| 1. |
- Alvarez, Victor, et al.
(författare)
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The Influence of Neck Muscle Tonus and Posture on Brain Tissue Strain in Pedestrian Head Impacts
- 2014
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191. ; 58, s. 63-101
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Tidskriftsartikel (refereegranskat)abstract
- Pedestrians are one of the least protected groups in urban traffic and frequently suffer fatal head injuries. An important boundary condition for the head is the cervical spine, and it has previously been demonstrated that neck muscle activation is important for head kinematics during inertial loading. It has also been shown in a recent numerical study that a tensed neck musculature also has some influence on head kinematics during a pedestrian impact situation. The aim of this study was to analyze the influence on head kinematics and injury metrics during the isolated time of head impact by comparing a pedestrian with relaxed neck and a pedestrian with increased tonus. The human body Finite Element model THUMS Version 1.4 was connected to head and neck models developed at KTH and used in pedestrian-to-vehicle impact simulations with a generalized hood, so that the head would impact a surface with an identical impact response in all simulations. In order to isolate the influence of muscle tonus, the model was activated shortly before head impact so the head would have the same initial position prior to impact among different tonus. A symmetric and asymmetric muscle activation scheme that used high level of activation was used in order to create two extremes to investigate. It was found that for the muscle tones used in this study, the influence on the strain in the brain was very minor, in general about 1-14% change. A relatively large increase was observed in a secondary peak in maximum strains in only one of the simulated cases.
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| 2. |
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| 3. |
- Giordano, Chiara, et al.
(författare)
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Development of an Unbiased Validation Protocol to Assess the Biofidelity of Finite Element Head Models used in Prediction of Traumatic Brain Injury
- 2016
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191. ; 60, s. 363-471
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Konferensbidrag (refereegranskat)abstract
- This study describes a method to identify laboratory test procedures and impact response requirements suitable for assessing the biofidelity of finite element head models used in prediction of traumatic brain injury. The selection of the experimental data and the response requirements were result of a critical evaluation based on the accuracy, reproducibility and relevance of the available experimental data. A weighted averaging procedure was chosen in order to consider different contributions from the various test conditions and target measurements based on experimental error. According to the quality criteria, 40 experimental cases were selected to be a representative dataset for validation. Based on the evaluation of response curves from four head finite element models, CORA was chosen as a quantitative method to compare the predicted time history response to the measured data. Optimization of the CORA global settings led to the recommendation of performing curve comparison on a fixed time interval of 0-30 ms for intracranial pressure and at least 0-40 ms for brain motion and deformation. The allowable maximum time shift was adjusted depending on the shape of the experimental curves (DMAX = 0.12 for intracranial pressure, DMAX = 0.40 for brain motion and DMAX = 0.25 for brain deformation). Finally, bigger penalization of ratings was assigned to curves with fundamentally incorrect shape compared to those having inaccuracies in amplitude or time shift (cubic vs linear). This rigorous approach is necessary to ensure confidence in the model results and progress in the usage of finite element head models for traumatic brain injury prediction.
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| 4. |
- Giordano, Chiara, et al.
(författare)
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Evaluation of Axonal Strain as a Predictor for Mild Traumatic Brain Injuries Using Finite Element Modeling
- 2014
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191. ; 58
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Tidskriftsartikel (refereegranskat)abstract
- Finite element (FE) models are often used to study the biomechanical effects of traumatic brain injury (TBI). Measures based on mechanical responses, such as principal strain or invariants of the strain tensor, are used as a metric to predict the risk of injury. However, the reliability of inferences drawn from these models depends on the correspondence between the mechanical measures and injury data, as well as the establishment of accurate thresholds of tissue injury. In the current study, a validated anisotropic FE model of the human head is used to evaluate the hypothesis that strain in the direction of fibers (axonal strain) is a better predictor of TBI than maximum principal strain (MPS), anisotropic equivalent strain (AESM) and cumulative strain damage measure (CSDM). An analysis of head kinematics-based metrics, such as head injury criterion (HIC) and brain injury criterion (BrIC), is also provided. Logistic regression analysis is employed to compare binary injury data (concussion/no concussion) with continuous strain/kinematics data. The threshold corresponding to 50% of injury probability is determined for each parameter. The predictive power (area under the ROC curve, AUC) is calculated from receiver operating characteristic (ROC) curve analysis. The measure with the highest AUC is considered to be the best predictor of mTBI.Logistic regression shows a statistical correlation between all the mechanical predictors and injury data for different regions of the brain. Peaks of axonal strain have the highest AUC and determine a strain threshold of 0.07 for corpus callosum and 0.15 for the brainstem, in agreement with previously experimentally derived injury thresholds for reversible axonal injury. For a data set of mild TBI from the national football league, the strain in the axonal direction is found to be a better injury predictor than MPS, AESM, CSDM, BrIC and HIC.
