Brain Injury Criteria Research Articles

Brain injury tolerance limit based on computation of axonal strain

Traumatic brain injury (TBI) is the leading cause of death and permanent impairment over the last decades. In both the severe and mild TBIs, diffuse axonal injury (DAI) is the most common pathology and leads to axonal degeneration. Computation of axonal strain by using finite element head model in numerical simulation can enlighten the DAI mechanism and help to establish advanced head injury criteria. The main objective of this study is to develop a brain injury criterion based on computation of axonal strain. To achieve the objective a state-of-the-art finite element head model with enhanced brain and skull material laws, was used for numerical computation of real world head trauma. The implementation of new medical imaging data such as, fractional anisotropy and axonal fiber orientation from Diffusion Tensor Imaging (DTI) of 12 healthy patients into the finite element brain model was performed to improve the brain constitutive material law with more efficient heterogeneous anisotropic visco hyper-elastic material law. The brain behavior has been validated in terms of brain deformation against Hardy et al. (2001), Hardy et al. (2007), and in terms of brain pressure against Nahum et al. (1977) and Trosseille et al. (1992) experiments. Verification of model stability has been conducted as well. Further, 109 well-documented TBI cases were simulated and axonal strain computed to derive brain injury tolerance curve. Based on an in-depth statistical analysis of different intra-cerebral parameters (brain axonal strain rate, axonal strain, first principal strain, Von Mises strain, first principal stress, Von Mises stress, CSDM (0.10), CSDM (0.15) and CSDM (0.25)), it was shown that axonal strain was the most appropriate candidate parameter to predict DAI. The proposed brain injury tolerance limit for a 50% risk of DAI has been established at 14.65% of axonal strain. This study provides a key step for a realistic novel injury metric for DAI.

Development of a Comprehensive Injury Criterion for Moderate and Mild Traumatic Brain Injuries

Traumatic brain injuries are commonly caused by blows that produce sudden accelerations of the head. A methodology to define a new global brain injury criterion and thresholds that account for time-dependent and combined translational-rotational kinematics of the head is described in this paper. In total 43 head impact tests with monkeys conducted in the past were reproduced, using a finite element model of the monkey head and neck. The study found that the new criterion predicted concussions and brain tissue strains more precisely than past criteria. A scheme that scales the proposed injury threshold to be applicable for humans is proposed. The new criterion and threshold may then be used in the design of superior protective systems.

OS7-7 Traumatic brain injury criteria in Judo based on reconstruction analysis(OS7: Injury Biomechanics II)

OS7-7 Traumatic brain injury criteria in Judo based on reconstruction analysis(OS7: Injury Biomechanics II)

Evaluation of Axonal Strain as a Predictor for Mild Traumatic Brain Injuries Using Finite Element Modeling.

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.

Evaluation of Near-Side Oblique Frontal Impacts Using THOR With SD3 Shoulder

Objective: Within the EC Seventh Framework project THORAX, the Mod-Kit THOR was upgraded with a new thorax and shoulder. The aim of this study was to investigate whether the THOR ATD met a set of prerequisites to a greater extent than Hybrid III and by that measure whether the dummy could serve as a potential tool for future evaluation of serious head and chest injuries in near-side oblique frontal impacts.Method: A small-overlap/oblique sled system was used to reflect occupant forces observed in oblique frontal crashes. The head and thoracic response from THOR was evaluated for 3 combinations: belt only with no deformation of the driver's side door (configuration A), belt only in combination with a predeformed door (configuration B), and prepretensioning belt and driver airbag (PPT+DAB) in combination with a predeformed door (configuration C). To evaluate head injury risk, the head injury criterion (HIC) and brain injury criteria (BrIC) were used. For evaluation of the thoracic injury risk, 3 injury criteria proposed by the THORAX project were evaluated: Dmax, DcTHOR, and strain (dummy rib fractures).Results: Unlike Hybrid III, the THOR with SD3 shoulder interacted with the side structure in a near-side oblique frontal impact. HIC values for the 3 test configurations corresponded to a 90% (A) and 100% (B and C) risk of Abbreviated Injury Scale (AIS) 2+ head injury, and BrIC values resulted in a 100% risk of AIS 2+ head injury in configurations A and B. In C the risk was reduced to 75%. The AIS 2+ thoracic injury risks based on Dmax were similar (14–18%) for all tests. Based on DcTHOR, AIS 2+ injury risk increased from 29 to 53% as the predeformed door side was introduced (A to B), and the risk increased, to 64%, as a PPT+DAB was added (C). Considering the AIS 2+ injury risk based on strain, tests in A resulted in an average of 3 dummy rib fractures (17%). Introducing the predeformed door (B) increased the average of dummy fractures to 5 (39%), but in C the average number of dummy rib fractures decreased to 4 (28%).Conclusions: THOR with an SD3 shoulder should be the preferred ATD rather than the Hybrid III for evaluating head and thorax injuries in oblique frontal impacts. Thoracic interaction with the predeformed door was not well captured by the 3D IR-Traccs; hence, use of deflection as an injury predictor in oblique loading is insufficient for evaluating injury risk in this load case. However, injury risk evaluation may be performed using the strain measurements, which characterize loading from seat belt and airbag as well as the lateral contribution of the structural impact in the loading condition used in this study.

