In vivo functional imaging of the human middle ear with a hand-held optical coherence tomography device

Optical Coherence Tomography as a Tool for Quantitative Imaging of the Tympanic Membrane and Middle Ear

OBJECTIVE

Advances in optical coherence tomography have improved diagnostic imaging for otologic pathologies. We investigated handheld OCT (HHOCT) otoscopic device's ability to quantitatively analyze the middle ear and provide valuable information for the management of middle ear pathologies.

STUDY DESIGN

Cross-sectional cohort.

METHODS

Eleven healthy patients, 5 patients with unilateral pathology, 6 patients with retraction pockets, and 1 patient undergoing ossiculoplasty were imaged using HHOCT in the clinic. Middle ear distances and retraction pocket depth were calculated using OCT volumes and compared to those on CT and in literature. Partial ossicular replacement prosthesis length was calculated before surgery and compared to the length chosen by an expert otologist. Data were characterized using descriptive statistics and paired t -tests. Volumes were analyzed and postprocessed using Amira (Thermofisher Scientific, Waltham, MA) and Fiji (NIH).

RESULTS

HHOCT could image and obtain quantitative measurements of the middle ear at the point of care with greater resolution and precision than traditional imaging modalities. Mean incus diameter on OCT was 0.728 ± 0.089 mm, in agreement with cadaver studies. Measured middle ear distances and retraction pocket depths were not statistically significantly different from those measured on CT. The predicted prosthesis size for the ossiculoplasty patient was 2.46 mm, closely matching the 2-mm length chosen by an expert otologist.

CONCLUSION

OCT can provide reliable measurements of the tympanic membrane and middle ear structures not readily available through traditional imaging modalities. Pre- or intrasurgical measurements with OCT may be beneficial for guidance on size and placement of ossicular prosthetics and may improve hearing outcomes.

Quantitative measurement of tympanic membrane structure and symmetry with optical coherence tomography in normal human subjects

Significance

Early detection of ear pathology is essential for preventing hearing loss, yet the sensitivity of otoscopic examinations by primary care providers during annual physicals remains low. Optical coherence tomography (OCT) offers a promising alternative for detailed imaging of the tympanic membrane (TM) and middle ear (ME), providing the potential for early identification of ear disease.

Aim

We aim to develop a quantitative method for assessing symmetry between the right and left ears and to establish a baseline for this approach in normal subjects.

Approach

Volumetric OCT images were acquired from 12 normal subjects using a custom hand-held OCT otoscope. A volume registration and fusion method was applied to expand the TM field of view, followed by TM thickness measurement and generation of 3D thickness maps. The symmetry between left and right TMs was quantitatively analyzed using the Dice similarity coefficient.

Results

The average TM thickness was measured as 73.89 ± 14.79    μ m for left ears and 70.72 ± 11.58    μ m for right ears, with no statistically significant difference at the 0.05 level. The symmetry analysis revealed a mean similarity coefficient of 0.79 ± 0.02 between left and right ears among the 12 normal subjects.

Conclusions

OCT imaging enables quantitative assessment of TM thickness and symmetry, offering a baseline for identifying early ear pathologies.

Fusion of Middle Ear Optical Coherence Tomography and Computed Tomography

Importance

Middle ear optical coherence tomography (OCT) imaging in patients has not previously been directly compared with a standard of care clinical 3-dimensional imaging technology, such as computed tomography (CT).

Objective

To qualitatively compare the capabilities of middle ear OCT with CT in normal and pathological ears on representative slices in coregistered OCT and CT datasets.

Design, Setting, and Participants

This case series included 3 patients and 3 ears: 1 normal middle ear, 1 ear affected by traumatic injury, and 1 ear with cholesteatoma. The ears were imaged with both OCT and high-resolution clinical temporal bone CT. Participants were drawn from the patient population of a tertiary otology clinic. CT and OCT images were aligned using rigid coregistration with manual landmark selection. Data were collected from January 2022 to April 2023, and data were analyzed from February 2022 to December 2023.

Main Outcomes and Measures

Images were analyzed qualitatively for field of view (FOV), resolution, shadowing, artifacts, soft tissue and bony tissue contrast, and presentation of diagnostically important features.

