Carotid artery stenosis near a bifurcation investigated by fluid dynamic analyses

Patient-Specific Numerical Simulations of Coronary Artery Hemodynamics and Biomechanics: A Pathway to Clinical Use

PURPOSE

Numerical models that simulate the behaviors of the coronary arteries have been greatly improved by the addition of fluid-structure interaction (FSI) methods. Although computationally demanding, FSI models account for the movement of the arterial wall and more adequately describe the biomechanical conditions at and within the arterial wall. This offers greater physiological relevance over Computational Fluid Dynamics (CFD) models, which assume the walls do not move or deform. Numerical simulations of patient-specific cases have been greatly bolstered by the use of imaging modalities such as Computed Tomography Angiography (CTA), Magnetic Resonance Imaging (MRI), Optical Coherence Tomography (OCT), and Intravascular Ultrasound (IVUS) to reconstruct accurate 2D and 3D representations of artery geometries. The goal of this study was to conduct a comprehensive review on CFD and FSI models on coronary arteries, and evaluate their translational potential.

METHODS

This paper reviewed recent work on patient-specific numerical simulations of coronary arteries that describe the biomechanical conditions associated with atherosclerosis using CFD and FSI models. Imaging modality for geometry collection and clinical applications were also discussed.

RESULTS

Numerical models using CFD and FSI approaches are commonly used to study biomechanics within the vasculature. At high temporal and spatial resolution (compared to most cardiac imaging modalities), these numerical models can generate large amount of biomechanics data.

CONCLUSIONS

Physiologically relevant FSI models can more accurately describe atherosclerosis pathogenesis, and help to translate biomechanical assessment to clinical evaluation.

Macro- and microvascular contributions to cerebral structural alterations in patients with asymptomatic carotid artery stenosis

Atherosclerosis can underly internal carotid artery stenosis (ICAS), a major risk factor for ischemic stroke, as well as small vessel disease (SVD). This study aimed to investigate hemodynamics and structural alterations associated with SVD in ICAS patients. 28 patients with unilateral asymptomatic ICAS and 30 age-matched controls underwent structural (T1-/T2-weighted and diffusion tensor imaging [DTI]) and hemodynamic (pseudo-continuous arterial spin labeling and dynamic susceptibility contrast) magnetic resonance imaging. SVD-related alterations were assessed using free water (FW), FW-corrected DTI, and peak-width of skeletonized mean diffusivity (PSMD). Furthermore, cortical thickness, cerebral blood flow (CBF), and capillary transit time heterogeneity (CTH) were analyzed. Ipsilateral to the stenosis, cortical thickness was significantly decreased in the posterior dorsal cingulate cortex (p = 0.024) and temporal pole (p = 0.028). ICAS patients exhibited elevated PSMD (p = 0.005), FW (p < 0.001), and contralateral alterations in FW-corrected DTI metrics. We found significantly lateralized CBF (p = 0.011) and a tendency for lateralized CTH (p = 0.067) in the white matter (WM) related to ICAS. Elevated PSMD and FW may indicate a link between SVD and WM changes. Contralateral alterations were seen in FW-corrected DTI, whereas hemodynamic and cortical changes were mainly ipsilateral, suggesting SVD might influence global brain changes concurrent with ICAS-related hemodynamic alterations.

Multimodal imaging approach for the diagnosis of intracranial atherosclerotic disease (ICAD): Basic principles, current and future perspectives

PURPOSE

To review the different imaging modalities utilized in the diagnosis of Intracranial Atherosclerotic Disease (ICAD) including their latest development and relevance in management of ICAD.

METHODS

A review of the literature was conducted through a search in google scholar, PubMed/Medline, EMBASE, Scopus, clinical trials.gov and the Cochrane Library. Search terms included, "imaging modalities in ICAD," "ICAD diagnostic," "Neuroimaging of ICAD," "Evaluation of ICAD". A summary and comparison of each modality's basic principles, advantages and disadvantages were included.

RESULTS

A total of 144 articles were identified and reviewed. The most common imaging used in ICAD diagnoses were DSA, CTA, MRA and TCD. They all had proven accuracy, their own benefits, and limitations. Newer modalities such as VWI, IVUS, OCT, PWI and CFD provide more detailed information regarding the vessel walls, plaque characteristics, and flow dynamics, which play a tremendous role in treatment guidance. In certain clinical scenarios, using more than one modality has been shown to be helpful in ICAD identification. The rapidly evolving software related to imaging studies, such as virtual histology, are very promising for the diagnostic and management of ICAD.

