Synchrotron Radiation-Based Reconstruction of the Human Spiral Ganglion: Implications for Cochlear Implantation

Abstract

Objective: To three-dimensionally reconstruct Rosenthal’s canal (RC) housing the human spiral ganglion (SG) using synchrotron radiation phase-contrast imaging (SR-PCI). Straight cochlear implant electrode arrays were inserted to better comprehend the electro-cochlear interface in cochlear implantation (CI). Design: SR-PCI was used to reconstruct the human cochlea with and without cadaveric CI. Twenty-eight cochleae were volume rendered, of which 12 underwent cadaveric CI with a straight electrode via the round window (RW). Data were input into the 3D Slicer software program and anatomical structures were modeled using a threshold paint tool. Results: The human RC and SG were reproduced three-dimensionally with artefact-free imaging of electrode arrays. The anatomy of the SG and its relationship to the sensory organ (Corti) and soft and bony structures were assessed. Conclusions: SR-PCI and computer-based three-dimensional reconstructions demonstrated the relationships among implanted electrodes, angular insertion depths, and the SG for the first time in intact, unstained, and nondecalcified specimens. This information can be used to assess stimulation strategies and future electrode designs, as well as create place-frequency maps of the SG for optimal stimulation strategies of the human auditory nerve in CI.

Long‐Term Influence of Electrode Array Length on Speech Recognition in Cochlear Implant Users

“…[41][42][43] Thus, as longer arrays generally convey temporal information closer to tonotopic place with default filters than shorter arrays, it is difficult to rule out coding strategy as a contributing factor when explaining the benefit observed for the standard cohort, particularly as the spiral ganglion extends to 630 to 720 . 30,44,45 Additionally, as recruitment of medium array recipients in the initial study was halted due to ethical concerns, the sample size is limited. Lastly, as many subjects experienced multiple changes to electric frequency filters over the 4-year study period, it is difficult to make strong conclusions regarding the long-term effects of frequency-to-place mismatch, and this remains an area of research that deserves further attention.…”

Vascular Supply of the Human Spiral Ganglion: Novel Three-Dimensional Analysis Using Synchrotron Phase-Contrast Imaging and Histology

“…The SR-PCI technique used, in-line PCI, was earlier described by Elfarnawany et al 19 and Koch et al 25 . Furthermore, the materials used in the present study were previously described in studies of the human RC using a combined analysis of μCT and synchrotron imaging performed on adult fresh-frozen cadaveric temporal bones 20,26 . In brief, the 26 human temporal bones were thawed and cut to 40 mm × 60 mm lengths and fixed in 3.7% formaldehyde and 1% glutaraldehyde in a phosphate buffer for five days.…”

Light sheet microscopy of the gerbil cochlea

“…However, the typically low contrast images obtained with these tomographic techniques limits their ability to isolate details of many structures of interest, and they are not generally compatible with immunocytochemical probes, although recent advances in methodology have incorporated use of fluorescent probes for optical tomography (e.g., Nolte et al, 2017). In human cadaveric material, contrast enhancement with osmium improves images quality in micro‐CT scans for three‐dimensional reconstructions with resolution on the order of 5–10 μm (Glueckert et al, 2018; van den Boogert et al, 2018) and synchrotron radiation imaging techniques generate impressive three‐dimensional cochlear images with resolutions of 9 μm (Helpard, Rohani, Ladak, & Agrawal, 2020; Iyer et al, 2018; Lareida et al, 2009; Li, Schart‐Moren, et al, 2020). However, as few facilities offer synchrotron capabilities, it remains ill‐suited for routine use in animal studies.…”