| 1. |
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| 2. |
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| 3. |
- Alvarez, Victor S, et al.
(författare)
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Effect of pediatric growth on cervical spine kinematics and deformations in automotive crashes
- 2018
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Ingår i: Journal of Biomechanics. - : Elsevier. - 0021-9290 .- 1873-2380. ; 71, s. 76-83
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Tidskriftsartikel (refereegranskat)abstract
- Finite element (FE) models are a powerful tool that can be used to understand injury mechanisms and develop better safety systems. This study aims to extend the understanding of pediatric spine biomechanics, where there is a paucity of studies available. A newly developed and continuously scalable FE model was validated and scaled to 1.5-, 3-, 6-, 10-, 14- and 18-year-old using a non-linear scaling technique, accounting for local topological changes. The oldest and youngest ages were also scaled using homogeneous geometric scaling. To study the effect of pediatric spinal growth on head kinematics and intervertebral disc strain, the models were exerted to 3.5 g acceleration pulse at the T1 vertebra to simulate frontal, rear and side impacts. It was shown that the head rotation increases with age, but is over predicted when geometrically scaling down from 18- to 1.5-year-old and under predicted when geometrically scaling up from 1.5- to 18-year-old. The strain in the disc, however, showed a clear decrease with age in side impact and for the upper cervical spine in rear impact, indicating a higher susceptibility for neck injury at younger ages. In the frontal impact, no clear age dependence could be seen, suggesting a large contribution from changed facet joint angles, and lower levels of strain, suggesting a lower risk of injury. The results also highlight the benefit of rearward facing children in a seat limiting head lateral motion.
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| 4. |
- 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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| 5. |
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| 6. |
- Cecchi, N. J., et al.
(författare)
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Identifying Factors Associated with Head Impact Kinematics and Brain Strain in High School American Football via Instrumented Mouthguards
- 2021
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Ingår i: Annals of Biomedical Engineering. - : Springer Nature. - 0090-6964 .- 1573-9686. ; 49:10, s. 2814-2826
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Tidskriftsartikel (refereegranskat)abstract
- Repeated head impact exposure and concussions are common in American football. Identifying the factors associated with high magnitude impacts aids in informing sport policy changes, improvements to protective equipment, and better understanding of the brain’s response to mechanical loading. Recently, the Stanford Instrumented Mouthguard (MiG2.0) has seen several improvements in its accuracy in measuring head kinematics and its ability to correctly differentiate between true head impact events and false positives. Using this device, the present study sought to identify factors (e.g., player position, helmet model, direction of head acceleration, etc.) that are associated with head impact kinematics and brain strain in high school American football athletes. 116 athletes were monitored over a total of 888 athlete exposures. 602 total impacts were captured and verified by the MiG2.0’s validated impact detection algorithm. Peak values of linear acceleration, angular velocity, and angular acceleration were obtained from the mouthguard kinematics. The kinematics were also entered into a previously developed finite element model of the human brain to compute the 95th percentile maximum principal strain. Overall, impacts were (mean ± SD) 34.0 ± 24.3 g for peak linear acceleration, 22.2 ± 15.4 rad/s for peak angular velocity, 2979.4 ± 3030.4 rad/s2 for peak angular acceleration, and 0.262 ± 0.241 for 95th percentile maximum principal strain. Statistical analyses revealed that impacts resulting in Forward head accelerations had higher magnitudes of peak kinematics and brain strain than Lateral or Rearward impacts and that athletes in skill positions sustained impacts of greater magnitude than athletes in line positions. 95th percentile maximum principal strain was significantly lower in the observed cohort of high school football athletes than previous reports of collegiate football athletes. No differences in impact magnitude were observed in athletes with or without previous concussion history, in athletes wearing different helmet models, or in junior varsity or varsity athletes. This study presents novel information on head acceleration events and their resulting brain strain in high school American football from our advanced, validated method of measuring head kinematics via instrumented mouthguard technology.
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| 7. |
- Cloots, Rudy J.H., et al.