Head impact exposure in youth football: middle school ages 12-14 years.

The head impact exposure experienced by football players at the college and high school levels has been well documented; however, there are limited data regarding youth football despite its dramatically larger population. The objective of this study was to investigate head impact exposure in middle school football. Impacts were monitored using a commercially available accelerometer array installed inside the helmets of 17 players aged 12-14 years. A total of 4678 impacts were measured, with an average (±standard deviation) of 275 ± 190 impacts per player. The average of impact distributions for each player had a median impact of 22 ± 2 g and 954 ± 122 rad/s², and a 95th percentile impact of 54 ± 9 g and 2525 ± 450 rad/s². Similar to the head impact exposure experienced by high school and collegiate players, these data show that middle school football players experience a greater number of head impacts during games than practices. There were no significant differences between median and 95th percentile head acceleration magnitudes experienced during games and practices; however, a larger number of impacts greater than 80 g occurred during games than during practices. Impacts to the front and back of the helmet were most common. Overall, these data are similar to high school and college data that have been collected using similar methods. These data have applications toward youth football helmet design, the development of strategies designed to limit head impact exposure, and child-specific brain injury criteria.

Comparison of the THOR and Hybrid III Responses in Oblique Impacts

NHTSA has been investigating a new test mode in which a research moving deformable barrier (RMDB) impacts a stationary vehicle at 90.1 kph, a 15 degree angle, and a 35% vehicle overlap. The test utilizes the THOR NT with modification kit (THOR) dummy positioned in both the driver and passenger seats. This paper compares the behavior of the THOR and Hybrid III dummies during this oblique research test mode. A series of four full vehicle oblique impact crash tests were performed. Two tests were equipped with THOR dummies and two tests were equipped with Hybrid III dummies. All dummies represent 50th percentile males and were positioned in the vehicle according to the FMVSS208 procedure. The Hybrid III dummies were instrumented with the Nine Accelerometer Package (NAP) to calculate brain injury criteria (BrIC) as well as THOR-Lx lower legs. Injury responses were recorded for each dummy during the event. High speed cameras were used to capture vehicle and dummy kinematics. The vehicle restraint devices and their associated deployment times remained the same for each test. Post test analysis investigated each dummy injury response, kinematics, and vehicle structural performance. The results of the current study show that during an oblique impact, where significant lateral motion of the vehicle is observed, there are differences between the THOR and Hybrid III dummies. Language: en

Mechanical characterization of brain tissue in simple shear at dynamic strain rates

