Abstract
The mammalian cochlea has historically resisted attempts at high-resolution, non-invasive imaging due to its small size, complex three-dimensional structure, and embedded location within the temporal bone. As a result, little is known about the relationship between an individual’s cochlear pathology and hearing function, and otologists must rely on physiological testing and imaging methods that offer limited resolution to obtain information about the inner ear prior to performing surgery. Micro-optical coherence tomography (μOCT) is a non-invasive, low-coherence interferometric imaging technique capable of resolving cellular-level anatomic structures. To determine whether μOCT is capable of resolving mammalian intracochlear anatomy, fixed guinea pig inner ears were imaged as whole temporal bones with cochlea in situ. Anatomical structures such as the tunnel of Corti, space of Nuel, modiolus, scalae, and cell groupings were visualized, in addition to individual cell types such as neuronal fibers, hair cells, and supporting cells. Visualization of these structures, via volumetrically-reconstructed image stacks and endoscopic perspective videos, represents an improvement over previous efforts using conventional OCT. These are the first μOCT images of mammalian cochlear anatomy, and they demonstrate μOCT’s potential utility as an imaging tool in otology research.
Highlights
Few treatments for human hearing loss exist, largely because the relationship between an individual patient’s cochlear pathology and their degree of hearing loss is poorly understood
To improve the spatial resolution of conventional Optical coherence tomography (OCT), we introduced a successor called micro-optical coherence tomography and demonstrated its ability to resolve individual endothelial cells, leukocytes, lymphocytes, and monocytes in human cadaver coronary arteries, at a resolution of 2 μm× 2 μm× 1 μm(x, y, z)23. μOCT has more recently been utilized to detect cholesterol crystals within macrophages in atherosclerosis[24], to visualize functional anatomy, including individual beating cilia involved in mucociliary clearance and transport in airway epithelium[25,26], and to resolve cellular details in zebrafish larvae in vivo27. μOCT technology may be suitable to resolve cochlear microanatomy at a cellular level
The dark space between the OPCs and outer hair cells (OHC) is the space of Nuel; the dark space between the OPCs and the inner pillar cells is the tunnel of Corti
Summary
Few treatments for human hearing loss exist, largely because the relationship between an individual patient’s cochlear pathology and their degree of hearing loss is poorly understood. The cochlea contains other soft tissue microstructures that are critical for hearing: Reissner’s membrane, which serves as a diffusion barrier separating the contents of two of the cochlea’s fluid-filled cavities; the tectorial membrane, which contacts hair cells’ stereocilia during sound transduction; the stria vascularis in the spiral ligament, which maintains ionic gradients of endocochlear fluids and provides a blood barrier; and the neurites of the spiral ganglion, which form one branch of the auditory nerve, and extend both radially and diagonally along the sensory epithelium[6] These structures fall beneath the detection limits of both MRI and CT. This study’s objective was to determine whether μOCT was capable of resolving major and micro-anatomical structures within the mammalian inner ear, and to generate the first μOCT images of fixed guinea pig intracochlear anatomy in situ
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