(författare)
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Multi-scale mechanics of traumatic brain injury : predicting axonal strains from head loads
- 2013
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Ingår i: Biomechanics and Modeling in Mechanobiology. - : Springer Science and Business Media LLC. - 1617-7959 .- 1617-7940. ; 12:1, s. 137-150
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Tidskriftsartikel (refereegranskat)abstract
- The length scales involved in the development of diffuse axonal injury typically range from the head level (i.e., mechanical loading) to the cellular level. The parts of the brain that are vulnerable to this type of injury are mainly the brainstem and the corpus callosum, which are regions with highly anisotropically oriented axons. Within these parts, discrete axonal injuries occur mainly where the axons have to deviate from their main course due to the presence of an inclusion. The aim of this study is to predict axonal strains as a result of a mechanical load at the macroscopic head level. For this, a multi-scale finite element approach is adopted, in which a macro-level head model and a micro-level critical volume element are coupled. The results show that the axonal strains cannot be trivially correlated to the tissue strain without taking into account the axonal orientations, which indicates that the heterogeneities at the cellular level play an important role in brain injury and reliable predictions thereof. In addition to the multi-scale approach, it is shown that a novel anisotropic equivalent strain measure can be used to assess these micro-scale effects from head-level simulations only.
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| 8. |
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| 9. |
- Cui, Zhao Ying, et al.
(författare)
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On the assessment of bridging vein rupture associated acute subdural hematoma through finite element analysis
- 2017
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Ingår i: Computer Methods in Biomechanics and Biomedical Engineering. - : Taylor & Francis. - 1025-5842 .- 1476-8259. ; 20:5, s. 530-539
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Tidskriftsartikel (refereegranskat)abstract
- Acute subdural hematoma (ASDH) is a type of intracranial haemorrhage following head impact, with high mortality rates. Bridging vein (BV) rupture is a major cause of ASDH, which is why a biofidelic representation of BVs in finite element (FE) head models is essential for the successful prediction of ASDH. We investigated the mechanical behavior of BVs in the KTH FE head model. First, a sensitivity study quantified the effect of loading conditions and mechanical properties on BV strain. It was found that the peak rotational velocity and acceleration and pulse duration have a pronounced effect on the BV strains. Both Young's modulus and diameter are also negatively correlated with the BV strains. A normalized multiple linear regression model using Young's modulus, outer diameter and peak rotational velocity to predict the BV strain yields an adjusted -value of 0.81. Secondly, cadaver head impact experiments were simulated with varying sets of mechanical properties, upon which the amount of successful BV rupture predictions was evaluated. The success rate fluctuated between 67 and 75%. To further increase the predictive capability of FE head models w.r.t. BV rupture, future work should be directed towards improvement of the BV representation, both geometrically and mechanically.
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| 10. |
- Fahlstedt, Madelen, 1983-, et al.
(författare)
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Current Playground Surface Test Standards Underestimate Brain Injury Risk for Children
- 2019
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Ingår i: Journal of Biomechanics. - : Elsevier BV. - 0021-9290 .- 1873-2380.
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Tidskriftsartikel (refereegranskat)abstract
- Playgrounds surface test standards have been introduced to reduce the number of fatal and severe injuries. However, these test standards have several simplifications to make it practical, robust and cost-effective, such as the head is represented with a hemisphere, only the linear kinematics is evaluated and the body is excluded. Little is known about how these simplifications may influence the test results. The objective of this study was to evaluate the effect of these simplifications on global head kinematics and head injury prediction for different age groups. The finite element human body model PIPER was used and scaled to seven different age groups from 1.5 up to 18 years old, and each model was impacted at three different playground surface stiffness and three head impact locations. All simulations were performed in pairs, including and excluding the body. Linear kinematics and skull bone stress showed small influence if excluding the body while head angular kinematics and brain tissue strain were underestimated by the same simplification. The predicted performance of the three different playground surface materials, in terms of head angular kinematics and brain tissue strain, was also altered when including the body. A body and biofidelic neck need to be included, together with suitable head angular kinematics based injury thresholds, in future physical or virtual playground surface test standards to better prevent brain injuries.
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| 11. |
- Fahlstedt, Madelen, 1983-, et al.
