Carotid Plaque Stiffness Measured with Supersonic Shear Imaging and Its Correlation with Serum Homocysteine Level in Ischemic Stroke Patients

Performance evaluation of commercial and non-commercial shear wave elastography implementations for vascular applications

BACKGROUND

Shear wave elastography (SWE) is mainly used for stiffness estimation of large, homogeneous tissues, such as the liver and breasts. However, little is known about its accuracy and applicability in thin (∼0.5-2 mm) vessel walls. To identify possible performance differences among vendors, we quantified differences in measured wave velocities obtained by commercial SWE implementations of various vendors over different imaging depths in a vessel-mimicking phantom. For reference, we measured SWE values in the cylindrical inclusions and homogeneous background of a commercial SWE phantom. Additionally, we compared the accuracy between a research implementation and the commercially available clinical SWE on an Aixplorer ultrasound system in phantoms and in vivo in patients.

METHODS

SWE measurements were performed over varying depths (0-35 mm) using three ultrasound machines with four ultrasound probes in the homogeneous 20 kPa background and cylindrical targets of 10, 40, and 60 kPa of a multi-purpose phantom (CIRS-040GSE) and in the anterior and posterior wall of a homogeneous polyvinyl alcohol vessel-mimicking phantom. These phantom data, along with in vivo SWE data of carotid arteries in 23 patients with a (prior) head and neck neoplasm, were also acquired in the research and clinical mode of the Aixplorer ultrasound machine. Machine-specific estimated phantom stiffness values (CIRS phantom) or wave velocities (vessel phantom) over all depths were visualized, and the relative error to the reference values and inter-frame variability (interquartile range/median) were calculated. Correlations between SWE values and target/vessel wall depth were explored in phantoms and in vivo using Spearman's correlations. Differences in wave velocities between the anterior and posterior arterial wall were assessed with Wilcoxon signed-rank tests. Intra-class correlation coefficients were calculated for a sample of ten patients as a measure of intra- and interobserver reproducibility of SWE analyses in research and clinical mode.

RESULTS

There was a high variability in obtained SWE values among ultrasound machines, probes, and, in some cases, with depth. Compared to the homogeneous CIRS-background, this variation was more pronounced for the inclusions and the vessel-mimicking phantom. Furthermore, higher stiffnesses were generally underestimated. In the vessel-mimicking phantom, anterior wave velocities were (incorrectly) higher than posterior wave velocities (3.4-5.6 m/s versus 2.9-5.9 m/s, p ≤ 0.005 for 3/4 probes) and remarkably correlated with measurement depth for most machines (Spearman's ρ = -0.873-0.969, p < 0.001 for 3/4 probes). In the Aixplorer's research mode, this difference was smaller (3.3-3.9 m/s versus 3.2-3.6 m/s, p = 0.005) and values did not correlate with measurement depth (Spearman's ρ = 0.039-0.659, p ≥ 0.002). In vivo, wave velocities were higher in the posterior than the anterior vessel wall in research (left p = 0.001, right p < 0.001) but not in clinical mode (left: p = 0.114, right: p = 0.483). Yet, wave velocities correlated with vessel wall depth in clinical (Spearman's ρ = 0.574-0.698, p < 0.001) but not in research mode (Spearman's ρ = -0.080-0.466, p ≥ 0.003).

CONCLUSIONS

We observed more variation in SWE values among ultrasound machines and probes in tissue with high stiffness and thin-walled geometry than in low stiffness, homogeneous tissue. Together with a depth-correlation in some machines, where carotid arteries have a fixed location, this calls for caution in interpreting SWE results in clinical practice for vascular applications.

Shear wave elastography for extracranial carotid atherosclerotic plaques: technical principles and how to do it

In the wake of studies targeting atherosclerotic plaques and searching for quantifiable variables that contribute additional information to therapeutic decision-making, plaque assessment using Shear Wave Elastography (SWE) is emerging as a reproducible and promising alternative. We used a single Logiq S8 device (General Electric, Boston, Massachusetts, United States) with an 8.5-11MHz multifrequency linear transducer at 10MHz in longitudinal section. We considered relevant criteria for image acquisition: adequate longitudinal insonation, differentiation of the intima-media complex, delineation of proximal and distal tunica adventitia and the vascular lumen, good visualization of the atherosclerotic plaque, cardiac cycle in ventricular diastole, and absence of incongruous changes. SWE is an emerging and extremely promising method for assessment of carotid plaques that may contribute to therapeutic decision-making based on characteristics related to the atherosclerotic plaque, with inter-device and inter-examiner reproducibility.

