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  • 1. Beillas, Philippe
    et al.
    Giordano, Chiara
    Alvarez, Victor
    Li, Xiaogai
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Neuronic Engineering.
    Ying, Xingjia
    Chevalier, Marie-Christine
    Kirscht, Stefan
    Kleiven, Svein
    Development and performance of the PIPER scalable child human body models2016In: 14th International Conference on the Protection of Children in Cars, 2016Conference paper (Refereed)
  • 2. Beillas, Philippe
    et al.
    Lafon, Yoann
    Frechede, Bertrand
    Janak, Tomas
    Dupeux, Thomas
    Mear, Matthieu
    Kleiven, Svein
    Giordano, Chiara
    Alvarez, Victor
    Li, Xiaogai
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Neuronic Engineering.
    Chawla, Anoop
    Chhabra, A
    Paruchuri, S an Singh, S
    Kaushik, D
    Mukherjee, S
    Kumar, S
    Devane, K
    Mishra, K
    Machina, G
    Jolivet, Erwan
    Lemaire, Thomas
    Faure, François
    Gilles, Benjamin
    Vimont, Ulysse
    Lecomte, Christophe
    D3. 8 Final version of the personalization and positioning software tool with documentation. PIPER EU Project2017Report (Refereed)
  • 3. Beillas, Philippe
    et al.
    Wang, Xuguang
    Lafon, Yoann
    Frechede, Bertrand
    Janak, Tomas
    Dupeux, Thomas
    Mear, Matthieu
    Pacquaut, Guillaume
    Chevalier, Marie-Christine
    Le Ruyet, Anicet
    Eichene, Alexandre
    Theodorakos, Ilias
    Yin, Xingjia
    Gardegaront, M
    Collot, Jerome
    Petit, Philippe
    Eric, Song
    Moreau, Baptiste
    Kleiven, Svein
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Neuronic Engineering.
    Giordano, Chiara
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Neuronic Engineering.
    Strömbäck, Alvarez Victor
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Neuronic Engineering.
    Li, Xiaogai
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Neuronic Engineering.
    et al,
    PIPER EU Project Final publishable summary2017Report (Refereed)
  • 4.
    Fahlstedt, Madelen
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Neuronic Engineering.
    Kleiven, Svein
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Neuronic Engineering.
    Li, Xiaogai
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Neuronic Engineering.
    Current Playground Surface Test Standards Underestimate Brain Injury Risk for Children2019In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380Article in journal (Refereed)
    Abstract [en]

    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.

  • 5.
    Fahlstedt, Madelen
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Neuronic Engineering.
    Kleiven, Svein
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Neuronic Engineering.
    Li, Xiaogai
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Neuronic Engineering.
    The Influence of the Body on Head Kinematics in Playground Falls for Different Age Groups2018In: Proceedings of International Research Council on Biomechanics of Injury (IRCOBI) Conference, 2018Conference paper (Refereed)
  • 6.
    Giordano, Chiara
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Neuronic Engineering.
    Li, Xiaogai
    KTH, School of Technology and Health (STH), Medical Engineering, Neuronic Engineering.
    Kleiven, Svein
    KTH, School of Technology and Health (STH), Medical Engineering, Neuronic Engineering.
    Performances of the PIPER scalable child human body model in accident reconstruction2017In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 12, no 11, article id e0187916Article in journal (Refereed)
    Abstract [en]

    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.

  • 7.
    Ho, Johnson
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Neuronic Engineering.
    Zhou, Zhou
    KTH, School of Technology and Health (STH), Medical Engineering, Neuronic Engineering.
    Li, Xiaogai
    KTH, School of Technology and Health (STH), Medical Engineering, Neuronic Engineering.
    Kleiven, Svein
    KTH, School of Technology and Health (STH), Medical Engineering, Neuronic Engineering.
    The peculiar properties of the faix and tentorium in brain injury biomechanics2017In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 60, p. 243-247Article in journal (Refereed)
    Abstract [en]

    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. 

  • 8.
    Li, Xiaogai
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Finite Element and Neuroimaging Techniques toImprove Decision-Making in Clinical Neuroscience2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Our brain, perhaps the most sophisticated and mysterious part of the human body, to some extent, determines who we are. However, it’s a vulnerable organ. When subjected to an impact, such as a traffic accident or sport, it may lead to traumatic brain injury (TBI) which can have devastating effects for those who suffer the injury. Despite lots of efforts have been put into primary injury prevention, the number of TBIs is still on an unacceptable high level in a global perspective.

    Brain edema is a major neurological complication of moderate and severe TBI, which consists of an abnormal accumulation of fluid within the brain parenchyma. Clinically, local and minor edema may be treated conservatively only by observation, where the treatment of choice usually follows evidence-based practice. In the first study, the gravitational force is suggested to have a significant impact on the pressure of the edema zone in the brain tissue. Thus, the objective of the study was to investigate the significance of head position on edema at the posterior part of the brain using a Finite Element (FE) model. The model revealed that water content (WC) increment at the edema zone remained nearly identical for both supine and prone positions. However, the interstitial fluid pressure (IFP) inside the edema zone decreased around 15% by having the head in a prone position compared with a supine position. The decrease of IFP inside the edema zone by changing patient position from supine to prone has the potential to alleviate the damage to axonal fibers of the central nervous system. These observations suggest that considering the patient’s head position during intensive care and at rehabilitation should be of importance to the treatment of edematous regions in TBI patients.

