Automated working distance adjustment enables optical coherence tomography of the human larynx in awake patients

Electronic frequency shifting enables long, variable working distance optical coherence tomography

Increased imaging range is of growing interest in many applications of optical coherence tomography to reduce constraints on sample location, size, and topography. The design of optical coherence tomography systems with sufficient imaging range (e.g., 10s of centimeters) is a significant challenge due to the direct link between imaging range and acquisition bandwidth. We have developed a novel and flexible method to extend the imaging range in optical coherence tomography using electronic frequency shifting, enabling imaging in dynamic environments. In our approach, a laser with a quasi-linear sweep is used to limit the interferometric bandwidth, enabling decoupling of imaging range and acquisition bandwidth, while a tunable lens allows dynamic refocusing in the sample arm. Electronic frequency shifting then removes the need for high frequency digitization. This strategy is demonstrated to achieve high contrast morphological imaging over a > 21 cm working distance range, while maintaining high resolution and phase sensitivity. The system design is flexible to the application while requiring only a simple phase correction in post-processing. By implementing this approach in an auto-focusing paradigm, the proposed method demonstrates strong potential for the translation of optical coherence tomography into emerging applications requiring variable and centimeter-scale imaging ranges.

Surface kinematic and depth-resolved analysis of human vocal folds in vivo during phonation using optical coherence tomography

SIGNIFICANCE

The human vocal fold (VF) oscillates in multiple vectors and consists of distinct layers with varying viscoelastic properties that contribute to the mucosal wave. Office-based and operative laryngeal endoscopy are limited to diagnostic evaluation of the VF epithelial surface only and are restricted to axial-plane characterization of the horizontal mucosal wave. As such, understanding of the biomechanics of human VF motion remains limited.

AIM

Optical coherence tomography (OCT) is a micrometer-resolution, high-speed endoscopic imaging modality which acquires cross-sectional images of tissue. Our study aimed to leverage OCT technology and develop quantitative methods for analyzing the anatomy and kinematics of in vivo VF motion in the coronal plane.

APPROACH

A custom handheld laryngeal stage was used to capture OCT images with 800 A-lines at 250 Hz. Automated image postprocessing and analytical methods were developed.

RESULTS

Novel kinematic analysis of in vivo, long-range OCT imaging of the vibrating VF in awake human subjects is reported. Cross-sectional, coronal-plane panoramic videos of the larynx during phonation are presented with three-dimensional videokymographic and space-time velocity analysis of VF motion.

CONCLUSIONS

Long-range OCT with automated computational methods allows for cross-sectional dynamic laryngeal imaging and has the potential to broaden our understanding of human VF biomechanics and sound production.

Euclidean distances of laryngopharyngeal structures obtained from CT data for preclinical development of laryngoscopic devices

PURPOSE

This study aims to determine Euclidean distances between landmark structures in the larynx and pharynx to optimize endoscope shaft designs with regard to gentle and patient-oriented handling.

METHODS

Four Euclidean distances between landmarks in the larynx and pharynx were analyzed based on CT data of 66 patients. Distance (1): labium inferius oris-posterior pharyngeal wall at the cervical vertebra C1 (atlas), anterior edge of the tuberculum anterius atlantis. Distance (2): posterior pharyngeal wall adjacent to C1-entrance of pyriform sinus. Distance (3): inferior edge of the uvula-superior edge of the epiglottis. Distance (4): base of the vallecula-posterior pharyngeal wall. The minimum angular field of view α required to observe the glottis with a rigid transoral laryngoscope was derived trigonometrically from distances (2) and (4).

RESULTS

Average Euclidean distances measured: Distance (1): 90.7 mm ± 6.9 mm in men and 86.9 mm ± 5.9 mm in women. (2): 73.7 mm ± 13.4 mm and 56.2 mm ± 7.6 mm. (3): 25.2 mm ± 8.6 mm and 18.5 mm ± 6.8 mm. (4): 20.8 mm ± 4.6 mm and 16.5 mm ± 3.4 mm. α: 16.0° ± 3.9° and 16.6 ± 4.3°.

CONCLUSIONS

As expected, statistically significant sex-related differences could be observed for distances (1)-(4). The results indicate that the length of transoral laryngoscopes should not be below 110 mm and that a minimum angular field of view of α = 17° is required to fully observe the laryngeal inlet.

Clinical translation of handheld optical coherence tomography: practical considerations and recent advancements

Since the inception of optical coherence tomography (OCT), advancements in imaging system design and handheld probes have allowed for numerous advancements in disease diagnostics and characterization of the structural and optical properties of tissue. OCT system developers continue to reduce form factor and cost, while improving imaging performance (speed, resolution, etc.) and flexibility for applicability in a broad range of fields, and nearly every clinical specialty. An extensive array of components to construct customized systems has also become available, with a range of commercial entities that produce high-quality products, from single components to full systems, for clinical and research use. Many advancements in the development of these miniaturized and portable systems can be linked back to a specific challenge in academic research, or a clinical need in medicine or surgery. Handheld OCT systems are discussed and explored for various applications. Handheld systems are discussed in terms of their relative level of portability and form factor, with mention of the supporting technologies and surrounding ecosystem that bolstered their development. Additional insight from our efforts to implement systems in several clinical environments is provided. The trend toward well-designed, efficient, and compact handheld systems paves the way for more widespread adoption of OCT into point-of-care or point-of-procedure applications in both clinical and commercial settings.

