Aortic dissection simulation models for clinical support: fluid-structure interaction vs. rigid wall models.

BACKGROUND: The management and prognosis of aortic dissection (AD) is often challenging and the use of personalised computational models is being explored as a tool to improve clinical outcome. Including vessel wall motion in such simulations can provide more realistic and potentially accurate results, but requires significant additional computational resources, as well as expertise. With clinical translation as the final aim, trade-offs between complexity, speed and accuracy are inevitable. The present study explores whether modelling wall motion is worth the additional expense in the case of AD, by carrying out fluid-structure interaction (FSI) simulations based on a sample patient case. METHODS: Patient-specific anatomical details were extracted from computed tomography images to provide the fluid domain, from which the vessel wall was extrapolated. Two-way fluid-structure interaction simulations were performed, with coupled Windkessel boundary conditions and hyperelastic wall properties. The blood was modelled using the Carreau-Yasuda viscosity model and turbulence was accounted for via a shear stress transport model. A simulation without wall motion (rigid wall) was carried out for comparison purposes. RESULTS: The displacement of the vessel wall was comparable to reports from imaging studies in terms of intimal flap motion and contraction of the true lumen. Analysis of the haemodynamics around the proximal and distal false lumen in the FSI model showed complex flow structures caused by the expansion and contraction of the vessel wall. These flow patterns led to significantly different predictions of wall shear stress, particularly its oscillatory component, which were not captured by the rigid wall model. CONCLUSIONS: Through comparison with imaging data, the results of the present study indicate that the fluid-structure interaction methodology employed herein is appropriate for simulations of aortic dissection. Regions of high wall shear stress were not significantly altered by the wall motion, however, certain collocated regions of low and oscillatory wall shear stress which may be critical for disease progression were only identified in the FSI simulation. We conclude that, if patient-tailored simulations of aortic dissection are to be used as an interventional planning tool, then the additional complexity, expertise and computational expense required to model wall motion is indeed justified.

Evaluation of the Frequency and Anatomy of Radix Entomolaris and Paramolaris in Lower Molars by Cone Beam Computed Tomography (CBCT) in Northern Iran, 2020-2021: A Retrospective Study.

INTRODUCTION AND OBJECTIVE: The presence of an additional root, known as a radix, in the lower molars is of significant importance in the context of root canal therapy since it has the potential to contribute to treatment failure. Furthermore, it is imperative to take this circumstance into consideration when doing tooth extraction using a radix. The present study investigated the anatomical characteristics and prevalence rates of radix entomolaris and paramolaris in mandibular molars using cone beam computed tomography. MATERIALS AND METHODS: Cone beam computed tomography scans of the lower molars of 376 patients were processed through Newtom's NNT viewer software. Radix type, radix root canal length, radix root curvature, Vertucci's classification of the canal, and gender of patients were recorded. The results of the research were analyzed with chi-squared. RESULTS: The prevalence of radix was found to be 0.74%, with entomolaris and paramolaris present in 54.54% and 45.46% of cases, respectively. There was no statistically significant difference between the two variables of radix type and gender, as indicated by a p-value of 0.08. The mean curvature and length of the radix root were measured to be 56.63° and 15.09 mm, respectively. The average root curvature in individuals diagnosed with radix entomolaris and paramolaris was found to be 62.33° and 49.80°, respectively. The study found that the root curvature of entomolaris exhibited a statistically significant difference compared to paramolaris (P=0.031). The mean length of the radix entomolaris and paramolaris roots was found to be 15.50 and 14.60 mm, respectively. There was no statistically significant difference observed in the mean root lengths of the various radix types (P=0.37). According to Vertucci's classification, all radixes were classified as type 1. CONCLUSION: The investigated population had a low incidence of radix. The curvature of radix entomolaris exhibited a statistically significant increase compared to radix paramolaris. There was no observed correlation between gender and the length of radix roots in relation to the type of radix root.

In-silico investigations of haemodynamic parameters for a blunt thoracic aortic injury case.

