Longitudinal common carotid artery wall motion is associated with plaque burden in man and mouse

The influence of physical activity and sex on carotid artery longitudinal wall motion in younger healthy adults

Carotid artery longitudinal wall motion (CALM) is a novel preclinical marker for atherosclerosis that describes the axial anterograde and retrograde motion of the intima-media complex. While regular physical activity and sex are known to independently influence arterial stiffness, their roles on axial arterial wall behaviour are unknown. The purpose of this study is to examine whether physical activity and sex impact CALM. We hypothesized that CALM retrograde displacement and total amplitude would be greater in females and active individuals, as a function of arterial stiffness. Fifty-seven young healthy adults (30 females; aged 22 ± 3 years) were evaluated for CALM outcomes and arterial stiffness and grouped by physical activity based on active (V̇O2 = 44.2 ± 8.9 mL/kg/min) or sedentary (V̇O2 = 33.7 ± 6.7 mL/kg/min) lifestyles defined by the Canadian 24-Hour Movement Guidelines. Arterial stiffness and CALM were measured by carotid-femoral pulse wave velocity (cfPWV) and vascular ultrasound at the right common carotid artery with speckle tracking analysis, respectively. cfPWV was greater in males (p < 0.01) with no interaction between sex and physical activity (p = 0.90). CALM anterograde displacement was greater in males (p = 0.03) resulting in a forward shift in total CALM pattern, which became less prominent when controlling for mean arterial pressure (p = 0.06). All other CALM outcomes were not different between activity and sex. V̇O2max was not correlated to any CALM outcome (all p > 0.05). Apparent sex differences in vascular function extend to novel CALM outcomes but may be confounded by blood pressure. We recommend sex-balanced design and reporting in future studies due to possible anterograde-shifted CALM patterns in healthy males.

The impact of geometry, intramural friction, and pressure on the antegrade longitudinal motion of the arterial wall: A phantom and finite element study

Longitudinal motion of the carotid arterial wall, as measured with ultrasound, has shown promise as an indicator of vascular health. The underlying mechanisms are however not fully understood. We have found, in in vivo studies, that blood pressure has a strong relation to the antegrade longitudinal displacement in early systole. Further, we have identified that a tapered geometry and the intramural friction in-between two parts of a vessel wall influence the longitudinal displacement. We therefore studied the interaction between pressure, vessel geometry and intramural friction, tapered and straight ultrasound phantoms in a paralleled hydraulic bench study and corresponding numerical models. Profound antegrade longitudinal motion was induced in the innermost part of both tapered phantoms and the numerical models, but to a lesser extent when intramural friction was increased in the simulations. Strong correlations (R = 0.82-0.96; p < 1e-3; k = 9.3-14 μm/mmHg) between longitudinal displacement and pulse pressure were found in six of seven regions of interest in tapered phantoms. The motion of the straight phantom and the corresponding numerical model was smaller, on average zero or close to zero. This study demonstrates that tapering of the lumen, low intramural friction, and pressure might be important conducive features to the antegrade longitudinal motion of the arterial wall in vivo.

Response of the carotid artery longitudinal motion to submaximal physical activity in healthy humans-Marked changes already at low workload

The longitudinal motion of the arterial wall, that is, the displacement of the arterial wall along the artery, parallel to blood flow, is still largely unexplored. The magnitude and nature of putative changes in longitudinal motion of the arterial wall in response to physical activity in humans remain unknown. The aim of this study was therefore to study the longitudinal motion of the carotid artery wall during physical activity in healthy humans. Using in-house developed non-invasive ultrasonic methods, the longitudinal motion of the intima-media complex and the diameter changes of the right common carotid artery (CCA) in 40 healthy volunteers (20 volunteers aged 22-35 years; 20 volunteers aged 55-68 years) were assessed at rest and during submaximal supine bicycle exercise. In a subset of the subjects (n = 18) also intramural shear strain were analyzed. The longitudinal motion of the intima-media complex underwent marked changes in response to physical activity, already at low workload; with most evident a marked increase of the first antegrade displacement (p < 0.001) in early systole. Likewise, the corresponding shear strain also increased significantly (p = 0.004). The increase in longitudinal motion showed significant correlation to increase in blood pressure, but not to blood flow velocity or wall shear stress. In conclusion, physical activity markedly influences the longitudinal motion of the carotid artery wall in healthy humans already at low load. A possible "cushioning" function as well as possible implications for the function of the vasa vasorum, endothelium, and smooth muscle cells and extracellular matrix of the media, are discussed.

