Cardiovascular Biomechanics
Sara Barati; Nasser Fatouraee; Malikeh Nabaei
Volume 15, Issue 4 , March 2022, , Pages 355-366
Abstract
Transcatheter aortic valves have become the standard procedure for high-risk patients with severe aortic valve stenosis. This minimally invasive procedure can expand to a wider range of patients with a lower risk of surgery. The complications after the implantation and the structural malfunction of these ...
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Transcatheter aortic valves have become the standard procedure for high-risk patients with severe aortic valve stenosis. This minimally invasive procedure can expand to a wider range of patients with a lower risk of surgery. The complications after the implantation and the structural malfunction of these prostheses are the obstacles of this transition. Design optimization of the stents of these prostheses can improve their performance and reduce the post-operative complications associated with them. Since all prostheses are crimped before implantation, the designs should guarantee an acceptable structural performance after expansion, especially self-expandable stents for which the fatigue behavior strongly depends on the strain. This study applies a simple, cost-effective optimization framework to optimize the geometric parameters of these stents regarding the maximum strain during the crimping process. The design parameters include diameter profile, cell size, number of repeating components, and strut cross-section. The simplified models are evaluated and verified by the 3D simulations. The results show that the middle cells' height, number of cells, and strut width have the most prominent effect on the maximum crimping strain of the stent. The maximum strain of the optimized stent in the selected design space was 0.52. This stent had a width of 0.2 mm, thickness of 0.3 mm, the number of cells and patterns of 3 and 15, respectively, and the diameter profile associated with the diameter ratio of 1.05. This framework can be applied to a wide range of stent designs and tremendously reduce the cost of stent design and optimization.
Fatemeh Ghafouri; Mohammad Hadi Honarvar; Mohammad Mahdi Jalili
Volume 14, Issue 1 , May 2020, , Pages 1-11
Abstract
Minimizing the energy expenditure as well as structure's size and weight is very important in biped walking robots. To achieve this target, a passive controller, which is a combination of spring and linear damper, is added to a biped walker. The important specification of the studied walker is that it ...
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Minimizing the energy expenditure as well as structure's size and weight is very important in biped walking robots. To achieve this target, a passive controller, which is a combination of spring and linear damper, is added to a biped walker. The important specification of the studied walker is that it has two convex soles at the end of the legs as feet, which is jointed to body with a passive revolute joint. Contact point moves on a sole curve. To reduce system's dynamic complexity, pointed mass approach is used. The main purpose of this research is studying the dynamical behavior of this underactuated walker before and after adding controller. In the first step, a model based on developed pointed mass model is offered and analyzed by adding two rigid convex soles as feet and passive revolute joint as ankle. To make leg length changes during walking, an active dynamic element is used. Next, a passive controller or dynamic element is used with the active one to reduce active element role during movement. Particle swarm optimization method is used to minimize this role by calculating optimized passive element parameters. The results show using the combination of optimized passive and active dynamic elements, the amount of energy consumption is decreased significantly. As a result, we can use a much smaller active element with less power to walk. Also using a passive dynamic element practically improves mechanical specifications of the structure such as dimensions and weight as well as providing simple use for users.
Bioelectrics
Amir Soleymankhani; Vahid Shalchyan
Volume 12, Issue 2 , September 2018, , Pages 85-96
Abstract
The extracellular recording from the brain's single neurons is known as a popular method in neuroscience and neuro-rehabilitation engineering. These recordings include the activity of all neurons around the electrode, for better use of which, spike sorting methods should be utilized to obtain the activity ...
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The extracellular recording from the brain's single neurons is known as a popular method in neuroscience and neuro-rehabilitation engineering. These recordings include the activity of all neurons around the electrode, for better use of which, spike sorting methods should be utilized to obtain the activity of single neurons. Based on the structural properties of the neuron, such as its dendritic tree, and the distance and direction of it relative to the electrode, it can be claimed that the form of its spike waveform is unique and constant. However, spike sorting under low signal-to-noise ratio (SNR) conditions is always accompanied with challenges. A spike sorting algorithm usually consists of three sections including the spike detection, feature extraction, and classification. In this paper, a method based on optimization of continuous wavelet coefficients is presented which is effective in low SNR values. In the proposed method, after the calculation of the parameterized wavelet coefficients, using the Euclidean distance and the area under the receiver operator characteristic curve, the best parameters were chosen to increase the separation of the features, so that a suitable scale was first found with the Euclidean distance criterion and then the translation parameter was obtained with the second criterion. In this research k-means algorithm was used for the clustering as a simple but efficient method. For evaluation, three simulated data sets were made in 9 different SNRs with a modeled background noise. The obtained results from simulated data showed that the optimization of parameters in continuous wavelet transform using the proposed algorithm could effectively improve the spike sorting performance compared to principal component analysis method.
