Anatomically correct visualization of the human upper airway using a high-speed long range optical coherence tomography system with an integrated positioning sensor

Long-range optical coherence tomography of pediatric airway during drug induced sleep endoscopy: A preliminary report

OBJECTIVE

Drug induced sleep endoscopy (DISE) is often performed for pediatric obstructive sleep apnea (OSA) when initial diagnostic studies do not provide adequate information for therapy. However, DISE scoring is subjective and with limitations. This proof-of-concept study demonstrates the use of a novel long-range optical coherence tomography (LR-OCT) system during DISE of two pediatric patients.

METHODS

LR-OCT was used to visualize the airway of pediatric patients during DISE. At the conclusion of DISE, the OCT probe was guided in the airway under endoscopic visual guidance, and cross-sectional images were acquired at the four VOTE locations. Data processing involved image resizing and alignment, followed by rendering of three-dimensional (3D) volumetric models of the airways.

RESULTS

Two patients were included in this study. Patient one had 18.4%, 20.9%, 72.3%, and 97.3% maximal obstruction at velum, oropharynx, tongue base, and epiglottis, while patient two had 40.2%, 41.4%, 8.0%, and 17.5% maximal obstruction at these regions, respectively. Three-dimensional reconstructions of patients' airways were also constructed from the OCT images.

CONCLUSION

This proof-of-concept study demonstrates the successful evaluation of pediatric airway during DISE using LR-OCT, which accurately identified sites and degrees of obstruction with respective 3D airway reconstruction.

In vivo volumetric depth-resolved imaging of cilia metachronal waves using dynamic optical coherence tomography

Motile cilia are dynamic hair-like structures covering epithelial surfaces in multiple organs. The periodic coordinated beating of cilia creates waves propagating along the surface, known as the metachronal waves, which transport fluids and mucus along the epithelium. Motile ciliopathies result from disrupted coordinated cilia beating and are associated with serious clinical complications, including reproductive disorders. Despite the recognized clinical significance, research of cilia dynamics is extremely limited. Here, we present quantitative imaging of cilia metachronal waves volumetrically through tissue layers using dynamic optical coherence tomography (OCT). Our method relies on spatiotemporal mapping of the phase of intensity fluctuations in OCT images caused by the ciliary beating. We validated our new method ex vivo and implemented it in vivo to visualize cilia metachronal wave propagation within the mouse fallopian tube. This method can be extended to the assessment of physiological cilia function and ciliary dyskinesias in various organ systems, contributing to better management of pathologies associated with motile ciliopathies.

Automatic 3D reconstruction of an anatomically correct upper airway from endoscopic long range OCT images

Endoscopic airway optical coherence tomography (OCT) is a non-invasive and high resolution imaging modality for the diagnosis and analysis of airway-related diseases. During OCT imaging of the upper airway, in order to reliably characterize its 3D structure, there is a need to automatically detect the airway lumen contour, correct rotational distortion and perform 3D airway reconstruction. Based on a long-range endoscopic OCT imaging system equipped with a magnetic tracker, we present a fully automatic framework to reconstruct the 3D upper airway model with correct bending anatomy. Our method includes an automatic segmentation method for the upper airway based on dynamic programming algorithm, an automatic initial rotation angle error correction method for the detected 2D airway lumen contour, and an anatomic bending method combined with the centerline detected from the magnetically tracked imaging probe. The proposed automatic reconstruction framework is validated on experimental datasets acquired from two healthy adults. The result shows that the proposed framework allows the full automation of 3D airway reconstruction from OCT images and thus reveals its potential to improve analysis efficiency of endoscopic OCT images.