Comparison of the multi-phasic longitudinal displacement of the left and right common carotid artery in healthy humans

BACKGROUND

During the cardiac cycle, there is a multi-phasic bidirectional longitudinal movement (LMov) of the intima-media complex of large arteries, i.e. along the arteries. On the left side the common carotid artery (CCA) arises directly from the aortic arc, whereas on the right side the CCA originate from the innominate artery.

AIM

The aim of this study was to compare LMov of the left and right CCA of healthy subjects to investigate whether the difference in anatomy is of importance for LMov.

MATERIAL AND METHODS

The CCA's of 93 healthy subjects were investigated using in-house developed ultrasound methods.

RESULTS

Although the basic pattern were the same in the majority of subjects, several phases of LMov were significantly larger on the left side (the first retrograde phase, p = 0.0006; the second antegrade, "returning" phase, p < 0.00001; and the rapid retrograde phase of movement at the end of the cardiac cycle, p < 0.000001). In contrast, no significant side-difference in the amplitude of the first antegrade movement was seen. The maximal (peak-to-peak) LMov was significantly larger on the left side (p = 0.002).

DISCUSSION AND CONCLUSION

The side-differences found in LMov may be related to the difference in anatomy, including possible difference in distance to the heart and especially the presence of an extra bifurcation on the right side. Our data provide an important base for the further study of the relation between LMov and cardiovascular risk factors and atherosclerosis.

Assessing the short-term effects of radiotherapy on the shear modulus of the common carotid artery as a new biomarker of radiation-induced atherosclerosis

Purpose

The purpose of this study was to investigate the incidence of short-term atherosclerosis in the common carotid arteries following radiotherapy.

Methods

The mean radiation dose to the arteries was 49.30±15.83 Gy. A computational ultrasound method was introduced to investigate the elastic modulus. Ultrasonography was performed 2-3 cm inferior to the bifurcation region before and after radiotherapy, and sequential images were extracted from a video of each artery. Instantaneous movement of the arterial wall in the radial and longitudinal directions was extracted by implementing the maximum gradient and block matching algorithms, respectively.

Results

There was a significant change in systolic blood pressure after radiotherapy (P=0.008). Irradiated arteries had significantly smaller systolic and end-diastolic diameters than non-irradiated arteries (P<0.001). The shear modulus was significantly different between irradiated and non-irradiated arteries (3.10±2.03 kPa vs. 1.38±0.98 kPa, P<0.001). The shear and Young moduli of radiation-induced arteries were 2.25±1.50 and 1.57±0.59 times higher than those of the pre-irradiation arteries.

Conclusion

The arterial shear modulus can be considered as a new biomarker of radiation-induced atherosclerosis in the common carotid artery.

Carotid Wall Longitudinal Motion in Ultrasound Imaging: An Expert Consensus Review

Motion extracted from the carotid artery wall provides unique information for vascular health evaluation. Carotid artery longitudinal wall motion corresponds to the multiphasic arterial wall excursion in the direction parallel to blood flow during the cardiac cycle. While this motion phenomenon has been well characterized, there is a general lack of awareness regarding its implications for vascular health assessment or even basic vascular physiology. In the last decade, novel estimation strategies and clinical investigations have greatly advanced our understanding of the bi-axial behavior of the carotid artery, necessitating an up-to-date review to summarize and classify the published literature in collaboration with technical and clinical experts in the field. Within this review, the state-of-the-art methodologies for carotid wall motion estimation are described, and the observed relationships between longitudinal motion-derived indices and vascular health are reported. The vast number of studies describing the longitudinal motion pattern in plaque-free arteries, with its putative application to cardiovascular disease prediction, point to the need for characterizing the added value and applicability of longitudinal motion beyond established biomarkers. To this aim, the main purpose of this review was to provide a strong base of theoretical knowledge, together with a curated set of practical guidelines and recommendations for longitudinal motion estimation in patients, to foster future discoveries in the field, toward the integration of longitudinal motion in basic science as well as clinical practice.