(författare)
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Importance of the Bicycle Helmet Design and Material for the Outcome in Bicycle Accidents
- 2014
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Ingår i: Proceedings, International Cycling Safety Conference 2014. - : Chalmers. ; , s. 1-14
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Konferensbidrag (refereegranskat)abstract
- In Sweden the most common traffic group that needs to be hospitalized due to injury is cyclists where head injuries are the most common severe injuries. According to current standards, the performance of a helmet is only tested against radial impact which is not commonly seen in real accidents. Some studies about helmet design have been published but those helmets have been tested for only a few loading conditions. Therefore, the purpose of this study was to use finite element models to evaluate the effect of the helmet’s design on the head in some more loading conditions.A detailed head model was used to evaluate three different helmet designs as well as non-helmet situations. The first helmet (Baseline Helmet) was an ordinary helmet available on the market. The two other helmet designs were a modification of the Baseline helmet with either a lower density of the EPS liner (Helmet 1) or a sliding layer between the scalp and the EPS liner (Helmet 2). Four different impact locations combined with four different impact directions were tested.The study showed that using a helmet can reduce the peak linear acceleration (85%), peak angular acceleration (87%), peak angular velocity (77%) and peak strain in the brain tissue (77%). The reduction of the strain level was dependent on the loading conditions. Moreover, in thirteen of the sixteen loading conditions Helmet 2 gave lowest peak strain.The alteration of the helmet design showed that more can be done to improve the protective effect of the helmet. This study highlighted the need of a modification of current helmet standard test which can lead to helmets with even better protective properties as well as some challenges in implementing new test standards.
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| 12. |
- Fahlstedt, Madelen, 1983-, et al.
(författare)
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Influence of Strain post-processing on Brain Injury Prediction
- 2022
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Ingår i: Journal of Biomechanics. - : Elsevier BV. - 0021-9290 .- 1873-2380. ; 132
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Tidskriftsartikel (refereegranskat)abstract
- Finite element head models are a tool to better understand brain injury mechanisms. Many of the models use strain as output but with different percentile values such as 100th, 95th, 90th, and 50th percentiles. Some use the element value, whereas other use the nodal average value for the element. Little is known how strain post-processing is affecting the injury predictions and evaluation of different prevention systems. The objective of this study was to evaluate the influence of strain output on injury prediction and ranking.& nbsp;Two models with different mesh densities were evaluated (KTH Royal Institute of Technology head model and the Total Human Models for Safety (THUMS)). Pulses from reconstructions of American football impacts with and without a diagnosis of mild traumatic brain injury were applied to the models. The value for 100th, 99th, 95th, 90th, and 50th percentile for element and nodal averaged element strain was evaluated based on peak values, injury risk functions, injury predictability, correlation in ranking, and linear correlation.& nbsp;The injury risk functions were affected by the post-processing of the strain, especially the 100th percentile element value stood out. Meanwhile, the area under the curve (AUC) value was less affected, as well as the correlation in ranking (Kendall's tau 0.71-1.00) and the linear correlation (Pearson's r2 0.72-1.00). With the results presented in this study, it is important to stress that the same post-processed strain should be used for injury predictions as the one used to develop the risk function.
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| 13. |
- Fahlstedt, Madelen, 1983-, et al.
(författare)
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Ranking and Rating Bicycle Helmet Safety Performance in Oblique Impacts Using Eight Different Brain Injury Models
- 2021
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Ingår i: Annals of Biomedical Engineering. - : Springer. - 0090-6964 .- 1573-9686.
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Tidskriftsartikel (refereegranskat)abstract
- Bicycle helmets are shown to offer protection against head injuries. Rating methods and test standards are used to evaluate different helmet designs and safety performance. Both strain-based injury criteria obtained from finite element brain injury models and metrics derived from global kinematic responses can be used to evaluate helmet safety performance. Little is known about how different injury models or injury metrics would rank and rate different helmets. The objective of this study was to determine how eight brain models and eight metrics based on global kinematics rank and rate a large number of bicycle helmets (n=17) subjected to oblique impacts. The results showed that the ranking and rating are influenced by the choice of model and metric. Kendall’s tau varied between 0.50 and 0.95 when the ranking was based on maximum principal strain from brain models. One specific helmet was rated as 2-star when using one brain model but as 4-star by another model. This could cause confusion for consumers rather than inform them of the relative safety performance of a helmet. Therefore, we suggest that the biomechanics community should create a norm or recommendation for future ranking and rating methods.
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| 14. |
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| 15. |
- Giordano, Chiara, 1988-, et al.
(författare)
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Anisotropic finite element models for brain injury prediction: the sensitivity of axonal strain to white matter tract inter-subjectvariability
- 2017
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Ingår i: Biomechanics and Modeling in Mechanobiology. - : Springer. - 1617-7959 .- 1617-7940.