Accounting for 1.5% of thoracic trauma, blunt thoracic aortic injury (BTAI) is a rare disease with a high mortality rate that nowadays is treated mostly via thoracic endovascular aortic repair (TEVAR). Personalised computational models based on fluid-solid interaction (FSI) principals not only support clinical researchers in studying virtual therapy response, but also are capable of predicting eventual outcomes. The present work studies the variation of key haemodynamic parameters in a clinical case of BTAI after successful TEVAR, using a two-way FSI model. The three-dimensional (3D) patient-specific geometries of the patient were coupled with three-element Windkessel model for both prior and post intervention cases, forcing a correct prediction of blood flow over each section. Results showed significant improvement in velocity and pressure distribution after stenting. High oscillatory, low magnitude shear (HOLMES) regions require careful examination in future follow-ups, since thrombus formation was confirmed in some previously clinically reported cases of BTAI treated with TEVAR. The strength of swirling flows along aorta was also damped after stent deployment. Highlighting the importance of haemodynamic parameters in case-specific therapies. In future studies, compromising motion of aortic wall due to excessive cost of FSI simulations can be considered and should be based on the objectives of studies to achieve a more clinical-friendly patient-specific CFD model.

The effect of beta-blockers on hemodynamic parameters in patient-specific blood flow simulations of type-B aortic dissection: a virtual study.

Aortic dissection (AD) is one of the fatal and complex conditions. Since there is a lack of a specific treatment guideline for type-B AD, a better understanding of patient-specific hemodynamics and therapy outcomes can potentially control the progression of the disease and aid in the clinical decision-making process. In this work, a patient-specific geometry of type-B AD is reconstructed from computed tomography images, and a numerical simulation using personalised computational fluid dynamics (CFD) with three-element Windkessel model boundary condition at each outlet is implemented. According to the physiological response of beta-blockers to the reduction of left ventricular contractions, three case studies with different heart rates are created. Several hemodynamic features, including time-averaged wall shear stress (TAWSS), highly oscillatory, low magnitude shear (HOLMES), and flow pattern are investigated and compared between each case. Results show that decreasing TAWSS, which is caused by the reduction of the velocity gradient, prevents vessel wall at entry tear from rupture. Additionally, with the increase in HOLMES value at distal false lumen, calcification and plaque formation in the moderate and regular-heart rate cases are successfully controlled. This work demonstrates how CFD methods with non-invasive hemodynamic metrics can be developed to predict the hemodynamic changes before medication or other invasive operations. These consequences can be a powerful framework for clinicians and surgical communities to improve their diagnostic and pre-procedural planning.

The effect of coarctation degrees on wall shear stress indices.

Coarctation of the aorta (CoA) is a congenital tightening of the proximal descending aorta. Flow quantification can be immensely valuable for an early and accurate diagnosis. However, there is a lack of appropriate diagnostic approaches for a variety of cardiovascular diseases, such as CoA. An accurate understanding of the disease depends on measurements of the global haemodynamics (criteria for heart function) and also the local haemodynamics (detailed data on the dynamics of blood flow). Playing a significant role in clinical processes, wall shear stress (WSS) cannot be measured clinically; thus, computation tools are needed to give an insight into this crucial haemodynamic parameter. In the present study, in order to enable the progress of non-invasive approaches that quantify global and local haemodynamics for different CoA severities, innovative computational blueprint simulations that include fluid-solid interaction models are developed. Since there is no clear approach for managing the CoA regarding its severity, this study proposes the use of WSS indices and pressure gradient to better establish a framework for treatment procedures in CoA patients with different severities. This provides a platform for improving CoA therapy on a patient-specific level, in which physicians can perform treatment methods based on WSS indices on top of using a mere experience. Results show how severe CoA affects the aorta in comparison to the milder cases, which can give the medical community valuable information before and after any intervention.

A simplified method to account for wall motion in patient-specific blood flow simulations of aortic dissection: Comparison with fluid-structure interaction.