Extending arterial stiffness assessment along the circumference using beam-steered ARFI and wave-tracking: A proof-of-principle study in phantoms and ex vivo

Background

To fully quantify arterial wall and plaque stiffness, acoustic radiation force impulse (ARFI)-induced wave-tracking along the entire vessel circumference is desired. However, attenuation and guided wave behavior in thin vessel walls limits wave-tracking to short trajectories. This study investigated the potential of beam-steered ARFI and wave-tracking to extend group velocity estimation over a larger proportion of the circumference compared to conventional 0° ARFI-induced wave-tracking.

Methods

Seven vessel-mimicking polyvinyl alcohol cryogel phantoms with various dimensions and compositions and an ex vivo human carotid artery were imaged in a dedicated setup. For every 20⁰ phantom rotation, transverse group wave velocity measurements were performed with an Aixplorer Ultimate system and SL18-5 transducer using 0⁰/20⁰/-20⁰-angled ultrasound pushes. Transmural angular wave velocities were derived along 60⁰-trajectories. A 360⁰-angular velocity map was composed from the top-wall 60⁰-trajectories 0°-data, averaged over all physical phantom rotations (reference). For each phantom rotation, 360⁰-angular velocity maps were composed using 0°-data (0⁰-approach) or data from all angles (beam-steered approach). Percentages of rotations with visible waves and relative angular velocity errors compared to the reference map as function of the circumferential angle were determined for both approaches.

Results

Reference 360°-angular velocity maps could be derived for all samples, representing their stiffness. Beam-steering decreased the proportion of the circumference where waves were untraceable by 20% in phantoms and 10% ex vivo, mainly at 0° push locations. Relative errors were similar for both approaches (phantoms: 10-15%, ex vivo: 15-35%).

Conclusion

Beam-steering enables wave-tracking along a higher proportion of the wall circumference than 0⁰ ARFI-induced wave-tracking.

Novel Imaging-Based Biomarkers for Identifying Carotid Plaque Vulnerability

Carotid artery disease has traditionally been assessed based on the degree of luminal narrowing. However, this approach, which solely relies on carotid stenosis, is currently being questioned with regard to modern risk stratification approaches. Recent guidelines have introduced the concept of the "vulnerable plaque," emphasizing specific features such as thin fibrous caps, large lipid cores, intraplaque hemorrhage, plaque rupture, macrophage infiltration, and neovascularization. In this context, imaging-based biomarkers have emerged as valuable tools for identifying higher-risk patients. Non-invasive imaging modalities and intravascular techniques, including ultrasound, computed tomography, magnetic resonance imaging, intravascular ultrasound, optical coherence tomography, and near-infrared spectroscopy, have played pivotal roles in characterizing and detecting unstable carotid plaques. The aim of this review is to provide an overview of the evolving understanding of carotid artery disease and highlight the significance of imaging techniques in assessing plaque vulnerability and informing clinical decision-making.

Novel ultrasound techniques in the identification of vulnerable plaques-an updated review of the literature

Atherosclerosis is an inflammatory disease partly mediated by lipoproteins. The rupture of vulnerable atherosclerotic plaques and thrombosis are major contributors to the development of acute cardiovascular events. Despite various advances in the treatment of atherosclerosis, there has been no satisfaction in the prevention and assessment of atherosclerotic vascular disease. The identification and classification of vulnerable plaques at an early stage as well as research of new treatments remain a challenge and the ultimate goal in the management of atherosclerosis and cardiovascular disease. The specific morphological features of vulnerable plaques, including intraplaque hemorrhage, large lipid necrotic cores, thin fibrous caps, inflammation, and neovascularisation, make it possible to identify and characterize plaques with a variety of invasive and non-invasive imaging techniques. Notably, the development of novel ultrasound techniques has introduced the traditional assessment of plaque echogenicity and luminal stenosis to a deeper assessment of plaque composition and the molecular field. This review will discuss the advantages and limitations of five currently available ultrasound imaging modalities for assessing plaque vulnerability, based on the biological characteristics of the vulnerable plaque, and their value in terms of clinical diagnosis, prognosis, and treatment efficacy assessment.

Association between plasma total homocysteine (tHcy) and strokes: A meta-analysis

Objective

Inconsistent findings have been reported regarding the association between elevated plasma total homocysteine (tHcy) and the risk of different types of strokes. We conducted this meta-analysis to identify the association between tHcy and different kinds of strokes or recurrences of strokes, and provide evidence for preventing.

