Narrow Results

A non-invasive method of measurement and analysis of the arterial input impedance of the carotid artery was applied to silicone models of the normal and stenosed carotid bifurcation. The experimental setup enabled the simulation of in vivo conditions. The experimental results were compared with impedance computed for a lumped element electrical model and a model containing transmission line elements. The stenosis resulted in increased impedance moduli and phase values. Similar phenomena were observed for both computational results. However, the transmission line model yielded phase plots closer to the experimental ones. The method of measurement and analysis of the arterial input impedance appears to be an efficient tool for the assessment of the properties of the carotid bifurcation.

The study presented in this paper is concerned with the analysis of the ultrasound Doppler signal of the arteries in the spectro-temporal domain using the wavelet packet transform. The spectro-temporal representation is obtained by the decomposition of the Doppler signal in frequency sub-band, using filter banks associated with a well chosen wavelet. It is shown that the decomposition level depends on the stationarity of the Doppler signal, and the best profile of blood flow velocity in arteries is obtained according to an appropriate choice of wavelet type.

Three types of wavelets have been tested on two Doppler signals previously recorded from the carotid and femoral arteries. The best representation is obtained when the frequency sub-bands of the filter bank associated with chosen wavelet are regularly distributed in the frequency domain and the level of decomposition is 7.

Objective. The aim of this paper is to show an algorithm for the automatic computer-based tracing (ACT) of common carotid artery (CCA) in longitudinal B-mode ultrasound images characterized by four main features: (i) user-independence; (ii) suitability to normal and pathological images; (iii) robustness to noise; and (iv) independent of ultrasound OEM scanner.

Methods. Three hundred longitudinal B-mode images (100 normal CCAs, 100 CCAs with increased intima-media thickness, 60 stable plaques, and 40 echolucent plaques) were acquired using three different (GE, Siemens, and Biosound) OEM ultrasound image scanners. The algorithm processed each image to delineate the region of interest containing the CCA. Output of the algorithm are three segmentation lines representing (a) distal (far) and (b) near adventitia layers, and (c) lumen of the CCA. Three operators qualitatively scored the ACTs.

Results. The CCA was correctly automatically traced in all the 300 B-mode images. The performance was independent on the image scanner used to acquire the image or on the type of the CCA (healthy versus pathologic). Eight ACTs out of 300 received a poor score after visual inspection due to an automated adventitia tracing that did not correctly follow the CCA wall in a small portion of the image.

Conclusions. The proposed algorithm is robust in ACTs of CCA since it is independent of scanner and normal/abnormal wall. This approach could constitute a general basis for a completely automated segmentation procedure.

Atherosclerosis, as the leading cause of mortality, is usually regarded as a systemic disease and several well-identified risk factors have been implicated in its pathogenesis. Low or highly oscillatory wall shear stress has mainly been linked to the development of atherosclerosis. Conditions under which human blood can be considered Newtonian for the purpose of arterial flow modeling are investigated with emphasis on near wall shear stresses. The Lattice Boltzmann method is implemented in parallel for both Newtonian and non-Newtonian models of blood and then examined in the context of steady and oscillatory flows. As the lattice method permits to adjust the morphology of the computational domain during the solving process, the artery walls are reshaped in a recursive manner by the progressive accumulation of deposits according to the conventional OSI criterion. Regions subjected to partial obstructions identified qualitatively well with those susceptible to atherosclerosis in the in vivo sample, thereby approving this criterion by verifying its accumulative effect. The present work demonstrates the suitability of LB method for studying flows across geometries that transform due to atherosclerotic progression and permits to explain the trend of deposit distribution across time.

