Finite Element Head Model Research Articles

3A01 頭部有限要素モデルを用いた症例解析における脳神経損傷の発症部位および重症度の予測(OS6-1:傷害とその軽減・予防のバイオメカニクス(傷害バイオメカニクス研究会)(1))

3A01 頭部有限要素モデルを用いた症例解析における脳神経損傷の発症部位および重症度の予測(OS6-1:傷害とその軽減・予防のバイオメカニクス(傷害バイオメカニクス研究会)(1))

Brain Response to Primary Blast Wave Using Validated Finite Element Models of Human Head and Advanced Combat Helmet

Blast-induced traumatic brain injury has emerged as a “signature injury” in combat casualty care. Present combat helmets are designed primarily to protect against ballistic and blunt impacts, but the current issue with helmets is protection concerning blasts. In order to delineate the blast wave attenuating capability of the Advanced Combat Helmet (ACH), a finite element (FE) study was undertaken to evaluate the head response against blast loadings with and without helmet using a partially validated FE model of the human head and ACH. Four levels of overpressures (0.27–0.66 MPa) from the Bowen’s lung iso-damage threshold curves were used to simulate blast insults. Effectiveness of the helmet with respect to head orientation was also investigated. The resulting biomechanical responses of the brain to blast threats were compared for human head with and without the helmet. For all Bowen’s cases, the peak intracranial pressures (ICP) in the head ranged from 0.68 to 1.8 MPa in the coup cortical region. ACH was found to mitigate ICP in the head by 10–35%. Helmeted head resulted in 30% lower average peak brain strains and product of strain and strain rate. Among three blast loading directions with ACH, highest reduction in peak ICP (44%) was due to backward blasts whereas the lowest reduction in peak ICP and brain strains was due to forward blast (27%). The biomechanical responses of a human head to primary blast insult exhibited directional sensitivity owing to the different geometry contours and coverage of the helmet construction and asymmetric anatomy of the head. Thus, direction-specific tolerances are needed in helmet design in order to offer omni-directional protection for the human head. The blasts of varying peak overpressures and durations that are believed to produce the same level of lung injury produce different levels of mechanical responses in the brain, and hence “iso-damage” curves for brain injury are likely different than the Bowen curves for lung injury.

Grand Challenge: Computational Models Validated Against Critical Experiments.

Grand Challenge: Computational Models Validated Against Critical Experiments.

Erratum to: Development, Validation, and Application of a Parametric Pediatric Head Finite Element Model for Impact Simulations

Erratum to: Development, Validation, and Application of a Parametric Pediatric Head Finite Element Model for Impact Simulations

Influence of anisotropic conductivity in the skull and white matter on transcranial direct current stimulation via an anatomically realistic finite element head model

To establish safe and efficient transcranial direct current stimulation (tDCS), it is of particular importance to understand the electrical effects of tDCS in the brain. Since the current density (CD) and electric field (EF) in the brain generated by tDCS depend on various factors including complex head geometries and electrical tissue properties, in this work, we investigated the influence of anisotropic conductivity in the skull and white matter (WM) on tDCS via a 3D anatomically realistic finite element head model. We systematically incorporated various anisotropic conductivity ratios into the skull and WM. The effects of anisotropic tissue conductivity on the CD and EF were subsequently assessed through comparisons to the conventional isotropic solutions. Our results show that the anisotropic skull conductivity significantly affects the CD and EF distribution: there is a significant reduction in the ratio of the target versus non-target total CD and EF on the order of 12–14%. In contrast, the WM anisotropy does not significantly influence the CD and EF on the targeted cortical surface, only on the order of 1–3%. However, the WM anisotropy highly alters the spatial distribution of both the CD and EF inside the brain. This study shows that it is critical to incorporate anisotropic conductivities in planning of tDCS for improved efficacy and safety.

