The principal focus of this study was the measurement of brain motion with respect to the skull using a high-speed, biplane x-ray system and neutral density targets (NDTs). This study was divided in two parts.

For the first part of this study, twenty-seven impacts were conducted using nine human cadaver head and neck specimens. An array of multiple NDTs was implanted in two or three columns with up to 6 targets in each column. During impact, local brain tissue tends to keep its position and shape with respect to the inertial frame, resulting in relative motion between the brain and skull and deformation of the brain. The localized motions of the brain generally follow loop or figure eight patterns, with peak displacements on the order of ± 5 mm. The primary direction of motion for each target is described as the Major Displacement Axis (MDA). Perpendicular bisectors from each MDA intersect at the Average Instant Center (AIC) of rotation. The MDA orientation rotates from inferior to superior. Linear input to the head produced little brain motion, while rotational input results in relative motion between the brain and skull. Motion for sagittal and coronal plane rotation is remarkably similar, and the brain motions exhibit interesting anterior-posterior and right-left symmetry.

For the second part of this study, clusters of seven NDTs were used to measure relative motion, maximum principal strain, maximum shear strain, and intracranial pressure. Thirty-five impacts were conducted using eight human cadaver head and neck specimens. The effect of a helmet was evaluated. Peak coup pressure and pressure rate increase with increasing linear acceleration, but coup pressure pulse duration decreases. Peak average maximum principal strain and maximum shear are on the order of 0.09 for CFC 60 Hz data for these tests. Peak average maximum principal strain and maximum shear decrease with increasing linear acceleration, coup pressure, and coup pressure rate. Linear and angular acceleration of the head are reduced with use of a helmet, but strain increases. Together, these results represent the first time the relative motion between the brain and skull during impact have been quantified.