    In TBI patients with diffuse brain edema, for most severe cases with refractory intracranial hypertension, decompressive craniotomy (DC) is performed as an ultimate therapy. However, a complete consensus on its effectiveness has not been achieved due to the high levels of severe disability and persistent vegetative state found in the patients treated with DC. DC allows expansion of the swollen brain outside the skull, thereby having the potential in reducing the Intracranial Pressure (ICP). However, the treatment causes stretching of the axons and may contribute to the unfavorable outcome of the patients. The second study aimed at quantifying the stretching and WC in the brain tissue due to the neurosurgical intervention to provide more insight into the effects upon such a treatment. A nonlinear registration method was used to quantify the strain. Our analysis showed a substantial increase of the strain level in the brain tissue close to the treated side of DC compared to before the treatment. Also, the WC was related to specific gravity (SG), which in turn was related to the Hounsfield unit (HU) value in the Computerized Tomography (CT) images by a photoelectric correction according to the chemical composition of the brain tissue. The overall WC of brain tissue presented a significant increase after the treatment compared to the condition seen before the treatment. It is suggested that a quantitative model, which characterizes the stretching and WC of the brain tissue both before as well as after DC, may clarify some of the potential problems with such a treatment.

    Diffusion Weighted (DW) Imaging technology provides a noninvasive way to extract axonal fiber tracts in the brain. The aim of the third study, as an extension to the second study was to assess and quantify the axonal deformation (i.e. stretching and shearing)at both the pre- and post-craniotomy periods in order to provide more insight into the mechanical effects on the axonal fibers due to DC.

    Subarachnoid injection of artificial cerebrospinal fluid (CSF) into the CSF system is widely used in neurological practice to gain information on CSF dynamics. Mathematical models are important for a better understanding of the underlying mechanisms. Despite the critical importance of the parameters for accurate modeling, there is a substantial variation in the poroelastic constants used in the literature due to the difficulties in determining material properties of brain tissue. In the fourth study, we developed a Finite Element (FE) model including the whole brain-CSF-skull system to study the CSF dynamics during constant-rate infusion. We investigated the capacity of the current model to predict the steady state of the mean ICP. For transient analysis, rather than accurately fit the infusion curve to the experimental data, we placed more emphasis on studying the influences of each of the poroelastic parameters due to the aforementioned inconsistency in the poroelastic constants for brain tissue. It was found that the value of the specific storage term S_epsilon is the dominant factor that influences the infusion curve, and the drained Young’s modulus E was identified as the dominant parameter second to S_epsilon. Based on the simulated infusion curves from the FE model, Artificial Neural Network (ANN) was used to find an optimized parameter set that best fit the experimental curve. The infusion curves from both the FE simulations and using ANN confirmed the limitation of linear poroelasticity in modeling the transient constant-rate infusion.

    To summarize, the work done in this thesis is to introduce FE Modeling and imaging technologiesincluding CT, DW imaging, and image registration method as a complementarytechnique for clinical diagnosis and treatment of TBI patients. Hopefully, the result mayto some extent improve the understanding of these clinical problems and improve theirmedical treatments.

  • 9.
    Li, Xiaogai
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Neuronic Engineering. Department of Mechanical Engineering, Southern Methodist University, P. O. Box 750337, Dallas, TX 75275-0337, United States.
    Gao, X-L
    Kleiven, Svein
    KTH, School of Technology and Health (STH), Medical Engineering, Neuronic Engineering.
    Behind helmet blunt trauma induced by ballistic impact: a computational model2016In: International Journal of Impact Engineering, ISSN 0734-743X, Vol. 91, p. 56-67Article in journal (Refereed)
    Abstract [en]

    Behind helmet blunt trauma (BHBT) has emerged as a serious injury type experienced by soldiers in battlefields. BHBT has been found to range from skin lacerations to brain damage and extensive skull fracture. It has been believed that such injuries are caused by forces transmitted from the helmet's back face deformation (BFD), which result in local deformations of the skull and translation or rotation of the head, leading to brain injuries. In this study, head injury risks resulting from the BFD of the Advanced Combat Helmet (ACH) under ballistic impact are evaluated using finite element simulations. The head model developed at KTH in Sweden is adopted, and a helmet shell model (including foam pads) is constructed. The examined mechanical parameters include the maximum von Mises stress in the skull, pressure (mean normal stress) and maximum principal strain in the brain tissue, contact force, and head acceleration. The influences of the foam pad hardness, stand-off distance, helmet shell thickness, and impact direction on head injury risks are studied. It is found that a softer foam pad offers a better protection, but the foam pad cannot be too soft. Also, it is shown that a slightly larger stand-off distance leads to a significant reduction in head injury. In addition, the simulation results reveal that an increase in the helmet thickness reduces the injury risk. It is further observed that a 45-degree oblique frontal impact results in a lower head injury risk than a 90-degree frontal impact. Moreover, for a helmet protected head under ballistic impact, it is seen that a high risk of skull fracture does not necessarily mean an equally high risk of injury to the brain tissue. The predictions from the current model of a helmeted head under ballistic impact agree with experimental findings independently obtained by others. The newly developed model provides a useful tool for studying injury mechanisms of BHBT and evaluating the existing standards for testing and designing combat helmets.