Aortic dissection (AD) is a complex and highly patient-specific vascular condition difficult to treat. Computational fluid dynamics (CFD) can aid the medical management of this pathology, yet its modelling and simulation are challenging. One aspect usually disregarded when modelling AD is the motion of the vessel wall, which has been shown to significantly impact simulation results. Fluid-structure interaction (FSI) methods are difficult to implement and are subject to assumptions regarding the mechanical properties of the vessel wall, which cannot be retrieved non-invasively. This paper presents a simplified 'moving-boundary method' (MBM) to account for the motion of the vessel wall in type-B AD CFD simulations, which can be tuned with non-invasive clinical images (e.g. 2D cine-MRI). The method is firstly validated against the 1D solution of flow through an elastic straight tube; it is then applied to a type-B AD case study and the results are compared to a state-of-the-art, full FSI simulation. Results show that the proposed method can capture the main effects due to the wall motion on the flow field: the average relative difference between flow and pressure waves obtained with the FSI and MBM simulations was less than 1.8% and 1.3%, respectively and the wall shear stress indices were found to have a similar distribution. Moreover, compared to FSI, MBM has the advantage to be less computationally expensive (requiring half of the time of an FSI simulation) and easier to implement, which are important requirements for clinical translation.

A multiscale modelling approach to understand atherosclerosis formation: A patient-specific case study in the aortic bifurcation.

Atherogenesis, the formation of plaques in the wall of blood vessels, starts as a result of lipid accumulation (low-density lipoprotein cholesterol) in the vessel wall. Such accumulation is related to the site of endothelial mechanotransduction, the endothelial response to mechanical stimuli and haemodynamics, which determines biochemical processes regulating the vessel wall permeability. This interaction between biomechanical and biochemical phenomena is complex, spanning different biological scales and is patient-specific, requiring tools able to capture such mathematical and biological complexity in a unified framework. Mathematical models offer an elegant and efficient way of doing this, by taking into account multifactorial and multiscale processes and mechanisms, in order to capture the fundamentals of plaque formation in individual patients. In this study, a mathematical model to understand plaque and calcification locations is presented: this model provides a strong interpretability and physical meaning through a multiscale, complex index or metric (the penetration site of low-density lipoprotein cholesterol, expressed as volumetric flux). Computed tomography scans of the aortic bifurcation and iliac arteries are analysed and compared with the results of the multifactorial model. The results indicate that the model shows potential to predict the majority of the plaque locations, also not predicting regions where plaques are absent. The promising results from this case study provide a proof of concept that can be applied to a larger patient population.

The effect of xerostomia and hyposalivation on the quality of life of patients with type II diabetes mellitus.

BACKGROUND: Diabetes mellitus is a chronic metabolic disease which can have numerous physical effects for patient. Xerostomia is one of these complications. Compared to healthy people, patients with diabetes mellitus, have a worse quality of life, and complications of diabetes are the main determinants of quality of life in these patients. OBJECTIVE: The aim of this study was to determine the effects of xerostomia and hyposalivation on quality of life of patients with type 2 diabetes mellitus. METHODS: This descriptive-analytical epidemiological study was conducted on 200 patients with type 2 diabetes mellitus referred to the diabetes clinic of Shahid Mostafavi in Sari city from October 2015 to January in 2016. A questionnaire containing personal characteristics and medical situation was completed by each person. Then, the Persian Oral Health Impact Profile-14 (OHIP-14-PER) questionnaire was completed by the patients. Eventually, with the use of chewable paraffin for 1.5 min by the patient, stimulated salivary flow rate (SSFR) test was performed, and in order to determine hyposalivation, their saliva amount underwent a gravimetric test. Finally, using statistical software SPSS16, the information was statistically analyzed by independent-samples t-test, Mann-Whitney U, Chi-squared and fisher exact tests. RESULTS: The average age of patient was 56.41 years old (43% male and 57% female). Mean SSFR was 0.7 ml/min in patients and xerostomia were confirmed in 112 patients. Difference between age, gender, drug use, years affecting to diabetes and FBS amount in patient with hyposalivation were not statistically meaningful in proportion to patients without it. But difference between HbA1C and SSFR in patients with hyposalivation were statistically meaningful than to patients without it (p=0.03, p=0.001 respectively). The mean patient score to OHIP-14 were obtained as 38.17. The questionnaire score difference in patients with hyposalivation in proportion to patients without it were not statistically meaningful. CONCLUSION: Hyposalivation possibility increases in diabetic patients with low metabolic control which can cause more severe side effects in relation to oral health. Xerostomia in diabetic patients has negative effects on oral health related quality of life. Diabetic control and patients' oral problem improvement is effective in their quality of life promotion.