Cranial electrotherapy stimulation and transcranial pulsed current stimulation: A computer based high-resolution modeling study

The field of non-invasive brain stimulation has developed significantly over the last two decades. Though two techniques of noninvasive brain stimulation--transcranial direct current stimulation (tDCS) and transcranial magnetic stimulation (TMS)--are becoming established tools for research in neuroscience and for some clinical applications, related techniques that also show some promising clinical results have not been developed at the same pace. One of these related techniques is cranial electrotherapy stimulation (CES), a class of transcranial pulsed current stimulation (tPCS). In order to understand further the mechanisms of CES, we aimed to model CES using a magnetic resonance imaging (MRI)-derived finite element head model including cortical and also subcortical structures. Cortical electric field (current density) peak intensities and distributions were analyzed. We evaluated different electrode configurations of CES including in-ear and over-ear montages. Our results confirm that significant amounts of current pass the skull and reach cortical and subcortical structures. In addition, depending on the montage, induced currents at subcortical areas, such as midbrain, pons, thalamus and hypothalamus are of similar magnitude than that of cortical areas. Incremental variations of electrode position on the head surface also influence which cortical regions are modulated. The high-resolution modeling predictions suggest that details of electrode montage influence current flow through superficial and deep structures. Finally we present laptop based methods for tPCS dose design using dominant frequency and spherical models. These modeling predictions and tools are the first step to advance rational and optimized use of tPCS and CES.

Human head–neck computational model for assessing blast injury

A human head finite element model (HHFEM) was developed to study the effects of a blast to the head. To study both the kinetic and kinematic effects of a blast wave, the HHFEM was attached to a finite element model of a Hybrid III ATD neck. A physical human head surrogate model (HSHM) was developed from solid model files of the HHFEM, which was then attached to a physical Hybrid III ATD neck and exposed to shock tube overpressures. This allowed direct comparison between the HSHM and HHFEM. To develop the temporal and spatial pressures on the HHFEM that would simulate loading to the HSHM, a computational fluid dynamics (CFD) model of the HHFEM in front of a shock tube was generated. CFD simulations were made using loads equivalent to those seen in experimental studies of the HSHM for shock tube driver pressures of 517, 690 and 862kPa. Using the selected brain material properties, the peak intracranial pressures, temporal and spatial histories of relative brain–skull displacements and the peak relative brain–skull displacements in the brain of the HHFEM compared favorably with results from the HSHM. The HSHM sensors measured the rotations of local areas of the brain as well as displacements, and the rotations of the sensors in the sagittal plane of the HSHM were, in general, correctly predicted from the HHFEM. Peak intracranial pressures were between 70 and 120kPa, while the peak relative brain–skull displacements were between 0.5 and 3.0mm.

Assessment of Relative Brain-Skull Motion in Quasistatic Circumstances by Magnetic Resonance Imaging

Brain-skull relative motion plays a pivotal role in the etiology of traumatic brain injury (TBI). The present study aims to assess brain-skull relative motion in quasistatic circumstances, and to correlate cortical regions with high motion amplitudes with sites prone to cerebral contusions. The study includes 30 healthy volunteers scanned using a clinical 3-T MR scanner in four different head positions. Through image processing and 3D model registration, pairwise comparisons were performed to calculate the brain shift between sagittal and coronal head positional change. Next, local brain deformation was evaluated by comparison between cortical and ventricular amplitudes. Finally, the influence of age, sex, and skull geometry on the cortical and ventricular motion was investigated. The results describe complex brain shift patterns, with high regional and inter-individual variations, outweighing age and sex patterns. Regions with maximum motion amplitudes were identified at the inferolateral aspects of the frontal and temporal lobes, congruent with predilection sites for contusions. No significant influences of age and sex on the cortical shift amplitudes were detected. The 3D cortical deviations varied from -7.86 mm to +5.71 mm for the sagittal head movement, and from -11.46 mm to +7.30 mm for head movement in the coronal plane, for a 95% confidence interval. The present study contributes to a better understanding of the mechanopathogenesis of frontotemporal contusions, and is useful for the optimization of finite-element head models and neurosurgical navigation procedures. Moreover, our results prove that in vivo MRI allows for accurate assessment of brain-skull relative motion in quasistatic conditions.

Assessment of the protective performance of hood using head FE model in car-to-pedestrian collisions

The objective of the present study was to present a method to assess the protective performance of a passenger car hood to decrease pedestrian head injuries in car-to-pedestrian collisions by using a validated human head finite element (FE) model. Three types of hoods, sandwich structure hood, multi-cone and wavilness inner-panel hoods, made of aluminium were proposed to protect the pedestrian's head. The head FE model was used to evaluate the protection performance of the proposed hood designs by modelling of head impact to the hood. The head intracranial pressure and the linear and rotational acceleration were measured using the head FE model to predict the risk of brain injury. The results indicated that the proposed hood designs showed a significant improvement in injury mitigation from simulations of the head FE model impact to the hood in the investigated passenger car.