Results

In the 3 imaged ears, OCT was capable of visualizing many of the important features indicative of middle ear pathology. Compared with CT, OCT exhibited a limited FOV largely confined to the mesotympanum and subject to shadowing from bony structures. However, OCT could resolve soft tissue features that were not readily apparent in the CT images to have a higher resolution than CT and to provide excellent anatomical fidelity with CT, which allowed OCT images to be accurately coregistered with CT images.

Conclusions and Relevance

In this case series, while OCT was not capable of replacing CT due to its limited FOV and inability to image through thick bony tissues, it visualized signs of pathology, including some soft tissue features, that are difficult to visualize with CT. Given OCT's ability to image in real time, its compatibility with in-office imaging, and its lack of ionizing radiation, it may, despite its limitations compared with CT, be an appealing imaging modality for many applications in middle ear diagnostics.

The Medial Olivocochlear Efferent Pathway Potentiates Cochlear Amplification in Response to Hearing Loss

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.

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

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    μ m OCT to test if the reduced scattering at 1.7    μ m provided any appreciable advantage for imaging the cochleae.

Approach

OCT interferometers were built for both 1.3 and 1.7    μ 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    μ 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    μ m with those taken at 1.7    μ m . At both wavelengths, we could see through the otic capsule and identify cochlear structures. In some cases, 1.7    μ 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    μ m .

Conclusions

We conclude that both 1.7    μ m and 1.3    μ 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    μ m light, we observed reduced multiple scattering in the otic capsule, leading to enhanced contrast of cochlear structures compared with 1.3    μ m . However, these improvements were marginal and came with trade-offs.

Optical Coherence Tomography Imaging and Angiography of Skull Base Tumors Presenting as a Middle Ear Mass in Clinic

Background: Skull base tumors can extend into the temporal bone and occasionally even be visible through the tympanic membrane (TM) if they grow into the middle ear cavity. The differential diagnosis of a skull base mass is extensive and ranges from non-tumorous lesions like cholesteatoma to benign tumors like schwannoma and to malignant lesions like metastatic cancer. Optical coherence tomography (OCT) is a noninvasive imaging technique that can image tissue with high resolution in three dimensions, including through structures such as the TM and bone. OCT angiography is also able to assess tissue vascularity. We hypothesized that OCT could help shrink the differential diagnosis in clinic on the day of initial presentation. Specifically, we thought that OCT angiography could help distinguish between highly vascular skull base tumors such as glomus jugulare and other less vascular tumors and middle ear pathologies such as cholesteatoma and schwannoma. Objectives: We sought to determine whether OCT can image through the TM in clinic to distinguish a normal ear from an ear with a mass behind the tympanic membrane. Furthermore, we sought to assess whether OCT angiography can detect vascularity in these masses to help inform the diagnosis. Methods: We designed and built a custom handheld OCT system that can be used like an otoscope in clinic. It is based off a 200 kHz swept-source laser with a center wavelength of 1310 nm and a bandwidth of 39 nm. It provides a 33.4 μm axial and 38 μm lateral resolution. Cross-sectional images of the middle ear space, including OCT angiography, were captured in an academic neurotology clinic. Patients with normal ear exams, glomus tumors, cholesteatomas, and facial nerve schwannoma were imaged. Results: OCT images revealed key structures within the middle ear space, including the TM, ossicles (malleus and incudostapedial joint), chorda tympani, and cochlear promontory. OCT also identified middle ear pathology (using pixel intensity ratio in the middle ear normalized to the TM) when compared with patients with normal ear exams (mean 0.082, n = 6), in all patients with a glomus tumor (mean 0.620, n = 6, p < 0.001), cholesteatoma (mean 0.153, n = 4, p < 0.01), and facial nerve schwannoma (0.573, n = 1). OCT angiography revealed significant vascularity within glomus tumors (mean 1.881, n = 3), but minimal vascularity was found in normal ears (mean 0.615, n = 3, p < 0.05) and ears with cholesteatoma (mean 0.709, n = 3, p < 0.01), as expected. Conclusions: OCT is able to image through the TM and detect middle ear masses. OCT angiography correctly assesses the vascularity within these masses. Thus, OCT permits the clinician to have additional point-of-care data that can help make the correct diagnosis.

