Detecting Deep Brain Stimulation Currents with High Resolution Transcranial Acoustoelectric Imaging

The efficacy of deep brain stimulation (DBS) for relieving motor symptoms from Parkinson's disease or essential tremor is highly dependent on accurate placement of the electrode. New current-steering electrodes can reduce the burden of placement by directing the stimulating currents toward the target locations. However, no imaging modality exists in the clinic or operating room to provide feedback of the currents as they are delivered/steered from the contacts. In this study we investigate the prospects of high resolution, transcranial acoustoelectric imaging (AEI) as a method for non-invasively imaging DBS currents. A DBS electrode was inserted into a brain gel phantom inside a human skull and monopoles were generated at individual contacts. A linear array ultrasound (US) transducer was coupled to the temporal window and focused toward the DBS electrode to induce AE signals proportional to the time-varying current densities. The AE signals using an injected current of 11 mA and focal pressures of 2.04 MPa were detected with SNRs between 716 dB, mean accuracy along the length of the electrode of 0.35 mm, radial separation of segmented contacts in a ring-triplet of 1.21 mm, mean monopole FWHMs of 3.54 mm, and a sensitivity of 0.283 pVfmA/MPa. Our results advocate AEI as a promising tool for providing non-invasive, high resolution feedback of the spread of current from a directional DBS electrode with potential roles in enhancing placement of the electrode and chronically monitoring the integrity of the stimulation.