  • 10.
    Li, Xiaogai
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Neuronic Engineering.
    Sandler, Håkan
    Kleiven, Svein
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Neuronic Engineering.
    Infant skull fractures: Accident or abuse?: Evidences from biomechanical analysis using finite element head models2019In: Forensic science international, Vol. 294, p. 173-182Article in journal (Refereed)
    Abstract [en]

    Abusive Head Trauma (AHT) is considered by some authors to be a leading cause of traumatic death in children less than two years of age and skull fractures are commonly seen in cases of suspected AHT. Today, diagnosing whether the observed fractures are caused by abuse or accidental fall is still a challenge within both the medical and the legal communities and the central question is a biomechanical question: can the described history explain the observed fractures? Finite element (FE) analysis has been shown a valuable tool for biomechanical analysis accounting for detailed head geometry, advanced material modelling, and case-specific factors (e.g. head impact location, impact surface properties). Here, we reconstructed two well-documented suspected abuse cases (a 3- and a 4-month-old) using subject-specific FE head models. The models incorporate the anatomical details and age-dependent anisotropic material properties of infant cranial bones that reflect the grainy fibres radiating from ossification centres. The impact locations are determined by combining multimodality images. The results show that the skull fracture patterns in both cases of suspected abuse could be explained by the described accidental fall history, demonstrating the inherent potential of FE analysis for providing biomechanical evidence to aid forensic investigations. Increased knowledge of injury mechanisms in children may have enormous medico-legal implications world-wide. 

  • 11.
    Li, Xiaogai
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Neuronic Engineering.
    Sandler, Håkan
    Kleiven, Svein
    KTH, School of Technology and Health (STH), Medical Engineering, Neuronic Engineering.
    The importance of nonlinear tissue modelling in finite element simulations of infant head impacts2017In: Biomechanics and Modeling in Mechanobiology, ISSN 1617-7959, E-ISSN 1617-7940, Vol. 16, no 3, p. 823-840Article in journal (Refereed)
    Abstract [en]

    Despite recent efforts on the development of finite element (FE) head models of infants, a model capable of capturing head responses under various impact scenarios has not been reported. This is hypothesized partially attributed to the use of simplified linear elastic models for soft tissues of suture, scalp and dura. Orthotropic elastic constants are yet to be determined to incorporate the direction-specific material properties of infant cranial bone due to grain fibres radiating from the ossification centres. We report here on our efforts in advancing the above-mentioned aspects in material modelling in infant head and further incorporate them into subject-specific FE head models of a newborn, 5- and 9-month-old infant. Each model is subjected to five impact tests (forehead, occiput, vertex, right and left parietal impacts) and two compression tests. The predicted global head impact responses of the acceleration-time impact curves and the force-deflection compression curves for different age groups agree well with the experimental data reported in the literature. In particular, the newly developed Ogden hyperelastic model for suture, together with the nonlinear modelling of scalp and dura mater, enables the models to achieve more realistic impact performance compared with linear elastic models. The proposed approach for obtaining age-dependent skull bone orthotropic material constants counts both an increase in stiffness and decrease in anisotropy in the skull bone-two essential biological growth parameters during early infancy. The profound deformation of infant head causes a large stretch at the interfaces between the skull bones and the suture, suggesting that infant skull fractures are likely to initiate from the interfaces; the impact angle has a profound influence on global head impact responses and the skull injury metrics for certain impact locations, especially true for a parietal impact.

  • 12.
    Li, Xiaogai
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Neuronic Engineering.
    von Holst, Hans
    Finite element modeling of decompressive craniectomy (DC) and its clinical validation2015In: ADVANCES IN BIOMEDICAL SCIENCE AND ENGINEERING, Vol. 2, no 1, p. 1-9Article in journal (Refereed)
    Abstract [en]

    Decompressive craniectomy (DC) is a reliable neurosurgical approach to reduce a pathologically increased intracranial pressure after neurological diseases such as severe traumatic brain injury (TBI) and stroke. The procedure has substantially reduced the mortality rate but at the expense of increased neurological cognitive impairments. Finite Element (FE) modeling in the past decades has become an important tool to develop innovative treatment strategies in various areas of the clinical neuroscience field. The aim of this study was to develop patient-specific FE models to simulate DC surgery and validate the models against patients' clinical data. The FE models were created based on the Computed Tomography (CT) images of six patients treated with DC. Brain tissue was modeled as poroelastic material. To validate the model prediction, the motion of brain surface at the DC area from the simulation was compared with the measured values from medical images which were derived from image registration. The results from the computational simulations gave a reliable prediction of brain surface motion at DC area for all the six patients evaluated. Both the deformation pattern and the quantitative values of the brain surface displacement from the model simulation were found in good agreement with measured values from medical images. The developed FE model and its validation in this study is a prerequisite for future investigations aiming at finding optimal treatment for a specific patient which hopefully will significantly improve patients' outcome.

  • 13.
    Li, Xiaogai
    et al.
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    von Holst, Hans
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Ho, Johnson
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Kleiven, Svein
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    3-D Finite Element Modeling of Brain Edema: Initial Studies on Intracranial Pressure Using COMSOL Multiphysics2009In: COMSOL Conference, 2009Conference paper (Refereed)
    Abstract [en]

    Brain edema is one of the most common consequences of serious traumatic brain injuries which is usually accompanied with increased Intracranial Pressure (ICP) due to water content increment. A three dimensional finite element model of brain edema is used to study intracranial pressure in this paper. Three different boundary conditions at the end of Cerebral Spinal Fluid (CSF) were used to investigate the boundary condition effects on the volume-pressure curve based on the current model. Compared with the infusion experiments, results from the simulations show that exponential pressure boundary condition model corresponds well with the experiment