Visualizing motions within the cochlea's organ of Corti and illuminating cochlear mechanics with optical coherence tomography

Beginning in 2006, optical coherence tomography (OCT) has been adapted for use as a vibrometer for hearing research. The application of OCT in this field, particularly for studying cochlear mechanics, represents a revolutionary advance over previous technologies. OCT provides detailed evidence of the motions of components within the organ of Corti, extending beyond the first-encountered surface of observation. By imaging through the bony capsule as well as through the round window membrane, OCT has measured vibration at multiple locations along the cochlear spiral, in vivo, under nearly natural conditions. In this document, we present examples of recent research findings to illustrate the applications of OCT in studying cochlear mechanics in both normal and impaired ears.

Optical coherence tomography otoscope for imaging of tympanic membrane and middle ear pathology

Significance

Pathologies within the tympanic membrane (TM) and middle ear (ME) can lead to hearing loss. Imaging tools available in the hearing clinic for diagnosis and management are limited to visual inspection using the classic otoscope. The otoscopic view is limited to the surface of the TM, especially in diseased ears where the TM is opaque. An integrated optical coherence tomography (OCT) otoscope can provide images of the interior of the TM and ME space as well as an otoscope image. This enables the clinicians to correlate the standard otoscopic view with OCT and then use the new information to improve the diagnostic accuracy and management.

Aim

We aim to develop an OCT otoscope that can easily be used in the hearing clinic and demonstrate the system in the hearing clinic, identifying relevant image features of various pathologies not apparent in the standard otoscopic view.

Approach

We developed a portable OCT otoscope device featuring an improved field of view and form-factor that can be operated solely by the clinician using an integrated foot pedal to control image acquisition. The device was used to image patients at a hearing clinic.

Results

The field of view of the imaging system was improved to a 7.4 mm diameter, with lateral and axial resolutions of 38    μ m and 33.4    μ m , respectively. We developed algorithms to resample the images in Cartesian coordinates after collection in spherical polar coordinates and correct the image aberration. We imaged over 100 patients in the hearing clinic at USC Keck Hospital. Here, we identify some of the pathological features evident in the OCT images and highlight cases in which the OCT image provided clinically relevant information that was not available from traditional otoscopic imaging.

Conclusions

The developed OCT otoscope can readily fit into the hearing clinic workflow and provide new relevant information for diagnosing and managing TM and ME disease.

Automated Segmentation of Optical Coherence Tomography Images of the Human Tympanic Membrane Using Deep Learning

Optical Coherence Tomography (OCT) is a light-based imaging modality that is used widely in the diagnosis and management of eye disease, and it is starting to become used to evaluate for ear disease. However, manual image analysis to interpret the anatomical and pathological findings in the images it provides is complicated and time-consuming. To streamline data analysis and image processing, we applied a machine learning algorithm to identify and segment the key anatomical structure of interest for medical diagnostics, the tympanic membrane. Using 3D volumes of the human tympanic membrane, we used thresholding and contour finding to locate a series of objects. We then applied TensorFlow deep learning algorithms to identify the tympanic membrane within the objects using a convolutional neural network. Finally, we reconstructed the 3D volume to selectively display the tympanic membrane. The algorithm was able to correctly identify the tympanic membrane properly with an accuracy of ~98% while removing most of the artifacts within the images, caused by reflections and signal saturations. Thus, the algorithm significantly improved visualization of the tympanic membrane, which was our primary objective. Machine learning approaches, such as this one, will be critical to allowing OCT medical imaging to become a convenient and viable diagnostic tool within the field of otolaryngology.

Assessment of middle ear structure and function with optical coherence tomography

BACKGROUND

Current clinical tests for middle ear (ME) injuries and related conductive hearing loss (CHL) are lengthy and costly, lacking the ability to noninvasively evaluate both structure and function in real time. Optical coherence tomography (OCT) provides both, but its application to the audiological clinic is currently limited.

OBJECTIVE

Adapt and use a commercial Spectral-Domain OCT (SD-OCT) to evaluate anatomy and sound-evoked vibrations of the tympanic membrane (TM) and ossicles in the human ME.

MATERIALS AND METHODS

SD-OCT was used to capture high-resolution three-dimensional (3D) ME images and measure sound-induced vibrations of the TM and ossicles in fresh human temporal bones.