Motion synchronisation patterns of the carotid atheromatous plaque from B-mode ultrasound

Asynchronous movement of the carotid atheromatous plaque from B-mode ultrasound has been previously reported, and associated with higher risk of stroke, but not quantitatively estimated. Based on the hypothesis that asynchronous plaque motion is associated with vulnerable plaque, in this study, synchronisation patterns of different tissue areas were estimated using cross-correlations of displacement waveforms. In 135 plaques (77 subjects), plaque radial deformation was synchronised by approximately 50% with the arterial diameter, and the mean phase shift was 0.4 s. Within the plaque, the mean phase shifts between the displacements of the top and bottom surfaces were 0.2 s and 0.3 s, in the radial and longitudinal directions, respectively, and the synchronisation about 80% in both directions. Classification of phase-shift-based features using Random Forests yielded Area-Under-the-Curve scores of 0.81, 0.79, 0.89 and 0.90 for echogenicity, symptomaticity, stenosis degree and plaque risk, respectively. Statistical analysis showed that echolucent, high-stenosis and high-risk plaques exhibited higher phase shifts between the radial displacements of their top and bottom surfaces. These findings are useful in the study of plaque kinematics.

Carotid Artery Longitudinal Wall Motion Is Unaffected by 12 Weeks of Endurance, Sprint Interval or Resistance Exercise Training

Carotid artery longitudinal wall motion (CALM) exhibits reduced magnitude in older adults and in individuals with chronic diseases, although longitudinal data are lacking to indicate how changes in CALM might develop over time. Therefore, the aim of this study was to investigate the effect of exercise training in healthy men on CALM using a retrospective design. Carotid ultrasound data were analysed from two previous studies in which men performed 12 wk of moderate-intensity continuous exercise training (n = 9), sprint-interval training (n = 7), higher-repetition resistance exercise training (n = 15) or lower-repetition resistance exercise training (n = 15). The CALM pattern was unaltered after 12 wk of exercise training, regardless of exercise mode, with no differences in systolic or diastolic CALM magnitudes (p > 0.05), similar to carotid intima-media thickness (p > 0.05). Our findings suggest that CALM is resistant to transient changes in lifestyle factors, similar to wall thickness in otherwise healthy populations.

Longitudinal Movement of the Common Carotid Artery Wall: New Information on Cardiovascular Aging

Putative changes in the multiphasic pattern of longitudinal movement of the common carotid artery wall in the normal aging process are unknown. The aim of this study was to explore the phases, and resulting patterns, of the longitudinal movement of the intima-media complex of the human common carotid artery with respect to age and gender. One hundred thirty-five healthy non-smoking patients of different ages were investigated using in-house-developed ultrasound methods. The patterns of longitudinal movement seen in middle-aged and older patients were markedly different from those commonly seen in young patients, including the appearance of two additional phases of motion and, thus, new complex patterns. The displacement and maximum velocity of one of the phases, occurring at the time of aortic valve closure, increased quadratically with age in both men and women.

Combining in vivo and in vitro biomechanical data reveals key roles of perivascular tethering in central artery function

Considerable insight into effectors of cardiovascular function can be gleaned from controlled studies on mice, especially given the diverse models that are available. Toward this end, however, there is a need for consistent and complementary methods of in vivo and in vitro data analysis, synthesis, and interpretation. The overall objective of this study is twofold. First, we present new semi-automated methods to quantify in vivo measurements of vascular function in anesthetized mice as well as new approaches to synthesize these data with those from in vitro biaxial mechanical characterizations. Second, we contrast regional differences in biomechanical behaviors along the central vasculature by combining biaxial strains measured in vivo with data on the unloaded geometry and biaxial material properties measured in vitro. Results support the hypothesis that the healthy ascending aorta stores significant elastic energy during systole, which is available to work on the heart and blood during diastole, particularly during periods of physical exertion, and further suggest that perivascular tethering allows arteries to work at lower values of wall stress and material stiffness than often assumed. The numerous measurements of vascular function and properties provided herein can also serve as reference values for normal wild-type male and female mice, to which values for myriad genetic, surgical, and pharmacological models can be compared in future studies.

Motion Tracking of the Carotid Artery Wall From Ultrasound Image Sequences: a Nonlinear State-Space Approach

The motion of the common carotid artery (CCA) wall has been established to be useful in early diagnosis of atherosclerotic disease. However, tracking the CCA wall motion from ultrasound images remains a challenging task. In this paper, a nonlinear state-space approach has been developed to track CCA wall motion from ultrasound sequences. In this approach, a nonlinear state-space equation with a time-variant control signal was constructed from a mathematical model of the dynamics of the CCA wall. Then, the unscented Kalman filter (UKF) was adopted to solve the nonlinear state transfer function in order to evolve the state of the target tissue, which involves estimation of the motion trajectory of the CCA wall from noisy ultrasound images. The performance of this approach has been validated on 30 simulated ultrasound sequences and a real ultrasound dataset of 103 subjects by comparing the motion tracking results obtained in this study to those of three state-of-the-art methods and of the manual tracing method performed by two experienced ultrasound physicians. The experimental results demonstrated that the proposed approach is highly correlated with (intra-class correlation coefficient ≥ 0.9948 for the longitudinal motion and ≥ 0.9966 for the radial motion) and well agrees (the 95% confidence interval width is 0.8871 mm for the longitudinal motion and 0.4159 mm for the radial motion) with the manual tracing method on real data and also exhibits high accuracy on simulated data (0.1161 ~ 0.1260 mm). These results appear to demonstrate the effectiveness of the proposed approach for motion tracking of the CCA wall.