Atherosclerotic plaque tends to occur and develop in carotid artery sinus, where stenoses and other lesions can cause cerebral disturbances. The hemodynamics and the platelet profiles in the carotid artery are simultaneously simulated in the present study to reveal the mechanism of the atherosclerotic plaque formation. Firstly, an unsteady PISO solver on unstructured tetrahedral grids is developed to simulate the hemodynamics of carotid artery bifurcation. And small platelets are treated as spherical solid particle described by Newtonian motion equation in the simulation, including inertial force, drag force, shear lift force, virtual mass force and pressure gradient force. Secondly, the visualization experiment for the platelet flow in the straight micro-channel is setup to validate the numerical model. Using the present method, the platelet flow in a carotid artery bifurcation is analyzed. The results show that the outer vascular wall near the bifurcation is more vulnerable in carotid artery sinus, which is mainly due to the lower wall shear stress (WSS) and platelets backflow in the region.

The further rupture of atherosclerotic ulceration plaque is one of the main triggers of the carotid ischemic stroke. However, the abnormal hemodynamics is not well addressed yet. A lesion-based computational fluid dynamic (CFD) analysis is proposed to investigate the complex hemodynamic change of the ulceration plaque that prevails in patients. The 3D models including eight groups of ulcerations (six groups with single ulceration and two groups with two consecutive ulcerations), were reconstructed based on the computer tomography (CT) images, and the tetrahedral grid was taken to mesh the models with the appropriate numbers. After setting the boundary conditions, numerical simulation was carried out to analyze the pulsatile blood flow in the models. The complex flow in the vicinity of the ulcerations directly leads to a significant effect on the distribution of the wall shear stress (WSS). WSS is respectively from 3.29 to 35.41 Pa at the upstream, from 11.90 to 41.85 Pa at the downstream ulceration, and 18.60 and 30.60 Pa in the area between the two consecutive ulcerations. The rupture from these regions could cause the further rupture of ulceration plaques, particularly at the downstream ulceration and the area between the two consecutive ulcerations. The twisting and the curling of the flow at the ulcerations can lead to thrombosis which may break free later and go through the downstream stenosis by the effect of the flow. The different degrees of WSS in downstream and upstream ulcerations will damage the ulceration on the plaque because of pulling and stretching forces at the ulcerations. Furthermore, high wall shear stress gradient (WSSG) also increases the risk of the further rupture. Our study gives a better understanding in the further rupture mechanism of ulceration plaques and provides the information of the location of thrombosis after aggravated rupturing, which can be referred by surgeons to improve the surgical planning.

Aim of this paper is to develop an automated system for the classification and characterization of carotid wall status and to develop a robust system based on local texture descriptors. A database of 200 longitudinal ultrasound images of carotid artery is used. One-hundred images with Intima-Media Thickness (IMT) value higher than 0.8mm are considered as high risk. Six different rectangular pixel neighborhoods were considered: four areas centered on the selected element, with sizes $7\times 15$, $15\times 7$, $7\times 3$, and $3\times 7$ pixels, and two noncentered areas with sizes $7\times 3$ pixels upwards and downwards. We have extracted various texture descriptors (31 based on the co-occurrence gray level matrix, 13 based on the spatial gray level dependence matrix, and 20 based on the gray level run length matrix (GLRLM) from neighborhood. We have used Quick Reduct Algorithm to select 12 most discriminant features from extracted 211 features. Each pixel is then assigned to the vessel lumen, to the intima-media complex, or to the adventitia by using an integrated system of three feed-forward neural networks. The boundaries between the three regions are used to estimate the IMT value. The texture features associated with GLRLM are found to be clinically most significant. We have obtained an overall classification accuracy of 79.5%, sensitivity of 87%, and specificity of 72%. We observed a unique classification pattern between low risk and high risk images: in the latter ones, a considerable number of pixels of the intima–media complex ($31.2\%\pm 14.4\%$) was classified as belonging to the adventitia. This percentage is statistically higher than that of low risk images ($18.2\%\pm 11.8\%$; $p<0.001$). Locally extracted and pixel-based descriptors are able to capture the inner characteristics of the carotid wall. The presence of misclassified pixels in the intima–media complex is associated to higher cardiovascular risk.