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| 5. |
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| 6. |
- Kleiven, Svein, et al.
(författare)
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Correlation of an FE Model of the Human Head with Local Brain Motion : Consequences for Injury Prediction
- 2002
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Ingår i: Stapp Car Crash Journal. - 1532-8546. ; 46, s. 123-144
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Tidskriftsartikel (refereegranskat)abstract
- A parameterized, or scalable, finite element (FE) model of the human head was developed and validated against the available cadaver experiment data for three impact directions (frontal, occipital and lateral). The brain material properties were modeled using a hyperelastic and viscoelastic constitutive law. The interface between the skull and the brain was modeled in three different ways ranging from purely tied (no-slip) to sliding (free-slip). Two sliding contact definitions were compared with the tied condition. Also, three different stiffness parameters, encompassing the range of published brain tissue properties, were tested. The model using the tied contact definition correlated well with the experimental results for the coup and contrecoup pressures in a frontal impact while the sliding interface models did not. Relative motion between the skull and the brain in lowseverity impacts appears to be relatively insensitive to the contact definitions. It is shown that a range of shear stiffness properties for the brain can be used to model the pressure experiments, while relative motion is a more complex measure that is highly sensitive to the brain tissue properties. Smaller relative motion between the brain and skull results from lateral impact than from a frontal or occipital blow for both the experiments and FE simulations. The material properties of brain tissue are important to the characteristics of relative brain-skull motion. The results suggest that significantly lower values of the shear properties of the human brain than currently used in most three-dimensional (3D) FE models today are needed to predict the localized brain response of an impact to the human head.
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| 7. |
- Kleiven, Svein
(författare)
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Predictors for Traumatic Brain Injuries Evaluated through Accident Reconstructions
- 2007
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Ingår i: Stapp Car Crash Journal. - WARRENDALE, PA : SOC AUTOMOTIVE ENGINEERS. - 1532-8546. - 9780768019742 ; 51, s. 81-114
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study is to evaluate all the 58 available NFL cases and compare various predictors for mild traumatic brain injuries using a detailed and extensively validated finite element model of the human head. Global injury measures such as magnitude in angular and translational acceleration, change in angular velocity, head impact power (HIP) and HIC were also investigated with regard to their ability to predict the intracranial pressure and strains associated with injury. The brain material properties were modeled using a hyperelastic and viscoelastic constitutive law. Also, three different stiffness parameters, encompassing a range of published brain tissue properties, were tested. 8 tissue injury predictors were evaluated for 6 different regions, covering the entire cerebrum, as well as for the whole brain. In addition, 10 head kinematics based predictors were evaluated both for correlation with injury as well as with strain and pressure. When evaluating the results, a statistical correlation between strain, strain rate, product of strain and strain rate, Cumulative Strain Damage Measure (CSDM), strain energy density, maximum pressure, magnitude of minimum pressure, as well as von Mises effective stress, with injury was found when looking into specific regions of the brain. However, the maximal pressure in the gray matter showed a higher correlation with injury than other evaluated measures. On the other hand, it was possible, through the reconstruction of a motocross accident, to re-create the injury pattern in the brain of the injured rider using maximal principal strain. It was also found that a simple linear combination of peak change in rotational velocity and HIC showed a high correlation (R=0.98) with the maximum principal strain in the brain, in addition to being a significant predictor of injury. When applying the rotational and translational kinematics separately for one of the cases, it was found that the translational kinematics contribute very little to the intracranial distortional strains while the rotational kinematics contributes insignificantly to the pressure response. This study underlines that the strain based brain tissue injury predictors are very sensitive to the choice of stiffness for the brain tissue.
