Comparison of degree of stenosis and plaque volume for the assessment of carotid atherosclerosis using 2-D ultrasound

Prediction of degree of carotid stenosis with the transluminal attenuation difference ratio

PURPOSE

We aimed to assess the diagnostic performance of transluminal attenuation difference (TAD) in predicting the severity of internal carotid artery (ICA) stenosis.

METHODS

The study cohort consisted of 48 patients with <50% stenosis, 50%-69% stenosis, 70%-99% stenosis, and 51 controls without plaque development in ICA. A total of 143 measurements were performed through right and left internal and common carotid arteries. The TAD ratio was calculated as the difference between the mean attenuation values of the common carotid artery (CCA) and ICA, divided by the MAV of the CCA, multiplied by 100.

RESULTS

TAD ratio was significantly higher in severe (>70%) stenosis compared with control arteries and low-moderate stenosis. A TAD ratio cutoff of 4.5 predicted 70%-99% stenosis with a sensitivity of 100% and specificity of 93%. The inter- and intraobserver agreements in TAD measurements were almost perfect (ICC, 0.89-0.86).

CONCLUSION

Assessment of TAD ratio predicts the degree of stenosis in concordance with NASCET system.

Criteria for Carotid Atherosclerotic Plaque Instability

BACKGROUND

The study aim is to determine the criteria for carotid atherosclerotic plaque instability with the use of an advanced ultrasound technology, immunohistochemical analysis, and electron paramagnetic resonance (EPR) and assess their correlations with histologic results.

METHODS

A total of 92 patients were included in the study and were examined by ultrasound duplex scanning and ultrasound elastography. Plaques harvested during carotid endarterectomy were obtained for histologic analysis, immunofluorescent assay, and EPR spectroscopic measurements.

RESULTS

Multivariate logistic regression analysis showed that plaques with an area >90 mm² (odds ratio [OR], 4.05; 95% confidence interval [CI], 1.32-13.2; P = 0.006), plaque volume index > 0.6 cm³ (OR, 2.72; 95% CI, 1.05-9.58; P = 0.04), and juxtaluminal black area ≥8 mm² (OR, 2.82; 95% CI, 1.22-6. 23; P = 0.02) were statistically significant independent predictors of histologically verified unstable plaques. Unstable plaques occurred in 94% of the patients with these indicators. Significant increases in the number of CD68+ and CD36+ cells (inflammatory markers) and CD31+ cells (neovasculogenesis markers) were revealed in unstable plaques by the immunohistochemical assay. EPR data analysis showed that divalent manganese could serve as a marker of plaque instability.

CONCLUSIONS

Additional ultrasound criteria, verified by histologic studies, significantly increased the information content for identifying patients with unstable plaques, which can be of great importance in stratifying the risk of ischemic stroke, especially in asymptomatic patients. The degree of calcification is not a mandatory criterion for plaque stabilization.

Determinants of carotid atherosclerotic plaque burden in a stroke-free population

BACKGROUND AND AIMS

In a large stroke-free population, we sought to identify cardiovascular risk factors and carotid plaque components associated with carotid plaque burden, lumen volume and stenosis.

METHODS

The carotid arteries of 1562 stroke-free participants from The Rotterdam Study were imaged on a 1.5-Tesla MRI scanner. Inner and outer wall of the carotid arteries were automatically segmented and lumen volume (mm³), wall volume (outer wall-inner wall) and plaque burden (wall volume/outer wall volume) (%) were quantified. Plaque components were visually determined and luminal stenosis was assessed. We analyzed associations of cardiovascular risk factors and carotid plaque components with plaque burden and lumen volumes using regression analysis.

RESULTS

We investigated 2821 carotid plaques and found that women had larger plaque burden (50.7 ± 7.8% vs. 49.2 ± 7.7%, p < 0.0001) and smaller lumen volumes (933 ± 286 mm³vs. 1078 ± 334 mm³, p < 0.0001) than men. In women, age, HDL-cholesterol and systolic blood pressure, and in men, total cholesterol, non-HDL cholesterol and statin use were independently associated with higher plaque burden and lumen volume. Furthermore, smoking and diabetes were associated with lumen volume in men (respectively p = 0.04 and p = 0.002). Intraplaque hemorrhage (IPH) and lipid were related to a larger plaque burden (OR 1.30 [1.05-1.60] and OR 1.28[1.06-1.55]). Finally, within the highest quartile of plaque burden, IPH was strongly associated with luminal stenosis independent of age, sex, plaque burden and composition (Beta = 15.2; [11.8-18.6]).

CONCLUSIONS

Several cardiovascular risk factors and plaque components, in particular IPH, are associated with higher plaque burden. Carotid IPH is strongly associated with an increased luminal stenosis.

Finite element analysis of mechanics of neovessels with intraplaque hemorrhage in carotid atherosclerosis

Background

Intraplaque hemorrhage is a widely known factor facilitating plaque instability. Neovascularization of plaque can be regarded as a compensatory response to the blood supply in the deep intimal and medial areas of the artery. Due to the physiological function, the deformation of carotid atherosclerotic plaque would happen under the action of blood pressure and blood flow. Neovessels are subject to mechanical loading and likely undergo deformation. The rupture of neovessels may deteriorate the instability of plaque. This study focuses on the local mechanical environments around neovessels and investigates the relationship between the biomechanics and the morphological specificity of neovessels.