  • 14.
    Li, Xiaogai
    et al.
    KTH, School of Technology and Health (STH), Neuronic Engineering (Closed 20130701).
    von Holst, Hans
    KTH, School of Technology and Health (STH), Neuronic Engineering (Closed 20130701).
    Ho, Johnson
    KTH, School of Technology and Health (STH), Neuronic Engineering (Closed 20130701).
    Kleiven, Svein
    KTH, School of Technology and Health (STH), Neuronic Engineering (Closed 20130701).
    Three Dimensional Poroelastic Simulation of Brain Edema: Initial studies on intracranial pressure2010In: IFMBE Proceedings, 2010, 2010, p. 1478-1481Conference paper (Refereed)
    Abstract [en]

    Brain edema is one of the most common consequences of serious head injury because of the enhancement of water content and thus the increased brain volume. Once the brain compensation mechanisms have been exhausted, the intracranial pressure (ICP) will increase exponentially because the brain is enclosed in the rigid skull. Previous research suggests that the poroelastic theory provides a solution for studying the fluid flow in the brain. In this paper, poroelastic theory is used to study the intracranial pressure distribution due to traumatic brain edema by a detailed 3D finite element brain model.

  • 15.
    Li, Xiaogai
    et al.
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    von Holst, Hans
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Ho, Johnson
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Kleiven, Svein
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Three Dimensional Poroelastic Simulation of Brain Edema: Initial Studies on Intracranial Pressure Using Comsol Multiphysics2009In: Proceedings of European Comsol Conference, Milan, Italy, October 7 - 9, 2009Conference paper (Refereed)
  • 16.
    Li, Xiaogai
    et al.
    KTH, School of Technology and Health (STH), Neuronic Engineering (Closed 20130701).
    von Holst, Hans
    KTH, School of Technology and Health (STH), Neuronic Engineering (Closed 20130701).
    Kleiven, Svein
    KTH, School of Technology and Health (STH), Neuronic Engineering (Closed 20130701).
    Decompressive craniotomy causes significant strain increase in axonal fiber tracts2012In: Journal of clinical neuroscience, ISSN 0967-5868, E-ISSN 1532-2653, Vol. 20, no 4, p. 509-513Article in journal (Refereed)
    Abstract [en]

    Background

    Decompressive craniotomy allows expansion of the swollen brain outside the skull, resulting in axonal stretch, which might lead to neural injury and consequently cause unfavorable outcome for the patients. The aim of this study was to assess and quantify the axonal deformation at both pre- and post-craniotomy period in order to provide more insight into the mechanical effects on the axonal fibers upon such a treatment.

    Methods

    Displacement fields representing the structural changes in whole brain were obtained by a nonlinear image registration method based on the three-dimensional CT imaging data sets of a patient both before and after decompressive craniotomy. Axonal fiber tracts together with their orientations were extracted from diffusion weighted (DW) images from a healthy brain and adapted to the patient’s brain by image registration. The deformation of the brain tissue in the form of Lagrangian finite strain tensor for the entire brain was then calculated from the displacement field. Based on the obtained brain tissue strain tensor and the axonal fiber tracts, 1st principal strain was extracted at axonal fibers. Furthermore, other axonal deformation measures, i.e., axonal strain, and axonal effective shear strain were also quantified.

    Results

    Greatest axonal fiber displacement (up to 12 mm) was found predominantly located in the treated part of the craniotomy, accompanied by a large axonal deformation, e.g., 1st principal strain up to 0.49. This indicated the extent of axonal fiber stretching due to the neurosurgical intervention. Other strain measures, such as axonal strain and axonal effective shear strain also showed an increased level at the treated part for post-craniotomy compared to that found in the pre-craniotomy period.

    Conclusions

    The distortion (stretching or shearing) of axonal fibers at the treated part of the craniotomy may influence the axonal fibers in such a way that the neurochemical events are jeopardized. It is suggested that such a quantitative model may clarify some of the potential problems with such a treatment. Also, by further development of the technology it is quite possible to judge the outcome of strain levels already before the decompressive craniotomy is performed. This may have the possibility to optimize the size as well as the area of craniotomy.

  • 17.
    Li, Xiaogai
    et al.
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    von Holst, Hans
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Kleiven, Svein
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Influence of gravity for optimal head positions in the treatment of head injury patients2011In: Acta Neurochirurgica, ISSN 0001-6268, Vol. 153, no 10, p. 2057-2064Article in journal (Refereed)
    Abstract [en]

    BACKGROUND:

    Brain edema is a major neurological complication of traumatic brain injury (TBI), commonly including a pathologically increased intracranial pressure (ICP) associated with poor outcome. In this study, gravitational force is suggested to have a significant impact on the pressure of the edema zone in the brain tissue and the objective of the study was to investigate the significance of head position on edema at the posterior part of the brain using a finite element (FE) model.

    METHODS:

    A detailed FE model including the meninges, brain tissue and a fully connected cerebrospinal fluid (CSF) system was used in this study. Brain tissue was modelled as a poroelastic material consisting of an elastic solid skeleton composed of neurons and neuroglia, permeated by interstitial fluid. The effect of head positions (supine and prone position) due to gravity was investigated for a localized brain edema at the posterior part of the brain.

    RESULTS:

    The water content increment at the edema zone remained nearly identical for both positions. However, the interstitial fluid pressure (IFP) inside the edema zone decreased around 15% by having the head in a prone position compared with a supine position.