Optical coherence tomography evaluation of vaginal epithelial thickness during CO2 laser treatment: A pilot study

Genitourinary syndrome of menopause (GSM) negatively affects more than half of postmenopausal women. Energy-based therapy has been explored as a minimally invasive treatment for GSM; however, its mechanism of action and efficacy is controversial. Here, we report on a pilot imaging study conducted on a small group of menopause patients undergoing laser treatment. Intravaginal optical coherence tomography (OCT) endoscope was used to quantitatively monitor the changes in the vaginal epithelial thickness (VET) during fractional-pixel CO2 laser treatment. Eleven patients with natural menopause and one surgically induced menopause patient were recruited in this clinical study. Following the laser treatment, 6 out of 11 natural menopause patient showed increase in both proximal and distal VET, while two natural menopause patient showed increase in VET in only one side of vaginal tract. Furthermore, the patient group that showed increased VET had thinner baseline VET compared to the patients that showed decrease in VET after laser treatment. These results demonstrate the potential utility of intravaginal OCT endoscope in evaluating the vaginal tissue integrity and tailoring vaginal laser treatment on a per-person basis, with the potential to monitor other treatment procedures.

Tentative study on radial endobronchial ultrasonography evaluating airway wall thickness before and after bronchial thermoplasty

Aim

We aimed to observe the clinical practicing value of radial endobronchial ultrasonography evaluating airway wall thickness before and after bronchial thermoplasty.

Methods

We selected two patients who received bronchial thermoplasty in our hospital. We measured the thickness of each segmental airway wall of each patient by radial endobronchial ultrasonography, and observed the difference before and after the therapy. All the treatments and measurement were performed by a designated bronchoscopist and the locations and depths of the ultrasound probe were relatively fixed, to reduce the operational error.

Results

In both two patients, the mean thicknesses of all segmental airway walls was 4.9 ± 0.7 mm before the first session of BT; the mean thickness was 4.13 ± 0.92 mm before the second session; the mean thickness was 2.69 ± 0.68 mm before the third session; the mean thickness was 2.7 ± 0.5 mm in the follow-up measurement at six months after the BT treatment; all thicknesses of airway wall were significantly reduced comparing with those before treatment; all the thicknesses of the airway walls were stable without any tendency of thickening after six months. Although the airways in the right middle lobe of both two patients were not received BT, their thicknesses were also decreased comparing with those before the treatment; both upper lobes bronchus of both two patients were not activated in the first and second sessions, but their thicknesses were also decreased at the third measurement.

Conclusion

Radial endobronchial ultrasonography is a simple and practical method to measure the thickness of patient's airway wall. Bronchial thermoplasty can effectively reduce the thickness of airway wall. It can reduce airway smooth muscle by direct activation and other possible more complicated mechanism, which need further research.

Automatic correction of the initial rotation angle error improves 3D reconstruction in endoscopic airway optical coherence tomography

Endoscopic airway optical coherence tomography (OCT) is an advanced imaging modality capable of capturing the internal anatomy and geometry of the airway. Due to fiber-optic catheter bending and friction, the rotation speed of the endoscopic probe is usually non-uniform: at each B-scan image, the initial rotation angle of the probe is easily misaligned with that of the previous slices. During the pullback operation, this initial rotation angle error (IRAE) will be accumulated and will result in distortion and deformation of the reconstructed 3D airway structure. Previous attempts to correct this error were mainly manual corrections, which are time-consuming and suffered from observer variation. In this paper, we present a method to correct the IRAE for anatomically improved visualization of the airway. Our method derived the rotation angular difference of adjacent B-scans by measuring their contour similarity and then tracks the IRAE by formulating its continuous drift as a graph-based problem. The algorithm was tested on a simulated airway contour dataset, and also on experimental datasets acquired by two different long range endoscopic airway OCT platforms. Effective and smooth compensation of the frame-by-frame initial angle difference was achieved. Our method has real-time capability and thus has the potential to improve clinical imaging efficiency.

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.

Graph-based rotational nonuniformity correction for localized compliance measurement in the human nasopharynx

Recent advancements in the high-speed long-range optical coherence tomography (OCT) endoscopy allow characterization of tissue compliance in the upper airway, an indicator of collapsibility. However, the resolution and accuracy of localized tissue compliance measurement are currently limited by the lack of a reliable nonuniform rotational distortion (NURD) correction method. In this study, we developed a robust 2-step NURD correction algorithm that can be applied to the dynamic OCT images obtained during the compliance measurement. We demonstrated the utility of the NURD correction algorithm by characterizing the local compliance of nasopharynx from an awake human subject for the first time.