RESULTS

The 3D images provided thickness maps of the TM. The system was, with some software adaptations, also capable of phase-sensitive vibrometry. Measurements revealed several modes of TM vibration that became more complex with frequency. Vibrations were also measured from the incus, through the TM. This quantified ME sound transmission, which is the essential measure to assess CHL.

CONCLUSION AND SIGNIFICANCE

We adapted a commercial SD-OCT to visualize the anatomy and function of the human ME. OCT has the potential to revolutionize point-of-care assessment of ME disruptions that lead to CHL which are otherwise indistinguishable via otoscopy.

Geometrically accurate real-time volumetric visualization of the middle ear using optical coherence tomography

We introduce a novel system for geometrically accurate, continuous, live, volumetric middle ear optical coherence tomography imaging over a 10.9mm×30∘×30∘ field of view (FOV) from a handheld imaging probe. The system employs a discretized spiral scanning (DC-SC) pattern to rapidly collect volumetric data and applies real-time scan conversion and lateral angular distortion correction to reduce geometric inaccuracies to below the system's lateral resolution over 92% of the FOV. We validate the geometric accuracy of the resulting images through comparison with co-registered micro-computed tomography (micro-CT) volumes of a phantom target and a cadaveric middle ear. The system's real-time volumetric imaging capabilities are assessed by imaging the ear of a healthy subject while performing dynamic pressurization of the middle ear in a Valsalva maneuver.

Toward Personalized Diagnosis and Therapy for Hearing Loss: Insights From Cochlear Implants

ABSTRACT

Sensorineural hearing loss (SNHL) is the most common sensory deficit, disabling nearly half a billion people worldwide. The cochlear implant (CI) has transformed the treatment of patients with SNHL, having restored hearing to more than 800,000 people. The success of CIs has inspired multidisciplinary efforts to address the unmet need for personalized, cellular-level diagnosis, and treatment of patients with SNHL. Current limitations include an inability to safely and accurately image at high resolution and biopsy the inner ear, precluding the use of key structural and molecular information during diagnostic and treatment decisions. Furthermore, there remains a lack of pharmacological therapies for hearing loss, which can partially be attributed to challenges associated with new drug development. We highlight advances in diagnostic and therapeutic strategies for SNHL that will help accelerate the push toward precision medicine. In addition, we discuss technological improvements for the CI that will further enhance its functionality for future patients. This report highlights work that was originally presented by Dr. Stankovic as part of the Dr. John Niparko Memorial Lecture during the 2021 American Cochlear Implant Alliance annual meeting.

Transtympanic Visualization of Cochlear Implant Placement With Optical Coherence Tomography: A Pilot Study

OBJECTIVE

This study aimed to evaluate the ability of transtympanic middle ear optical coherence tomography (ME-OCT) to assess placement of cochlear implants (CIs) in situ.

PATIENT

A 72-year-old man with bilateral progressive heredodegenerative sensorineural hearing loss due to work-related noise exposure received a CI with a slim modiolar electrode for his right ear 3 months before his scheduled checkup.

INTERVENTION

A custom-built swept source ME-OCT system (λo = 1550 nm, ∆λ = 40 nm) designed for transtympanic middle ear imaging was used to capture a series of two- and three-dimensional images of the patient's CI in situ. Separately, transtympanic OCT two-dimensional video imaging and three-dimensional imaging were used to visualize insertion and removal of a CI with a slim modiolar electrode in a human cadaveric temporal bone through a posterior tympanotomy.

MAIN OUTCOME MEASURE

Images and video were analyzed qualitatively to determine the visibility of implant features under ME-OCT imaging and quantitatively to determine insertion depth of the CI.

RESULTS

After implantation, the CI electrode could be readily visualized in the round window niche under transtympanic ME-OCT in both the patient and the temporal bone. In both cases, characteristic design features of the slim modiolar electrode allowed us to quantify the insertion depth from our images.

CONCLUSIONS

ME-OCT could potentially be used in a clinic as a noninvasive, nonionizing means to confirm implant placement. This study shows that features of the CI electrode visible under ME-OCT can be used to quantify insertion depth in the postoperative ear.

Possible clinical implications of the structural variations between the tympanic membrane quadrants

Introduction

Retraction pockets and marginal perforations of the pars tensa of the tympanic membrane (TM) are most commonly found at superior posterior quadrant (SPQ). The patulous Eustachian tube tends to manifest in the same quadrant. Variation in the structure of the TM may explain these observations.