Model-based vascular elastography improves the detection of flow-induced carotid artery remodeling in mice

Increased arterial thickness measured with ultrasound correlates with future cardiovascular events, but conventional ultrasound imaging techniques cannot distinguish between intima, media, or atherosclerotic plaque in the carotid artery. In this work, we evaluated how well vascular elastography can detect intimal changes in a mouse model of carotid remodeling. We ligated the left external and internal branches of the carotid artery of male FVB mice and performed sham operations for 2 weeks. High-resolution ultrasound imaging accurately detected lower blood velocities and low blood volume flow in the carotid arteries after ligation in FVB mice. However, ultrasound could not detect differences in the carotid wall even at 2 weeks post-surgery. The Young’s modulus was measured based on displacements of the carotid artery wall, and Young’s modulus was 2-fold greater in shams at 1 week post ligation, and 3-fold greater 2 weeks after ligation. Finally, the higher Young’s modulus was most associated with higher intimal thickness but not medial or adventitial thickness as measured by histology. In conclusion, we developed a robust ultrasound-based elastography method for early detection of intimal changes in small animals.

A combination of parabolic and grid slope interpolation for 2D tissue displacement estimations

Parabolic sub-sample interpolation for 2D block-matching motion estimation is computationally efficient. However, it is well known that the parabolic interpolation gives a biased motion estimate for displacements greater than |y.2| samples (y = 0, 1, …). Grid slope sub-sample interpolation is less biased, but it shows large variability for displacements close to y.0. We therefore propose to combine these sub-sample methods into one method (GS15PI) using a threshold to determine when to use which method. The proposed method was evaluated on simulated, phantom, and in vivo ultrasound cine loops and was compared to three sub-sample interpolation methods. On average, GS15PI reduced the absolute sub-sample estimation errors in the simulated and phantom cine loops by 14, 8, and 24% compared to sub-sample interpolation of the image, parabolic sub-sample interpolation, and grid slope sub-sample interpolation, respectively. The limited in vivo evaluation of estimations of the longitudinal movement of the common carotid artery using parabolic and grid slope sub-sample interpolation and GS15PI resulted in coefficient of variation (CV) values of 6.9, 7.5, and 6.8%, respectively. The proposed method is computationally efficient and has low bias and variance. The method is another step toward a fast and reliable method for clinical investigations of longitudinal movement of the arterial wall.

Imaging in Vascular Access

This review examines four imaging modalities; ultrasound (US), digital subtraction angiography (DSA), magnetic resonance imaging (MRI) and computed tomography (CT), that have common or potential applications in vascular access (VA). The four modalities are reviewed under their primary uses, techniques, advantages and disadvantages, and future directions that are specific to VA. Currently, US is the most commonly used modality in VA because it is cheaper (relative to other modalities), accessible, non-ionising, and does not require the use of contrast agents. DSA is predominantly only performed when an intervention is indicated. MRI is limited by its cost and the time required for image acquisition that mainly confines it to the realm of research where high resolution is required. CT’s short acquisition times and high resolution make it useful as a problem-solving tool in complex cases, although accessibility can be an issue. All four imaging modalities have advantages and disadvantages that limit their use in this particular patient cohort. Current imaging in VA comprises an integrated approach with each modality providing particular uses dependent on their capabilities. MRI and CT, which currently have limited use, may have increasingly important future roles in complex cases where detailed analysis is required.

Design and Fabrication of a Conceptual Arterial Ultrasound Phantom Capable of Exhibiting Longitudinal Wall Movement

The longitudinal movement of the arterial wall of large human arteries has shown promise to be an independent indicator of vascular health. Despite growing interest in this movement, its nature, causes, and implications are not fully understood, and existing phantoms have failed to show a pure longitudinal movement that is not secondary to the distension. An often overlooked aspect of the arterial wall is the interaction between the different layers. The longitudinal movement of the innermost layers, the intima and media, can be several hundred micrometers in the direction of flow during early systole. This is markedly larger than that of the adventitia, indicating that sliding occurs between the two layers. This feature was incorporated into a phantom by casting it in two parts. The molds were developed in-house using mainly a 3-D printer, a versatile and easy production method. Additionally, the phantom contains a tapered region. Using the phantom, we were able to demonstrate a pure longitudinal movement; when it was subjected to a pulsatile pressure, the wall displaced 220 [Formula: see text] (SD 40) radially and 560 [Formula: see text] (SD 74) longitudinally distal to the tapering. The motion followed the pressure variations. This paper serves as a guide for phantom production, explaining each step of the process.