Methods

Relevant studies published before May 1, 2022 in databases such as PubMed, EMBASE, the Cochrane Library, CNKI, and Wanfang were retrieved. Two researchers independently searched and extracted the data, and used Stata 16.0 statistical software for analysis. Results were presented as the odds risk (OR) and the corresponding 95% confidence intervals (CI).

Results

In total, 24 articles were included, involving 51,426 subjects, of which 4,983 had stroke events during follow-up. Relative to lower tHcy, higher tHcy were associated with increased stroke (OR = 1.95, 95% CI: 1.59–2.37), ischemic stroke (OR = 1.71, 95% CI: 1.39–2.11), hemorrhagic stroke (OR = 1.99, 95% CI: 1.03–3.84), and recurrent stroke (OR = 1.25, 95% CI: 1.12–1.39), respectively.

Conclusions

This study shows that elevated tHcy increases the risk of stroke, including ischemic stroke and hemorrhagic stroke, and is closely related to the recurrence of stroke. It is recommended to pay attention to the detection of tHcy in the management of stroke patients in the future, and take effective measures to prevent and delay the progression of stroke.

Advances in Noninvasive Carotid Wall Imaging with Ultrasound: A Narrative Review

Carotid atherosclerosis is a major cause for stroke, with significant associated disease burden morbidity and mortality in Western societies. Diagnosis, grading and follow-up of carotid atherosclerotic disease relies on imaging, specifically ultrasound (US) as the initial modality of choice. Traditionally, the degree of carotid lumen stenosis was considered the sole risk factor to predict brain ischemia. However, modern research has shown that a variety of other imaging biomarkers, such as plaque echogenicity, surface morphology, intraplaque neovascularization and vasa vasorum contribute to the risk for rupture of carotid atheromas with subsequent cerebrovascular events. Furthermore, the majority of embolic strokes of undetermined origin are probably arteriogenic and are associated with nonstenosing atheromas. Therefore, a state-of-the-art US scan of the carotid arteries should take advantage of recent technical developments and should provide detailed information about potential thrombogenic (/) and emboligenic arterial wall features. This manuscript reviews recent advances in ultrasonographic assessment of vulnerable carotid atherosclerotic plaques and highlights the fields of future development in multiparametric arterial wall imaging, in an attempt to convey the most important take-home messages for clinicians performing carotid ultrasound.

Safety of arterial shear wave elastography-ex-vivoassessment of induced strain and strain rates

Shear wave elastography (SWE) is a promising technique for characterizing carotid plaques and assessing local arterial stiffness. The mechanical stress to which the tissue is subjected during SWE using acoustic radiation force (ARF), leading to strain at a certain strain rate, is still relatively unknown. Because SWE is increasingly used for arterial applications where the mechanical stress could potentially lead to significant consequences, it is important to understand the risks of SWE- induced strain and strain rate. The aim of this study was to investigate the safety of SWE in terms of induced arterial strain and strain rateex-vivoand in a human carotid arteryin-vivo. SWE was performed on six porcine aortae as a model of the human carotid artery using different combinations of ARF push parameters (push voltage: 60/90 V, aperture width: f/1.0/1.5, push length: 100/150/200 μs) and distance to push position. The largest induced strain and strain rate were 1.46 % and 54 s^-1(90 V, f/1.0, 200 μs), respectively. Moreover, the SWE-induced strains and strain rates increased with increasing push voltage, aperture, push length, and decreasing distance between the region of interest and the push. In the human carotid artery, the SWE-induced maximum strain was 0.06 % and the maximum strain rate was 1.58 s^-1, compared with the maximum absolute strain and strain rate of 12.61 % and 5.12 s^-1, respectively, induced by blood pressure variations in the cardiac cycle. Our results indicate thatex-vivoarterial SWE does not expose the artery to higher strain rate than normal blood pressure variations, and to strain one order of magnitude higher than normal blood pressure variations, at the push settings and distances from the region of interest used in this study.

Arterial Stiffness Assessment in Healthy Participants Using Shear Wave Elastography

BACKGROUND

Arterial stiffness is an important biomarker for cardiovascular disease. Shear wave elastography (SWE) provides quantitative estimates of tissue stiffness.

OBJECTIVE

This study aimed to provide reference values for arterial wall, assessing the suitability of SWE to quantify elasticity of the common carotid artery (CCA) and evaluating inter- and intra-observer reproducibility.

