An Approach for Individualized Cochlear Frequency Mapping Determined From 3D Synchrotron Radiation Phase-Contrast Imaging

Abstract

Objective: Cochlear implants are traditionally programmed to stimulate according to a generalized frequency map, where individual anatomic variability is not considered when selecting the centre frequency of stimulation of each implant electrode. However, high variability in cochlear size and spatial frequency distributions exist among individuals. Generalized cochlear implant frequency maps can result in large pitch perception errors and reduced hearing outcomes for cochlear implant recipients. The objective of this work was to develop an individualized frequency mapping technique for the human cochlea to allow for patient-specific cochlear implant stimulation. Methods: Ten cadaveric human cochleae were scanned using synchrotron radiation phase-contrast imaging (SR-PCI) combined with computed tomography (CT). For each cochlea, ground truth angle-frequency measurements were obtained in three-dimensions using the SR-PCI CT data. Using an approach designed to minimize perceptual error in frequency estimation, an individualized frequency function was determined to relate angular depth to frequency within the cochlea. Results: The individualized frequency mapping function significantly reduced pitch errors in comparison to the current gold standard generalized approach. Conclusion and Significance: This paper presents for the first time a cochlear frequency map which can be individualized using only the angular length of cochleae. This approach can be applied in the clinical setting and has the potential to revolutionize cochlear implant programming for patients worldwide.

A Web-Based Automated Image Processing Research Platform for Cochlear Implantation-Related Studies

“…Electrode intracochlear positioning is characterized both by distance and angular measures at each electrode contact (where RW relates to 0 • and Ap corresponds to the maximum cochlear angle, which is typically around 900 • ) cochlear coverage). From these, the characteristic frequencies associated with each electrode are proposed in relation to OC [12] or SG [13,14]. In addition, the distance of each electrode contact to the MW and the estimated BM position are also computed.…”

“…Provided with a delineation of the bony labyrinth, various techniques permit the estimation of important metrics relevant to CI implantation, such as the cochlear duct length (CDL), which serves as an indicator of general cochlear size and what depth of insertion is reasonable to try to reach for that specific cochlea. The CDL and other metrics also enable the computation of normalized tonotopic frequencies according to Greenwood [12], Stakhovskaya [13], or Helpard et al [14].…”

“…They also proposed to take advantage of the left/right symmetry of inner-ear anatomy by utilizing the pre-operative image of the normal contra-lateral ear for cochlear structure delineation for cases where pre-operative CT images were not available [24]. Granting the successful reconstruction of electrode placement within cochlear structures, the characteristic frequency (CF) at each contact can legitimately be computed at the estimated corresponding place on the organ of Corti (OC) [12] or at the nearest spiral ganglion (SG) [13,14,25]. The accurate inference of the relative position between an electrode and the basilar membrane (BM) lining up the ST can also enable the assessment of the potential translocation of the electrode in SV or inferential predictions of the degree of traumaticity of the insertion, e.g., if the electrode were to have either elevated or ripped through the BM and entered the SV.…”

Fully Automated Measurement of Cochlear Duct Length From Clinical Temporal Bone Computed Tomography

“…Differences between the array length and the CDL may contribute to a frequency mismatch as the result of an electrode being misaligned with the frequency encoded at a particular location within the scalae 3–8 . Preoperative imaging studies, particularly high‐resolution temporal bone computed tomography (CT), may offer insights into a given individual's cochlear anatomy that can be prospectively used to select devices that may optimize hearing outcomes 9–14 …”

Place Coding in the Human Cochlea

“…2D). The modified SG and OC functions were compared using established frequency-position equations from synchrotron radiation phase-contrast imaging, providing better measurements of the helicotrema and hook region within the cochlea 18 . The electrophysiologically-derived frequency map was found to be shifted at least one octave downwards or more basal in location compared to both the OC and SG maps.…”