The aim of this paper is to evaluate the association between four simple B-mode image descriptors and age, to further assess the association between the descriptors and automated intima-media thickness (IMT) and intima-media thickness variability (IMTV) measurements, and finally analyze the predictive value of the B-mode image descriptors. A database of 1774 images of the carotid artery is used to manually calculate the contrast and the signal-to-noise ratio (SNR) between the (i) intima-media complex and lumen, and (ii) adventitial wall layer and intima-media complex. A subset of 200 images is then used to automatically measure the IMT and IMTV parameters with a previously developed algorithm. Correlation studies and logistic regression analysis are then performed. The contrast and SNR between the intima-media complex and lumen (contrast_IM and SNR_IM) are 112.691$\pm$247.427 and 19.542$\pm$6.236, respectively; whereas between the adventitial wall layer and intima-media complex the parameters (contrast_ADV and SNR_ADV) are found to be 1.684$\pm$1.182 and 32.859$\pm$10.766, respectively. Pearson’s rho is significantly different from zero considering the contrast_IM and the SNR_ADV descriptors when tested for the association with age. The automated IMT and IMTV measurements are 0.796$\pm$0.152mm and 0.096$\pm$0.044mm, respectively. Testing the association with the IMT and IMTV measurements yielded Pearson’s rho values which are significantly different from zero except in the case of contrast_IM for the IMTV measurement. The logistic regression results showed the IMTV measurement and the SNR descriptor between the intima-media complex and the lumen has a significant predictive value. Considering the association between the IMT and IMTV, the B-mode image descriptors showed a strong and statistically significant association. Moreover, the SNR between the intima-media complex and lumen is found to be a predictive variable in demonstrating its effectiveness as an image descriptor.

Certain systems relevant to circulatory disease have walls which are neither rigid nor static, for example, the coronary arteries, the carotid artery and the heart chambers. In vitro modeling allows the fluid mechanics of the circulatory system to be studied without the ethical and safety issues associated with animal and human experiments. Computational methods in which the equations are coupled governing the flow and the elastic walls are maturing. Currently there is a lack of experimental data in compliant arterial systems to validate the numerical predictions. Previous experimental work has commonly used rigid wall boundaries, ignoring the effect of wall compliance. Particle Image Velocimetry is used to provide a direct comparison of both the flow field and wall shear stress (WSS) observed in experimental phantoms of rigid and compliant geometries representing an idealized common carotid artery. The input flow waveform and the mechanical response of the phantom are physiologically realistic. The results show that compliance affects the velocity profile within the artery. A rigid boundary causes severe overestimation of the peak WSS with a maximum relative difference of 61% occurring; showing compliance protects the artery from exposure to high magnitude WSS. This is important when trying to understand the development of diseases like atherosclerosis. The maximum, minimum and time averaged WSS in the rigid geometry was 2.3, 0.51 and 1.03Pa and in the compliant geometry 1.4, 0.58 and 0.84Pa, respectively.

Stress concentration in carotid stenosis has been proven to assist plaque morphology in disease diagnosis and vulnerability. This work focuses on numerical analysis of stress and strain distribution in the cross-section of internal carotid artery using a 2D structure-only method. The influence of four different idealized plaque geometries (circle, ellipse, oval and wedge) is investigated. Numerical simulations are implemented utilizing linear elastic model along with four hyperelastic constitutive laws named neo-Hookean, Ogden, Yeoh and Mooney–Rivlin. Each case is compared to the real geometry. Results show significant strength of oval and wedged geometries in predicting stress and strain values. Our results emphasize that Yeoh and Ogden hyperelastic materials are more reliable in stress prediction with errors less than 3%. The same concept is observed in locating critical stresses where oval and wedged plaque geometries are the most accurate models. Similar results are observed in predicting maximum principal elastic strain with errors less than 1%. However, the strain distribution in idealized plaque models showed a considerable difference in comparison with real geometry.

