Validation of Computational Knee Models Using a Dynamic Knee Simulator

2008 ◽  
Author(s):  
Trent M. Guess ◽  
Mohammad Kia ◽  
Katherine Weimer ◽  
Kevin Dodd ◽  
Lorin Maletsky
Keyword(s):  
Computational Models ◽  
Patient Specific ◽  
Specific Reference ◽  
Knee Biomechanics ◽  
Computational Simulations ◽  
Body Model ◽  
Knee Simulator ◽  
Multi Body ◽  
Models And Modeling

Computational models of the knee provide valuable information on knee biomechanics, but validation of these models is challenging as in-vivo parameters such as muscle forces and tissue loading cannot be measured. Machines that simulate the dynamic loading and motion of physiological activities on cadaver knees can provide a means for validating computational knee models and modeling methods. In this approach, all forces applied to cadaver knees are known and can be replicated in computational simulations. The resulting experimental and computational kinematics can then be compared. Presented here is the development and use of a modeling platform comprised of a multi-body computational model of a cadaver knee and dynamic knee simulator and experimental measurements from the cadaver knee loaded in the machine. This modeling platform has been used to study: 1) patient specific reference lengths versus literature obtained reference lengths [1], 2) inclusion of ligament and tendon wrapping [2] and, 3) the development of a multi-body model of the meniscus [3].

scholarly journals Computational models for contact current dosimetry at frequencies below 1 MHz

2020 ◽  
Author(s):  
Pia Schneeweiss ◽  
Dorin Panescu ◽  
Dominik Stunder ◽  
Mark W. Kroll ◽  
Christopher J. Andrews ◽  
...  
Keyword(s):  
Computational Models ◽  
Scientific Basis ◽  
The Body ◽  
In Vivo Studies ◽  
International Electrotechnical Commission ◽  
Safety Standards ◽  
Body Model ◽  
Current Path ◽  
Cadaver Studies

AbstractElectric contact currents (CC) can cause muscle contractions, burns, or ventricular fibrillation which may result in life-threatening situations. In vivo studies with CC are rare due to potentially hazardous effects for participants. Cadaver studies are limited to the range of tissue’s electrical properties and the utilized probes’ size, relative position, and sensitivity. Thus, the general safety standards for protection against CC depend on a limited scientific basis. The aim of this study was therefore to develop an extendable and adaptable validated numerical body model for computational CC dosimetry for frequencies between DC and 1 MHz. Applying the developed model for calculations of the IEC heart current factors (HCF) revealed that in the case of transversal CCs, HCFs are frequency dependent, while for longitudinal CCs, the HCFs seem to be unaffected by frequency. HCFs for current paths from chest or back to hand appear to be underestimated by the International Electrotechnical Commission (IEC 60479-1). Unlike the HCFs provided in IEC 60479-1 for longitudinal current paths, our work predicts the HCFs equal 1.0, possibly due to a previously unappreciated current flow through the blood vessels. However, our results must be investigated by further research in order to make a definitive statement. Contact currents of frequencies from DC up to 100 kHz were conducted through the numerical body model Duke by seven contact electrodes on longitudinal and transversal paths. The resulting induced electric field and current enable the evaluation of the body impedance and the heart current factors for each frequency and current path.

scholarly journals Validating Patient-Specific Finite Element Models of Direct Electrocortical Stimulation

2021 ◽  
Vol 15 ◽  
Author(s):  
Chantel M. Charlebois ◽  
David J. Caldwell ◽  
Sumientra M. Rampersad ◽  
Andrew P. Janson ◽  
Jeffrey G. Ojemann ◽  
...  
Keyword(s):  
Computational Models ◽  
Projection Methods ◽  
Patient Specific ◽  
Clinical Effects ◽  
Cortical Surface ◽  
Brain Shift ◽  
Model Errors ◽  
Computer Interfaces ◽  
Electrode Localization

