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The objective of this research effort is to provide experimental data for validation of numerical studies of head injury. Two questions are addressed: First, what are the linear and angular accelerations of the skull during a mild head impact typical of contact sports? Second, how does the brain deform in response to angular acceleration of the skull? The specific aims are: (1) to measure the linear and angular acceleration of the head during heading of a soccer ball; and (2) to measure, non-invasively, the strain field in the human brain during voluntary head motion using tagged magnetic resonance (MR) imaging. Thus far with regard to the first specific aim, data from linear and angular accelerations of the head from 10 subjects were acquired during heading. Neuropsychological tests were also performed before and after heading. Mean (± std. dev.) peak linear acceleration of 184±42 m/s2 and peak angular accelerations of 1820 rad/s2 ±510 m/s2 have been observed. The magnitude of acceleration was similar in expert subjects compared to novice or recreational subjects. In neuropsychological tests before and after heading, a small but statistically significant increase in false identifications of a target (signifying inattention) was detected after heading. Thus far with regard to the second specific aim, brain deformation was measured in human subjects during controlled occipital deceleration of the head. Peak magnitudes of acceleration during the head motion were 2-3G (20-30 m/s2). Tagged MR images were acquired by repeating the motion and acquiring part of the image during each repetition. Brain deformation in MR images was quantified with the Lagrangian strain tensor. Maximum principal Lagrangian strains of 5-6% were observed. Anterior-posterior shortening was seen frontally and stretching was seen occipitally. It appears that the brain is suspended or restrained frontally by bony structures, membranes and vasculature, which prevent compression of the brain against the back of the skull at these acceleration levels. We believe these studies have provided the first quantitative measurements of brain deformation in response to skull acceleration. These results will be highly useful for validation of finite element simulations. |