CONCLUSIONS

ICAD is a common cause of recurrent ischemic stroke. Its management can be both medical and/or procedural. Many different imaging modalities are used in its diagnosis. In certain clinical scenario, a combination of two more modalities can be critical in the management of ICAD. We expect that continuous development of imaging technique will lead to individualized and less invasive management with adequate outcome.

Hemodynamic analysis of unilateral and bilateral renal artery stenosis based on fluid-structure interaction

Renal artery stenosis (RAS) hypertension is a common type of secondary hypertension. This paper aimed to explore how unilateral renal artery stenosis (Uni-RAS) and bilateral renal artery stenosis (Bi-RAS) caused renovascular hypertension with the fluid-structure interaction (FSI) method. Based on a real RAS model, 20 ideal models with different stenosis degrees were established by modifying the stenosis segment. The hemodynamic parameters at different degrees of stenosis, mass flow rate (MFR), pressure drop (PD), fractional flow reserve (FFR), oscillatory shear index (OSI), and relative residence time (RRT), were numerically calculated by the computational fluid dynamics (CFD) method. The numerical results showed that RAS caused the decrease of MFR, and the increase of PD and the proportion of high OSI and high RRT. In the case of RAS, it could not be regarded as a reference indicator for causing renovascular hypertension that the value of FFR was greater than 0.9. In addition, the results of the statistical analysis indicated that Uni-RAS and Bi-RAS were statistically different for MFR, PD and the proportion of high RRT.

Development of a Model for Plaque Induction in Rat Carotid Arteries

Objective  Plaque induction through intimal injury using a balloon catheter in small animals and by artificial ligation of the carotid artery in large animals have been reported. However, these reports have not yet succeeded in inducing stable plaques nor creating a high degree of intimal thickening to be used as animal models. We have previously developed a plaque induction model in rats but have failed to obtain a plaque incidence frequency that can be used as a model. Thus, in the current study, we aimed to create a versatile disease model to examine the pharmacokinetics of drug administration, determine the efficacy of treatment, and examine the process of intimal thickening. We also attempted to create an improved model with shorter, more frequent, and more severe intimal thickening. Materials and Methods  The common carotid artery of male Wistar rats was surgically exposed and completely ligated with a wire and 6-0 nylon thread. Then, the wire was removed to create a partial ligation. To create a high frequency and high degree of intimal thickening, 72 rats were divided into two groups: a single lesion group with a 0.25-mm wire and a single ligature point, and a tandem lesion group with a 0.3-mm wire and two ligature points. Each group was further divided into normal diet and high cholesterol diet groups. The presence and frequency of intimal thickening were examined for each group after 4, 8, and 16 weeks of growth. Results  In the single lesion group, intimal thickening was observed in 42% of the 4-week group and 75% of the 8-week group. In the tandem lesion group, intimal thickening was observed in 75% of the 4-week group and 50% of the 8-week group. In addition, 50% of the individuals reared for 16 weeks developed intimal thickening. Conclusion  We successfully induced intimal thickening in the carotid arteries of rats with high frequency in the single lesion and tandem lesion groups. The results also showed that the tandem lesion group tended to induce intimal thickening earlier than the single lesion group.

Relationship Between Carotid Artery Angle and Plaque Morphology in Acute Cerebral Infarction Patients

BACKGROUND

High-resolution magnetic resonance imaging (HRMRI) can be used to clearly distinguish the luminal structure of the carotid artery (CA); measure the lumen, vessel wall, and total blood vessel area; and accurately describe the morphologic features of plaques.

METHODS

This study used HRMRI to investigate the relationship between geometric features and volume and composition of carotid atherosclerotic plaques. Patients (n=81) who had experienced acute cerebral infarction (CI) within 7±3 days before admission to the Neurology Department of Beijing Tiantan Hospital between November 2011 and June 2012 were enrolled in the study. CA HRMRI was performed to analyze the geometry and morphology of plaques in 160 blood vessels.

RESULTS

The median left and right internal carotid artery angles (ICAAs) were 32.79 and 31.00 degrees, respectively. Aside from the nonplanar external CA angle, plaque volume and angles did not differ significantly between the left and right sides. Age ( B =3.77; P =0.03) and nonplanar ICAA ( B =4.70; P =0.01) were predictors of left but not right carotid plaque volume. ICAA and bifurcation angle did not predict plaque volume.

