Completed Projects

1. Computational Modeling of coronary blood flow in 3D: An insight into the mechanical environment of atherosclerosis; using Image based FE – Modeling and Fluid Structure Interaction (FSI).

Coronary heart disease (CHD) is a leading cause of death in today’s century. More than 7 million people die each year from this disease (WHO, 2015). The main cause of CHD is atherosclerosis which is characterized by accumulation of fat, cholesterol, calcium, and other deposits (collectively called plaque) along the inner lining of the vessel wall. Plaque material and structural characteristics are important factors in the natural progression of the disease and has an important clinical predictive value. Extensive calcification most likely represents a later stage of atherosclerosis and is not only an independent predictor of CHD, but also has prognostic significance in patients with known CHD.

The social and economic burden of this disease remains very high. It is important to understand the cause and consequences of CHD. The main objective of this study is to investigate the role of hemodynamically induced biomechanical forces in predicting the mechanical strength of stage ѵ atherosclerotic coronary artery.

This study is therefore using the numerical methods and techniques in computational mechanics and Biomedical Engineering to investigate the synergy of CHD. Three-dimensional Image based models of normal and atherosclerotic vessel were built using image processing suite and a computer solver. These models were then utilized for the quantification of structural forces induced by the underlying blood flow in a virtual reality set up using Finite Element Modeling.FSI coupling approach was used to address the blood-vessel-plaque-simulation. Calcium score was calculated using an algorithm to evaluate its contribution in overall plaque burden. The results has been validated and compared with Digital Volume correlation and structural analysis methods.

The results show an increased stiffness and Wall Shear Stress (WSS) in atherosclerotic arteries as compared with the healthy ones. Large curvatures under tortional loading are found to be the regions where maximum stress is accumulated making them more liable to the formation of plaque lesions in normal arteries. Furthermore, larger strain rates were recorded in Healthy arteries. Fibrous plaque was found to exhibit stiffest response to loading than calcified lesions. Coronary Artery Calcium Score (CACS) shows a positive correlation with atherosclerosis and pose a moderate risk of suffering an acute CHD event in the near future.

2. INVESTIGATION OF INTRA CRANIAL PRESSURE (ICP) IN BRAIN TUMOR MODELS AND AUTOMATIC DETECTION OF BRAIN TUMORS

Elevated intracranial pressure (ICP) is one of the common consequences of traumatic conditions and has a profound influence on outcome. There are well established methods for the measurement, continuous monitoring and treatment of raised ICP. However, there is a need to build computer models for investigation of ICP before any invasive procedures are applied. To-date, there is a lot of research on going, on the measurement of ICP in patients with different conditions e.g. ICP due to edema, ICP due to formation of embolus in CSF and ICP due to accidental head injuries. However, there is still one area in this domain which is lacking enough knowledge, i.e. investigating ICP due to the presence of brain tumor.

In this research, therefore the ICP is investigated due to the presence of tumor. Brain tumor is the most vulnerable state, with an abnormal growth of cells, which is usually accompanied with an increased ICP due to the mass content increment. The relation between volume and pressure is non-linear. Skull is usually, considered as an enclosed and in-elastic container like a sac. The positioning of layers within this sac generates a constant pressure which is normal according to the body homeostasis. An increase in the volume of any of the intra cranial contents (Sac contents) is naturally offset by a decrease in pressure in one or the other content in it. However, when the size of the tumor (which is not an intra-cranial content) increases, the compensatory mechanisms gets exhausted and further increase in the brain sac in terms of volume results in an extremely elevated ICP. This mechanism is replicated in this research by using Image based Finite Element modeling and mathematical modeling. Reportedly the normal range of ICP lies between 3.75~15mmHg in humans.

We have generated two head models with different mesh densities provided the same boundary conditions and loading parameters using Image Based Finite Element Modeling. Results show that that presence of foreign mass (e.g. tumor) contributes to the elevation of intra-cranial pressure. This study is done on a single slice of brain and may not incorporate the realism however it does address a preliminary solution to the detection of increased intra-cranial pressure due to the presence of brain tumor. The results are also validated using mathematical solution at the end.

3. Investigating Locomotion Performance Using Evolutionary Robotics (ER) Based Simulation Program and Finite Element Analysis (FEA)

Locomotion is a functional measure of the walking ability of vertebrates. It involves parameters like maximum running speed and gait analysis. Gait analysis has been previously employed using parameters like bone scaling, strength, calculating safety factor and typical ground reaction forces (GRFs). Other approaches rely on developing musculoskeletal models of vertebrates in reference to the locomotion patterns.

Recently, scientists have developed forward dynamic evolutionary robotics simulation program (GaitSym) led by a research team at the University of Manchester UK. This program is used to study locomotion and gait using input parameters like muscle mass and joint coordinates with the lowest possible metabolic cost. The major advantage of this program is that we can understand how vertebrates moved in the past utilizing their size to function features based on animal’s morphology. However, the disadvantage is that we do not still understand how large or small magnitude of force is required to execute a reasonable gait pattern.

In this research, we have generated computer models of gait analysis using a vertebrate model (Phasianus colchicum). The uniqueness of this study lies in a fact that the analysis was performed outside evolutionary robotics simulation program (i.e. GaitSym) using the same strategy as in GaitSym. However, additional finite elements is also incorporated to overcome the GaitSym’s inability to consider bone’s geometry. This has provided an opportunity to incorporate parameters which was otherwise not possible GaitSym in order to acquire realistic gait patterns e.g. geometry and layers. Hence, a more sensible gait pattern. This study also utilized laws of mechanics for proper definition of gait boundary condition by utilizing correct vectors.