Direct electrocortical stimulation (DECS) with electrocorticography electrodes is an established therapy for epilepsy and an emerging application for stroke rehabilitation and brain-computer interfaces. However, the electrophysiological mechanisms that result in a therapeutic effect remain unclear. Patient-specific computational models are promising tools to predict the voltages in the brain and better understand the neural and clinical response to DECS, but the accuracy of such models has not been directly validated in humans. A key hurdle to modeling DECS is accurately locating the electrodes on the cortical surface due to brain shift after electrode implantation. Despite the inherent uncertainty introduced by brain shift, the effects of electrode localization parameters have not been investigated. The goal of this study was to validate patient-specific computational models of DECS against in vivo voltage recordings obtained during DECS and quantify the effects of electrode localization parameters on simulated voltages on the cortical surface. We measured intracranial voltages in six epilepsy patients during DECS and investigated the following electrode localization parameters: principal axis, Hermes, and Dykstra electrode projection methods combined with 0, 1, and 2 mm of cerebral spinal fluid (CSF) below the electrodes. Greater CSF depth between the electrode and cortical surface increased model errors and decreased predicted voltage accuracy. The electrode localization parameters that best estimated the recorded voltages across six patients with varying amounts of brain shift were the Hermes projection method and a CSF depth of 0 mm (r = 0.92 and linear regression slope = 1.21). These results are the first to quantify the effects of electrode localization parameters with in vivo intracranial recordings and may serve as the basis for future studies investigating the neuronal and clinical effects of DECS for epilepsy, stroke, and other emerging closed-loop applications.

scholarly journals Various Knee Model Measurement Techniques to Find the Knee Geometries

2016 ◽  
Vol 3 (3) ◽  
pp. 4-6
Author(s):  
Kavinaya C ◽  
Ashuthoshkumar L
Keyword(s):  
Computational Models ◽  
Measurement Techniques ◽  
Knee Kinematics ◽  
Load Measurement ◽  
Knee Simulator ◽  
Subject Specific ◽  
The Subject ◽  
Model Measurement

Computation of knee modeling is a subject-specific techniquethatdefining the zero-load measurements of the cruciate and indemnity ligaments.The dynamic knee simulator was used to test the three carcass knees. The carcass knees also experiencedphysicalsachet of motion testing to discovery their inactivesort of motion in order to regulate the zero-load measurements for everymuscle bundle. Compotation multibody knee representations were shaped for each knee and classical kinematics were likened to investigational kinematics for a replicated walk series. Simple-minded non-linear mechanisminhibition elements were used to characterize cruciate and deposited particles in musclepackages in the knee representations. This learningoriginate that knee kinematics was enormously sensitive to changing of the zero-load measurement. The domino effects also recommendoptimum methods for describing each of the muscle bundle zero-load measurements, irrespective of the subject. These consequencesvalidate the significance ofthe zero-load length when modeling the knee united and verify that physicalcloak of motion dimensions can be usedto determine the passive range of motion of the knee joint. It is also supposed that the method defined here forresponsible zero-load measurement can be used for in vitro or in vivo subject-specific computational models.

Impact of Patient-Specific In Vivo Vessel Material Properties on Carotid Atherosclerotic Plaque Stress/Strain Calculations

2019 ◽  
Vol 16 (03) ◽  
pp. 1842002 ◽  
Author(s):  
Qingyu Wang ◽  
Dalin Tang ◽  
Gador Canton ◽  
Thomas S. Hatsukami ◽  
Kristen L. Billiar ◽  
...  
Keyword(s):  
Material Properties ◽  
Carotid Plaque ◽  
Computational Models ◽  
Patient Specific ◽  
Stress And Strain ◽  
Carotid Atherosclerotic Plaque ◽  
Plaque Vulnerability ◽  
Material Models ◽  
Vessel Material

Patient-specific vessel material properties are in general lacking in image-based computational models. Carotid plaque stress and strain conditions with in vivo material and old material models were investigated (8 patients, 16 plaques). Plaque models using patient-specific in vivo vessel material properties showed significant differences from models using old material properties from the literature on stress and strain calculations. These differences demonstrated that models using in vivo material properties could improve the accuracy of stress and strain calculations which could potentially lead to more accurate plaque vulnerability assessment.

scholarly journals Evaluation of a modified Cheatham-Platinum stent for the treatment of aortic coarctation by finite element modelling

2018 ◽  
Vol 7 ◽  
pp. 204800401877395 ◽  
Author(s):  
Barbara EU Burkhardt ◽  
Nicholas Byrne ◽  
Marí Nieves Velasco Forte ◽  
Francesco Iannaccone ◽  
Matthieu De Beule ◽  
...  
Keyword(s):  
Finite Element ◽  
Aortic Coarctation ◽  
Computational Models ◽  
Three Dimensional ◽  
Computational Modelling ◽  
Patient Specific ◽  
Stent Design ◽  
Initial Length ◽  
Element Analysis