Transfer Function Analysis of the Longitudinal Motion of the Common Carotid Artery Wall

The longitudinal motion of the carotid wall is a potential new measure of arterial stiffness. Despite the over decade long research on the subject, the driving force and the specific longitudinal kinetics of the carotid wall has remained unclear. In this study, a transfer function analysis with 20 healthy subjects is presented to derive how the energy from the blood pressure moves the innermost arterial wall longitudinally and how the kinetic energy is then transferred to the outermost arterial layer. The power spectrums display that the main kinetic energy of the longitudinal motion is on band 0-3 Hz with a peak on the 1.1 Hz frequency. There is a large variation among the individuals, how the energy from the blood pressure transfers into the longitudinal motion of the arterial wall since the main direction of the longitudinal motion varies individually and because early arterial stiffening potentially has an effect on the time characteristics of the energy transfer. The energy transfer from the innermost to the outermost wall layer is more straightforward: on average, a 17% of the longitudinal amplitude is lost and an 18.9 ms delay is visible on the 1.0 Hz frequency.

Principal Component Analysis of the Longitudinal Carotid Wall Motion in Association with Vascular Stiffness: A Pilot Study

The longitudinal motion of the carotid wall during a heart cycle has a multiphasic waveform. Recent studies have examined the amplitude of this motion. Instead of amplitude measurements, we focus on making a detailed characterization of the motion waveform. Two-minute carotid ultrasound videos were obtained for 19 healthy volunteers, and a speckle tracking algorithm was used to measure the motion of the carotid wall. Principal component analysis revealed the characteristic features of wall motion and their relation to known arterial stiffness indices. By estimating two principal components, we could account for more than 92% of the variation in the motion graphs. The first principal component derived from the longitudinal motion curves was significantly correlated to pulse pressure, indicating that the main dominant base waveform of the longitudinal motion was related to blood pressure. The second principal component derived from the longitudinal motion curves had multiple significant correlations to known stiffness indices, indicating that the stronger biphasic structure of the motion curve, especially on the adventitia layer, was associated with higher distensibility and compliance, as well as reduced carotid artery stiffness. According to this study, the second principal component of the longitudinal motion may be a useful parameter reflecting vascular health.

Carotid artery longitudinal wall motion is associated with local blood velocity and left ventricular rotational, but not longitudinal, mechanics

Recent studies have identified a predictable movement pattern of the common carotid artery wall in the longitudinal direction. While there is evidence that the magnitude of this carotid artery longitudinal wall motion (CALM) is sensitive to cardiovascular health status, little is known about the determinants of CALM. The purpose of this integrative study was to evaluate the contribution of left ventricular (LV) cardiac motion and local blood velocity to CALM. Simultaneous ultrasound measurements of CALM, common carotid artery mean blood velocity (MBV), and left ventricular motion were performed in ten young, healthy individuals (6 males; 22 ± 1 years). Peak anterograde CALM occurred at a similar time as peak MBV (18.57 ± 3.98% vs. 18.53 ± 2.81% cardiac cycle; t‐test: P = 0.94; ICC: 0.79, P < 0.01). The timing of maximum retrograde CALM displacement was different, but related, to both peak apical (41.00 ± 7.81% vs. 35.33 ± 5.79% cardiac cycle; t‐test: P < 0.01; ICC: 0.79, P < 0.01) and basal rotation (41.80 ± 6.12% vs. 37.30 ± 5.66% cardiac cycle; t‐test: P < 0.01; ICC: 0.74, P < 0.01) with peak cardiac displacements preceding peak CALM displacements in both cases. The association between basal rotation and retrograde CALM was further supported by strong correlations between their peak magnitudes (r = −0.70, P = 0.02), whereas the magnitude of septal longitudinal displacement was not associated with peak CALM (r = 0.11, P = 0.77). These results suggest that the rotational mechanical movement of the LV base may be closely associated with longitudinal mechanics in the carotid artery. This finding may have important implications for interpreting the complex relationship between ventricular and vascular function.