Spinal Biomechanics
Yousef Mohammadi; Rasoul Abedi; Navid Arjmand; Gholamreza Ataei; Nasser Fatouraee
Volume 11, Issue 4 , February 2018, , Pages 351-363
Abstract
The growth of low back pain and disoreders are increasing in different societies. Furthermore,the direct in vivo measurement of spinal and muscle forces is so difficult. Hence, the use of musculoskeletal biomechanical models has been emerged applicably as a tool for calculating and estimating spinal ...
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The growth of low back pain and disoreders are increasing in different societies. Furthermore,the direct in vivo measurement of spinal and muscle forces is so difficult. Hence, the use of musculoskeletal biomechanical models has been emerged applicably as a tool for calculating and estimating spinal forces under various activities. Thus, the purpose of this study is to estimate the mentioned forces with different methods especially in lifting tasks. To this end, a six-joint model with eighteen degrees of freedom and 76 trunk muscle fascicles has been developed. Due to more number of unknowns (muscle forces) than equilibrium equations, the system is redundant and the problem is indeterminate to be solved. So the electromyography assisted optimization (EMGAO) approach is used for estimating muscle forces. Since foregoing EMG muscle forces do not satisfy equilibrium equations, correction coefficients have been used for satisfying equilibrium at all lumbar joint levels. According to results in an identical task, all of the approaches indicated substantial differences in correction coefficients for each muscle. Although the stability and muscle forces are different in various EMGAO methods, spinal compression and shear forces are closer to each other in these methods. For validation of results, the intradiscal pressure (IDP) at L4-L5 in various methods are in agreement with in vivo IDP value of an experimental test measurement so that both of them reported this quantity in the range of 0.3-1.8 (MPa).
Spinal Biomechanics
Mohammad Nikkhoo; Sajjad Najafzadeh; Romina Kargar
Volume 9, Issue 4 , February 2015, , Pages 317-326
Abstract
Understanding the mechanism of artificial disc degeneration using animal models is useful to study the regenerative techniques in hope of finding potential therapeutic strategies. For any type of potential therapeutic techniques, first we need to have the degenerated model. Disc degeneration ...
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Understanding the mechanism of artificial disc degeneration using animal models is useful to study the regenerative techniques in hope of finding potential therapeutic strategies. For any type of potential therapeutic techniques, first we need to have the degenerated model. Disc degeneration can be mimicked in animal studies using needle puncture. However, the detailed mechanical response of the artificial degenerated disc using needle puncture under physiological diurnal activities has not been analyzed well.Hence, reverse finite element analyses combined with in-vitro experiments were used in this study to find the mechanical properties of intact (N=8) and injured discs using needle puncture (N=8). Afterward, specimen-specific FE models for 16 discs were simulated during physiological diurnal activity. The results showed that the variation of axial displacement, intradiscal pressure, and total fluid exchangein intact discs were significantly higher than the injured ones after 24h. But the maximum axial stress within disc was significantly higher in injured group. The achieved results are correlated with previous human cadaver data for natural disc degeneration. Therefore, it is concluded that the G-16needle puncture injury is a simple and cost-effective methodology which can be used to mimic the degeneration mechanism in animal models.
Biomedical Image Processing / Medical Image Processing
Ali Kermani; Ahmad Ayatollahi; Sorour Mohajerani
Volume 8, Issue 4 , February 2015, , Pages 325-337
Abstract
IVUS imaging is a minimally invasive blood vessel cross-sectional imaging procedure in which accurate data is obtained from what is in there. Processing on these images or raw signals can provide wide range information for experts and practitioners, and can help them in making an accurate diagnosis and ...