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Tidskriftsartikel (refereegranskat)abstract
- Computational models incorporating anisotropic features of brain tissue have become a valuable tool for studying the occurrence of traumatic brain injury. The tissue deformation in the direction of white matter tracts (axonal strain) was repeatedly shown to be an appropriate mechanical parameter to predict injury. However, when assessing the reliability of axonal strain to predict injury in a population, it is important to consider the predictor sensitivity to the biological inter-subject variability of the human brain. The present study investigated the axonal strain response of 485 white matter subject-specific anisotropic finite element models of the head subjected to the same loading conditions. It was observed that the biological variability affected the orientation of the preferential directions (coefficient of variation of 39.41% for the elevation angle—coefficient of variation of 29.31% for the azimuth angle) and the determination of the mechanical fiber alignment parameter in the model (gray matter volume 55.55–70.75%). The magnitude of the maximum axonal strain showed coefficients of variation of 11.91%. On the contrary, the localization of the maximum axonal strain was consistent: the peak of strain was typically located in a 2 cm3 volume of the brain. For a sport concussive event, the predictor was capable of discerning between non-injurious and concussed populations in several areas of the brain. It was concluded that, despite its sensitivity to biological variability, axonal strain is an appropriate mechanical parameter to predict traumatic brain injury.
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| 16. |
- Giordano, Chiara
(författare)
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Development of an Anisotropic Finite Element Head Model for Traumatic Brain Injury Prediction
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Traumatic brain injury (TBI) is a worldwide health care problem with very high associatedmorbidity and mortality rates. In particular, the diagnosis of TBI is challenging: symptomsoverlap with other pathologies and the injury is typically not visible with conventionalneuroimaging techniques.Finite element (FE) head models can provide valuable insight into uncovering themechanism underlying brain damage. These models enable the calculation of tissue loadsand deformation patterns, which are thought to be associated with the injury. Measuresbased on tissue strain or invariants of the strain tensor are used as injury predictors and riskinjury curves can be inferred to establish the tolerance of the human head to external loads.However, while in-vitro research shows that the vulnerability to injury is due to highlyorganized structure in white matter tracts, the majority of the current FE models model thebrain as isotropic and homogenous. The deformation of white matter tracts is not calculated.The aim of this doctoral thesis was to incorporate the effects of inhomogeneity andanisotropy of brain tissue into injury analysis. Based on in-vitro experimental evidence, thestrain in the direction of the axons (axonal strain) was proposed as a new, more anatomicallyrelevant, injury predictor. The initial hypothesis to investigate was that an FE anisotropichead model is a better tool to represent TBI because it is more biofidelic in describing thelocal mechanism of axonal impairment.The studies reported in this thesis describe a method for implementing the orientation of thewhite matter tracts in an anisotropic constitutive law for FE modeling. Results from thestudies suggested that the anisotropy of the brain significantly affected the injury predictionsof an FE head model. For an injury dataset from the American National Football League, thepeak of axonal strain - MAS - was found to be a better predictor of injury than isotropic localor global predictors. Finally, based on 27 cases of intracranial pressure, relative skull-brainmotion and brain deformation, the introduction of the brain anisotropy in the FE modelpartially enhanced the biofidelity of the simulations. However, given that the enhancementin biofidelity was not major, it was concluded that further research is necessary forunderstanding the relationship between tissue-level loading and axonal injury.
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| 17. |
- 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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| 18. |
- 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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| 19. |
- Giordano, Chiara, et al.
(författare)
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Performances of the PIPER scalable child human body model in accident reconstruction
- 2017
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Ingår i: PLOS ONE. - : Public Library Science. - 1932-6203. ; 12:11
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Tidskriftsartikel (refereegranskat)abstract
- Human body models (HBMs) have the potential to provide significant insights into the pediatric response to impact. This study describes a scalable/posable approach to perform child accident reconstructions using the Position and Personalize Advanced Human Body Models for Injury Prediction (PIPER) scalable child HBM of different ages and in different positions obtained by the PIPER tool. Overall, the PIPER scalable child HBM managed reasonably well to predict the injury severity and location of the children involved in real-life crash scenarios documented in the medical records. The developed methodology and workflow is essential for future work to determine child injury tolerances based on the full Child Advanced Safety Project for European Roads (CASPER) accident reconstruction database. With the workflow presented in this study, the open-source PIPER scalable HBM combined with the PIPER tool is also foreseen to have implications for improved safety designs for a better protection of children in traffic accidents.
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| 20. |
- Halldin, Peter, et al.
(författare)
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Evaluation of blunt impact protection in a military helmet designed to offer blunt & ballistic impact protection.
- 2013
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Ingår i: Proceedings of the 1<sup>st</sup> International Conference on Helmet Performance and Design.