    CONCLUSIONS:

    The decrease of IFP inside the edema zone by changing patient position from supine to prone has the potential to alleviate the damage to central nervous system nerves. These observations indicate that considering the patient's head position during intensive care and at rehabilitation might be of importance to the treatment of edematous regions in TBI patients.

  • 18.
    Li, Xiaogai
    et al.
    KTH, School of Technology and Health (STH), Neuronic Engineering (Closed 20130701).
    von Holst, Hans
    KTH, School of Technology and Health (STH), Neuronic Engineering (Closed 20130701). Karolinska institutet.
    Kleiven, Svein
    KTH, School of Technology and Health (STH), Neuronic Engineering (Closed 20130701).
    Influences of brain tissue poroelastic constants on intracranial pressure (ICP) during constant-rate infusion2013In: Computer Methods in Biomechanics and Biomedical Engineering, ISSN 1025-5842, E-ISSN 1476-8259, Vol. 16, no 12, p. 1330-1343Article in journal (Refereed)
    Abstract [en]

    A 3D finite element (FE) model has been developed to study the mean intracranial pressure (ICP) response during constant-rate infusion using linear poroelasticity. Due to the uncertainties in the poroelastic constants for brain tissue, the influence of each of the main parameters on the transient ICP infusion curve was studied. As a prerequisite for transient analysis, steady-state simulations were performed first. The simulated steady-state pressure distribution in the brain tissue for a normal cerebrospinal fluid (CSF) circulation system showed good correlation with experiments from the literature. Furthermore, steady-state ICP closely followed the infusion experiments at different infusion rates. The verified steady-state models then served as a baseline for the subsequent transient models. For transient analysis, the simulated ICP shows a similar tendency to that found in the experiments, however, different values of the poroelastic constants have a significant effect on the infusion curve. The influence of the main poroelastic parameters including the Biot coefficient alpha, Skempton coefficient B, drained Young's modulus E, Poisson's ratio nu, permeability kappa, CSF absorption conductance C-b and external venous pressure p(b) was studied to investigate the influence on the pressure response. It was found that the value of the specific storage term S-epsilon is the dominant factor that influences the infusion curve, and the drained Young's modulus E was identified as the dominant parameter second to S-epsilon. Based on the simulated infusion curves from the FE model, artificial neural network (ANN) was used to find an optimised parameter set that best fit the experimental curve. The infusion curves from both the FE simulation and using ANN confirmed the limitation of linear poroelasticity in modelling the transient constant-rate infusion.

  • 19. Li, Y. Q.
    et al.
    Li, Xiaogai
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Neuronic Engineering. Southern Methodist University, United States.
    Gao, X. -L
    Modeling of advanced combat helmet under ballistic impact2015In: Journal of applied mechanics, ISSN 0021-8936, E-ISSN 1528-9036, Vol. 82, no 11, article id 111004Article in journal (Refereed)
    Abstract [en]

    The use of combat helmets has greatly reduced penetrating injuries and saved lives of many soldiers. However, behind helmet blunt trauma (BHBT) has emerged as a serious injury type experienced by soldiers in battlefields. BHBT results from nonpenetrating ballistic impacts and is often associated with helmet back face deformation (BFD). In the current study, a finite element-based computational model is developed for simulating the ballistic performance of the Advanced Combat Helmet (ACH), which is validated against the experimental data obtained at the Army Research Laboratory. Both the maximum value and time history of the BFD are considered, unlike existing studies focusing on the maximum BFD only. The simulation results show that the maximum BFD, the time history of the BFD, and the shape and size of the effective area of the helmet shell agree fairly well with the experimental findings. In addition, it is found that ballistic impacts on the helmet at different locations and in different directions result in different BFD values. The largest BFD value is obtained for a frontal impact, which is followed by that for a crown impact and then by that for a lateral impact. Also, the BFD value is seen to decrease as the oblique impact angle decreases. Furthermore, helmets of four different sizes - extra large, large, medium, and small - are simulated and compared. It is shown that at the same bullet impact velocity the small-size helmet has the largest BFD, which is followed by the medium-size helmet, then by the large-size helmet, and finally by the extra large-size helmet. Moreover, ballistic impact simulations are performed for an ACH placed on a ballistic dummy head form embedded with clay as specified in the current ACH testing standard by using the validated helmet model. It is observed that the BFD values as recorded by the clay in the head form are in good agreement with the experimental data.

  • 20.
    von Holst, Hans
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Neuronic Engineering. Section of Neurosurgery, Division of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden.
    Li, Xiaogai
    KTH, School of Technology and Health (STH), Medical Engineering, Neuronic Engineering.
    Consequences of the dynamic triple peak impact factor in traumatic brain injury as measured with numerical simulation2013In: Frontiers in Neurology, ISSN 1664-2295, E-ISSN 1664-2295, Vol. 4 MARArticle in journal (Refereed)
    Abstract [en]

    There is a lack of knowledge about the direct neuromechanical consequences in traumatic brain injury (TBI) at the scene of accident. In this study we use a finite element model of the human head to study the dynamic response of the brain during the first milliseconds after the impact with velocities of 10, 6, and 2 meters/second (m/s), respectively. The numerical simulation was focused on the external kinetic energy transfer, intracranial pressure (ICP), strain energy density and first principal strain level, and their respective impacts to the brain tissue. We show that the oblique impacts of 10 and 6 m/s resulted in substantial high peaks for the ICP, strain energy density, and first principal strain levels, however, with different patterns and time frames. Also, the 2 m/s impact showed almost no increase in the above mentioned investigated parameters. More importantly, we show that there clearly exists a dynamic triple peak impact factor to the brain tissue immediately after the impact regardless of injury severity associated with different impact velocities. The dynamic triple peak impacts occurred in a sequential manner first showing strain energy density and ICP and then followed by first principal strain. This should open up a new dimension to better understand the complex mechanisms underlying TBI. Thus, it is suggested that the combination of the dynamic triple peak impacts to the brain tissue may interfere with the cerebral metabolism relative to the impact severity thereby having the potential to differentiate between severe and moderate TBI from mild TBI.