Blood flow simulations can identify arterial regions that are vulnerable to atherosclerotic or thrombotic evolution. To accurately define vulnerable arterial regions, hemodynamic parameters such as arterial geometry, blood flow velocity and blood viscosity (BV) must be measured individually. However, previous numerical studies have largely employed either a single representative value or simply used a nonspecific curve of non-Newtonian characteristics of BV. This study aimed to evaluate whether various BV models could produce similar arterial wall shear stress (WSS) results. We performed a blood flow simulation in carotid arteries obtained from time-of-flight magnetic resonance (TOF MR) angiography using the hemodynamic characteristics of subjects via carotid duplex ultrasonography. The BV models were categorized into the following five types: patient-specific non-Newtonian BV (model 1), representative non-Newtonian BV based on the Carreau model (BV model 2), Newtonian BV measured at a specific shear rate of 300${\text{s}}^{-1}$ (BV model 3), Newtonian BV obtained from a hematocrit-based equation (BV model 4) and a representative Newtonian BV of 4cP (BV model 5). In total, 20 carotid arteries from 20 healthy volunteers (mean age $\pm$ SD of $63.5\pm 8.1$ years; 50% women) were examined. Compared with the mean values of carotid WSS in BV model 1 as the reference model, the other four models showed significant differences in both genders for all carotid segments. To obtain reliable physiological WSS results, patient-specific non-Newtonian BV should be carefully employed.

The carotid artery sinus is often the site of vascular diseases such as atherosclerosis, which may induce cerebral stroke. Individual differences in the carotid artery can lead to different possibilities for atherosclerosis, and the different hemodynamics of the carotid artery with stenosis can help to reveal the occurrence of atherosclerosis. In this work, the hemodynamics in the patient-specific carotid bifurcation are studied by using the modified Herschel–Bulkley model. Calculations show that the helical flow is presented in the healthy carotid sinus and disappears in the stenosed carotid sinus. The disappearance of helical flow in the carotid artery enhances the risk of atherosclerosis. The atherosclerotic lesion is more prone to occur in the distal portion of the carotid sinus than in the proximal portion where the oscillatory shear index (OSI) is also high. The presence of stenosis makes the atherosclerotic lesion develop toward the proximal portion. The disappearance of helical flow in the carotid artery is an important risk signal for the occurrence of atherosclerosis.

Stroke and heart attack, which could be led by a kind of cerebrovascular and cardiovascular disease named as atherosclerosis, would seriously cause human morbidity and mortality. It is important for the early stage diagnosis and monitoring medical intervention of the atherosclerosis. Carotid stenosis is a classical atherosclerotic lesion with vessel wall narrowing down and accumulating plaques burden. The carotid artery of intima-media thickness (IMT) is a key indicator to the disease. With the development of computer assisted diagnosis technology, the imaging techniques, segmentation algorithms, measurement methods, and evaluation tools have made considerable progress. Ultrasound imaging, being real-time, economic, reliable, and safe, now seems to become a standard in vascular assessment methodology especially for the measurement of IMT. This review firstly attempts to discuss the clinical relevance of measurements in clinical practice at first, and then followed by the challenges that one has to face when approaching the segmentation of ultrasound images. Secondly, the commonly used methods for the IMT segmentation and measurement are presented. Thirdly, discussion and evaluation of different segmentation techniques are performed. An overview of summary and future perspectives is given finally.

Carotid artery intima-media thickness (IMT) is used as an indicator of atherosclerosis and a risk predictor for stroke and cardiovascular diseases. In macroscopic view, the atherosclerotic process constitutes changes in structure and mechanical function of vessels. The aim of this study was to investigate the relationship between carotid IMT and elastic property, or compliance, of the vessel.

Eighteen patients (10 males, 8 females, mean age: 65.5+/−12.2) who received coronary angiography due to coronary artery disease (CAD) were enrolled in this study. The IMT was measured at left carotid artery 5 cm below bifurcation. The blood pressure was measured through a catheter placed in aortic arch and continuous pressure change was recorded simultaneously during performing of carotid sonography. A sequence of cross section images of carotid sonogram was recorded. An image analysis algorithm is developed for serial luminal area measurements. Then the estimation of compliance was computed according to Windkessel model.

Regression analysis shows negative correlation (r=−0.704) between IMT and vascular compliance. The results correlate the elastic property and structural change of carotid artery during the process of atherosclerosis. This finding further support that IMT is a good parameter for evaluation of the severity of atherosclerosis.