CONCLUSIONS

In this study, CA morphology in acute stroke patients is not associated with plaque volume or composition, but age and nonplanar ICAA can predict left carotid plaque volume.

Correlation between Carotid Stenosis Degree and Blood Pressure Variability in Patients with Carotid Stenosis

Background

Carotid artery stenosis is one of the most serious diseases that endanger human health in contemporary times. It is a frequently occurring and common disease of the middle-aged and elderly people. Its incidence is increasing year by year, bringing a heavy economic burden to society and families. Whether there is a relationship between the degree of carotid artery stenosis and blood pressure variability is less studied.

Aims

To investigate the correlation between the degree of carotid stenosis and blood pressure variability in patients with carotid stenosis.

Materials and Methods

A total of 200 patients with carotid artery stenosis who were treated in our hospital from January 2017 to January 2020 were selected as the subjects of prospective study and were divided into mild stenosis according to the degree of carotid stenosis (carotid artery stenosis rate was 0-50%), moderate stenosis (carotid artery stenosis rate was between 50% and 70%), severe stenosis (carotid artery stenosis rate≧70%), and the control group with 50 cases each. The correlations between the hemodynamics, the degree of carotid artery stenosis, and blood pressure variability in patients with carotid artery stenosis were analyzed.

Results

The levels of 24hSSD, 24hDSD, dSSD, dDSD, and nSSD in the mild stenosis group and moderate stenosis group were significantly higher than those in the control group. In the stenosis group, the levels of 24hSSD, 24hDSD, dSSD, dDSD, and nSSD in the severe stenosis group were significantly higher than those in the moderate stenosis group, with statistical significance (P < 0.05). The levels of PSV, EDV, and MV in the mild stenosis group and moderate stenosis group were lower than those in the control group, while the PI and RI indexes were higher than those in the control group. PI and RI levels were significantly higher than those in the mild stenosis group and moderate stenosis group (P < 0.05). Logistic analysis showed that EDV (P = 0.001, OR = 2.245, 95%CI = 1.638 ~ 3.078), SSD (P = 0.014, OR = 0.725, 95%CI = 0.528 ~ 0.996), and PSV (P = 0.001, OR = 1.970, 95%CI = 1.300 ~ 2.990) were closely related to the degree of carotid artery stenosis.

Conclusion

Hemodynamics and blood pressure variability are related to the severity of carotid stenosis, which provides a reference and basis for clinical treatment of carotid stenosis.

A significant role of permeability on blood flow for hybrid nanofluid through bifurcated stenosed artery: Drug delivery application

OBJECTIVE

The prime objective of concerned article is to discuss the permeability impacts on blood flow by considering hybrid nanofluid through bifurcated stenosed artery.

DESIGN/APPROACH

The human body circulatory framework involves the arrangement of veins that fuse the bifurcation on parent, at apex and on regions of daughter artery with nanoparticles is viewed. Blood streaming is recognized as Newtonian along vessel segment. The walls of the stenosed bifurcated artery is considered to be permeable as well as compliant. Copper and its oxide as used as drug to minimize the stress and the lesions of the atherosclerotic artery.

FINDINGS

The theoretical investigation is carried out by invoking the experimental values of hybrid nanoparticles into the structured equations. Moreover, impacts of hemodynamics are also make sense of to inspect the progression of blood for atherosclerotic vein. Daughter and parent artery comparison is described through parabolic graph of velocity. Graphical illustration is utilized to present the theoretical results of this drug delivery model. Metallic nanoparticles justify their use in drug delivery.

CONCLUSIONS

The flow of blood is viewed as not quite the same as pressure between segments of atherosclerotic and non-atherosclerotic course. Bifurcation angle minimize the stress for daughter artery whereas trend is opposite for parent daughter. The change in compliant wall parameter reduces the circulating bolus size for parent daughter whereas for daughter artery the change in bolus shape is observed.

Hallux valgus (HV): A multi-approach investigation analysis

Objective

this study aims to develop a 3D FE model of the foot suffering from valgus hallux in order to investigate the plantar pressure distributions between bony structures.

Methods

in a first phase a baropodometric analysis was performed, successively a FE analysis was performed comparing results and obtaining information on the stress shielding.

Results

the valgus hallux deforms the correct spreading of the stress inside the bony structures causing an overloading of pressure located on the hallux and downloading the other toes.

