The Magnetic Properties of Electrical Pulses Delivered by Deep-Brain Stimulation Systems

The aim of this article is to analyze the magnetic field properties for both the monopolar and bipolar electrode configurations of deep-brain stimulation electrodes using 3-D magnetic field measurements and to investigate if the magnetic measurements enable a localization of the electrode as a proof of concept. Therefore, a simplified head phantom with an integrated deep-brain stimulation electrode was created to measure the magnetic flux densities in all the three dimensions with a fluxgate magnetometer over a sensor trajectory of measuring points inside the magnetically shielded chamber. The magnitude of the magnetic flux density for monopolar stimulation and bipolar stimulation is in the nT and pT ranges for the frequency 160 Hz, depending on the stimulation amplitude and on the distance between the sensor and the electrode. The field distributions show a linear decline in the magnetic field for the monopolar and a quadratic decline for the bipolar stimulation. We were able to reconstruct the magnetic field using multiple recording sites. As the magnetic field of deep-brain stimulation can be measured and its field strength can be reconstructed, it is feasible to estimate the strength of the field within the limits of programmable stimulation parameters and distance between the sensor and the electrode. The presented results are intended as preliminary work for the further development of electrode localization methods using magnetic measurements. As an example of the feasibility of electrode localization, this article presents a bipolar measurement that creates a more focused spatial field distribution and results in an accurate localization.