Carotid Atherosclerotic Plaque Alters the Direction of Longitudinal Motion in the Artery Wall

Longitudinal motion of the artery, a cyclical, bidirectional movement of the wall in the long axis of the artery, has recently gained interest in the characterization of artery function. The aim of this study was to evaluate longitudinal motion in patients with internal carotid atherosclerotic plaques. Speckle tracking ultrasound was used to assess common carotid artery wall motion in 12 patients with carotid plaque causing either moderate (50%-79%) or severe (80%-99%) stenosis based on the North American Carotid Endarterectomy Trial, and 23 healthy participants. Although healthy individuals were found to have a retrograde wall motion pattern, a distinct anterograde pattern was noted with plaque presence. Importantly, patients with severe plaque stenosis had greater anterograde motion (0.53 ± 0.36 mm) than those with moderate stenosis (0.17 ± 0.15 mm) (p < 0.05), likely owing to high wall shear stresses associated with greater peak systolic velocities at the site of stenosis (severe: 342.0 ± 99.4 cm/s, moderate: 177.5 ± 31.2 cm/s, p < 0.01). There were no differences in peak systolic velocities at plaque-free segments between plaque groups (severe: 80.2 ± 24.8 cm/s, moderate: 92.7 ± 23.0 cm/s). Blood flow at stenotic areas better predicted motion than plaque-free segments. We conclude that the presence of carotid plaque can have significant influence on longitudinal motion, with significantly greater anterograde displacements with increased stenosis. Future studies are needed to further investigate carotid artery wall mechanics.

Reduced common carotid artery longitudinal wall motion and intramural shear strain in individuals with elevated cardiovascular disease risk using speckle tracking

Longitudinal motion of the intima-media and adventitia layers of the common carotid artery (CCA) wall were assessed with ultrasound speckle tracking in seven individuals with spinal cord injury (SCI), who are considered at increased risk of cardiovascular disease, and in seven able-bodied participants. CCA longitudinal wall displacement and intramural shear strain were compared to traditional markers of arterial health, including CCA stiffness and intima-media thickness (IMT). For each cardiac cycle, longitudinal CCA wall motion was characterized by bidirectional movement patterns containing motion retrograde to blood flow during systole, followed by antegrade motion during diastole. Relative displacement of the intima-media versus the adventitia was used to calculate longitudinal intramural shear strain and provided insight to local arterial wall properties. The retrograde intramural shear strain was smaller in individuals with SCI by 60·2% (P<0·05) compared to able-bodied participants, showing smaller peak displacements in both the intima-media (P<0·05) and adventitia (P<0·05). In the antegrade direction, there were no group differences in either longitudinal displacements or shear strain. The group differences observed in the retrograde wall motion phase were greater than those observed for CCA stiffness or IMT and were found to be independent of both indices, indicating indices of the retrograde phase intramural shear strain may be a novel and sensitive marker of vascular health. Our findings demonstrate that assessment of longitudinal arterial wall shear strain may provide valuable insight into vascular structure and function and may hold potential for the early detection of cardiovascular disease.

A viscoelastic fluid-structure interaction model for carotid arteries under pulsatile flow

In this study, a fluid-structure interaction model (FSI) incorporating viscoelastic wall behaviour is developed and applied to an idealized model of the carotid artery under pulsatile flow. The shear and bulk moduli of the arterial wall are described by Prony series, where the parameters can be derived from in vivo measurements. The aim is to develop a fully coupled FSI model that can be applied to realistic arterial geometries with normal or pathological viscoelastic wall behaviour. Comparisons between the numerical and analytical solutions for wall displacements demonstrate that the coupled model is capable of predicting the viscoelastic behaviour of carotid arteries. Comparisons are also made between the solid only and FSI viscoelastic models, and the results suggest that the difference in radial displacement between the two models is negligible.

Profound increase in longitudinal displacements of the porcine carotid artery wall can take place independently of wall shear stress: a continuation report

The mechanisms underlying longitudinal displacements of the arterial wall, that is, displacements of the wall layers along the artery, and the resulting intramural shear strain remain largely unknown. We have already found that these displacements undergo profound changes in response to catecholamines. Wall shear stress, closely related to wall shear rate, represents the viscous drag exerted on the vessel wall by flowing blood. The aim of the work described here was to study possible relations between the wall shear rate and the longitudinal displacements. We investigated the carotid arteries of five anesthetized pigs in different hemodynamic situations using in-house developed non-invasive ultrasound techniques. The study protocol included administration of epinephrine, norepinephrine and β-blockade (metoprolol). No significant correlation between longitudinal displacement of the intima-media complex and wall shear rate was found. This result suggests that one or multiple pulsatile forces other than wall shear stress are also working along arteries, strongly influencing arterial wall behavior.