Conclusion

This comparative study can furnish important indications about the distribution of the stress patterns on the foot.

The stronger one-sided relative hypoperfusion, the more pronounced ipsilateral spatial attentional bias in patients with asymptomatic carotid stenosis

Patients with asymptomatic, high-grade internal carotid artery stenosis often suffer from subtle cognitive impairments with unclear underlying neuro-cognitive mechanisms. Thus, we hypothesized that stenosis-related unilateral cerebral hypoperfusion leads to an ipsilateral attentional bias; 22 patients with asymptomatic, one-sided high-grade carotid stenosis and 24 age-matched healthy controls underwent pseudo-continuous arterial spin labeling to assess brain perfusion in the territory of the carotid arteries. Furthermore, a parametric assessment of attention functions was carried out on the basis of the computational Theory of Visual Attention. Both patients' perfusion and spatial attention were significantly more lateralized than those of healthy controls. Critically, both asymmetry indices were significantly correlated in patients, i.e. the stronger one-sided relative hypoperfusion, the stronger ipsilateral bias of attention. This association was specifically pronounced in parietal cortices and independent of white matter hyperintensities as a surrogate for cerebrovascular brain damage. Results provide evidence for a link between lateralized hypoperfusion and lateralized attentional weighting in asymptomatic, high-grade carotid stenosis. Data suggest that lateralized hypoperfusion with simultaneous spatial attentional bias might serve as a potential therapeutic target in one-sided carotid stenosis.

Flow-metabolism uncoupling in patients with asymptomatic unilateral carotid artery stenosis assessed by multi-modal magnetic resonance imaging

Oxygen extraction (OEF), oxidative metabolism (CMRO₂), and blood flow (CBF) in the brain, as well as the coupling between CMRO₂ and CBF due to cerebral autoregulation are fundamental to brain's health. We used a clinically feasible MRI protocol to assess impairments of these parameters in the perfusion territories of stenosed carotid arteries. Twenty-nine patients with unilateral high-grade carotid stenosis and thirty age-matched healthy controls underwent multi-modal MRI scans. Pseudo-continuous arterial spin labeling (pCASL) yielded absolute CBF, whereas multi-parametric quantitative blood oxygenation level dependent (mqBOLD) modeling allowed imaging of relative OEF and CMRO₂. Both CBF and CMRO₂ were significantly reduced in the stenosed territory compared to the contralateral side, while OEF was evenly distributed across both hemispheres similarly in patients and controls. The CMRO₂-CBF coupling was significantly different between both hemispheres in patients, i.e. significant interhemispheric flow-metabolism uncoupling was observed in patients compared to controls. Given that CBF and CMRO₂ are intimately linked to brain function in health and disease, the proposed easily applicable MRI protocol of pCASL and mqBOLD imaging might serve as a valuable tool for early diagnosis of potentially harmful cerebral hemodynamic and metabolic states with the final aim to select clinically asymptomatic patients who would benefit from carotid revascularization therapy.

Stress shielding analysis on easy step staple prosthesis for calcaneus fractures

Objective

The calcaneus is the most frequently injured tarsal bone, with calcaneal fractures meaning that 60% of the fractures affect the foot and about 1%-2% of all fractures.

Methods

Two 3D FE model of the foot were realized in order to compare the stress shielding occurring in a health foot and in a fractured one implanted with an easy step prosthesis by Stryker. This dispositive is indicated for calcaneus fractures.

Results

Results evidence the efficacy of this kind of prosthesis as the Eq. Von mises stresses are comparable in the two model. Higher concentration of stress are concentered on the Easy step.

Conclusion

In conclusion, the easy step staple prosthesis allows obtaining excellent results in terms of calcaneus fracture treatments. The correct implant size for a given patient can be determined by evaluating the patient's height, weight, functional demands and anatomy.

Stress shielding FE analysis on the temporomandibular joint

Aims

The purpose of this study is to develop a FE model of the temporomandibular joint (TMJ) to investigate a musculoskeletal System of forces able to taking into account the effect of all the muscles on the TMJ in terms of stress evaluated on the bone.

Methods

A 3-dimensional finite element model of the mandible was constructed from the images generated by cone-beam computed tomography of a patient undergoing fixed orthodontic treatment. In order to define the loading force system an exustive study was developed to investigated the entity of the Lateral pterygoid, Masseter, medial pterygoid, Temporalis, and Geniohoid digastric, muscles.