  • 21.
    von Holst, Hans
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Neuronic Engineering. Karolinska Institutet, Sweden .
    Li, Xiaogai
    KTH, School of Technology and Health (STH), Medical Engineering, Neuronic Engineering.
    Decompressive craniectomy (DC) at the non-injured side of the brain has the potential to improve patient outcome as measured with computational simulation2014In: Acta Neurochirurgica, ISSN 0001-6268, E-ISSN 0942-0940, Vol. 156, no 10, p. 1961-1967Article in journal (Refereed)
    Abstract [en]

    Decompressive craniectomy (DC) is efficient in reducing the intracranial pressure in several complicated disorders such as traumatic brain injury (TBI) and stroke. The neurosurgical procedure has indeed reduced the number of deaths. However, parallel with the reduced fatal cases, the number of vegetative patients has increased significantly. Mechanical stretching in axonal fibers has been suggested to contribute to the unfavorable outcome. Thus, there is a need for improving treatment procedures that allow both reduced fatal and vegetative outcomes. The hypothesis is that by performing the DC at the non-injured side of the head, stretching of axonal fibers at the injured brain tissue can be reduced, thereby having the potential to improve patient outcome. Six patients, one with TBI and five with stroke, were treated with DC and where each patient's pre- and postoperative computerized tomography (CT) were analyzed and transferred to a finite element (FE) model of the human head and brain to simulate DC both at the injured and non-injured sides of the head. Poroelastic material was used to simulate brain tissue. The computational simulation showed slightly to substantially increased axonal strain levels over 40 % on the injured side where the actual DC had been performed in the six patients. However, when the simulation DC was performed on the opposite, non-injured side, there was a substantial reduction in axonal strain levels at the injured side of brain tissue. Also, at the opposite, non-injured side, the axonal strain level was substantially lower in the brain tissue. The reduced axonal strain level could be verified by analyzing a number of coronal sections in each patient. Further analysis of axial slices showed that falx may tentatively explain part of the different axonal strain levels between the DC performances at injured and opposite, non-injured sides of the head. By using a FE method it is possible to optimize the DC procedure to a non-injured area of the head thereby having the potential to reduce axonal stretching at the injured brain tissue. The postoperative DC stretching of axonal fibers may be influenced by different anatomical structures including falx. It is suggested that including computational FE simulation images may offer guidance to reduce axonal strain level tailoring the anatomical location of DC performance in each patient.

  • 22.
    von Holst, Hans
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Neuronic Engineering. Section of Neurosurgery, Division of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden .
    Li, Xiaogai
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Neuronic Engineering.
    Higher impact energy in traumatic brain injury interferes with noncovalent and covalent bonds resulting in cytotoxic brain tissue edema as measured with computational simulation2015In: Acta Neurochirurgica, ISSN 0001-6268, E-ISSN 0942-0940, Vol. 157, no 4, p. 639-648Article in journal (Refereed)
    Abstract [en]

    Cytotoxic brain tissue edema is a complicated secondary consequence of ischemic injury following cerebral diseases such as traumatic brain injury and stroke. To some extent the pathophysiological mechanisms are known, but far from completely. In this study, a hypothesis is proposed in which protein unfolding and perturbation of nucleotide structures participate in the development of cytotoxic edema following traumatic brain injury (TBI). An advanced computational simulation model of the human head was used to simulate TBI. The consequences of kinetic energy transfer following an external dynamic impact were analyzed including the intracranial pressure (ICP), strain level, and their potential influences on the noncovalent and covalent bonds in folded protein structures. The result shows that although most of the transferred kinetic energy is absorbed in the skin and three bone layers, there is a substantial amount of energy reaching the gray and white matter. The kinetic energy from an external dynamic impact has the theoretical potential to interfere not only with noncovalent but also covalent bonds when high enough. The induced mechanical strain and pressure may further interfere with the proteins, which accumulate water molecules into the interior of the hydrophobic structures of unfolded proteins. Simultaneously, the noncovalent energy-rich bonds in nucleotide adenosine-triphosphates may be perturbed as well. Based on the analysis of the numerical simulation data, the kinetic energy from an external dynamic impact has the theoretical potential to interfere not only with noncovalent, but also with covalent bonds when high enough. The subsequent attraction of increased water molecules into the unfolded protein structures and disruption of adenosine-triphosphate bonds could to some extent explain the etiology to cytotoxic edema.