Ultrasound imaging for risk assessment in atherosclerosis

Atherosclerosis and its consequences like acute myocardial infarction or stroke are highly prevalent in western countries, and the incidence of atherosclerosis is rapidly rising in developing countries. Atherosclerosis is a disease that progresses silently over several decades before it results in the aforementioned clinical consequences. Therefore, there is a clinical need for imaging methods to detect the early stages of atherosclerosis and to better risk stratify patients. In this review, we will discuss how ultrasound imaging can contribute to the detection and risk stratification of atherosclerosis by (a) detecting advanced and early plaques; (b) evaluating the biomechanical consequences of atherosclerosis in the vessel wall;

The application of ultrasonic velocity vector imaging technique of carotid plaque in predicting large-artery atherosclerotic stroke

BACKGROUND

Large-artery atherosclerotic stroke (LAAs) is related to carotid plaque, but the mechanical mechanism is unclear. We aimed to use ultrasonic velocity vector imaging (VVI) technique to study the mechanical difference of carotid plaque in patients with LAAs and controls.

METHODS

We enrolled 43 LAAs patients and 38 controls but all showing plaque on carotid ultrasonography. Ultrasonic VVI technique was used to analyze radial systolic and diastolic peak velocity (R-vs, R-vd), radial and circumferential peak strain (R-s, C-s) and radial displacement (R-dis) of carotid plaque.

RESULTS

Compared with controls, LAAs patients showed higher pulse pressure (P = .001), pulse pressure index (PPI, P = .006), and greater stress at carotid plaque as manifested by higher absolute value of radial diastolic peak velocity (R-vd, P = .021), radial systolic peak velocity (R-vs, P = .007), radial peak strain (R-s, P = .015), and radial displacement (R-dis, P = .022). PPI was significantly correlated with R-vs (r = -.274, P = .013), R-vd (r = .304, P = .006), and R-dis (r = -.28, P = .011). But there was no correlation between R-s and blood pressure. R-s was screened to be the most predictable parameters for LAAs (odds ratio, 1.118; 95% confidence interval, 1.012∼1.236; P = .029). The area under the curve of R-s was .627.

CONCLUSIONS

Radial peak strain (R-s) is a predictable parameter for the occurrence of LAAs. We predict using ultrasonic VVI technique to analyze whether the mechanics of carotid plaque is helpful to screen patients with high risks of LAAs.

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 speckle tracking for carotid strain assessment has in the past decade gained interest in studies of arterial stiffness and cardiovascular diseases. The aim of this study was to validate and directly contrast carotid strain assessment by speckle tracking applied on clinical and high-frequency ultrasound images in vitro. Four polyvinyl alcohol phantoms mimicking the carotid artery were constructed with different mechanical properties and connected to a pump generating carotid flow profiles. Gray-scale ultrasound long- and short-axis images of the phantoms were obtained using a standard clinical ultrasound system, Vivid 7 (GE Healthcare, Horten, Norway) and a high-frequency ultrasound system, Vevo 2100 (FUJIFILM, VisualSonics, Toronto, Canada) with linear-array transducers (12L/MS250). Radial, longitudinal and circumferential strains were estimated using an in-house speckle tracking algorithm and compared with reference strain acquired by sonomicrometry. Overall, the estimated strain corresponded well with the reference strain. The correlation between estimated peak strain in clinical ultrasound images and reference strain was 0.91 (p<0.001) for radial strain, 0.73 (p<0.001) for longitudinal strain and 0.90 (p<0.001) for circumferential strain and for high-frequency ultrasound images 0.95 (p<0.001) for radial strain, 0.93 (p<0.001) for longitudinal strain and 0.90 (p<0.001) for circumferential strain. A significant larger bias and root mean square error was found for circumferential strain estimation on clinical ultrasound images compared to high frequency ultrasound images, but no significant difference in bias and root mean square error was found for radial and longitudinal strain when comparing estimation on clinical and high-frequency ultrasound images. The agreement between sonomicrometry and speckle tracking demonstrates that carotid strain assessment by ultrasound speckle tracking is feasible.