Results

Stresses in the TMJ components (disc, mandible condyle and the fossa eminence on the skull) were obtained. The results have shown stress distribution during normal occlusion.

Conclusion

An appreciation of the anatomical and mechanical features associated with the TMJ can serve as a foundation for understanding a patient's clinical presentation. Performance of a thorough patient history and clinical examination can guide the clinician toward an improved diagnostic process.

Geometric determinants of local hemodynamics in severe carotid artery stenosis

In cases of severe carotid artery stenosis (CAS), carotid endarterectomy (CEA) is performed to recover lumen patency and alleviate stroke risk. Under current guidelines, the decision to surgically intervene relies primarily on the percent loss of native arterial lumen diameter within the stenotic region (i.e. the degree of stenosis). An underlying premise is that the degree of stenosis modulates flow-induced wall shear stress elevations at the lesion site, and thus indicates plaque rupture potential and stroke risk. Here, we conduct a retrospective study on pre-CEA computed tomography angiography (CTA) images from 50 patients with severe internal CAS (>60% stenosis) to better understand the influence of plaque and local vessel geometry on local hemodynamics, with geometrical descriptors that extend beyond the degree of stenosis. We first processed CTA images to define a set of multipoint geometric metrics characterizing the stenosed region, and next performed computational fluid dynamics simulations to quantify local wall shear stress and associated hemodynamic metrics. Correlation and regression analyses were used to relate obtained geometric and hemodynamic metrics, with inclusion of patient sub-classification based on the degree of stenosis. Our results suggest that in the context of severe CAS, prediction of shear stress-based metrics can be enhanced by consideration of readily available, multipoint geometric metrics in addition to the degree of stenosis.

Design of a microfluidic chip consisting of micropillars and its use for the enrichment of nasopharyngeal cancer cells

The aim of the present study was to discuss the design of a microfluidic chip consisting of columns, and its use for the enrichment of nasopharyngeal cancer (NPC) cells. A microfluidic chip experiment was simulated using FLUENT software. Within the microfluidic chip, aptamers were bound to the reaction chamber (consisting of columns) using a biotin-avidin system. Cell suspension was introduced into the reaction chamber to capture NPC cells. NPC cells were subsequently eluted, and the capture rate of the cells was calculated. The modified aptamer-bound microfluidic chip was able to capture NPC cells with a capture rate of ~90%. The modified aptamer-bound microfluidic chip has a wide range of potential applications for the diagnosis of NPC.

Cerebral arteriovenous malformation venous stenosis is associated with hemodynamic changes at the draining vein-venous sinus junction

Cerebral arteriovenous malformations (AVMs) are an uncommon vascular anomaly that carry the risk of rupture and hemorrhage. Several factors have been implicated in the propensity of an AVM to bleed. One such factor is stenosis of AVM draining veins, as impairment of the AVM venous drainage system is associated with increased risk of intracranial hemorrhage. Currently, our understanding of the pathogenesis of AVM venous outflow stenosis is limited, as there is insufficient data on the blood flow patterns and local hemodynamic parameters of these draining veins. The angioarchitecture of AVMs features a nidus lacking a high resistance capillary network. Accordingly, our previous studies on AVM arterial feeders have demonstrated an abnormally high flow volume rate along with low pulsatility and resistance indices on quantitative magnetic resonance angiography. As such, AVM vessels endure high, non-physiologic levels of flow that may partially contribute to ectasia or stenosis depending on whether wall shear stress (WSS) is high or low, respectively. We hypothesize that AVM venous outflow stenosis occurs most commonly near the junction of the draining vein and the dural venous sinus. Increased flow volume rate through the AVM circuit coupled with the variation in compliance and rigidity between the walls of the draining vein and the dural venous sinus likely create turbulence of blood flow. The resulting flow separation, low WSS, and departure from axially aligned, unidirectional flow may create atherogenic conditions that can be implicated in venous intimal hyperplasia and outflow stenosis. We have previously found there to be a significant association between intimal hyperplasia risk factors and venous outflow stenosis. Additionally, we have found a significant association between age and likelihood as well as degree of stenosis, suggesting a progressive disease process. Similar conditions have been demonstrated in the pathophysiology of stenosis of the carotid artery and dialysis arteriovenous fistulas. In both of these conditions, the use of computational fluid dynamics (CFD) has been employed to characterize the local hemodynamic features that contribute to the pathogenesis of intimal hyperplasia and stenosis. We recommend the utilization of CFD to characterize the anatomic and hemodynamic features of AVM venous outflow stenosis. An improved understanding of the possible causative features of venous outflow stenosis may impact how clinicians choose to manage the treatment of patients with AVMs.