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Konferensbidrag (refereegranskat)abstract
- This paper describes both a numerical and an experimental approach to measuring the ballistic and blunt impact protection offered by military helmets. The primary purpose of military helmets is to protect users from ballistic impact but modern military helmets protect users from blunt force as well. Altering ballistic shell stiffness, lining the shell with material of different density, even separating the liner from the shell so that they can move independently all affect the transfer of stress to the head and the resulting strain experienced by the brain. The results of this study suggest that there is potential for a helmet that protects the user from both blunt and ballistic impact and can be further improved by implementing an energy absorbing sliding layer, such as the MIPS system, between the shell and the liner to mitigate the effect of oblique impacts.
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| 21. |
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| 22. |
- Halldin, Peter, 1968-, et al.
(författare)
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Improved helmet design and test methods to reduce rotational induced brain injuries
- 2003
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Konferensbidrag (refereegranskat)abstract
- Accidental impacts to the human head are often a combination of translational and rotational accelerations. The most frequent severe brain injuries from accidents are diffuse axonal injury (DAI) and subdural hematoma that both are reported to arise from rotational violence to the head. Most helmet standards used today do only take the translational accelerations into account. It is therefore suggested that an oblique impact test that measures both translational and rotational accelerations should be a complement to the helmet standards used today. This study investigates the potential to reduce the risk for DAI by improving the helmet design by use of an oblique helmet impact test rig. The method used is a detailed finite element (FE) model of the human head. The FE model is used to measure the maximum principal strain in the brain which is suggested as a measurement for the risk to get DAI. The results clearly show the importance of testing a helmet in oblique impacts. Comparing a pure vertical impact with a 45 degree oblique impact with the same initial impact energy shows that the strain in the central parts of the brain is increased with a factor of 6. It is therefore suggested that a future helmet impact standard should include a rotational component so that the helmet is designed for both radial and tangential forces. Such a test method, an oblique impact test, was used to compare two different helmet designs. One helmet was manufactured with the shell glued to the liner and one helmet was designed with a low friction layer between the shell and the liner (MIPS). It was shown that the strain in the FE model of the human head was reduced be 27% comparing the MIPS helmet to the glued helmet design.
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| 23. |
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| 24. |
- Halldin, Peter, 1968-, et al.
(författare)
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Reduced risk for DAI by use of a new safety helmet
- 2003
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Konferensbidrag (refereegranskat)abstract
- Accidental impacts to the human head are often a combination of translational and rotational accelerations. The most frequent severe brain injuries from accidents are diffuse axonal injury (DAI) and subdural hematoma that both are reported to arise from rotational violence to the head. Most helmet standards used today do only take the translational accelerations into account. It is therefore suggested that an oblique impact test that measures both translational and rotational accelerations should be a complement to the helmet standards used today. This study investigates the potential to reduce the risk for DAI by improving the helmet design by use of an oblique helmet impact test rig. The method used is a detailed finite element (FE) model of the human head. The FE model is used to measure the maximum principal strain in the brain which is suggested as a measurement for the risk to get DAI. The results clearly show the importance of testing a helmet in oblique impacts. Comparing a pure vertical impact with a 45 degree oblique impact with the same initial impact energy shows that the strain in the central parts of the brain is increased with a factor of 6. It is therefore suggested that a future helmet impact standard should include a rotational component so that the helmet is designed for both radial and tangential forces. Such a test method, an oblique impact test, was used to compare two different helmet designs. One helmet was manufactured with the shell glued to the liner and one helmet was designed with a low friction layer between the shell and the liner (MIPS). It was shown that the strain in the FE model of the human head was reduced be 27% comparing the MIPS helmet to the glued helmet design.
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| 25. |
- Halldin, Peter, et al.
(författare)
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The development of next generation test standards for helmets.
- 2013
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Ingår i: The development of next generation test standards for helmets..
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Konferensbidrag (refereegranskat)abstract
- Injury statistics show that accidents with a head impact often happen with an angle to the impacting object. An angled impact will result in a rotation of the head if the friction is high enough. It is also known that the head is more sensitive to rotation than pure linear motion of the head. CEN has initiated the work to design a new helmet test oblique or angled impact test method a helmet test method that can measure the rotational energy absorption in a helmet during an angled impact. This paper presents a short summary of possibilities and limitations on how to build a helmet test method that can measure the rotational energy absorption in a helmet during an angled impact.
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| 26. |
- Henningsen, Mikkel Jon, et al.