Design and evaluation of new color-corrected rigid endomicroscopic high NA GRIN-objectives with a sub-micron resolution and large field of view

We demonstrate new GRIN-based endomicroscopic objectives for high resolution single photon fluorescence imaging modalities. Two endoscopic optical design approaches are presented in detail utilizing firstly diffractive and secondly refractive optical elements for the color correction in a spectral range from 488 nm to 550 nm. They are compared with their precursor device experimentally and by simulation. Inherent aberrations for off-axis field points could be lowered remarkably compared with the values of the state-of-the-art system by increasing the intrinsic optical complexity but maintaining the outer spatial dimensions. As a result, those presented objectives predict a diffraction-limited imaging of objects up to 300 μm in diameter with a numerical aperture of 0.8 while keeping an overall outer diameter of the assembly at 1.4 mm. Lastly, confocal fluorescence imaging experiments focus on the comparison between the numerical predicted and the practically achieved quality parameters.

Effect of saline inhalation on vocal fold epithelial morphology evaluated by optical coherence tomography

OBJECTIVES/HYPOTHESIS

Examination of tissue structures by optical coherence tomography (OCT) has been shown to be useful on mucous membranes of the vocal folds, but so far its application to the human larynx has been limited because it is technically cumbersome and usually needs to be performed with sedation. Here a newly developed, noninvasive combined laryngoscopy and OCT procedure is described and its suitability for ambulatory OCT studies evaluated. Because inhalation therapies utilizing saline solutions are commonly used as a treatment option for disorders of the airways, and vocal fold epithelium is most likely to be affected due to its superficial positioning, epithelial thickness was chosen as a relevant test parameter and evaluated before and after saline inhalation.

METHODS

Seven vocally healthy participants performed a 10-minute inhalation of saline solution and underwent a combined laryngoscopy and OCT before and after the inhalation therapy. Endoscopy was performed using a newly developed combined laryngoscopy and OCT device. The OCT images were used to estimate the epithelial thickness of the vocal folds.

RESULTS

Epithelial thickness measured in all participants before treatment was comparable in size reported in previous studies. Statistical differences before and after inhalation were not detected.

CONCLUSION

The newly developed combined laryngoscopy and OCT procedure enables rapid investigation of the vocal fold epithelium. Inhalation of saline solution did not appear to affect the thickness of the epithelium of the vocal folds in vocally healthy subjects, as evaluated by OCT.

LEVEL OF EVIDENCE

N/A. Laryngoscope, 126:E332-E336, 2016.

In vivo cross-sectional imaging of the phonating larynx using long-range Doppler optical coherence tomography

Diagnosis and treatment of vocal fold lesions has been a long-evolving science for the otolaryngologist. Contemporary practice requires biopsy of a glottal lesion in the operating room under general anesthesia for diagnosis. Current in-office technology is limited to visualizing the surface of the vocal folds with fiber-optic or rigid endoscopy and using stroboscopic or high-speed video to infer information about submucosal processes. Previous efforts using optical coherence tomography (OCT) have been limited by small working distances and imaging ranges. Here we report the first full field, high-speed, and long-range OCT images of awake patients’ vocal folds as well as cross-sectional video and Doppler analysis of their vocal fold motions during phonation. These vertical-cavity surface-emitting laser source (VCSEL) OCT images offer depth resolved, high-resolution, high-speed, and panoramic images of both the true and false vocal folds. This technology has the potential to revolutionize in-office imaging of the larynx.

Using attenuation coefficients from optical coherence tomography as markers of vocal fold maturation

OBJECTIVES/HYPOTHESIS

Optical coherence tomography (OCT) is a promising technology to noninvasively assess vocal fold microanatomy. The goal of this study was to develop a methodology using OCT to identify quantifiable markers of vocal fold development.

STUDY DESIGN

In vivo study.

METHODS

A two-step process was developed to reproducibly image the midmembranous vocal fold edge of 10 patients younger than 2 years and 10 patients between 11 and 16 years of age using OCT. An image analysis algorithm was implemented to extract OCT-derived A-lines for each patient. These A-lines were divided into three zones according to apparent changes in slope. Relative attenuation coefficients, or tissue- and system-dependent parameters that describe the rate at which optical signal decays, were calculated for each zone.

RESULTS

Young patients had distinct relative attenuation coefficients in zone 1 (P < .0001), whereas zones 2 and 3 were indistinct (P = .1129). Older patients had distinct relative attenuation coefficients in zones 1, 2, and 3 (P < .0370). Between age groups, relative attenuation coefficients were different in zones 2 and 3 (P < .0001, P = .0315, respectively) and indistinct in zone 1 (P = .1438).

CONCLUSIONS

Relative attenuation coefficients can be used as markers of vocal fold development. Differences in relative attenuation coefficients likely represent changes in extracellular matrix structure within the lamina propria and may become useful for guiding treatment of voice disorders in the pediatric population.

LEVEL OF EVIDENCE

NA Laryngoscope, 126:E218-E223, 2016.