Computational Fluid Dynamics as an Engineering Tool for the Reconstruction of Hemodynamics after Carotid Artery Stenosis Operation: A Case Study

Background and objectives: Brain ischemic stroke is caused by impaired or absolutely blocked blood flow into the brain regions. Despite the large number of possible origins, there is no general strategy for preventive treatment. In this paper, we aimed to predict the hemodynamics in a patient who experienced a critical stenosis operation in the carotid artery. This is a unique study where we used medical data together with the computational fluid (CFD) technique not to plan the surgery, but to predict its outcome. Materials and Methods: AngioCT data and blood perfusion of brain tissue (CT-perfusion) together with CFD technique were applied for stroke formation reconstruction in different clinical conditions. With the use of self-made semiautomatic algorithm for image processing and 3DDoctror software, 3D-vascular geometries before and after surgical intervention were reconstructed. As the paper is focused on the analysis of stroke appearance, apparent stroke was simulated as higher and lower pressure values in the cranial part due to different outcomes of the surgical intervention. This allowed to investigate the influence of spatial configuration and pressure values on blood perfusion in the analyzed circulatory system. Results: Application of CFD simulations for blood flow reconstruction for clinical conditions in the circulatory system accomplished on average 98.5% and 98.7% accuracy for CFD results compared to US-Doppler before and after surgical intervention, respectively. Meanwhile, CFD results compared to CT-perfusion indicated an average 89.7% and 92.8% accuracy before and after surgical intervention, respectively. Thus, the CFD is a reliable approach for predicting the patient hemodynamics, as it was confirmed by postoperative data. Conclusions: Our study indicated that the application of CFD simulations for blood flow reconstruction for clinical conditions in circulatory system reached 98% and 90% accuracy for US-Doppler and CT-perfusion, respectively. Therefore, the proposed method might be used as a tool for reconstruction of specific patients' hemodynamics after operation of critical stenosis in the carotid artery. However, further studies are necessary to confirm its usefulness in clinical practice.

Hemodynamics in Transplant Renal Artery Stenosis and its Alteration after Stent Implantation Based on a Patient-specific Computational Fluid Dynamics Model

Background:

Accumulating studies on computational fluid dynamics (CFD) support the involvement of hemodynamic factors in artery stenosis. Based on a patient-specific CFD model, the present study aimed to investigate the hemodynamic characteristics of transplant renal artery stenosis (TRAS) and its alteration after stent treatment.

Methods:

Computed tomography angiography (CTA) data of kidney transplant recipients in a single transplant center from April 2013 to November 2014 were reviewed. The three-dimensional geometry of transplant renal artery (TRA) was reconstructed from the qualified CTA images and categorized into three groups: the normal, stenotic, and stented groups. Hemodynamic parameters including pressure distribution, velocity, wall shear stress (WSS), and mass flow rate (MFR) were extracted. The data of hemodynamic parameters were expressed as median (interquartile range), and Mann–Whitney U-test was used for analysis.

Results:

Totally, 6 normal, 12 stenotic, and 6 stented TRAs were included in the analysis. TRAS presented nonuniform pressure distribution, adverse pressure gradient across stenosis throat, flow vortex, and a separation zone at downstream stenosis. Stenotic arteries had higher maximal velocity and maximal WSS (2.94 [2.14, 3.30] vs. 1.06 [0.89, 1.15] m/s, 256.5 [149.8, 349.4] vs. 41.7 [37.8, 45.3] Pa at end diastole, P = 0.001; 3.25 [2.67, 3.56] vs. 1.65 [1.18, 1.72] m/s, 281.3 [184.3, 364.7] vs. 65.8 [61.2, 71.9] Pa at peak systole, P = 0.001) and lower minimal WSS and MFRs (0.07 [0.03, 0.13] vs. 0.52 [0.45, 0.67] Pa, 1.5 [1.0, 3.0] vs. 11.0 [8.0, 11.3] g/s at end diastole, P = 0.001; 0.08 [0.03, 0.19] vs. 0.70 [0.60, 0.81] Pa, 2.0 [1.3, 3.3] vs. 16.5 [13.0, 20.3] g/s at peak systole, P = 0.001) as compared to normal arteries. Stent implantation ameliorated all the alterations of the above hemodynamic factors except low WSS.

