Imaging the ex-vivo human cochlea using 1.3- μ m and 1.7- μ m optical coherence tomography

Abstract

Significance: There is no clinical imaging method to visualize the soft tissues of the human cochlea, which are crucial for sound transduction and are damaged in sensorineural hearing loss. Although optical coherence tomography (OCT) has been effective in small animal models, we show for the first time that it can image through the full thickness of the ex-vivo human otic capsule and resolve cochlear microstructures despite increased scattering.

Aim: We aim to investigate whether OCT could image the cochlea through the otic capsule. We compared 1.7 and $1.3\mu m$ OCT to test if the reduced scattering at $1.7\mu m$ provided any appreciable advantage for imaging the cochleae.

Approach: OCT interferometers were built for both 1.3 and $1.7\mu m$ wavelengths, using identical sample and reference arm optics in both systems. Imaging was performed on two fixed human temporal bones with intact cochleae. The interferometers were designed to allow seamless switching between 1.3 and $1.7\mu m$ OCT without disrupting the temporal bone during imaging.

Results: We took volumetric OCT images at the base, apex, and hook regions of fixed ex-vivo human cochleae and compared the images taken at $1.3\mu m$ with those taken at $1.7\mu m$ . At both wavelengths, we could see through the otic capsule and identify cochlear structures. In some cases, $1.7\mu m$ OCT resulted in clearer images of the lateral wall, interior scala, and fine cochlear structures due to reduced multiple scattering at depth compared with $1.3\mu m$ .

Conclusions: We conclude that both $1.7\mu m$ and $1.3\mu m$ OCT can image through the human otic capsule, offering the potential for direct measurement of cochlear vibrometry or blood flow in living humans. Using $1.7\mu m$ light, we observed reduced multiple scattering in the otic capsule, leading to enhanced contrast of cochlear structures compared with $1.3\mu m$ . However, these improvements were marginal and came with trade-offs.

Keywords: cochleae; inner ear; optical coherence tomography; otolaryngology; otology.

Fig. 1

Instrumentation for OCT imaging of ex-vivo human temporal bones. (a) Schematic diagram of the Mach–Zehnder OCT interferometers that were used for imaging. (b) Human temporal bone positioned under the OCT sample arm. We coarsely positioned the temporal bones using a vertical jack stand (blue) and finely adjusted the position of the OCT sample arm using a three-axis translation stage (black). Abbreviations: BPD, balanced photodetector; PC, personal computer; DAQ, data acquisition board; MEMS, microelectromechanical system.

Fig. 2

Imaging of the apical turn of a fixed human cochlea near the helicotrema. (a) TB1 shown with fenestrations at the apical (A) and basal (B) turns. The round window niche (RWN) and the stapes are also visible The location of the OCT cross-section is shown in green. (b) Cross-section of the apical turn taken using $1.3\mu \mathrm{m}$ OCT. Small anatomical features were visible in both 1.3 and $1.7\mu \mathrm{m}$ images, including Reissner’s membrane (RM), sensory epithelium (SE), spiral limbus (SLm), scala media (SM), scala tympani (ST), and scala vestibuli (SV). The separation between apical and basal turns could be seen at the bottom (yellow-dotted arrow). (c) OCT cross-section taken using $1.7\mu \mathrm{m}$. (d) Averaged $1.7\mu \mathrm{m}$ cross-section (SNR normalized to that of $1.3\mu \mathrm{m}$). Scale bars are 1 mm.

Fig. 3

Imaging of the basal turn of a fixed human cochlea. (a) TB2 shown with the stapes (S), promontory (P), and round window niche (RWN) visible. The approximate location of the OCT cross-section is shown in green. (b) Cross-section of the basal turn using $1.3\mu \mathrm{m}$ OCT showing the lateral wall (LW) and part of the cochlear partition (yellow-dotted arrow). (c) OCT cross-section taken using $1.7\mu \mathrm{m}$. (d) Averaged $1.7\text{-}\mu \mathrm{m}$ cross-section (SNR normalized to that of $1.3\mu \mathrm{m}$). Scale bars are 1 mm.

Fig. 4

Imaging of the hook region of a fixed human cochlea. (a) View of TB2 shown with the stapes (S), promontory (P), and round window (RW) visible. The approximate location of the OCT cross-section is shown in green. (b) Cross-section of the hook region using $1.3\mu \mathrm{m}$ OCT. (c) OCT cross-section taken using $1.7\mu \mathrm{m}$. (d) Averaged $1.7\text{-}\mu \mathrm{m}$ cross-section (SNR normalized to that of $1.3\mu \mathrm{m}$). At both 1.3 and $1.7\mu \mathrm{m}$, the oval window niche (OWN), osseous spiral lamina (OSL), basilar membrane (BM), and spiral ligament (SLg) are visible. Scale bars are 1 mm.