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IVUS imaging is a minimally invasive blood vessel cross-sectional imaging procedure in which accurate data is obtained from what is in there. Processing on these images or raw signals can provide wide range information for experts and practitioners, and can help them in making an accurate diagnosis and appropriate treatment. Extraction of tissue boundaries in the blood vessels is one of the challenging parts as a first step in this direction. In this paper a new method was proposed based on the minimax technique and connected components for extracting Adventitia tissue boundary in intravascular ultrasound images. For this purpose, initial boundary will be extracted using improved minimax technique. Then final boundary is extracted with high precision using connected components. The method was tested on a set of real data with regard to the Hausdorff distance and Jaccard index to evaluate its performance. Mean of Hausdorff distance and mean of Jaccard index were obtained 95% and 0.45 millimeter, consequently. These results show that the proposed method in this paper can extract Adventitia tissue boundaries more accurately than existing methods with regard to the distance Hausdorff distance and Jaccard index.
Gait Analysis
Mohsen Sadeghi Mehr; Davoud Naderi; Nader Farahpour; Saeed Davoud Abadi Farahani
Volume 3, Issue 3 , June 2009, , Pages 179-187
Abstract
The present study was devoted to determine the standing human body reactions to perturbation of a base plate in the frontal plane, in order to preserve its stability. A base plate with sinusoidal fluctuation was designed and built and then markers were mounted on the specified locations on it and the ...
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The present study was devoted to determine the standing human body reactions to perturbation of a base plate in the frontal plane, in order to preserve its stability. A base plate with sinusoidal fluctuation was designed and built and then markers were mounted on the specified locations on it and the skin of subjects before testing. During testing the subjects (N=10) tried to preserve their stability against perturbations. By using Motion Analysis System, the body responses of subjects were analyzed. Using inverse dynamic methods and experimental kinematic results, forces and moments applied to the joints and between feet soles and the base plate were determined. In theoretical study, the kinematic and dynamic equations of motion of a robotic model of human body in frontal plane by using repetitive Newton-Euler method were obtained. Based on the stability of the model and supporting vertical forces criterion an object function was defined, in order to assure the stability of the model. By optimization of the object function, angle of the model joints under perturbation and its first and second derivatives were determined. The good agreement of the theoretical and experimental results states that in similar conditions a robotic model can be used instead of expensive and time-consuming experiments.
Neuro-Muscular Engineering
Davoud Naderi; Mohsen Sadeghi Mehr; Nader Farahpour; Behnam Miripour-Fard
Volume 2, Issue 2 , June 2008, , Pages 85-93
Abstract
Cognition of human postural responses can provide valuable insight on the control of stability. Researchers can use this finding to design rehabilitation exercises to improve the patients, balance. This study was done with the aim of conducting theoretical and experimental investigations on human response ...
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Cognition of human postural responses can provide valuable insight on the control of stability. Researchers can use this finding to design rehabilitation exercises to improve the patients, balance. This study was done with the aim of conducting theoretical and experimental investigations on human response to tilting base plate in the sagittal plane. A four-segment model with three degrees of freedom was used as a biomechanical model of human body and its motion was studied in the sagittal plane. The postures of model were found by optimization technique such that the stability of model to be optimum. Zero moment point stability criterion was applied to find the optimum posture against the tilting base plate. To verify the theoretical results experimentally, the stability measure device was designed and manufactured. In several trials, the responses of ten male healthy persons standing on a tilting platform under perturbations were recorded by using the motion analysis system. Through data analysis, the response of each subject was surveyed and the experimental and theoretical results were compared. Both the experimental and theoretical results showed that the human central nervous system evokes the ankle strategy to keep its balance under tilting base plate conditions. A good coincident between the experimental results and theoretical predictions was observed, indicating that the model basis optimization method can be well relied upon to predict the human joints angle trajectories in response to base plate tilting.
Cardiovascular Biomechanics
Mansour Alizadeh; Iman Mohebbi Nejad
Volume 2, Issue 4 , June 2008, , Pages 317-324
Abstract
Mechanical characteristic of arteries is very important for stent producing and cardiovascular implants. In this study mechanical behavior of a piece of left anterior descending coronary artery with specified dimension and separated layers which was prepared by holtzapfel and tested under tensile test ...
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Mechanical characteristic of arteries is very important for stent producing and cardiovascular implants. In this study mechanical behavior of a piece of left anterior descending coronary artery with specified dimension and separated layers which was prepared by holtzapfel and tested under tensile test bas been considered. Ogden hyperelastic model has been implemented for the experimental data and related parameters were obtained. These parameters have been optimized. The obtained results showed that by using the same experimental data the Ogden model can be fitted well with holtzapfel model and the errors fall within acceptable range.