Relation of arterial stiffness and axial motion of the carotid artery wall - a pilot study to test our motion tracking algorithm in practice

Recently researchers have shown growing interest in axial motion of common carotid artery wall. The amplitude of the axial motion of the wall has been initially linked to arterial stiffness and the direction of the axial stretch has been noted to vary, although not highlighted in the studies. In this study, an enhanced block matching algorithm, developed in our earlier study, was used to measure 2D-motion of the human carotid artery wall. A total of 19 healthy subjects were imaged and divided into two groups based on whether their axial motion of intima-media in left common carotid artery was primarily oriented along or against the direction of the blood flow. Statistically significant differences in two independent indices of arterial stiffness, as well as in the size of the artery, were found between the groups, suggesting that retrograde motion of intima-media is associated with smaller carotid arteries and is a possible sign of arterial stiffness.

Progressive attenuation of the longitudinal kinetics in the common carotid artery: preliminary in vivo assessment

Longitudinal kinetics (LOKI) of the arterial wall consists of the shearing motion of the intima-media complex over the adventitia layer in the direction parallel to the blood flow during the cardiac cycle. The aim of this study was to investigate the local variability of LOKI amplitude along the length of the vessel. By use of a previously validated motion-estimation framework, 35 in vivo longitudinal B-mode ultrasound cine loops of healthy common carotid arteries were analyzed. Results indicated that LOKI amplitude is progressively attenuated along the length of the artery, as it is larger in regions located on the proximal side of the image (i.e., toward the heart) and smaller in regions located on the distal side of the image (i.e., toward the head), with an average attenuation coefficient of -2.5 ± 2.0%/mm. Reported for the first time in this study, this phenomenon is likely to be of great importance in improving understanding of atherosclerosis mechanisms, and has the potential to be a novel index of arterial stiffness.

Improved tracking performance of Lagrangian block-matching methodologies using block expansion in the time domain: in silico, phantom and in vivo evaluations

The aim of this study was to evaluate tracking performance when an extra reference block is added to a basic block-matching method, where the two reference blocks originate from two consecutive ultrasound frames. The use of an extra reference block was evaluated for two putative benefits: (i) an increase in tracking performance while maintaining the size of the reference blocks, evaluated using in silico and phantom cine loops; (ii) a reduction in the size of the reference blocks while maintaining the tracking performance, evaluated using in vivo cine loops of the common carotid artery where the longitudinal movement of the wall was estimated. The results indicated that tracking accuracy improved (mean = 48%, p < 0.005 [in silico]; mean = 43%, p < 0.01 [phantom]), and there was a reduction in size of the reference blocks while maintaining tracking performance (mean = 19%, p < 0.01 [in vivo]). This novel method will facilitate further exploration of the longitudinal movement of the arterial wall.

Asymmetric radial expansion and contraction of rat carotid artery observed using a high-resolution ultrasound imaging system

The geometry of carotid artery bifurcation is of high clinical interest because it determines the characteristics of blood flow that is closely related to the formation and development of atherosclerotic plaque. However, information on the dynamic changes in the vessel wall of carotid artery bifurcation during a pulsatile cycle is limited. This pilot study investigated the cyclic changes in carotid artery geometry caused by blood flow pulsation in rats. A high-resolution ultrasound imaging system with a broadband scanhead centered at 40 MHz was used to obtain longitudinal images of the rat carotid artery. A high frame rate retrospective B-scan imaging technique based on the use of electrocardiogram to trigger signal acquisition was used to examine precisely the fast arterial wall motion. Two-dimensional geometry data obtained from nine rats showed that the rat carotid artery asymmetrically contracts and dilates during each cardiac cycle. Systolic/diastolic vessel diameters near the upstream and downstream regions from the bifurcation were 0.976 ± 0.011/0.825 ± 0.015 mm and 0.766 ± 0.015/0.650 ± 0.016 mm, respectively. Their posterior/anterior wall displacement ratios in the radial direction were 41.0 ± 14.9% and 2.9 ± 1.6%, respectively. These results indicate that in the vicinity of bifurcation, the carotid artery favorably expands to the anterior side during the systolic phase. This phenomenon was observed to be more prominent in the downstream region near the bifurcation. The cyclic variation pattern in wall movement varies depending on the measurement site, which shows different patterns at far upstream and downstream of the bifurcation. The asymmetric radial expansion and contraction of the rat carotid artery observed in this study may be useful in studying the hemodynamic etiology of cardiovascular diseases because the pulsatile changes in vessel geometry may affect the local hemodynamics that determines the spatial distribution of wall shear stress, one of important cardiovascular risk factors. Further systematic study is needed to clarify the effects of wall elasticity, branch angle and vessel diameter ratio on the asymmetric wall motion of carotid artery bifurcation.

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

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.