Available online at www.sciencedirect.com Medical Engineering & Physics 31 (2009) 392–399 Optical characterization of acceleration-induced strain fields in inhomogeneous brain slices C. Lauret, M. Hrapko, J.A.W. van Dommelen ∗ , G.W.M. Peters, J.S.H.M. Wismans Materials Technology Institute, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands Received 19 February 2008; received in revised form 17 March 2008; accepted 16 May 2008 Abstract The aim of this study was to measure high-resolution strain fields in planar sections of brain tissue during translational acceleration to obtain validation data for numerical simulations. Slices were made from fresh, porcine brain tissue, and contained both grey and white matter as well as the complex folding structure of the cortex. The brain slices were immersed in artificial cerebrospinal fluid (aCSF) and were encapsulated in a rigid cavity representing the actual shape of the skull. The rigid cavity sustained an acceleration of about 900 m/s 2 to a velocity of 4 m/s followed by a deceleration of more than 2000 m/s 2 . During the experiment, images were taken using a high-speed video camera and Von Mises strains were calculated using a digital image correlation technique. The acceleration of the sampleholder was determined using the same digital image correlation technique. A rotational motion of the brain slice relative to the sampleholder was observed, which may have been caused by a thicker posterior part of the slice. Local variations in the displacement field were found, which were related to the sulci and the grey and white matter composition of the slice. Furthermore, higher Von Mises strains were seen in the areas around the sulci. © 2008 IPEM. Published by Elsevier Ltd. All rights reserved. Keywords: Brain tissue; Strain concentration; Acceleration; Digital image correlation; Heterogeneity 1. Introduction Annually 1.4 million people sustain a traumatic brain injury (TBI) in the United States, of which 20% is caused by vehicle traffic accidents [1]. Although vehicles are already equipped with belts and airbags, even more sophisticated pre- ventive measures are needed to further reduce this number of injuries. The development of these measures can be based on injury predictions with numerical head models, by simulating crash situations. Many numerical head models have been developed [2–7], differing in the constitutive models used and the level of detail in the modelled geometries of the brain and the skull. Con- stitutive models describe the mechanical behaviour of tissue, which is nonlinear and visco-elastic in the case of brain tissue [8]. Moreover, brain tissue may be anisotropic and show inter- regional variations. The quality of numerical head model simulations depends partly on the ability of the constitutive model to describe this complex mechanical behaviour, and ∗ Corresponding author. Tel.: +31 40 247 4521; fax: +31 40 244 7355. E-mail address: j.a.w.v.dommelen@tue.nl (J.A.W. van Dommelen). partly on the modelled geometry. Therefore, the constitutive model and the head model need to be validated in order to give reliable and representative injury predictions. However, only limited experimental data exist because of the inaccessibility of the cranium. Pudenz and Shelden [9] measured the deformation in a macaque brain through a cranial window. Although this was one of the first successful strain measurements of the brain during acceleration, only the deformation of the surface could be observed. Furthermore, in the past two decades the use of living animals is being restricted due to legislations. To validate model predictions, Brands et al. [3] used both open and closed cylindrical cups filled with silicon gel, which were subjected to transient rotational acceleration. In both setups, the gel response was measured using optical markers and a high-speed video camera. Ivarsson et al. [10,11] studied the natural protection of the brain, also using gel and high- speed tracing of markers. More specifically, lateral ventricle substitutes were included in this physical model to investigate if these structures give strain relief during head impact. Mar- gulies et al. [12] and Meaney et al. [13] recorded the motion of grid patterns painted on gel inside animal and human skulls 1350-4533/$ – see front matter © 2008 IPEM. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.medengphy.2008.05.004