Conclusions:

Hemodynamic factors were significantly changed in severe TRAS. Stent implantation can restore or ameliorate deleterious change of hemodynamic factors except low WSS at stent regions.

Accurate lumen diameter measurement in curved vessels in carotid ultrasound: an iterative scale-space and spatial transformation approach

Monitoring of cerebrovascular diseases via carotid ultrasound has started to become a routine. The measurement of image-based lumen diameter (LD) or inter-adventitial diameter (IAD) is a promising approach for quantification of the degree of stenosis. The manual measurements of LD/IAD are not reliable, subjective and slow. The curvature associated with the vessels along with non-uniformity in the plaque growth poses further challenges. This study uses a novel and generalized approach for automated LD and IAD measurement based on a combination of spatial transformation and scale-space. In this iterative procedure, the scale-space is first used to get the lumen axis which is then used with spatial image transformation paradigm to get a transformed image. The scale-space is then reapplied to retrieve the lumen region and boundary in the transformed framework. Then, inverse transformation is applied to display the results in original image framework. Two hundred and two patients' left and right common carotid artery (404 carotid images) B-mode ultrasound images were retrospectively analyzed. The validation of our algorithm has done against the two manual expert tracings. The coefficient of correlation between the two manual tracings for LD was 0.98 (p < 0.0001) and 0.99 (p < 0.0001), respectively. The precision of merit between the manual expert tracings and the automated system was 97.7 and 98.7%, respectively. The experimental analysis demonstrated superior performance of the proposed method over conventional approaches. Several statistical tests demonstrated the stability and reliability of the automated system.

Two Automated Techniques for Carotid Lumen Diameter Measurement: Regional versus Boundary Approaches

The degree of stenosis in the carotid artery can be predicted using automated carotid lumen diameter (LD) measured from B-mode ultrasound images. Systolic velocity-based methods for measurement of LD are subjective. With the advancement of high resolution imaging, image-based methods have started to emerge. However, they require robust image analysis for accurate LD measurement. This paper presents two different algorithms for automated segmentation of the lumen borders in carotid ultrasound images. Both algorithms are modeled as a two stage process. Stage one consists of a global-based model using scale-space framework for the extraction of the region of interest. This stage is common to both algorithms. Stage two is modeled using a local-based strategy that extracts the lumen interfaces. At this stage, the algorithm-1 is modeled as a region-based strategy using a classification framework, whereas the algorithm-2 is modeled as a boundary-based approach that uses the level set framework. Two sets of databases (DB), Japan DB (JDB) (202 patients, 404 images) and Hong Kong DB (HKDB) (50 patients, 300 images) were used in this study. Two trained neuroradiologists performed manual LD tracings. The mean automated LD measured was 6.35 ± 0.95 mm for JDB and 6.20 ± 1.35 mm for HKDB. The precision-of-merit was: 97.4 % and 98.0 % w.r.t to two manual tracings for JDB and 99.7 % and 97.9 % w.r.t to two manual tracings for HKDB. Statistical tests such as ANOVA, Chi-Squared, T-test, and Mann-Whitney test were conducted to show the stability and reliability of the automated techniques.

MODELING BLOOD FLOW IN AN ECCENTRIC STENOSED ARTERY USING LARGE EDDY SIMULATION AND PARALLEL COMPUTING

Computational fluid dynamics (CFD) is an excellent computational tool to assess the hemodynamics and detailed blood-flow structure for cardiovascular applications. Modeling turbulence for cardiovascular applications can be achieved (to some extent) using available numerical models such as Reynolds average Navier–Stokes (RANS), the large eddy simulation (LES) and the direct numerical solution (DNS). In order to develop an efficient model which is as accurate as DNS and as quick as RANS, our laboratory's focus is on LES. In this study, we develop an efficient numerical model which is based on LES and structured but non-orthogonal finite volumes. Using the proposed model, the detailed flow structure and turbulent features of the blood stream in a complicated geometry is captured. The aim of this study is to model blood-flow through an eccentric stenosis accurately and quickly. The results are similar to those obtained using DNS but in a fraction of the CPU time. The computational tools implemented in this study are based on a FORTRAN based in-house code coupled with parallel computing using SHARCNET. The developed model is a significant computational tool which can be used to assess the hemodynamic properties for cardiovascular applications, e.g., prosthetic heart valves and atherosclerosis.