During severe impact conditions, brain tissue experiences a rapid and complex deformation, which can be seen as a mixture of compression, tension and shear. Diffuse axonal injury (DAI) occurs in animals and humans when both the strains and strain rates exceed 10% and 10/s, respectively. Knowing the mechanical properties of brain tissue in shear at these strains and strain rates is thus of particular importance, as they can be used in finite element simulations to predict the occurrence of brain injuries under different impact conditions. However, very few studies in the literature provide this information. In this research, an experimental setup was developed to perform simple shear tests on porcine brain tissue at strain rates ≤120/s. The maximum measured shear stress at strain rates of 30, 60, 90 and 120/s was 1.15±0.25kPa, 1.34±0.19kPa, 2.19±0.225kPa and 2.52±0.27kPa, (mean±SD), respectively at the maximum amount of shear, K=1. Good agreement of experimental, theoretical (Ogden and Mooney–Rivlin models) and numerical shear stresses was achieved (p=0.7866–0.9935). Specimen thickness effects (2.0–10.0mm thick specimens) were also analyzed numerically and we found that there is no significant difference (p=0.9954) in the shear stress magnitudes, indicating a homogeneous deformation of the specimens during simple shear tests. Stress relaxation tests in simple shear were also conducted at different strain magnitudes (10–60% strain) with the average rise time of 14ms. This allowed us to estimate elastic and viscoelastic parameters (initial shear modulus, μ=4942.0Pa, and Prony parameters: g1=0.520, g2=0.3057, τ1=0.0264s, and τ2=0.011s) that can be used in FE software to analyze the non-linear viscoelastic behavior of brain tissue. This study provides new insight into the behavior in finite shear of brain tissue under dynamic impact conditions, which will assist in developing effective brain injury criteria and adopting efficient countermeasures against traumatic brain injury.

A tissue-level anisotropic criterion for brain injury based on microstructural axonal deformation

Different length scales from micrometers to several decimeters play an important role in diffuse axonal injury. The kinematics at the head level result in local impairments at the cellular level. Finite element methods can be used for predicting brain injury caused by a mechanical loading of the head. Because of its oriented microstructure, the sensitivity of brain tissue to a mechanical load can be expected to be orientation dependent. However, the criteria for injury that are currently used at the tissue level in finite element head models are isotropic and therefore do not consider this orientation dependence, which might inhibit a reliable assessment of injury. In this study, an anisotropic brain injury criterion is developed that is able to describe the effects of the oriented microstructure based on micromechanical simulations. The effects of both the main axonal direction and of local deviations from this direction are accounted for. With the anisotropic criterion for brain injury, computational head models will be able to account for aspects of diffuse axonal injury at the cellular level and can therefore more reliably predict injury.

Computation of axonal elongations: towards a new brain injury criterion

Finite element head models are a well-known way to describe the intracerebral mechanical behaviour during a head impact and, hence, to develop diffuse axonal injury (DAI) prediction tools. Owing to the lack of experimental data, the brain model is usually considered as homogeneous and isotropic. This hypothesis is acceptable from a mechanical point of view, but the classical computed metrics are not adequate according to the varying vulnerability of the neurological cells in the brain. The present study aims to show that the brain axonal orientations map provided by diffusion MRI can be combined with the computed strains in order to evaluate axonal elongations. This new metric seems to be more representative of the DAI mechanisms, which are known to be due to axon elongation.

Poster 8: Accuracy of Mild Brain Injury Diagnosis

Objective: To determine how often emergency department (ED) patients meeting the Centers for Disease Control and Prevention mild traumatic brain injury (TBI) criteria were diagnosed with a mild TBI by the ED physician. Design: Prospective identification of cases of mild TBI in the ED by study personnel using scripted interviews and medical record data was compared with a retrospective review of ED medical record documentation of mild TBI. Setting: EDs of a Level I trauma center and an academic nontrauma hospital.

Accuracy of Mild Traumatic Brain Injury Diagnosis

Powell JM, Ferraro JV, Dikmen SS, Temkin NR, Bell KR. Accuracy of mild traumatic brain injury diagnosis. Objective To determine how often emergency department (ED) patients meeting the Centers for Disease Control and Prevention (CDC) mild traumatic brain injury (TBI) criteria were diagnosed with a mild TBI by the ED physician. Design Prospective identification of cases of mild TBI in the ED by study personnel using scripted interviews and medical record data was compared with retrospective review of ED medical record documentation of mild TBI. Setting EDs of a level I trauma center and an academic nontrauma hospital. Participants Prospective cohort of subjects (N=197; mean age, 32.6y; 70% men) with arrival at the ED within 48 hours of injury, Glasgow Coma Scale score of 13 to 15, and injury circumstances, alteration of consciousness, and memory dysfunction consistent with the CDC mild TBI definition. Interventions Not applicable. Main Outcome Measure ED medical record documentation of mild TBI. Results Fifty-six percent of mild TBI cases identified by study personnel did not have a documented mild TBI-related diagnosis in the ED record. The greatest agreement between study personnel and ED physicians for positive mild TBI-related findings was for loss of consciousness (72% vs 65%) with the greatest discrepancy for confusion (94% vs 28%). Conclusions The diagnosis of mild TBI was frequently absent from ED medical records despite patients reporting findings consistent with a mild TBI diagnosis when interviewed by study personnel. Asking a few targeted questions of ED patients with likely mechanisms of injury that could result in mild TBI could begin to improve diagnosis and, in turn, begin to improve patient management and the accuracy of estimates of mild TBI incidence.

