RESEARCH ARTICLE Effect of cerebrospinal fluid modeling on spherically convergent shear waves during blunt head trauma Amit Madhukar 1 | Ying Chen 2 | Martin Ostoja‐Starzewski 2 1 Department of Mechanical Science and Engineering, University of Illinois at Urbana‐Champaign, Champaign, IL, USA 2 Department of Mechanical Science and Engineering and Beckman Institute, University of Illinois at Urbana‐Champaign, Champaign, IL, USA Correspondence Martin Ostoja‐Starzewski, Department of Mechanical Science and Engineering and Beckman Institute, University of Illinois at Urbana‐Champaign, Champaign, IL 61801, USA. Email: martinos@illinois.edu Funding information NSF, Grant/Award Number: CMMI‐ 1462749; NCSA/IACAT Fellows; Illinois Distinguished Fellows Abstract The MRI‐based computational model, previously validated by tagged MRI and harmonic phase imaging analysis technique on in vivo human brain deformation, is used to study transient wave dynamics during blunt head trauma. Three different constitutive models are used for the cerebrospinal fluid: incompressible solid elastic, viscoelastic, and fluid‐like elastic using an equation of state model. Three impact cases are simulated, which indicate that the blunt impacts give rise not only to a fast pressure wave but also to a slow, and potentially much more damaging, shear (distortional) wave that converges spherically towards the brain center. The wave amplification due to spherical geometry is balanced by damping due to tissues' viscoelasticity and the heterogeneous brain structure, suggesting a stochastic competition of these 2 opposite effects. It is observed that this convergent shear wave is dependent on the constitutive property of the cerebrospinal fluid, whereas the peak pressure is not as significantly affected. KEYWORDS blunt head trauma, cerebrospinal fluid, constitutive laws, human brain, MRI, shear wave 1 | INTRODUCTION 1.1 | Need for improved blunt head trauma modeling Blunt head trauma (BHT) is a brain injury without damage to the skull. It occurs in traumatic events such as transportation accidents, falls, sports‐related injuries, and explosions. While several brain injury mechanisms, even including the skull bone flexure, 1 have been proposed, we approach the topic from the standpoint that understanding wave dynamics in a human brain is key to understanding brain damage in BHT, eg, in previous studies. 2-4 This insight is also fundamental for proper design of helmets and any protections against traumatic brain injury. In particular, we use a powerful MRI‐based (ie, having a spatial resolution of 1 mm) finite element (FE) head model allowing studies of head impact processes. 5 That model has been compared with, and validated by, the tagged MRI and harmonic phase (HARP) imaging analysis technique on in vivo human brain deformation data. 6 1.2 | BHT in literature It is instructive to review prior research on BHT as the mechanics of wave propagation during a traumatic event is crucial to understanding the biomechanical effects. The BHT is brought about either by a direct blow to the head (impact loading) or a jerk of the head due to the motion of the body (impulse loading). During this process, the brain is subjected to both linear and rotational acceleration. Early experiments investigated the damage caused by linear acceleration during BHT. Work by Thomas et al 7 and Nahum 8 demonstrated the relationship between linear acceleration and the intracranial pressure: Impacts without appreciable deformation led to the formation of a pressure Received: 9 August 2016 Revised: 19 February 2017 Accepted: 10 March 2017 DOI: 10.1002/cnm.2881 Int J Numer Meth Biomed Engng. 2017;e2881. https://doi.org/10.1002/cnm.2881 Copyright © 2017 John Wiley & Sons, Ltd. wileyonlinelibrary.com/journal/cnm 1 of 11