Correlation Between the Neural Response Telemetry (NRT) and Radiological Measurements in Detection of Position of the Electrode Inside the Cochlea

Cochlear implantation (CI) is a worldwide accepted and effective surgical procedure for patients with profound sensory neural hearing loss to gain near normal hearing.1 The position of electrode inside the cochlea affects the outcomes. Full insertion of the CI electrode array and insertion in scala tympani usually has optimal results and better words recognition.2 Translocation of electrode array from scala tympani to scala vestibule or outword migration of electrode array may result in poor response.2 There are many intraoperative and post operative techniques to determine the position of electrode array inside the cochlea, some are radiological as transorbital view plan x-ray or computed tomography or 3D rotational x ray and others are electrophysiological measurements.3 Although the accuracy of the radiological techinques they are time and cost consuming1. The electrically evoked cochlear action potential (ECAP) threshold is dependent on the distance between the electrodes and the spiral ganglion cells. The neural response telemetry-ratio (NRT-ratio) is one of the electrophysiological measurments techniques and it is based on each individual electrode's ECAP threshold and can identify the intracochlear electrode array position 4. According to a study done by Philipp Mittmann in 2015, a NRT-ratio above 1.05 indicates an electrode translocation from scala tympani to scala vestibuli and a NRT-ratio below 1.05 shows correlation to a pure scala tympani placement5, but another study found variation of the NRT-ratio in a group of patients with an electrode placement within scala tympani.6