METHODS

A Supersonic Aixplorer ultrasound system with L15-4 probe was used to scan longitudinal sections of the CCA. Young's modulus (YM) was measured within 2-mm regions of interest. Reproducibility was assessed within a subgroup of 16 participants by two operators (one novice and one experienced) during two sessions >one week apart.

RESULTS

This study involves seventy-three participants with a mean age of 40±10 years and body mass index of 26 ±6 kg/m2. YM estimates were 59 kPa ±19 in men and 56 kPa ±12 in women. The average YM of the CCA walls was 58 kPa ±15 (57 ±15 kPa for the anterior wall and 58 ±20 kPa for the posterior wall, p=0.75). There was no significant difference in the mean of YM estimates of the CCA between the observers (observer: one 51 ±14 kPa and observer two: 55 ±17 kPa [p=0.46]). inter- and intra-observer reproducibility was fair to good (Intra-class correlations, ranging from 0.46 to 0.71). Inter-frame variability was 28%.

CONCLUSION

In healthy individuals, SWE provided an estimate of YM of the CCA (58 kPa) with fair to good reproducibility. This study demonstrated the potential of using SWE for assessing biomechanical properties of blood vessels.

Supersonic shear wave imaging of the tibial nerve for diagnosis of diabetic peripheral neuropathy: A meta-analysis

BACKGROUND

Diabetic peripheral neuropathy (DPN) is the most common diabetes-associated complication and imposes a significant burden to healthcare systems. Thus, early diagnosis of DPN is extremely critical for management and outcome of diabetic patients. Supersonic Shear Wave Imaging (SSI) enables the noninvasive measurement of nerve stiffness. However, previous studies on SSI in the diagnosis of DPN were limited in sample sizes and reported various results. In this meta-analysis, we aimed to obtain comprehensive evidence on the value of tibial nerve stiffness measurement by SSI in the diagnosis of DPN.

METHODS

A comprehensive literature search in English and Chinese electronic database was conducted for studies (published until January 25, 2022) that investigated the diagnostic performance of tibial nerve stiffness measurement by SSI for detecting DPN. Summary receiver operating characteristics (SROC) modelling was constructed to conduct the meta-analysis of diagnostic accuracy of SSI for detecting DPN.

RESULTS

Finally, a total of 12 eligible studies with 1325 subjects were included for evaluation, and a meta-analysis was conducted to evaluate the diagnostic performance of tibial nerve stiffness measurement by SSI for detecting DPN. For tibial nerve stiffness measurement by SSI, the summary sensitivity and specificity for the diagnosis of DPN were 80% (95% confidence interval [CI]: 73%-86%) and 86% (95% CI: 82%-89%), respectively. The summary area under the ROC curve (AUROC) value of the SROC was 0.90 (95% CI: 0.87-0.92), for diagnosing DPN. A subgroup analysis of 11 SSI studies from China revealed similar diagnostic performance, with a summary sensitivity of 79% (95% CI: 72%-85%), specificity of 86% (95% CI: 82%-89%) and summary AUROC value of the SROC of 0.90 (95% CI: 0.87-0.92) for diagnosing DPN.

CONCLUSIONS

Our meta-analysis suggests that a tibial nerve stiffness measurement by SSI shows good performance in diagnosing DPN and has considerable potential as a noninvasive tool for detecting DPN.

Plaque Elasticity and Intraplaque Neovascularisation on Carotid Artery Ultrasound: A Comparative Histological Study

OBJECTIVE

Plaque elasticity and intraplaque neovascularisation are strongly suggestive of vulnerable plaque. This study aimed to investigate the relationship between intraplaque neovascularisation and plaque elasticity, and to compare the ultrasound findings with histopathological changes.

METHODS

Patients enrolled in this study presented with symptomatic carotid stenosis (> 70%) and later underwent both pre-operative ultrasonography and endarterectomy. Contrast enhanced ultrasound (CEUS) and shear wave elastography (SWE) were used to measure the neovascularisation and elasticity of the plaque, respectively. After removal, plaques were histologically assessed to determine the microvessel density (MVD), matrix metalloproteinase (MMP)-9 expression, and type I/type III collagen ratio using immunohistochemistry staining and morphometry. A correlation analysis was used to establish the relationship among the aforementioned quantitative parameters. Inter- and intra-observer consistency evaluations were performed using the intraclass correlation coefficient and Bland-Altman plots.

