Background: Current approaches to detect the positions and orientations of directional deep brain stimulation (DBS) electrodes rely on radiative imaging data. In this study, we aim to present an improved version of a radiation-free method for magnetic detection of the position and the orientation (MaDoPO) of directional electrodes based on a series of magnetoencephalography (MEG) measurements and a possible future solution for optimized results using emerging on-scalp MEG systems. Methods: A directional DBS system was positioned into a realistic head–torso phantom and placed in the MEG scanner. A total of 24 measurements of 180 s each were performed with different predefined electrode configurations. Finite element modeling and model fitting were used to determine the position and orientation of the electrode in the phantom. Related measurements were fitted simultaneously, constraining solutions to the a priori known geometry of the electrode. Results were compared with the results of the high-quality CT imaging of the phantom. Results: The accuracy in electrode localization and orientation detection depended on the number of combined measurements. The localization error was minimized to 2.02 mm by considering six measurements with different non-directional bipolar electrode configurations. Another six measurements with directional bipolar stimulations minimized the orientation error to 4°. These values are mainly limited due to the spatial resolution of the MEG. Moreover, accuracies were investigated as a function of measurement time, number of sensors, and measurement direction of the sensors in order to define an optimized MEG device for this application. Conclusion: Although MEG introduces inaccuracies in the detection of the position and orientation of the electrode, these can be accepted when evaluating the benefits of a radiation-free method. Inaccuracies can be further reduced by the use of on-scalp MEG sensor arrays, which may find their way into clinics in the foreseeable future.

The aim of this study is to localize the electrode of the deep brain stimulation with three dimensional magnetic field measurements by applying the dipole fitting approach. The deep brain stimulation electrode was positioned successively at five increasing depths with well-known positions in a cylindrical head phantom and the magnetic field distribution was measured with a fluxgate magnetometer around the phantom. At each measuring point, the total magnetic field was measured by rotating the sensor in all three orthogonal directions. Finite element method was used to model the volume conduction of the phantom with its exact dimensions and electromagnetic simulations were performed to calculate the magnetic field distribution at the same measuring points around the phantom. The dipole fitting approach was then used to localize the position of the electrode by means of minimizing the normalized root mean square error between measured and calculated data. The results show an average localization accuracy of less than 1 mm over all performed measurements for both near surface and deep positions. Small deviations in the results can be explained by the measuring accuracy of the used fluxgate sensor. It can be concluded that the deep brain stimulation electrode can be precisely localized by three dimensional magnetic field measurements by using an accurate head volume conduction model and by applying the dipole fitting approach. The presented results are intended as preparatory work for real magnetic field measurements with patients implanted with deep brain stimulation electrodes.

Objective. The aim of the present study was to investigate the accuracy of localization and rotational orientation detection of a directional deep brain stimulation (DBS) electrode using a state-of-the-art magnetoencephalography (MEG) scanner. Approach. A directional DBS electrode along with its stimulator was integrated into a head phantom and placed inside the MEG sensor array. The electrode was comprised of six directional and two omnidirectional contacts. Measurements were performed while stimulating with different contacts and parameters in the phantom. Finite element modeling and fitting approach were used to compute electrode position and orientation. Main results. The electrode was localized with a mean accuracy of 2.2 mm while orientation was determined with a mean accuracy of 11 ^∘ . The limitation in detection accuracy was due to the lower measurement precision of the MEG system. Considering an ideal measurement condition, these values represent the lower bound of accuracy that can be achieved in patients. Significance. However, a future magnetic measuring system with higher precision will potentially detect location and orientation of a DBS electrode with an even greater accuracy.

Detection of magnetic fields generated by deep brain stimulation (DBS) using optically pumped magnetometers (OPMs) operating in the spin-exchange relaxation-free (SERF) regime holds significant promise. High bandwidth DBS signals are particularly valuable for understanding current OPM limitations and developing predictive strategies to overcome them. This primary study investigates the response of commercially available SERF-OPMs (QZFM Gen-2, QuSpin Inc.) with their limited 135 Hz bandwidth and open-loop operation when exposed to magnetic DBS signals emitted by a commercially available DBS lead and generated by a DBS implantable pulse generator (IPG), which are characterized by short-duration rectangular pulses. Such magnetic fields emitted from a real DBS lead were measured using OPMs across a range of DBS pulse repetition frequencies from 2 to 255 Hz. A versatile 304-channel superconducting quantum interference device (SQUID) vector magnetometer system was employed in the Berlin Magnetically Shielded Room-2.1 for reference measurements. Our findings identified peaks at several spectral frequencies in addition to those relevant to the DBS signal, including the known DBS repetition frequency and its spectral harmonics peaks. These additional peaks are attributed to the interaction between the lock-in detection-based OPM's 923 Hz modulating field, supplied by the OPM's on-sensor coils, and the DBS repetition frequency. These peaks were successfully reconstructed by developing an OPM lock-in model and applying this model to signal characteristics provided by SQUID reference measurements. This letter identifies and clarifies the origin of various spectral peaks observed when using bandlimited OPMs for high bandwidth signal detection. This understanding allows magnetometer users of this particular sensor technology to differentiate between artificially introduced signal components and the DBS signal components. These findings are essential for improving the application utility of OPM-based detection for DBS and contribute to the advancement and understanding of OPM technology and address its current limitations.