Methods

Stress and stretch were used to evaluate the rupture risk of the neovessels in plaque. Computational structural analysis was performed based on two human carotid plaque slice samples. Two-dimensional models containing neovessels and other components were built according to the plaque slice samples. Each component was assumed to be non-linear isotropic, piecewise homogeneous and incompressible. Different mechanical boundary conditions, i.e. static pressures, were imposed in the carotid lumen and neovessels lumen respectively. Finite element method was used to simulate the mechanical conditions in the atherosclerotic plaque.

Results

Those neovessels closer to the carotid lumen undergo larger stress and stretch. With the same distance to the carotid lumen, the longer the perimeter of neovessels is, the larger stress and the deformation of the neovessels will be. Under the same conditions, the neovessels with larger curvature suffer greater stress and stretch. Neovessels surrounded by red blood cells undergo a much larger stretch.

Conclusions

Local mechanical conditions may result in the hemorrhage of neovessels and accelerate the rupture of plaque. The mechanical environments of the neovessel are related to its shape, curvature, distance to the carotid lumen and the material properties of plaque.

Adaptation of the main peripheral artery and vein to long term confinement (Mars 500)

Purpose

The objective was to check if 520 days in confinement (MARS 500), may affect the main peripheral arterial diameter and wall thickness and the main vein size.

Method

Common carotid (CC) femoral artery (FA) portal vein (PV), jugular (JG), femoral vein (FV) and tibial vein were assessed during MARS 500 by echography, performed by the subjects. A hand free volumic echographic capture method and a delayed 3D reconstruction software developed by our lab were used for collecting and measuring the vascular parameters.

Results

During the MARS 500 experiment the subjects performed 6 sessions among which 80% of the echographic data were of sufficient quality to be processed. No significant change was found for the Common carotid, Jugular vein, femoral artery, femoral vein, portal vein, and tibial vein diameter. CC and FA IMT (intima media thickness) were found significantly increased (14% to 28% P<0.05) in all the 6 subjects, during the confinement period and also at +2 days after the confinement period, but there was no significant difference 6 month later compare to pre MARS 500.

Conclusion

The experiment confirmed that even untrained to performing echography the subjects were able to capture enough echographic data to reconstruct the vessel image from which the parameters were measured. The increase in both CC and FA IMT should be in relation with the stress generated by the confined environment or absence of solar radiation, as there was no change in gravity, temperature and air in the MARS 500 module, and minor changes in physical exercise and nutrition.

Correlation between Doppler velocities and duplex ultrasound carotid cross-sectional percent stenosis

RATIONALE AND OBJECTIVES

Cross-sectional imaging is being increasingly proposed as a suitable tool to characterize carotid plaques. The aim of this work was to correlate the Doppler velocity parameters with the cross-sectional percent stenosis (CPoS) of internal carotid artery (ICA) and to identify the cutoff values of these parameters in five progressive classes of stenosis area severity (ie, 40%-49%, 50%-59%, 60%-69%, 70%-79%, 80%-90%).

MATERIALS AND METHODS

High-quality scans from 90 patients (mean age, 74 ± 9 years) with 43%-90% ICA stenosis were analyzed. ICA peak-systolic (PSV) and end-diastolic (EDV) velocities were measured at maximum stenosis level. Total ICA area and residual lumen (RL) were measured to derive the CPoS. A simple physical model described by the equation Velocity = Flow rate/Area was considered. Effectively, the CPoS is expected to negatively correlate with the inverse of velocity parameters, assuming flow rate to be constant. Multiple stepwise regression analyses were used to investigate the relationships between velocity and echographic measures.

RESULTS

With CPoS as the dependent variable, the first significant regressor was the inverse ICA-EDV (r(2) = 0.64; P < .0001) followed by inverse ICA-PSV (r(2) = 0.43; P < .0001). ICA-EDV mean values throughout five progressive classes of stenosis were: 28 cm/second for 40%-49% stenosis, 35 cm/second for 50%-59%, 43 cm/second for 60%-69%, 69 cm/second for 70%-79%. and 103 cm/second for 80%-90%. ICA-PSV mean values were: 97 cm/second for 40%-49%, 110 cm/second for 50%-59%, 136 cm/second for 60%-69%, 224 cm/second for 70%-79%, and 286 cm/second for 80%-90%.

CONCLUSION

ICA-EDV is the parameter that better correlates with CPoS. Nevertheless, ICA-PSV maintained a highly significant correlation with CPoS. Moreover, the categorization of Doppler parameters in five progressive classes of severity of stenosis could provide physicians with an easily accessible tool in clinical practice, complementary to the morphological evaluation of cross-sectional stenosis.

3D quantitative evaluation of atherosclerotic plaque based on rotational angiography

BACKGROUND AND PURPOSE

Atherosclerosis is a systemic disease that has been shown to cause various cardiovascular diseases and stroke. However, technologies to evaluate the volume of atherosclerotic plaque are limited. We present a method for determination of 3D plaque volume based on RA.

MATERIALS AND METHODS

3DRA images obtained from patients were used to evaluate the plaque. Six patients who were diagnosed with atherosclerotic lesions were included. The PR model developed for 3DRA was applied to analyze the geometry of the vessel and calculate the plaque volume. To validate the present method, we tested computer-generated phantoms with different degrees of stenosis.

RESULTS

Application of PR to clinical cases allowed the estimation of plaque morphology and quantification of plaque volume. Technique validation showed that on average, PR can rebuild 92% of the plaque and provide satisfactory determination of plaque volume.

CONCLUSIONS

A new approach to obtain plaque volume based on 3DRA is presented. The initial tests in 6 clinical cases and validation with different phantoms showed that this method is feasible. Further validation in a larger clinical series is required to assess the ultimate value of the present technique.