RESULTS

Ninety-four symptomatic patients with 98 plaques were included. The area under the curve (AUC) of the carotid plaque detected using CEUS correlated with its shear wave velocity (SWV) (r = -.714; p < .001), MVD (r = .842; p < .001), collagen type I/III ratio (r = -.833; p < .001), and MMP-9 (r = .738; p < .001). SWE was positively correlated with the type I/III collagen ratio (r = .805; p < .001). The overall interexaminer consistency of the SWE was acceptable (r = .638; p < .001). The interobserver correlation coefficient of the AUC, time to peak (TP), mean transit time (MTT), and SWV were .719, .756, .733, and .686, respectively. The intra-observer variability values of the AUC, TP, MTT, and SWV were .826, .845, .633, and .748, respectively.

CONCLUSION

SWE and CEUS can comprehensively evaluate the vulnerability of the carotid plaque by assessing the elasticity of the plaque and neovascularisation within it. The negative correlation between the intraplaque neovascularisation and elasticity, further validated by histological findings, suggests that the more abundant the neovascularisation, the less elasticity.

Vascular Shear Wave Elastography in Atherosclerotic Arteries: A Systematic Review

Ischemic stroke is a leading cause of death and disability worldwide, so adequate prevention strategies are crucial. However, current stroke risk stratification is based on epidemiologic studies and is still suboptimal for individual patients. The aim of this systematic review was to provide a literature overview on the feasibility and diagnostic value of vascular shear wave elastography (SWE) using ultrasound (US) in (mimicked) human and non-human arteries affected by different stages of atherosclerotic diseases or diseases related to atherosclerosis. An online search was conducted on Pubmed, Embase, Web of Science and IEEE databases to identify studies using US SWE for the assessment of vascular elasticity. A quality assessment was performed using Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS-2) checklist, and relevant data were extracted. A total of 19 studies were included: 10 with human patients and 9 with non-human subjects (i.e., [excised] animal arteries and polyvinyl alcohol phantoms). All studies revealed the feasibility of using US SWE to assess individually stiffness of the arterial wall and plaques. Quantitative elasticity values were highly variable between studies. However, within studies, SWE could detect statistically significant elasticity differences in patient/subject characteristics and could distinguish different plaque types with good reproducibility. US SWE, with its unique ability to assess the elasticity of the vessel wall and plaque throughout the cardiac cycle, might be a good candidate to improve stroke risk stratification. However, more clinical studies have to be performed to assess this technique's exact clinical value.

Ultrasound assessment of tensile stress in carotid arteries of healthy human subjects with varying age

Background

Arterial remodeling is thought to reflect the adaptation of the vessel wall to mechanical and hemodynamic stimuli and contributes to the progression of cardiovascular and cerebrovascular diseases. Tensile stress (TS) is one of the mechanical properties of the artery wall. The purpose of this study was to investigate the tensile stress change (TS) of carotid artery with varying viscoelasticity in healthy subjects within two groups of different ages.

Methods

Forty-five subjects were recruited and randomly assigned into the group at the age above 50 years and below 50 years. The carotid arteries were examined by ultrasonography, using the techniques of shear wave elastography (SWE), shear wave dispersion (SWD) and radiofrequency (RF) -based ultrasound. The following values, including elastic modulus (SWER) and viscous index (SWDR), as well as the peak and mean TS of the left and right carotid arteries (L-PTS, R-PTS, L-MTS and R-MTS) were measured. The correlations between SWER, SWDR and tensile stress were evaluated.

Results

The SWE_R and SWD_R of carotid arteries are lower in the subjects ≥50 years old than the subjects younger than 50 years (SWE_R, 10.29 ± 9.57 kPa VS 17.24 ± 14.07 kPa; SWD_R, 11.99 ± 3.51 (m/s)/kHz VS 13.97 ± 3.71 (m/s)/kHz, P < 0.05). The R-PTS was lower in the group with younger age (P < 0.05). Pearson correlation analysis showed that SWE_R of carotid artery was positively correlated with the parameters of tensile stress, R-PTS, R-MTS, L-PTS and L-MTS(r = 0.218, r = 0.359, r = 0.209 and r = 0.369, respectively, P < 0.05). However, SWD_R of carotid arteries was not significantly associated with TS.

Conclusion

Ultrasonic shear wave imaging could be used to quantitatively assess carotid viscoelasticity. The carotid TS was related to its elasticity while little related to its viscosity, suggesting that mechanical properties of the arterial wall might be better revealed.

Trial registration

Date of our trial registration: 2018-06-11. Registered with the official website of China Clinical Trial Registration Center (ChiCTR1800016590)