(författare)
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Subject-specific finite element head models for skull fracture evaluation—a new tool in forensic pathology
- 2024
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Ingår i: International journal of legal medicine. - : Springer Nature. - 0937-9827 .- 1437-1596. ; 138:4, s. 1447-1458
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Tidskriftsartikel (refereegranskat)abstract
- Post-mortem computed tomography (PMCT) enables the creation of subject-specific 3D head models suitable for quantitative analysis such as finite element analysis (FEA). FEA of proposed traumatic events is an objective and repeatable numerical method for assessing whether an event could cause a skull fracture such as seen at autopsy. FEA of blunt force skull fracture in adults with subject-specific 3D models in forensic pathology remains uninvestigated. This study aimed to assess the feasibility of FEA for skull fracture analysis in routine forensic pathology. Five cases with blunt force skull fracture and sufficient information on the kinematics of the traumatic event to enable numerical reconstruction were chosen. Subject-specific finite element (FE) head models were constructed by mesh morphing based on PMCT 3D models and A Detailed and Personalizable Head Model with Axons for Injury Prediction (ADAPT) FE model. Morphing was successful in maintaining subject-specific 3D geometry and quality of the FE mesh in all cases. In three cases, the simulated fracture patterns were comparable in location and pattern to the fractures seen at autopsy/PMCT. In one case, the simulated fracture was in the parietal bone whereas the fracture seen at autopsy/PMCT was in the occipital bone. In another case, the simulated fracture was a spider-web fracture in the frontal bone, whereas a much smaller fracture was seen at autopsy/PMCT; however, the fracture in the early time steps of the simulation was comparable to autopsy/PMCT. FEA might be feasible in forensic pathology in cases with a single blunt force impact and well-described event circumstances.
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| 27. |
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| 28. |
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| 29. |
- Ho, Johnson, 1977-, et al.
(författare)
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The peculiar properties of the faix and tentorium in brain injury biomechanics
- 2017
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Ingår i: Journal of Biomechanics. - : ELSEVIER SCI LTD. - 0021-9290 .- 1873-2380. ; 60, s. 243-247
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the faix and tentorium on brain injury biomechanics during impact was studied with finite element (FE) analysis. Three detailed 3D FE head models were created based on the images of a healthy, normal size head. Two of the models contained the addition of falx and tentorium with material properties from previously published experiments. Impact loadings from a reconstructed concussive case in a sport accident were applied to the two players involved. The results suggested that the faix and tentorium could induce large strains to the surrounding brain tissues, especially to the corpus callosum and brainstem. The tentorium seemed to constrain the motion of the cerebellum while inducing large strain in the brainstem in both players involved in the accident (one player had mainly coronal head rotation and the other had both coronal and transversal rotations). Since changed strain levels were observed in the brainstem and corpus callosum, which are classical sites for diffuse axonal injuries (DAI), we confirmed the importance of using accurate material properties for falx and tentorium in a FE head model when studying traumatic brain injuries.
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| 30. |
- Huang, Qi, et al.
(författare)
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A method for generating case-specific vehicle models from a single-view vehicle image for accurate pedestrian injury reconstructions
- 2024
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Ingår i: Accident Analysis and Prevention. - : Elsevier BV. - 0001-4575 .- 1879-2057. ; 200
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Tidskriftsartikel (refereegranskat)abstract
- Developing vehicle finite element (FE) models that match real accident-involved vehicles is challenging. This is related to the intricate variety of geometric features and components. The current study proposes a novel method to efficiently and accurately generate case-specific buck models for car-to-pedestrian simulations. To achieve this, we implemented the vehicle side-view images to detect the horizontal position and roundness of two wheels to rectify distortions and deviations and then extracted the mid-section profiles for comparative calculations against baseline vehicle models to obtain the transformation matrices. Based on the generic buck model which consists of six key components and corresponding matrices, the case-specific buck model was generated semi-automatically based on the transformation metrics. Utilizing this image-based method, a total of 12 vehicle models representing four vehicle categories including family car (FCR), Roadster (RDS), small Sport Utility Vehicle (SUV), and large SUV were generated for car-to-pedestrian collision FE simulations in this study. The pedestrian head trajectories, total contact forces, head injury criterion (HIC), and brain injury criterion (BrIC) were analyzed comparatively. We found that, even within the same vehicle category and initial conditions, the variation in wrap around distance (WAD) spans 84–165 mm, in HIC ranges from 98 to 336, and in BrIC fluctuates between 1.25 and 1.46. These findings highlight the significant influence of vehicle frontal shape and underscore the necessity of using case-specific vehicle models in crash simulations. The proposed method provides a new approach for further vehicle structure optimization aiming at reducing pedestrian head injury and increasing traffic safety.