Material and Methods

A line defined by the manubrium was used to divide the pars tensa into anterior and posterior portions. A transverse line centered on the umbo divides the pars tensa into superior and inferior parts, resulting in four quadrants. Surface areas of each of the TM quadrants were measured in a sample of 23 human adult formalin-fixed temporal bones. The TMs were completely excised, faced medially, and placed against graph paper to maintain scale measurements, photoed, and measured.TM thickness was measured on a different set of 20 human temporal bones (TB) preparations with normal external and middle ears. Four random loci were chosen from each pars tensa's TM quadrant. The thickness was measured using high-magnification power microscopy.

Results

The SPQ was the largest and thinnest of the four quadrants. It occupies 31% of the pars tensa area. It is 69 μm as compared to approximately 85 μm in the other quadrants. The radial lines between the umbo and the annulus are in descending order from superior posterior toward the anterior-superior radials.

Conclusion

The SPQ has the largest vibratory area and is the thinnest of the four TM quadrants. Variation in the thickness of the middle, fibrous layer accounts for the variation in the thickness of the TM. These findings may explain the tendency of pathologies related to Eustachian tube dysfunction to preferentially manifest in or originate from the SPQ.

Level of evidence 5

Automated classification of otitis media with OCT: augmenting pediatric image datasets with gold-standard animal model data

Otitis media (OM) is an extremely common disease that affects children worldwide. Optical coherence tomography (OCT) has emerged as a noninvasive diagnostic tool for OM, which can detect the presence and quantify the properties of middle ear fluid and biofilms. Here, the use of OCT data from the chinchilla, the gold-standard OM model for the human disease, is used to supplement a human image database to produce diagnostically relevant conclusions in a machine learning model. Statistical analysis shows the datatypes are compatible, with a blended-species model reaching ∼95% accuracy and F1 score, maintaining performance while additional human data is collected.

Ex vivo transtympanic permeation of the liposome encapsulated S. pneumoniae endolysin MSlys

An increase in bacterial resistance to systemic antibiotics has sparked interest into alternative antimicrobial compounds as well as methods for effective local, non-invasive drug delivery. Topical treatments, however, may be hindered by the presence of biological barriers, such as the tympanic membrane in the case of otitis media. Herein, the transtympanic permeation ability of liposomes loaded with the pneumococcal endolysin MSlys and of free MSlys was evaluated ex vivo. MSlys loaded in PEGylated liposomes showed an increased permeation across human tympanic membranes, as compared to its free form, being able to reduce the pneumococcal cell load after 2 h of permeation. However, antipneumococcal activity was no longer detected after 4 h of permeation and hydrolysis of the endolysin was observed after an extended incubation time (≥48 h). This work provides a first assessment of a successful, non-invasive delivery method for endolysins across an intact tympanic membrane. Findings have implications for non-systemic, local treatment of otitis media.

Endolymphatic Hydrops is a Marker of Synaptopathy Following Traumatic Noise Exposure

After acoustic trauma, there can be loss of synaptic connections between inner hair cells and auditory neurons in the cochlea, which may lead to hearing abnormalities including speech-in-noise difficulties, tinnitus, and hyperacusis. We have previously studied mice with blast-induced cochlear synaptopathy and found that they also developed a build-up of endolymph, termed endolymphatic hydrops. In this study, we used optical coherence tomography to measure endolymph volume in live CBA/CaJ mice exposed to various noise intensities. We quantified the number of synaptic ribbons and postsynaptic densities under the inner hair cells 1 week after noise exposure to determine if they correlated with acute changes in endolymph volume measured in the hours after the noise exposure. After 2 h of noise at an intensity of 95 dB SPL or below, both endolymph volume and synaptic counts remained normal. After exposure to 2 h of 100 dB SPL noise, mice developed endolymphatic hydrops and had reduced synaptic counts in the basal and middle regions of the cochlea. Furthermore, round-window application of hypertonic saline reduced the degree of endolymphatic hydrops that developed after 100 dB SPL noise exposure and partially prevented the reduction in synaptic counts in the cochlear base. Taken together, these results indicate that endolymphatic hydrops correlates with noise-induced cochlear synaptopathy, suggesting that these two pathologic findings have a common mechanistic basis.