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| 8. |
- Philippens, Mat, et al.
(författare)
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Comparison of the Rear Impact Biofidelity of BioRID II and RID2
- 2002
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Ingår i: Stapp car crash journal. - 1532-8546. ; 46, s. 461-76
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Tidskriftsartikel (refereegranskat)abstract
- Researchers worldwide try to define a unique test procedure for the assessment of whiplash protection of seats and restraint systems in low speed rear-end impact. Apart from valid injury criteria and uniform crash conditions, there is no clear answer to the question, which dummy to use. There are two impact dummies currently available, which have been designed for rear-end impact testing: BioRID and RID2. Both dummies have been evaluated in several test programs, however, both dummies have never been compared with each other in the test conditions, which form the basis of their design. BioRID was based on and validated against volunteer tests performed by Davidsson and Ono, while RID2 was designed with and validated against PMHS tests done by Bertholon and compared to volunteer tests reported by Van den Kroonenberg. This paper compares the responses of both rear impact dummies and the Hybrid III for the test conditions mentioned above. The setup of Davidsson used a rigid seat with flexible back and head restraint panels, while the setups from Ono and Bertholon used a rigid seat without a head restraint, in spite of being not representative for real car seats. This configuration creates a well defined test environment which will not affect nor obscure the dummy response Results of the performance of both rear impact dummies and the Hybrid III in comparison to the human responses will be presented in this paper. The results show that both rear impact dummies are capable of simulating rear impact responses, especially the head-neck kinematics. A difference in load pattern was found, which could be relevant when injury criteria will be based on neck forces and/or torques. Moreover, the dummies show a different interaction with the seat back, illustrated by the differences in T1 kinematics: BioRID shows larger T1 rotation and more ramping up than RID2, while spine straightening is comparable for both dummies. The current study showed good scores for both dummies in the setup on which they are based. The biofidelity score of BioRID is slightly better than for RID2, while the performance of the Hybrid III is relatively poor. However, repeatability, reproducibility and handling are not part of the evaluation, even though they are important for the practical use of the dummies.
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| 9. |
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| 10. |
- Strandroth, Johan, 1978, et al.
(författare)
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A New Method to Evaluate Future Impact of Vehicle Safety Technology in Sweden
- 2012
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627. ; 56, s. 497-509
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Tidskriftsartikel (refereegranskat)abstract
- In the design of a safe road transport system there is a need to better understand the safety challenges lying ahead. One way of doing that is to evaluate safety technology with retrospective analysis of crashes. However, by using retrospective data there is the risk of adapting safety innovations to scenarios irrelevant in the future. Also, challenges arise as safety interventions do not act alone but are rather interacting components in a complex road transport system. The objective of this study was therefore to facilitate the prioritizing of road safety measures by developing and applying a new method to consider possible impact of future vehicle safety technology. The key point was to project the chain of events leading to a crash today into the crashes for a given time in the future. Assumptions on implementation on safety technologies were made and these assumptions were applied on the crashes of today. It was estimated which crashes would be prevented and the residual was analyzed to identify the characteristics of future crashes. The Swedish Transport Administration's in-depth studies of fatal crashes from 2010 involving car passengers (n=156) were used. This study estimated that the number of killed car occupant would be reduced with 53 percent from the year 2010 to 2020. Through this new method, valuable information regarding the characteristic of the future crashes was found. The results of this study showed that it was possible to evaluate future impact of vehicle safety technology if detailed and representative crash data is available.
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