Optimization of the Engine Hood to Reduce the Head Injury during the Vehicle-Human Collision

Effect of hard point of the engine hood on the head injury during the vehicle-human collision was studied to improve the design of engine hood. Firstly, the current common model of the engine hood was established with three-dimensional finite element modeling software, and 20 areas were divided, also a standard head finite element model was imported, secondly, each area of the engine hood was clashed by the standard head model, then the impact on the head injure was analyzed and the hard point of the hood area was achieved, thirdly, the optimization of the inside and outside panel materials and the plate structure were carried out to reduce the head damage. The simulation results show that the engine hood after optimization gave less damage to the head, which means the research carried out here is of a good reference to the engine hood optimization design for human protection

An investigation into the use and limitations of different spatial integration schemes and finite element software in head impact analyses

To understand the mechanopathogenesis of brain lesions, finite element (FE) head models are used. There is a broad range of material properties, contact interfaces and integration schemes used for the different parts in current FE head models. The effect of material behaviour and contact definitions on a head impact analysis is reported in the literature, whereas the effect of FE integration schemes is a rather unexplored domain. This paper starts with the development of a simplified head model to which small adaptations are made in the integration scheme to obtain multiple analyses that are compared using an accident reconstruction. The performed study highlighted potential hazards of different integration schemes and the significant effect they have on the simulated mechanical responses of the head. Based on a comparison between FE softwares using an impact test and patch test, it was seen that also the software could have an effect on the FE analysis results.

Minimization of Analytical Injury Metrics for Head Impact Injuries

Objective: To compare the predictions of the head injury criterion (HIC), currently used to predict the risk of traumatic brain injury in frontal vehicle impact and pedestrian impact tests, with the predictions of other empirical and analytical injury metrics. Methods: The appropriateness of different criteria relative to injury metrics derived from a head finite element (FE) model is investigated for different deceleration pulses in this research. Empirical injury metrics are computed by direct calculation for different analyzed pulses. In addition, for each pulse full FE model simulations of a complete human head were performed by means of the SIMon model. The computations are used to calculate the analytical injury metrics. Results: This article shows that an optimal head deceleration curve based on HIC does not minimize other analytical injury metrics. The results obtained in this study suggest that the HIC criterion does not necessarily provide the same severity ranking for different external loadings to the head as the injury metrics derived from the FE models. Conclusion: Countermeasures designed based only on HIC could differ significantly from those based on analytical injury measures computed by FE models. The use of multiple injury metrics is recommended given that no scalar measure seems to be positively and strongly correlated with relevant injury metrics.

Hierarchical Bayesian inference for the EEG inverse problem using realistic FE head models: Depth localization and source separation for focal primary currents

The estimation of the activity-related ion currents by measuring the induced electromagnetic fields at the head surface is a challenging and severely ill-posed inverse problem. This is especially true in the recovery of brain networks involving deep-lying sources by means of EEG/MEG recordings which is still a challenging task for any inverse method. Recently, hierarchical Bayesian modeling (HBM) emerged as a unifying framework for current density reconstruction (CDR) approaches comprising most established methods as well as offering promising new methods. Our work examines the performance of fully-Bayesian inference methods for HBM for source configurations consisting of few, focal sources when used with realistic, high-resolution finite element (FE) head models. The main foci of interest are the correct depth localization, a well-known source of systematic error of many CDR methods, and the separation of single sources in multiple-source scenarios. Both aspects are very important in the analysis of neurophysiological data and in clinical applications. For these tasks, HBM provides a promising framework and is able to improve upon established CDR methods such as minimum norm estimation (MNE) or sLORETA in many aspects. For challenging multiple-source scenarios where the established methods show crucial errors, promising results are attained. Additionally, we introduce Wasserstein distances as performance measures for the validation of inverse methods in complex source scenarios.