Objectives Stent implantation for the treatment of aortic coarctation has become a standard approach for the management of older children and adults. Criteria for optimal stent design and construction remain undefined. This study used computational modelling to compare the performance of two generations of the Cheatham-Platinum stent (NuMED, Hopkinton, NY, USA) deployed in aortic coarctation using finite element analysis. Design Three-dimensional models of both stents, reverse engineered from microCT scans, were implanted in the aortic model of one representative patient. They were virtually expanded in the vessel with a 16 mm balloon and a pressure of 2 atm. Results The conventional stent foreshortened to 96.5% of its initial length, whereas the new stent to 99.2% of its initial length. Diameters in 15 slices across the conventional stent were 11.6–15 mm (median 14.2 mm) and slightly higher across the new stent: 10.7–15.3 mm (median 14.5 mm) (p= 0.021). Apposition to the vessel wall was similar: conventional stent 31.1% and new stent 28.6% of total stent area. Conclusions The new design Cheatham-Platinum stent showed similar deployment results compared to the conventional design. The new stent design showed slightly higher expansion, using the same delivery balloon. Patient-specific computational models can be used for virtual implantation of new aortic stents and promise to inform subsequent in vivo trials.

scholarly journals Unmasking Arrhythmogenic Hubs of Reentry Driving Persistent Atrial Fibrillation for Patient‐Specific Treatment

2020 ◽  
Vol 9 (19) ◽  
Author(s):  
Brian J. Hansen ◽  
Jichao Zhao ◽  
Katelynn M. Helfrich ◽  
Ning Li ◽  
Alexander Iancau ◽  
...  
Keyword(s):  
Atrial Fibrillation ◽  
Near Infrared ◽  
Ex Vivo ◽  
Specific Treatment ◽  
Persistent Atrial Fibrillation ◽  
Patient Specific ◽  
Computational Simulations ◽  
3 Dimensional ◽  
Atrial Refractoriness

Background Atrial fibrillation (AF) driver mechanisms are obscured to clinical multielectrode mapping approaches that provide partial, surface‐only visualization of unstable 3‐dimensional atrial conduction. We hypothesized that transient modulation of refractoriness by pharmacologic challenge during multielectrode mapping improves visualization of hidden paths of reentrant AF drivers for targeted ablation. Methods and Results Pharmacologic challenge with adenosine was tested in ex vivo human hearts with a history of AF and cardiac diseases by multielectrode and high‐resolution subsurface near‐infrared optical mapping, integrated with 3‐dimensional structural imaging and heart‐specific computational simulations. Adenosine challenge was also studied on acutely terminated AF drivers in 10 patients with persistent AF. Ex vivo, adenosine stabilized reentrant driver paths within arrhythmogenic fibrotic hubs and improved visualization of reentrant paths, previously seen as focal or unstable breakthrough activation pattern, for targeted AF ablation. Computational simulations suggested that shortening of atrial refractoriness by adenosine may (1) improve driver stability by annihilating spatially unstable functional blocks and tightening reentrant circuits around fibrotic substrates, thus unmasking the common reentrant path; and (2) destabilize already stable reentrant drivers along fibrotic substrates by accelerating competing fibrillatory wavelets or secondary drivers. In patients with persistent AF, adenosine challenge unmasked hidden common reentry paths (9/15 AF drivers, 41±26% to 68±25% visualization), but worsened visualization of previously visible reentry paths (6/15, 74±14% to 34±12%). AF driver ablation led to acute termination of AF. Conclusions Our ex vivo to in vivo human translational study suggests that transiently altering atrial refractoriness can stabilize reentrant paths and unmask arrhythmogenic hubs to guide targeted AF driver ablation treatment.

Modeling of a Dynamic Knee Simulator With Advanced PID Controller to Evaluate Joint Loading Conditions

2014 ◽  
Author(s):  
Fallon Fitzwater ◽  
Amber Lenz ◽  
Lorin Maletsky
Keyword(s):  
Computational Models ◽  
Total Joint Replacement ◽  
External Loading ◽  
Loading Conditions ◽  
Dynamic Simulations ◽  
Knee Simulator ◽  
Joint Loads ◽  
External Loads

In-vitro dynamic knee simulators allow researchers to investigate changes in natural knee biomechanics due to pathologies, injuries or total joint replacement. The advent of the instrumented tibia, which directly measures knee loads in-vivo, has provided a wealth data for various activities that in-vitro studies now aim to replicate [1, 2]. Dynamic knee simulators, such as the Kansas Knee Simulator (KKS), achieve these physiological loads at the joint by applying external loads to either bone ends or musculature. Determining the external loading conditions necessary to replicate activity specific joint loads, obtained from instrumented tibia data, during dynamic simulations are calculated using computational models.

scholarly journals Effects of Fibrosis Morphology on Reentrant Ventricular Tachycardia Inducibility and Simulation Fidelity in Patient-Derived Models

