TISSUE-LEVEL STRESSES WITHIN THE BRAIN DURING ROTATIONALLY-INDUCED mTBI: A 3D FINITE ELEMENT MODEL...

TISSUE-LEVEL STRESSES WITHIN THE BRAIN DURING ROTATIONALLY-INDUCED mTBI: A 3D

FINITE ELEMENT MODEL OF THE RAT COUPLED WITH EXPERIMENTS

D. BAUMGARTNER, M. LAMY, R. WILLINGER DEPARTMENT OF FLUID AND SOLID MECHANICS

STRASBOURG UNIVERSITY – FRANCE

N. YOGANANDAN, B.D. STEMPER DEPARTMENT OF NEUROSURGERY

MEDICAL COLLEGE OF WISCONSIN – USA

5th European HTC

Bonn – Germany – November 2011

CONTEXT

TISSUE-LEVEL STRESSES WITHIN THE BRAIN DURING ROTATIONALLY-INDUCED mTBI: A 3D FINITE ELEMENT MODEL OF THE RAT COUPLED WITH EXPERIMENTS

5th European HTC – Bonn – Germany – November 2011

Context: TBI

Traumatic Brain Injuries (TBI): Major cause of deaths and disabilities

235/100,000 (EU) 103/100,000 (USA)

Double cost

Mild TBI : not fully explored

Motor-vehicle incidents

Falls Sport-related

Other



Context: Mechanical sollicitations

Mechanical loading results in an brain response

Criteria in head protection systems and standards Not accounting for angular acceleration

Need for injury criteria models

Experimental models Numerical models

(Deck et al., 2008)



Context: Rat brain FE models

Shreiber et al., 1997 (University of Pennsylvania)

Gefen et al., 2003 (University of Pennsylvania)

Levchakov et al., 2006 (University of Pennsylvania)

Pena et al., 2005 (University of Cambridge)

Mao et al., 2006 (Wayne State University)

Zhu et al., 2010 (Wayne State University)

Fijalkowski et al., 2009 (Medical College of Wisconsin)

Strasbourg University Model, 2009



Context: Objectives of the study

Reconstruct real experimental protocols with our rat head FEM

Pure rotational loading Compare experimental findings and calculated mechanical response.

Contribute to the knowledge on mild TBI from a mechanical point of view.



EXPERIMENTAL

PROTOCOL



Experimental setup: Device

Submission of the rat head to a coronal plane pure rotational acceleration input

The Medical College of Wisconsin

device for the induction of rat head

rotation



Experimental setup: Groups

Three levels of amplitude: 290 krad/s² (M1), 420 krad/s² (M2) and 530 krad/s² (M3) Three durations: 1ms (D1), 2ms (D2) and 3ms (D3)

Five experimental groups:

Varying duration (D1,D2,D3) Fixed amplitude (M2)

Varying amplitude (M1,M2,M3) Fixed duration (D2)

Four complementary pulses



Experimental results: Behaviour

Observation of unconscious times (UC times)

UC times increase with amplitude &/or duration of acceleration



Experimental results: Histology

GFAP immunohistochemistry in the hippocampus

MAP2 immunohistochemistry in the parietal cortex



NUMERICAL

SIMULATIONS



Simulations: Model (mesh, 1)

Continuous mesh (Hypermesh 10.0)

Brain 14,752 hexahedrons

Skull

3,220 shells Brain/skull interface 3,220 hexahedrons



Simulations: Model (mesh, 2)



Simulations: Model (behaviour, 1)

The model is assumed to be Linear viscous elastic (Boltzman model) for brain Linear elastic for brain/skull interface With a rigid skull Homogeneous and isotropic

Material properties of the brain

Short term

shear modulus

Long term

shear modulus Time constant Density Bulk modulus

10 kPa 2 kPa 8 s 1,040 kg/m3 2.19 GPa



Simulations: Model (behaviour, 2)

Choice of material properties for the brain

Based on Fijalkowski et al. (2009)

In agreement with MRE data from Vappou et al. (2008)

Short term shear modulus Long term shear modulus

10 kPa 2 kPa



Simulations: Computed parameters

The model is submitted to coronal plane angular acceleration inputs (one per group) Main parameter (Radioss)

Von Mises stresses Regions of interest

Hippocampus and parietal cortex



NUMERICAL

RESULTS



Results: VM stresses (distribution, 1)




Rotation direction



Results: VM stresses (distribution,5)

Rotation direction



Results: Influence of pulse amplitude

1 ms 2 ms 3 ms Fixed

Duration



Results: Influence of pulse duration

290 krad/s² 420 krad/s² 530 krad/s² Fixed

Amplitude



Results: First observations

Fixed duration If the amplitude of the loading increases, then the VM stresses increase too.

Fixed amplitude

If the duration of the loading varies, no sensitive trend can be found in VM stresses evolution. How can it be explained ?



Usually observed Peak value

But

The same constraint will have differing consequences, the longer it is maintained

How to account for both amplitude and duration of loading ? Notion of « shape factor » Integrated parameters

A new metric: The stress-time (1)



Integrated parameter for the duration of the loading pulse

A new metric: The stress-time (2)



Results: Stress-time and pulse amplitude

1 ms 2 ms 3 ms Fixed

Duration



290 krad/s² 420 krad/s² 530 krad/s² Fixed

Amplitude

Results: Stress-time and pulse duration



Results: Numerical vs experimental (1) H

ipp

oca

mp

us



Results: Numerical vs experimental (2) Pa

riet

al C

ort

ex



CONCLUSIONS



Conclusions

FEM including anatomical structures for in-vivo TBI investigation

Good relation between VM stresses distributions and the histological observations

Amplitude of VM stresses do not seem influenced by the impact duration, whereas integrated stresses are

Proposition of a new metric accounting for this observation

Better agreement with experimental outcomes



Future developments

Expanding the range of existing simulations with New inputs &/or new protocols

Achieving a more detailed mechanical characterization i.e. taking into account inhomogeneity, anatomically based distribution, …

Realizing a refined mesh for the model

In the long term, transfering the results to human brain



THANK YOU FOR

YOUR ATTENTION



TISSUE-LEVEL STRESSES WITHIN THE BRAIN DURING ROTATIONALLY-INDUCED mTBI: A 3D

FINITE ELEMENT MODEL OF THE RAT COUPLED WITH EXPERIMENTS

D. BAUMGARTNER, M. LAMY, R. WILLINGER DEPARTMENT OF FLUID AND SOLID MECHANICS

STRASBOURG UNIVERSITY – FRANCE

N. YOGANANDAN, B.D. STEMPER DEPARTMENT OF NEUROSURGERY

MEDICAL COLLEGE OF WISCONSIN – USA

5th European HTC

Bonn – Germany – November 2011

TISSUE-LEVEL STRESSES WITHIN THE BRAIN DURING ROTATIONALLY-INDUCED mTBI: A 3D FINITE ELEMENT MODEL...

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