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| 31. |
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| 32. |
- Huang, Qi, et al.
(författare)
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Finite Element Analysis of Energy-Absorbing Floors for Reducing Head Injury Risk during Fall Accidents
- 2023
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Ingår i: Applied Sciences. - : Multidisciplinary Digital Publishing Institute (MDPI). - 2076-3417. ; 13:24
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Tidskriftsartikel (refereegranskat)abstract
- Featured Application: The results proposed a new approach to evaluate the protection effectiveness of energy-absorbing floors for fall-related injury prevention. Also, it could help to reduce the huge associated costs related to fall-related injuries among the children and elderly population. Energy-absorbing floor (EAF) has been proposed as one of several biomechanically effective strategies to mitigate the risk of fall-related injuries by decreasing peak loads and enhancing system energy absorption. This study aims to compare the protective capacity of four commercially available EAF products (Igelkott Floor, Kradal, SmartCells, and OmniSports) in terms of head impacts using the finite element (FE) method. The stress–strain curves acquired from mechanical tests were applied to material models in LS-Dyna. The established FE models were then validated using Hybrid III or hemispheric drop tests to compare the acceleration–time curves between experiments and simulations. Finally, the validated FE models were utilized to simulate a typical pedestrian fall accident scenario. It was demonstrated that EAFs can substantially reduce the peak forces, acceleration, and velocity changes during fall-related head impacts. Specifically, in the accident reconstruction scenario, SmartCells provided the largest reduction in peak linear acceleration and skull fracture risk, while Igelkott Floor provided the largest reduction in peak angular velocity and concussion risk. This performance was caused by different energy absorption mechanisms. Consequently, the results can contribute to supporting the implementation of EAFs and determine the effectiveness of various protective strategies for fall-related head injury prevention.
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| 33. |
- Huber, Colin M., et al.
(författare)
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Finite element brain deformation in adolescent soccer heading
- 2024
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Ingår i: Computer Methods in Biomechanics and Biomedical Engineering. - : Informa UK Limited. - 1025-5842 .- 1476-8259. ; 27:10, s. 1239-1249
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Tidskriftsartikel (refereegranskat)abstract
- Finite element (FE) modeling provides a means to examine how global kinematics of repetitive head loading in sports influences tissue level injury metrics. FE simulations of controlled soccer headers in two directions were completed using a human head FE model to estimate biomechanical loading on the brain by direction. Overall, headers were associated with 95th percentile peak maximum principal strains up to 0.07 and von Mises stresses up to 1450 Pa, and oblique headers trended toward higher values than frontal headers but below typical injury levels. These quantitative data provide insight into repetitive loading effects on the brain.
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| 34. |
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| 35. |
- Ji, S., et al.
(författare)
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Use of Brain Biomechanical Models for Monitoring Impact Exposure in Contact Sports
- 2022
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Ingår i: Annals of Biomedical Engineering. - : Springer Nature. - 0090-6964 .- 1573-9686. ; 50:11, s. 1389-1408
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Tidskriftsartikel (refereegranskat)abstract
- Head acceleration measurement sensors are now widely deployed in the field to monitor head kinematic exposure in contact sports. The wealth of impact kinematics data provides valuable, yet challenging, opportunities to study the biomechanical basis of mild traumatic brain injury (mTBI) and subconcussive kinematic exposure. Head impact kinematics are translated into brain mechanical responses through physics-based computational simulations using validated brain models to study the mechanisms of injury. First, this article reviews representative legacy and contemporary brain biomechanical models primarily used for blunt impact simulation. Then, it summarizes perspectives regarding the development and validation of these models, and discusses how simulation results can be interpreted to facilitate injury risk assessment and head acceleration exposure monitoring in the context of contact sports. Recommendations and consensus statements are presented on the use of validated brain models in conjunction with kinematic sensor data to understand the biomechanics of mTBI and subconcussion. Mainly, there is general consensus that validated brain models have strong potential to improve injury prediction and interpretation of subconcussive kinematic exposure over global head kinematics alone. Nevertheless, a major roadblock to this capability is the lack of sufficient data encompassing different sports, sex, age and other factors. The authors recommend further integration of sensor data and simulations with modern data science techniques to generate large datasets of exposures and predicted brain responses along with associated clinical findings. These efforts are anticipated to help better understand the biomechanical basis of mTBI and improve the effectiveness in monitoring kinematic exposure in contact sports for risk and injury mitigation purposes.