2014 ◽  
Vol 8s1 ◽  
pp. CMC.S15712 ◽  
Author(s):  
Jordan Ringenberg ◽  
Makarand Deo ◽  
David Filgueiras-Rama ◽  
Gonzalo Pizarro ◽  
Borja Ibañez ◽  
...  
Keyword(s):  
Ventricular Tachycardia ◽  
Computational Models ◽  
Border Zone ◽  
Patient Specific ◽  
Narrow Channels ◽  
Simulation Fidelity ◽  
Strong Indicator ◽  
Significant Step ◽  
Magnetic Resonance Imaging Mri

Myocardial fibrosis detected via delayed-enhanced magnetic resonance imaging (MRI) has been shown to be a strong indicator for ventricular tachycardia (VT) inducibility. However, little is known regarding how inducibility is affected by the details of the fibrosis extent, morphology, and border zone configuration. The objective of this article is to systematically study the arrhythmogenic effects of fibrosis geometry and extent, specifically on VT inducibility and maintenance. We present a set of methods for constructing patient-specific computational models of human ventricles using in vivo MRI data for patients suffering from hypertension, hypercholesterolemia, and chronic myocardial infarction. Additional synthesized models with morphologically varied extents of fibrosis and gray zone (GZ) distribution were derived to study the alterations in the arrhythmia induction and reentry patterns. Detailed electrophysiological simulations demonstrated that (1) VT morphology was highly dependent on the extent of fibrosis, which acts as a structural substrate, (2) reentry tended to be anchored to the fibrosis edges and showed transmural conduction of activations through narrow channels formed within fibrosis, and (3) increasing the extent of GZ within fibrosis tended to destabilize the structural reentry sites and aggravate the VT as compared to fibrotic regions of the same size and shape but with lower or no GZ. The approach and findings represent a significant step toward patient-specific cardiac modeling as a reliable tool for VT prediction and management of the patient. Sensitivities to approximation nuances in the modeling of structural pathology by image-based reconstruction techniques are also implicated.

scholarly journals Computational Knee Ligament Modeling Using Experimentally Determined Zero-Load Lengths

2012 ◽  
Vol 6 (1) ◽  
pp. 33-41 ◽  
Author(s):  
Katherine H Bloemker ◽  
Trent M Guess ◽  
Lorin Maletsky ◽  
Kevin Dodd
Keyword(s):  
Knee Joint ◽  
Range Of Motion ◽  
Computational Models ◽  
Knee Kinematics ◽  
Specific Method ◽  
Knee Ligament ◽  
Knee Simulator ◽  
Subject Specific

This study presents a subject-specific method of determining the zero-load lengths of the cruciate and collateral ligaments in computational knee modeling. Three cadaver knees were tested in a dynamic knee simulator. The cadaver knees also underwent manual envelope of motion testing to find their passive range of motion in order to determine the zero-load lengths for each ligament bundle. Computational multibody knee models were created for each knee and model kinematics were compared to experimental kinematics for a simulated walk cycle. One-dimensional non-linear spring damper elements were used to represent cruciate and collateral ligament bundles in the knee models. This study found that knee kinematics were highly sensitive to altering of the zero-load length. The results also suggest optimal methods for defining each of the ligament bundle zero-load lengths, regardless of the subject. These results verify the importance of the zero-load length when modeling the knee joint and verify that manual envelope of motion measurements can be used to determine the passive range of motion of the knee joint. It is also believed that the method described here for determining zero-load length can be used for in vitro or in vivo subject-specific computational models.

Determination of Human Carotid Atherosclerotic Plaque Material Properties Non-Invasively Using In Vivo Cine and 3D Magnetic Resonance Imaging and Image-Based Modeling Techniques

2011 ◽  
Author(s):  
Haofei Liu ◽  
Gador Canton ◽  
Chun Yuan ◽  
Marina Ferguson ◽  
Chun Yang ◽  
...  
Keyword(s):  
Magnetic Resonance ◽  
Atherosclerotic Plaque ◽  
Material Properties ◽  
Computational Models ◽  
Plaque Rupture ◽  
Patient Specific ◽  
Material Strength ◽  
Modeling Techniques ◽  
Human Carotid

Atherosclerotic plaque rupture is believed to be associated with high critical stress exceeding plaque cap material strength. In vivo magnetic resonance image (MRI)-based computational models have been introduced to calculate critical plaque stress and assess plaque vulnerability [1–5]. However, accuracy of computational stress predictions is heavily dependent on the data used by the models. Patient-specific plaque material properties are desirable for accurate stress predictions but are not currently available. In this paper, non-invasive in vivo Cine and 3D multicontrast MRI data and modeling techniques were combined to obtain patient-specific plaque material properties to improve model prediction accuracies. A 2D human carotid plaque model was used to demonstrate impact of material stiffness on computational stress predictions.

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