Development of a Patient-Specific Multi-Scale Model to Understand Atherosclerosis and Calcification Locations: Comparison with In vivo Data in an Aortic Dissection.

Vascular calcification results in stiffening of the aorta and is associated with hypertension and atherosclerosis. Atherogenesis is a complex, multifactorial, and systemic process; the result of a number of factors, each operating simultaneously at several spatial and temporal scales. The ability to predict sites of atherogenesis would be of great use to clinicians in order to improve diagnostic and treatment planning. In this paper, we present a mathematical model as a tool to understand why atherosclerotic plaque and calcifications occur in specific locations. This model is then used to analyze vascular calcification and atherosclerotic areas in an aortic dissection patient using a mechanistic, multi-scale modeling approach, coupling patient-specific, fluid-structure interaction simulations with a model of endothelial mechanotransduction. A number of hemodynamic factors based on state-of-the-art literature are used as inputs to the endothelial permeability model, in order to investigate plaque and calcification distributions, which are compared with clinical imaging data. A significantly improved correlation between elevated hydraulic conductivity or volume flux and the presence of calcification and plaques was achieved by using a shear index comprising both mean and oscillatory shear components (HOLMES) and a non-Newtonian viscosity model as inputs, as compared to widely used hemodynamic indicators. The proposed approach shows promise as a predictive tool. The improvements obtained using the combined biomechanical/biochemical modeling approach highlight the benefits of mechanistic modeling as a powerful tool to understand complex phenomena and provides insight into the relative importance of key hemodynamic parameters.

Development of a patient-specific simulation tool to analyse aortic dissections: assessment of mixed patient-specific flow and pressure boundary conditions.

Aortic dissection has high morbidity and mortality rates and guidelines regarding surgical intervention are not clearly defined. The treatment of aortic dissection varies with each patient and detailed knowledge of haemodynamic and mechanical forces would be advantageous in the process of choosing a course of treatment. In this study, a patient-specific dissected aorta geometry is constructed from computed tomography scans. Dynamic boundary conditions are implemented by coupling a three element Windkessel model to the 3D domain at each outlet, in order to capture the essential behaviour of the downstream vasculature. The Windkessel model parameters are defined based on clinical data. The predicted minimum and maximum pressures are close to those measured invasively. Malperfusion is indicated and complex flow patterns are observed. Pressure, flow and wall shear stress distributions are analysed. The methodology presented here provides insight into the haemodynamics in a patient-specific dissected aorta and represents a development towards the use of CFD simulations as a diagnostic tool for aortic dissection.

Evaluation of the hemodynamic effectiveness of aortic dissection treatments via virtual stenting.

Aortic dissection treatment varies for each patient and stenting is one of a number of approaches that are utilized to Stabilize the condition. Information regarding the hemodynamic forces in the aorta in dissected and virtually stented cases could support clinicians in their choices of treatment prior to medical intervention. Computational fluid dynamics coupled with lumped parameter models have shown promise in providing detailed information that could be used in the clinic; for this, it is necessary to develop personalized workflows in order to produce patient-specific simulations. In the present study, a case of pre- and post-stenting (virtual stent-graft) of an aortic dissection is investigated with a particular focus on the role of personalized boundary conditions. For each virtual case, velocity, pressure, energy loss, and wall shear stress values are evaluated and compared. The simulated single stent-graft only marginally reduced the pulse pressure and systemic energy loss. The double stent-graft results showed a larger reduction in pulse pressure and a 40% reduction in energy loss as well as a more physiological wall shear stress distribution.Regions of potential risk were highlighted. The methodology applied in the present study revealed detailed information about two possible surgical outcome cases and shows promise as both a diagnostic and an interventional tool.