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| 36. |
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| 37. |
- Kapeliotis, Markos, et al.
(författare)
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The sensitivity to inter-subject variability of the bridging vein entry angles for prediction of acute subdural hematoma
- 2019
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Ingår i: Journal of Biomechanics. - : Elsevier. - 0021-9290 .- 1873-2380. ; 92, s. 6-10
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Tidskriftsartikel (refereegranskat)abstract
- Acute subdural hematoma (ASDH) is one of the most frequent traumatic brain injuries (TBIs) with high mortality rate. Bridging vein (BV) ruptures is a major cause of ASDH. The KTH finite element head model includes bridging veins to predict acute subdural hematoma due to BV rupture. In this model, BVs were positioned according to Oka et al. (1985). The aim of the current study is to investigate whether the location and entry angles of these BVs could be modelled using data from a greater statistical sample, and what the impact of this improvement would be on the model's predictive capability of BV rupture. From the CT angiogram data of 78 patients, the relative position of the bridging veins and their entry angles along the superior sagittal sinus was determined. The bridging veins were repositioned in the model accordingly. The performance of the model, w.r.t. BV rupture prediction potential was tested on simulations of full body cadaver head impact experiments. The experiments were simulated on the original version of the model and on three other versions which had updated BV positions according to mean, maximum and minimum entry angles. Even though the successful prediction rate between the models stayed the same, the location of the rupture site significantly improved for the model with the mean entry angles. Moreover, the models with maximum and minimum entry angles give an insight of how BV biovariability can influence ASDH. In order to further improve the successful prediction rate, more biofidelic data are needed both with respect to bridging vein material properties and geometry. Furthermore, more experimental data are needed in order to investigate the behaviour of FE head models in depth.
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| 38. |
- Kleiven, Svein, 1966-
(författare)
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A Parametric Study of Energy Absorbing Foams for Head Injury Prevention
- 2007
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Ingår i: The 20th ESV Conference Proceedings.
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Konferensbidrag (refereegranskat)abstract
- This paper describes a parametric study of foammaterial properties for interior car surfaces usingfinite element calculations. Two different headmodels were used for the impact simulations, aHybrid III dummy head and a biomechanical headmodel. The objective was to study the head injurycriterion (dummy) (HIC(d)), the angular velocity, theresultant acceleration and, for the human headmodels, the strain in the brain tissue and the stress inthe skull for a variation in foam material propertiessuch as stiffness, plateau stress and energyabsorption. The analysis gave at hand that the bestchoice of material properties with respect to impactusing the Hybrid III head model reached differentresults compared to an impact with the biomechanicalhead model. For a purely perpendicular impact, theHIC(d) for the head model managed to predict thestrain level in the brain quite well. Even though theHIC reached acceptable levels for both aperpendicular and oblique impact towards a 31 kg/m3EPP padding, the maximum strain in the human headmodel for an oblique impact was almost twicesuggested allowable levels. The difference in thestrain in the brain between an oblique andperpendicular impact when impacted with sameinitial velocity towards the same padding was notpredicted by the HIC(d).
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| 39. |
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| 40. |
- Kleiven, Svein, 1966-
(författare)
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Biomechanics and Prevention
- 2020
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Ingår i: Management of Severe Traumatic Brain Injury. - Cham : Springer.
-
Bokkapitel (refereegranskat)abstract
- Injury statistics have found the most common accident situation to be an oblique impact. An oblique impact will give rise to both linear and rotational head kinematics. The low shear modulus and nearly incompressible properties of brain tissue make it to deform primarily in shear for a given impact. This gives a large sensitivity of the brain to rotational loading and a small sensitivity to linear kinematics. Therefore, rotational kinematics is the best indicator of TBI risk. A radial impact, such as in fall accidents, causes substantially higher stresses in the skull with an associated higher risk of skull fractures and TBIs secondary to those impacts.
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| 41. |
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| 42. |
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| 43. |
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| 44. |
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| 45. |
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| 46. |
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| 47. |
- Kleiven, Svein, 1966-
(författare)
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Cycle helmets
- 2011
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Ingår i: IOC World Conference on Prevention of Injury & Illness in Sports.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 48. |
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| 49. |
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| 50. |
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