The mammalian cochlea receives efferent feedback from the brain. Many functions for this feedback have been hypothesized, including on short timescales, such as mediating attentional states, and long timescales, such as buffering acoustic trauma. Testing these hypotheses has been impeded by an inability to make direct measurements of efferent effects in awake animals. Here, we assessed the role of the medial olivocochlear (MOC) efferent nerve fibers on cochlear amplification by measuring organ of Corti vibratory responses to sound in both sexes of awake and anesthetized mice. We studied long-term effects by genetically ablating the efferents and/or afferents. Cochlear amplification increased with deafferentation using VGLUT3-/- mice, but only when the efferents were intact, associated with increased activity within OHCs and supporting cells. Removing both the afferents and the efferents using VGLUT3-/- Alpha9-/- mice did not cause this effect. To test for short-term effects, we recorded sound-evoked vibrations while using pupillometry to measure neuromodulatory brain state. We found no state dependence of cochlear amplification or of the auditory brainstem response. However, state dependence was apparent in the downstream inferior colliculus. Thus, MOC efferents upregulate cochlear amplification chronically with hearing loss, but not acutely with brain state fluctuations. This pathway may partially compensate for hearing loss while mediating associated symptoms, such as tinnitus and hyperacusis.

We present a flexible catheter endoscope using a 3D printed miniature side-viewing reflective lens for OCT imaging. A reflective lens with a depth of field (DOF) of 3mm and a maximum spot size of 80 microns was first designed and optimized in OpticStudio (ZEMAX). The structure of the lens and the fiber mating part of the optic was then constructed using 2-photon polymerization technique, and a gold reflective coating was added as the final step for the reflective lens. The reflective lens was then glued to cleaved optical fiber, and the assembly was covered by a torque coil to allow rotation of the catheter endoscope. This endoscope was used with a fiber-optic rotary joint and custom-built Mach-Zehnder interferometer to acquire OCT images.

Endolymphatic hydrops, increased endolymphatic fluid within the cochlea, is the key pathologic finding in patients with Meniere's disease, a disease of episodic vertigo, fluctuating hearing loss, tinnitus, and aural fullness. Endolymphatic hydrops also can occur after noise trauma and its presence correlates with cochlear synaptopathy, a form of hearing loss caused by reduced numbers of synapses between hair cells and auditory nerve fibers. Here we tested whether there is a mechanistic link between these two phenomena by using multimodal imaging techniques to analyze the cochleae of transgenic mice exposed to blast and osmotic challenge. In vivo cochlear imaging after blast exposure revealed dynamic increases in endolymph that involved hair cell mechanoelectrical transduction channel block but not the synaptic release of glutamate at the hair cell-auditory nerve synapse. In contrast, ex vivo and in vivo auditory nerve imaging revealed that synaptopathy requires glutamate release from hair cells but not endolymphatic hydrops. Thus, although endolymphatic hydrops and cochlear synaptopathy are both observed after noise exposure, one does not cause the other. They are simply co-existent sequelae that derive from the traumatic stimulation of hair cell stereociliary bundles. Importantly, these data argue that Meniere's disease derives from hair cell transduction channel blockade.

Optical coherence tomography (OCT) is a non-invasive, label-free biomedical imaging technique that can produce three-dimensional images up to several millimeters deep, with cellular-scale resolution. Functional extensions of OCT can also generate image contrast from different mechanisms, such as tissue birefringence, blood flow, and picometer-scale motion/vibration. We begin with an introduction to OCT, its functional extensions, and current research areas for technology development. We then follow with a selection of clinical and pre-clinical applications from a variety of medical specialties, including ophthalmology, cardiology, oncology, gastroenterology, dermatology, otolaryngology, and others.

We report dynamic optical coherence tomography (D-OCT) images of the organ of Corti (ooC) in ex vivo mouse cochleas. The ooC is responsible for transducing sound-evoked mechanical vibrations and amplifying them in the process of hearing. Thorough knowledge of the micromechanical properties of the ooC is required for understanding how hearing functions. Recently, OCT has emerged as a safe and effective tool to probe the inner workings of the cochlea and ooC. However, OCT is limited in its ability to directly resolve cellular architecture due to limited optical scattering-based contrast between different cell types. D-OCT is a label-free method capable of probing sub-resolution movements by analyzing speckle and phase information from standard OCT data as a function of time. We show that key structures in the ooC can be identified with D-OCT versus standard OCT, and that D-OCT has the potential to characterize the ooC and advance our understanding of the process of hearing.

A common processing approach for optical coherence tomography (OCT) uses a window function (e.g., Hann or rectangular window) for spectral shaping prior to calculating the Fourier transform. Here we build on a multi-window approach [ Opt. Express 8 , 5267 ( 2017 ) 10.1364/BOE.8.005267 ] that enables improved resolution while still suppressing side-lobe intensity. The shape of the window function defines the trade-off between main-lobe width (resolution) and side-lobe intensity. We have extended the approach to include the interferometric phase for phase-sensitive applications like vibrometry and Doppler OCT. Using the Hann window as a reference, we show that 11 Taylor windows are sufficient to achieve 50% improvement in axial resolution, -31 dB side-lobe intensity, and 20% improvement in phase sensitivity with low computational cost.

OBJECTIVE:Create an aerosol containment mask (ACM) for common otolaryngologic endoscopic procedures which also provides nanoparticle-level protection to patients. STUDY DESIGN:Prospective feasibility study. SETTING:In-person testing with a novel ACM. METHODS:The mask was designed in Solidworks and 3-dimensional printed. Measurements were made on 100 consecutive clinic patients who underwent medically necessarily endoscopy, 50 rigid nasal and 50 flexible, by 9 surgeons. RESULTS:Of the 50 patients who underwent rigid nasal endoscopy with the ACM, 0 of 25 patients with the suction off and 0 of 25 patients with the suction on had evidence of leakage of 0.3 μm particles. Of the 50 patients who underwent flexible endoscopy with the ACM, 0 of 25 patients with the suction off and 0 of 25 patients with the suction on had evidence of leakage of 0.3 μm particles. In terms of comfort, 73% of patients found the ACM somewhat or very comfortable without suction, compared to 86% with the suction on. Surgeons were able to visualize all necessary anatomic areas in 98% of procedures. In 97% of procedures, the masks were able to be placed easily. CONCLUSION:ACM can accommodate rigid nasal and flexible endoscopes and may prevent leakage of patient-generated aerosols, thus avoiding contamination of the room and protecting health care workers from airborne contagions. LEVEL OF EVIDENCE:The level of evidence is 2.

We describe optimization of a multi-window approach for improved resolution, side-lobe suppression, and phase sensitivity. Using the Hann window as a reference, we show that 10 windows are sufficient to achieve 43% resolution improvement, comparable side-lobe intensity, and 20% improvement in phase sensitivity.