Optimal frequency range for electrical impedance tomography of neural activity in peripheral nerve

Neural electrical impedance tomography (EIT) images changes in tissue impedance, associated with neural activity, by passing a carrier signal through neural tissue and measuring changes in the boundary voltages. In this paper, the frequency limits of an EIT carrier signal are investigated across the range 1 to 32 kHz, using a nerve cuff on rat sciatic nerve in-vitro. The upper frequency limit was determined, from impedance measurements of inactive nerve tissue, to be 20 kHz, and the lower limit, from frequency analysis of an artificially evoked compound action potentials, to be 2 kHz. This operating frequency range, of 2 to 20 kHz, is broad enough to multiplex several carrier signals, which is expected to be an essential feature of future real-time EIT systems for peripheral nerve.