  • 23.
    von Holst, Hans
    et al.
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Li, Xiaogai
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Numerical Impact Simulation of Gradually Increased Kinetic Energy Transfer Has the Potential To Break Up Folded Protein Structures Resulting in Cytotoxic Brain Tissue Edema2013In: Journal of Neurotrauma, ISSN 0897-7151, E-ISSN 1557-9042, Vol. 30, no 13, p. 1192-1199Article in journal (Refereed)
    Abstract [en]

    Although the consequences of traumatic brain injury (TBI) and its treatment have been improved, there is still a substantial lack of understanding the mechanisms. Numerical simulation of the impact can throw further lights on site and mechanism of action. A finite element model of the human head and brain tissue was used to simulate TBI. The consequences of gradually increased kinetic energy transfer was analyzed by evaluating the impact intracranial pressure (ICP), strain level, and their potential influences on binding forces in folded protein structures. The gradually increased kinetic energy was found to have the potential to break apart bonds of Van der Waals in all impacts and hydrogen bonds at simulated impacts from 6 m/s and higher, thereby superseding the energy in folded protein structures. Further, impacts below 6 m/s showed none or very slight increase in impact ICP and strain levels, whereas impacts of 6 m/s or higher showed a gradual increase of the impact ICP and strain levels reaching over 1000 KPa and over 30%, respectively. The present simulation study shows that the free kinetic energy transfer, impact ICP, and strain levels all have the potential to initiate cytotoxic brain tissue edema by unfolding protein structures. The definition of mild, moderate, and severe TBI should thus be looked upon as the same condition and separated only by a gradual severity of impact.

  • 24.
    von Holst, Hans
    et al.
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Li, Xiaogai
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Quantification of Stretching in the Ventricular Wall and Corpus Callosum and Corticospinal Tracts in Hydrocephalus before and after Ventriculoperitoneal Shunt Operation2013In: Journal of Applied Mathematics, ISSN 1110-757X, E-ISSN 1687-0042, p. 350359-Article in journal (Refereed)
    Abstract [en]

    In this study, we establish a quantitative model to define the stretching of brain tissue, especially in ventricular walls, corpus callosum (CC) and corticospinal (CS) fiber tracts, and to investigate the correlation between stretching and regional cerebral blood flow (rCBF) before and after ventriculoperitoneal shunt operations. A nonlinear image registration method was used to calculate the degree of displacement and stretching of axonal fiber tracts based on the medical images of six hydrocephalus patients. Also, the rCBF data from the literature was analyzed and correlated with the strain level quantified in the present study. The results showed substantial increased displacement and strain levels in the ventricular walls as well as in the CC and CS fiber tracts on admission. Following shunt operations the displacement as well as the strain levels reduced substantially. A linear correlation was found to exist between strain level and the rCBF. The reduction in postoperative strain levels correlated with the improvement of rCBF. All patients improved clinically except for one patient due to existing dementia. These new quantitative data provide us with new insight into the mechanical cascade of events due to tissue stretching, thereby provide us with more knowledge into understanding of the role of brain tissue and axonal stretching in some of the hydrocephalus clinical symptoms.

  • 25.
    von Holst, Hans
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Neuronic Engineering.
    Li, Xiaogai
    KTH, School of Technology and Health (STH), Medical Engineering, Neuronic Engineering.
    The dynamic triple peak impact factor in traumatic brain injury influences native protein structures in gray and white matter as measured with computational simulation2013In: Neurological Research, ISSN 0161-6412, E-ISSN 1743-1328, Vol. 35, no 8, p. 782-789Article in journal (Refereed)
    Abstract [en]

    Background: Traumatic brain injuries (TBIs) cause a substantial burden to the patient, relatives, and the society as a whole. Much experience and knowledge during the last two decades have improved the neurosurgical treatment as well as the outcome. However, there is still much debate on what actually happens when external kinetic energy is transferred to the head immediately after a TBI. Better knowledge about the cascades of mechanical events at the time of accident is a prerequisite to further reduce the burden in all categories and improve the neurosurgical care of TBI patients. Methods: In the present study, we use the finite element modeling of the human brain to numerically simulate impact velocities of 10, 6, and 2 m/s to clarify some of the immediate consequences of the external kinetic energy transfer focusing on the gray (GM) and white matters (WM). Results: The numerical simulation was focused on the external kinetic energy transfer with a level of 227.3 J reaching the head, intracranial pressure (ICP), strain energy density, 1st principal strain level, and their respective impacts on the brain tissue. The results show that, for a 10 m/s impact, a total internal potential energy of 208.6 J was absorbed, of which 14.3% (29.81 J) was absorbed by the scalp, 22.05% (46.0 J) by the outer compact bone, 17.12% (35.72 J) by the porous bone, 27.44% (57.23 J) by the inner compact bone, and 7.31% (15.24 J) by the facial bone. The rest of the internal potential energy was defined to reach the GM (3.6%, 7.51 J) and the WM 1.59% (3.31 J). Also, the ICP, strain energy density, and 1st principal strain levels, defined as the dynamic triple peak impact factor, influenced the GM and WM with their own impact peaks during the first 10 ms after the accident and were the highest for the 10 and 6 m/s impacts, while the 2 m/s impact had only a slight influence on the GM and WM structures. Conclusions: The present study shows for the first time that following an impact of 10 m/s, 88.31% of the calculated external kinetic energy was absorbed by the external parts of the head before the remaining energy of 5.19% reached the GM and WM. GM absorbed about twice as much of the energy compared to the WM. It is suggested that the dynamic triple peak impact factor may have a profound effect on native protein structures in the cerebral metabolism after a TBI.

