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

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.

MEMS Micromirror Actuation Techniques: A Comprehensive Review of Trends, Innovations, and Future Prospects

Micromirrors have recently emerged as an essential component in optical scanning technology, attracting considerable attention from researchers. Their compact size and versatile capabilities, such as light steering, modulation, and switching, are leading them as potential alternatives to traditional bulky galvanometer scanners. The actuation of these mirrors is critical in determining their performance, as it contributes to factors such as response time, scanning angle, and power consumption. This article aims to provide a thorough exploration of the actuation techniques used to drive micromirrors, describing the fundamental operating principles. The four primary actuation modalities-electrostatic, electrothermal, electromagnetic, and piezoelectric-are thoroughly investigated. Each type of actuator's operational principles, key advantages, and their limitations are discussed. Additionally, the discussion extends to hybrid micromirror designs that combine two types of actuation in a single device. A total of 208 closely related papers indexed in Web of Science were reviewed. The findings indicate ongoing advancements in the field, particularly in terms of size, controllability, and field of view, making micromirrors ideal candidates for applications in medical imaging, display projections, and optical communication. With a comprehensive overview of micromirror actuation strategies, this manuscript serves as a compelling resource for researchers and engineers aiming to utilize the appropriate type of micromirror in the field of optical scanning technology.

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.

Algorithm and software for field distortion correction in a commercial SD-OCT for corneal curvature assessment

Accurate assessment of corneal curvatures using frequency domain optical coherence tomography (OCT) with galvanometer scanners remains challenging due to the well-known scan field distortion. This paper presents an algorithm and software for correcting the distortion using only two simple measurements in which a readily available standard sphere is positioned in different depths in front of the OCT scanner. This offers a highly accessible and easily reproducible method for the field distortion correction (FDC). The correction was validated by measuring different spherical phantoms and conducting corneal curvature measurements of ex vivo porcine corneas using a commercial spectral-domain OCT system and a clinically approved swept-source OCT as a reference instrument. Thus, the error in radius measurements of spherical phantoms was reduced by >90% and astigmatism by >80% using FDC. In explanted porcine eyes, the error in astigmatism measurements with the Telesto was reduced by 75% for power and 70% for angle. The best fitting sphere radius was determined up to a deviation of 0.4% from the Anterion. This paper describes a correction algorithm for OCT immanent distortion that is applicable to any scanning OCT setup and enables precise corneal curvature measurements. The MATLAB software for the FDC is publicly available on GitHub.

30 Years of Optical Coherence Tomography: introduction to the feature issue

The guest editors introduce a feature issue commemorating the 30th anniversary of Optical Coherence Tomography.