less ignored. This study shows the feasibility of a speckle-tracking-based algorithm for simultaneous estimation of radial and longitudinal strain in the carotid artery in silico. Additionally, these results were preliminarily confirmed in vivo.

Ultrasound-based radial and longitudinal strain estimation of the carotid artery: a feasibility study

Ultrasound speckle tracking for radial, longitudinal and circumferential strain estimation of the carotid artery - An in vitro validation via sonomicrometry using clinical and high-frequency ultrasound

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 c ...

Ultrasound-based Speckle Tracking for 3D Strain estimation of the Arterial wall — An experimental validation study in a tissue mimicking phantom

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.

Ultrasound-based 2D strain estimation of the carotid artery: an in-silico feasibility study

Myocardial strain quantification in the mouse based on 2-D speckle tracking using real-time ultrasound datasets is feasible but remains challenging. The major difficulty lies in the fact that the frame rate-to-heart rate ratio is relatively low, causing significant decorrelation between subsequent frames. In this setting, regularization is therefore particularly important to discard motion estimates that are improbable. Different regularization methods have been proposed, among which is a class of regularizers based on enforcing preset geometrical characteristics of the motion field. To date, these regularization methods have not been contrasted. The aim of this study was thus to compare the performance of different geometric regularizers in the setting of myocardial motion and strain estimation in murine echocardiography using simulated datasets. In normal models, restricting the spatial curvature of the motion fields resulted in worse radial strain estimates (mean root-mean-square [RMS] error increased from 0.06 to 0.09; p < 0.05), but better circumferential strain estimates (mean RMS error decreased from 0.035 to 0.01; p < 0.05). More accurate circumferential strain estimates were also obtained by convolving a Gaussian function with the lateral motion components (mean RMS error decreased to 0.015; p < 0.05). In infarcted models, no significant differences were found between regularized and nonregularized radial strains. However, for circumferential strain, the curvature method yielded better strain estimates in all regions (mean RMS error decreased from 0.043 to 0.015; p < 0.05), whereas the Gaussian method only improved strain assessment in the remote myocardium (mean RMS error decreased to 0.021; p < 0.05).

Florence Kremer

Papers

Ultrasound-based radial and longitudinal strain estimation of the carotid artery: a feasibility study

Ultrasound speckle tracking for radial, longitudinal and circumferential strain estimation of the carotid artery - An in vitro validation via sonomicrometry using clinical and high-frequency ultrasound

Ultrasound-based Speckle Tracking for 3D Strain estimation of the Arterial wall — An experimental validation study in a tissue mimicking phantom

Ultrasound-based 2D strain estimation of the carotid artery: an in-silico feasibility study

Geometric regularization for 2-D myocardial strain quantification in mice: an in-silico study.