Biomechanics of Traumatic Brain Injury: Influences of the Morphologic Heterogeneities of the Cerebral Cortex

Traumatic brain injury (TBI) can be caused by accidents and often leads to permanent health issues or even death. Brain injury criteria are used for assessing the probability of TBI, if a certain mechanical load is applied. The currently used injury criteria in the automotive industry are based on global head kinematics. New methods, based on finite element modeling, use brain injury criteria at lower scale levels, e.g., tissue-based injury criteria. However, most current computational head models lack the anatomical details of the cerebrum. To investigate the influence of the morphologic heterogeneities of the cerebral cortex, a numerical model of a representative part of the cerebral cortex with a detailed geometry has been developed. Several different geometries containing gyri and sulci have been developed for this model. Also, a homogeneous geometry has been made to analyze the relative importance of the heterogeneities. The loading conditions are based on a computational head model simulation. The results of this model indicate that the heterogeneities have an influence on the equivalent stress. The maximum equivalent stress in the heterogeneous models is increased by a factor of about 1.3–1.9 with respect to the homogeneous model, whereas the mean equivalent stress is increased by at most 10%. This implies that tissue-based injury criteria may not be accurately applied to most computational head models used nowadays, which do not account for sulci and gyri.

A109 実験に基づく静水圧応力基準による脳損傷評価手法の開発(A1-2 細胞工学2)

A109 実験に基づく静水圧応力基準による脳損傷評価手法の開発(A1-2 細胞工学2)

Development of tissue level brain injury criteria by finite element analysis.

A three-dimensional finite element model of the direct cortical impact experiment was built and a preliminary validation against mechanical response was completed. The motion of the impactor was enforced in the model by applying the same acceleration history as that of the experimental impactor. A nonlinear contact surface algorithm was used for impactor-brain interface with the ABAQUS general purpose finite element program. The resulting motion of the impactor and the contacting node in the brain model confirmed that the impactor moved realistically and contacted the brain surface. The pressure generated in the model compared favorably with that measured by a pressure transducer in the experiment. The pattern of high shear deformation generated at the impact site in the model was similar to the pattern of contusion hemorrhage seen in the experiment. The pressure generated at the impact site propagated to the skull-brain boundary, especially, at the posterior margin of the cerebellum. Analysis of experimental data using a biomechanically validated finite element model will enable determination of tissue-level injury criteria for application in human brain models to predict head injury potential in contact, noncontact, or side impact situations.

Literature review of head injury biomechanics

The high incidence of head injuries resulting from transportation system crashes, sports, military activities, falls, assaults, etc. contributes to a preponderance of head injury biomechanics research. A wealth of publications result, addressing phenomenological and mechanistic issues associated with head response to mechanical impact. This literature survey provides an assessment of hypothesized brain injury mechanisms, brain injury criteria, mathematical models of head injury and available techniques for measuring head kinematics and brain tissue deformations associated with exposure to dynamic loads.

Effect of Pulse Duration on Head Injury

The human head is modelled as a fluid-filled spherical sandwich shell. The fluid is inviscid, irrotational, and compressible. The axisymmetric loading function is a timewise Heaviside function with a variable duration. The effect of the pulse duration on skull fracture and brain injury is investigated numerically. Short loading pulses are found to be less damaging. Human tolerance curves are obtained using hypothetical skull fracture and brain injury criteria. The curves follow the some trend as that of the Wayne State Curve.