  • 26.
    von Holst, Hans
    et al.
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Li, Xiaogai
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Kleiven, Svein
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Increased strain levels and water content in brain tissue after decompressive craniotomy2012In: Acta Neurochirurgica, ISSN 0001-6268, E-ISSN 0942-0940, Vol. 154, no 9, p. 1583-1593Article in journal (Refereed)
    Abstract [en]

    At present there is a debate on the effectiveness of the decompressive craniotomy (DC). Stretching of axons was speculated to contribute to the unfavourable outcome for the patients. The quantification of strain level could provide more insight into the potential damage to the axons. The aim of the present study was to evaluate the strain level and water content (WC) of the brain tissue for both the pre- and post-craniotomy period. The stretching of brain tissue was quantified retrospectively based on the computerised tomography (CT) images of six patients before and after DC by a non-linear image registration method. WC was related to specific gravity (SG), which in turn was related to the Hounsfield unit (HU) value in the CT images by a photoelectric correction according to the chemical composition of brain tissue. For all the six patients, the strain level showed a substantial increase in the brain tissue close to the treated side of DC compared with that found at the pre-craniotomy period and ranged from 24 to 55 % at the post-craniotomy period. Increase of strain level was also observed at the brain tissue opposite to the treated side, however, to a much lesser extent. The mean area of craniotomy was found to be 91.1 +/- 12.7 cm(2). The brain tissue volume increased from 27 to 127 ml, corresponding to 1.65 % and 8.13 % after DC in all six patients. Also, the increased volume seemed to correlate with increased strain level. Specifically, the overall WC of brain tissue for two patients evaluated presented a significant increase after the treatment compared with the condition seen before the treatment. Furthermore, the Glasgow Coma Scale (GCS) improved in four patients after the craniotomy, while two patients died. The GCS did not seem to correlate with the strain level. We present a new numerical method to quantify the stretching or strain level of brain tissue and WC following DC. The significant increase in strain level and WC in the post-craniotomy period may cause electrophysiological changes in the axons, resulting in loss of neuronal function. Hence, this new numerical method provides more insight of the consequences following DC and may be used to better define the most optimal size and area of the craniotomy in reducing the strain level development.

  • 27.
    Zhou, Zhou
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Neuronic Engineering.
    Li, Xiaogai
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Neuronic Engineering.
    Kleiven, Svein
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Neuronic Engineering.
    Biomechanics of acute subdural hematoma in the elderly: A fluid-structure interaction study2019In: Journal of Neurotrauma, ISSN 0897-7151, E-ISSN 1557-9042, Vol. 36, no 13, p. 2099-2108Article in journal (Refereed)
    Abstract [en]

    Acute subdural hematoma (ASDH) due to bridging vein (BV) rupture is a frequent and lethal head injury, especially in the elderly. Brain atrophy has been hypothesized to be a primary pathogenesis associated with the increased risk of ASDH in the elderly. Though decades of biomechanical endeavours have been made to elucidate the potential mechanisms, a thorough explanation for this hypothesis appears lacking. Thus, a recently improved finite element head model, in which the brain-skull interface was modelled using a fluid-structure interaction (FSI) approach with special treatment of the cerebrospinal fluid as arbitrary Lagrangian-Eulerian fluid formulation, is used to partially address this understanding gap. Models with various degrees of atrophied brains and thereby different subarachnoid thicknesses are generated and subsequently exposed to experimentally determined loadings known to cause ASDH or not. The results show significant increases in the cortical relative motion and BV strain in the atrophied brain, which consequently exacerbates the ASDH risk in the elderly. Results of this study are suggested to be considered while developing age-adapted protecting strategies for the elderly in the future.

  • 28.
    Zhou, Zhou
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Neuronic Engineering.
    Li, Xiaogai
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Neuronic Engineering.
    Kleiven, Svein
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Neuronic Engineering.
    Shah, Chirag S.
    Hardy, Warren N.
    A Reanalysis of Experimental Brain Strain Data: Implication for Finite Element Head Model Validation2019In: SAE Technical Papers, SAE International , 2019, Vol. 2019, article id NovemberConference paper (Refereed)
    Abstract [en]

    Relative motion between the brain and skull and brain deformation are biomechanics aspects associated with many types of traumatic brain injury (TBI). Thus far, there is only one experimental endeavor (Hardy et al., 2007) reported brain strain under loading conditions commensurate with levels that were capable of producing injury. Most of the existing finite element (FE) head models are validated against brain-skull relative motion and then used for TBI prediction based on strain metrics. However, the suitability of using a model validated against brain-skull relative motion for strain prediction remains to be determined. To partially address the deficiency of experimental brain deformation data, this study revisits the only existing dynamic experimental brain strain data and updates the original calculations, which reflect incremental strain changes. The brain strain is recomputed by imposing the measured motion of neutral density target (NDT) to the NDT triad model. The revised brain strain and the brain-skull relative motion data are then used to test the hypothesis that an FE head model validated against brain-skull relative motion does not guarantee its accuracy in terms of brain strain prediction. To this end, responses of brain strain and brain-skull relative motion of a previously developed FE head model (Kleiven, 2007) are compared with available experimental data. CORrelation and Analysis (CORA) and Normalized Integral Square Error (NISE) are employed to evaluate model validation performance for both brain strain and brain-skull relative motion. Correlation analyses (Pearson coefficient) are conducted between average cluster peak strain and average cluster peak brain-skull relative motion, and also between brain strain validation scores and brain-skull relative motion validation scores. The results show no significant correlations, neither between experimentally acquired peaks nor between computationally determined validation scores. These findings indicate that a head model validated against brain-skull relative motion may not be sufficient to assure its strain prediction accuracy. It is suggested that a FE head model with intended use for strain prediction should be validated against the experimental brain deformation data and not just the brain-skull relative motion.

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