Ultrasound Current Source Density Imaging of a time-varying current field in a multielectrode nerve chamber

Drug resistant epilepsy can in some cases be treated with surgery. To minimize potentially crippling side effects of surgery, a detailed functional map of the brain is usually required prior to resection. Conventional mapping techniques rely on a coarse grid of electrodes with limited spatial resolution. Ultrasound Current Source Density Imaging (UCSDI) is new high resolution method to image electric current based on ultrasound. UCSDI potentially enhances conventional mapping procedures as it produces 4D (space and time) maps of current flow co-registered to ultrasound. In this paper, we describe a new system for studying UCSDI in peripheral nerves and neural tissue. This system allows multi-electrode detection of conventional electrophysiological signals simultaneous with UCSDI. UCSDI was used to map short bursts of current injected through the rat sciatic nerve. The amplitude of the current was varied to test the sensitivity of the system. The detection threshold was 0.1 mA/cm² at ~250 kPa, well within range for detecting bioelectric signals in neural tissue.