Development of a Finite Element Model for Blast Brain Injury and the Effects of CSF Cavitation

Blast-related traumatic brain injury is the most prevalent injury for combat personnel seen in the current conflicts in Iraq and Afghanistan, yet as a research community,we still do not fully understand the detailed etiology and pathology of this injury. Finite element (FE) modeling is well suited for studying the mechanical response of the head and brain to blast loading. This paper details the development of a FE head and brain model for blast simulation by examining both the dilatational and deviatoric response of the brain as potential injury mechanisms. The levels of blast exposure simulated ranged from 50 to 1000 kPa peak incident overpressure and 1–8 ms in positive-phase duration, and were comparable to real-world blast events. The frontal portion of the brain had the highest pressures corresponding to the location of initial impact, and peak pressure attenuated by 40–60% as the wave propagated from the frontal to the occipital lobe. Predicted brain pressures were primarily dependent on the peak overpressure of the impinging blast wave, and the highest predicted brain pressures were 30%less than the reflected pressure at the surface of blast impact. Predicted shear strain was highest at the interface between the brain and the CSF. Strain magnitude was largely dependent on the impulse of the blast, and primarily caused by the radial coupling between the brain and deforming skull.The largest predicted strains were generally less than 10%,and occurred after the shock wave passed through the head.For blasts with high impulses, CSF cavitation had a large role in increasing strain levels in the cerebral cortex and periventricular tissues by decoupling the brain from the skull. Relating the results of this study with recent experimental blast testing suggest that a rate-dependent strain-based tissue injury mechanism is the source primary blast TBI.

Complete electrode model in EEG: relationship and differences to the point electrode model

In electroencephalography (EEG) source analysis, a primary current density generated by the neural activity of the brain is reconstructed from external electrode voltage measurements. This paper focuses on accurate and effective simulations of EEG through the complete electrode model (CEM). The CEM allows for the incorporation of the electrode size, shape and effective contact impedance into the forward simulation. Both neural currents in the brain and shunting currents between the electrodes and the skin can affect the measured voltages in the CEM. The goal of this study was to investigate the CEM by comparing it with the point electrode model (PEM), which is the current standard electrode model for EEG. We used a three-dimensional, realistic and high-resolution finite element head model as the reference computational domain in the comparison. The PEM could be formulated as a limit of the CEM, in which the effective impedance of each electrode goes to infinity and the size tends to zero. Numerical results concerning the forward and inverse errors and electrode voltage strengths with different impedances and electrode sizes are presented. Based on the results obtained, limits for extremely high and low impedance values of the shunting currents are suggested.

Volume conduction effects in tDCS using a 1mm geometry-adapted hexahedral finite element head model

Article Volume conduction effects in tDCS using a 1mm geometry-adapted hexahedral finite element head model was published on September 6, 2012 in the journal Biomedical Engineering / Biomedizinische Technik (volume 57, issue SI-1-Track-O).

Development and validation of a 5th percentile human head finite element model based on the Chinese population

A high biofidelic 5th percentile human head finite element (FE) model, based on the Chinese population, was developed and validated. Geometrical characteristics of the finite element model were extracted from the medical CT scan images of a 5th percentile living human from the Chinese population, instead of using the scaling law copying down from a 50th percentile model. The newly created model incorporates the essential features of the human head, which include the scalp, three layers of skull, cerebrum, cerebellum, brain stem, corpus callosum, cerebrospinal fluid, ventricles, sinus, falx cerebri, tentorium cerebelli, pia mater, dura mater, facial bone, mandible, facial muscle, masseter, temporalis, submandibular soft tissue, detailed ocular structures and teeth. Model validations under different impact conditions from Nahum and Trosseille's experiments were carried out. Parametric studies were subsequently performed to investigate model responses with variations of tissue material properties. Furthermore, the effect of cavitation pressure was also investigated. Keywords: 5th percentile human head models; impact injury; brain pressure; Chinese population; finite element method; FEM; modelling; head injuries; China; model validation; tissue materials; cavitation pressure.

Development and Application of Stress-Based Skull Fracture Criteria Using a Head Finite Element Model

Development and Application of Stress-Based Skull Fracture Criteria Using a Head Finite Element Model

C107 神経線維の幾何学的配置を実装した頭部有限要素モデルの開発(C1-2 軟組織・血液のバイオメカニクス1)

C107 神経線維の幾何学的配置を実装した頭部有限要素モデルの開発(C1-2 軟組織・血液のバイオメカニクス1)

Effects of model complexity and tissue anisotropic conductivity on cortical modulation during transcranial direct current stimulation

An anatomically accurate high-resolution finite-element head model and its derivatives have been employed to examine the influence of subcutaneous fat and muscle tissues on cortical modulation. The effects of skull, muscle and white matter (WM) directional conductivity have also been investigated. Results indicate that the inclusion of additional tissues in the head model have a profound effect on the magnitude and distribution pattern of induced current density. Similarly, anisotropic tissue conductivity caused a significant deterioration in spatial focality of cortical currents along with a more distorted and diffused distribution pattern across the cortex.