Objective: To analyze the relationship between the electric field and the volume of tissue activated (VTA) during model-based investigations of deep brain stimulation (DBS).
Background: An important factor for the therapeutic outcome of DBS is the spatial distribution of the stimulation field in the target area. Finite element models and simulations of DBS are increasingly being used to study the distribution of the stimulation field in relation to patient specific anatomy. The stimulation field is often defined as a VTA derived from computational axon models that are coupled to the finite element simulations. This approach however, is not feasible in many research centers due to the complexity of developing a computational axon model, as well as the extensive execution time when solving such models.
Methods: A detailed computer axon cable model was developed to study axonal activation in response to various DBS stimulation configurations. A range of axon models were set up and coupled to finite element models of DBS. DBS simulations were performed for Medtronic lead model 3389 during monopolar configurations for a range of amplitudes and pulse widths. Activation thresholds for the electric fields were derived by measuring the field strength at the maximum radius of activation for each configuration.
Results: Simulations showed that the electric field thresholds were related to stimulation amplitude, pulse width, and axon diameter. For large axons, the electric field threshold was not dependent on the amplitude, thus implying a low sensitivity of the electric field curvature.
Conclusions: Electric field thresholds can be used to predict the VTA during model-based investigations of DBS without the necessity of computer axon models. The use of electric field thresholds may substantially simplify the process of performing model-based investigations of DBS in the future.