Investigation of Traumatic Brain Injuries Using the Next Generation of Simulated Injury Monitor (SIMon) Finite Element Head Model

Abstract

The objective of this study was to investigate potential for traumatic brain injuries (TBI) using a newly developed, geometrically detailed, finite element head model (FEHM) within the concept of a simulated injury monitor (SIMon). The new FEHM is comprised of several parts: cerebrum, cerebellum, falx, tentorium, combined pia-arachnoid complex (PAC) with cerebro-spinal fluid (CSF), ventricles, brainstem, and parasagittal blood vessels. The model's topology was derived from human computer tomography (CT) scans and then uniformly scaled such that the mass of the brain represents the mass of a 50 th percentile male's brain (1.5 kg) with the total head mass of 4.5 kg. The topology of the model was then compared to the preliminary data on the average topology derived from Procrustes shape analysis of 59 individuals. Material properties of the various parts were assigned based on the latest experimental data. After rigorous validation of the model using neutral density targets (NDT) and pressure data, the stability of FEHM was tested by loading it simultaneously with translational (up to 400 g) combined with rotational (up to 24,000 rad/s 2) acceleration pulses in both sagittal and coronal planes. Injury criteria were established in the manner shown in Takhounts et al. (2003a). After thorough validation and injury criteria establishment (cumulative strain damage measure-CSDM for diffuse axonal injuries (DAI), relative motion damage measure-RMDM for acute subdural hematoma (ASDH), and dilatational damage measure-DDM for contusions and focal lesions), the model was used in investigation of mild TBI cases in living humans based on a set of head impact data taken from American football players at the collegiate level. It was found that CSDM and especially RMDM correlated well with angular acceleration and angular velocity. DDM was close to zero for most impacts due to their mild severity implying that cavitational pressure anywhere in the brain was not reached. Maximum principal strain was found to correlate well with RMDM and angular head kinematic measures. Maximum principal stress didn't correlate with any kinematic measure or injury metric. The model was then used in the investigation of brain injury potential in NHTSA conducted side impact tests. It was also used in parametric investigations of various "what if" scenarios, such as side versus frontal impact, to establish a potential link between head kinematics and injury outcomes. The new SIMon FEHM offers an advantage over the previous version because it is geometrically more representative of the human head. This advantage, however, is made possible at the expense of additional computational time.

Mild Traumatic Brain Injury Predictors Based on Angular Accelerations During Impacts

“…On the contrary, Takhounts et al 31 reported that the maximum angular velocity was correlated with CSDM 25% predicted by their SIMon brain FE model in their linear regression analyses using the same 6DOF device data used in this study. Then they proposed another brain injury criterion based on head rotational kinematics called BRIC.…”

Development of the STAR Evaluation System for Football Helmets: Integrating Player Head Impact Exposure and Risk of Concussion

“…32,33 Finite element models will likely be an important factor in understanding this relationship. 45 Once a better understanding of these relationships is gathered, more complex methods can be used to predict brain injury in the future.…”

Mechanical properties of bovine pia–arachnoid complex in shear

“…Partially due to a lack of these properties, many assumptions have been made to model the skull/brain junction. These simplifications include: direct connection/ coupling without slipping (Ruan et al, 1991;Zhou et al, 1994;Turquier et al, 1996;Zhang et al, 2001;Kleiven and Hardy, 2002;Takhounts et al, 2008), sliding interface with different values for the coefficient of friction or tie-break thresholds (Bandak and Eppinger, 1994;Claessens et al, 1997;Miller et al, 1998), and a layer of low-shear modulus solid and frictional sliding contact (Al-Bsharat et al, 1999). Table 1 summarizes the material properties assigned to the CSF layer (PAC and CSF) in the previous modeling studies.…”

“…In most brain models, CSF layer has been modeled as incompressible, elastic material with a low shear modulus to simulate the fluid and trabeculae in the subarachnoid space. In a recent study by Takhounts et al (2008), a linear viscoelastic model simulated the CSF layer was used to allow for rate effects. Due to the lack of data to accurately characterize the biomechanical response of PAC, it is hard to determine with confidence which method best represents the in vivo situation.…”