Comparison of Mechanical Variable Identifiers of Brain Injury

Multiple mechanical variables have been used to describe the occurrence of brain injury in impact modeling of the human head [1, 2]. The validity of these variables for this purpose is usually established separately through the following process. First, a loading test is performed on an animal. Location, type and spatial extent of injury on the brain are measured upon or after loading. Subsequently, computational simulation is performed based on a particular constitutive model of the brain. Mechanical variables such as pressure or effective stress are plotted for the region of interest. The magnitude of the mechanical variable that results in a contour of the same size as the observed extent of experimental injury is declared as the critical value for that type of injury. The choice of mechanical variable itself could be based on conventional wisdom, precedence, or experience of the researcher. Another, much simpler variable-injury correlation process, which does not rely upon simulations, uses the ex vivo failure response of brain tissue as the criterion. For example, the uniaxial failure strain of the tissue may be taken as the critical value for injury.