Using image based-finite element analysis (FEA) boundary conditions were applied for both phases of gait i.e. stance phase and swing phase. Results from both phases were compared to investigate realistic magnitude of force parameters to address the overall vertebrate‘s skeleton integrity which was found reasonable.

FE results acquired from this study are promising compared to the results available in literature to-date. . Stresses acquired from stance phase and swing phase are

16MPa and 99MPa respectively which are a bit under estimated yet within the safety range of bone’ compared to the ultimate compressive strength of bone reported as 180MPa – 200MPa (Currey, 2002). However both models (Stance and Swing) depicts a reasonable metabolic cost. Moreover the deformation models with varying mesh densities have also been reasonably converged.

It is concluded that GaitSym may hold true for existing models exoskeletons, joint and muscle coordinates without geometry to a certain limit. However there is a need to optimize the genetic algorithm of GaitSym for balanced locomotion. This is only possible if GaitSym alters its forces in the ODE or optimize its coordinates of skeleton relative to the simulations conducted in this study to retain skeleton integrity. A novel synergy for incorporation of stress into GaitSym has also been proposed at the end of this research.

4. Computational Modeling of Avascular Femoral Necrosis using Finite Element Analysis

The purpose of this study was to conduct computational modeling and simulation of Avascular Femoral Necrosis (AVN) using linear elastic finite element analysis to predict failure in femoral neck. AVN is complex disease of the femoral head. Since femur is the only weight bearing bone in the body, AVN may cause hindered movements and stiffness in the hip joint. Clinical and anatomical significance of AVN has been well established already in the literature. Moreover, it is extensively studied that bone become weaker to provide mechanical support after necrosis. Until now, different animal models have been developed to study mechanical strength and properties of healthy and necrotic bones. However not a single human model is reported in the literature to predict rate of degradation for estimation analysis.

In this research, an effort is made to create computer models using physics of different stages of AVN deploying techniques like image based modeling and Finite Elements. This will enable us to understand more about distribution of stresses localized in the groin area and femoral head w.r.t load alignment.

A mechanically elastic finite element analysis was performed. Our results show that with the progress in bone damage during necrosis, bone behavior changes. Stress become higher in the femoral neck at the point of articulation and shaft become weaker hence prone to fracture. With the increase in the load, femoral neck narrowing risk also increases due to more stresses in this localized region. Von Mises Stress on the superior and inferior regions of femoral neck intersected with frontal plane. Additionally, this study also conducted a mechno-elastic finite element analysis with varying body weights. Increasing weights tend to increase the unborn stresses. Convergence analysis was also carried out for finer meshes. Maximum stress of (146MPa) and displacement of (0.04mm) was observed in stage IV of the AVN models whole bone model whereas in the necrotic region a localized Von Mises stress value of 4.6MPa is observed compared to the health model which was only 1.6MPa. The stresses inferred from this research reasonably correlates with values reported in the literature. We believe that results obtained from this study will be very useful for clinical prognosis in future; since these computer models will be used as an aid to understand in depth analysis and etiology of necrosis in various stages with numerical accuracy.

5. Development of Location Specific Finite Element Head Model for the Study of Damage Progression in Head Impact Injury

Background: Brain injuries are a primary health and a pecuniary issue all through the world. Numerical techniques like finite element (FE) methods may be used to investigate head injuries and optimize the safety, which can reduce the number of injuries. The FE head models were at first assessed for biofidelity by comparing with cadavers experiments. In any case, there are a few constraints in analyses as the body starts degrading after death. Human head FE models are mainly used for dynamic studies by creating scenarios of car crash, pedestrian & vehicle accidents in which different assumptions were considered. Objective: The aim of the research is the development of realistic FE head model to study damage progression in head impact injury under external loading, sensitivity of the head impact injury to the elastic modulus and homogenized brain modeling in response to quasistatic loading at different locations.

Methodology: The FE model of the human head was used to study Von mises stress and displacement during location specific impact of the head. The human head FE model was divided into two models, one was simple and other was complex model. Both models consist of scalp, skull, spongiosa, cerebrospinal fluid (CSF), brain gray matter and white matter. These two models were then tested in three different cases with identical boundary conditions, forces and locations. Case I: Sensitivity of the injury to the elastic modulus of the brain layer by keeping all the other layers linear elastic with constant applied force to frontal region. Case II: Force Displacement Study i.e. by varying amount of force on homogenized brain model with frontal impact. Case III: Constant force was applied to homogenized brain model by varying locations of impact. Displacement and stress predicted from these models are then observed and analyzed.

Results: Preliminary outcomes of these simulations show that the brain injury may occur under applied conditions for simple model and is sensitive to the complexity of geometry. The stress and displacement profiles showed lower values for the complex model than simple model. Both the models showed linear relationship between force and displacement. By varying location, the maximum stress varied and was found maximum when the force was applied from the lateral side. So it was found that lateral impacts are more injurious and prone towards brain injury. Thus a complex model is more accurate and showed no injury in all cases in given amount of force while the simple model showed injury in two cases with the same applied conditions.

Conclusion: This study would be beneficial in order to better understand the brain response during head impact injury at different locations. It would serve as a guide line for non linear dynamic study of the head injury to the researchers in optimizing head protection and clinicians in terms of providing aid to the injured.