Intraoperative use of optical coherence tomography to differentiate normal and diseased thyroid and parathyroid tissues from lymph node and fat

The purpose of this study is twofold: (1) to determine the feasibility of optical coherence tomography (OCT) to differentiate normal and diseased tissue of the neck region intraoperatively and (2) to evaluate how accurately a cohort of test subjects can identify various tissue types when shown a sample set of OCT images. In this in vivo, prospective, single institutional study, an OCT imaging system (Niris, Imalux, Cleveland, OH) was used to image parathyroid, thyroid, lymph node, and fat tissue in 76 patients during neck surgery. Biopsies were performed for comparison of OCT images with histology in select cases (n = 20). Finally, a group of either surgeons or scientists familiar with OCT (n = 17) were shown a sample of OCT images and asked to identify the tissue. A total of 437 OCT images were analyzed, and characteristic features of each tissue type were identified. OCT demonstrated distinct differences in structural architecture and signal intensity that allows differentiation between thyroid and parathyroid tissues, lymph nodes, and fat. OCT images were also compared with histology with good correlation. There was no difference in correctly identifying OCT-imaged tissue type between surgeons and scientists. This study is the first in vivo OCT imaging study to evaluate both normal and diseased tissues that may be encountered during neck surgery. OCT has the potential to become a valuable intraoperative tool to differentiate diseased and normal thyroid tissue intraoperatively to obtain an "optical biopsy" in real time without fixation, staining, or tissue resection.

Speckle reducing OCT using optical chopper

Optical coherence tomography (OCT) has been an important and powerful tool for biological research and clinical applications. However, speckle noise significantly degrades the image quality of OCT and has a negative impact on the clinical diagnosis accuracy. In this paper, we propose a novel speckle noise suppression technique which changes the spatial distribution of sample beam using a special optical chopper. Then a series of OCT images with uncorrelated speckle patterns could be captured and compounded to improve the image quality without degradation of resolution. Typical signal-to-noise ratio improvement of ∼6.4 dB is experimentally achieved in tissue phantom imaging with average number n = 100. Furthermore, compared with conventional OCT, the proposed technique is demonstrated to view finer and clearer biological structures in human skin in vivo, such as sweat glands and blood vessels. The advantages of low cost, simple structure and compact integration will benefit the future design of handheld or endoscopic probe for biomedical imaging in research and clinical applications.

In vivo multifunctional optical coherence tomography at the periphery of the lungs

Remodeling of tissue, such as airway smooth muscle (ASM) and extracellular matrix, is considered a key feature of airways disease. No clinically accepted diagnostic method is currently available to assess airway remodeling or the effect of treatment modalities such as bronchial thermoplasty in asthma, other than invasive airway biopsies. Optical coherence tomography (OCT) generates cross-sectional, near-histological images of airway segments and enables identification and quantification of airway wall layers based on light scattering properties only. In this study, we used a custom motorized OCT probe that combines standard and polarization sensitive OCT (PS-OCT) to visualize birefringent tissue in vivo in the airway wall of a patient with severe asthma in a minimally invasive manner. We used optic axis uniformity (OAxU) to highlight the presence of uniformly arranged fiber-like tissue, helping visualizing the abundance of ASM and connective tissue structures. Attenuation coefficient images of the airways are presented for the first time, showing superior architectural contrast compared to standard OCT images. A novel segmentation algorithm was developed to detect the surface of the endoscope sheath and the surface of the tissue. PS-OCT is an innovative imaging technique that holds promise to assess airway remodeling including ASM and connective tissue in a minimally invasive, real-time manner.

Endoscopic Optical Coherence Tomography for Assessing Inhalation Airway Injury: A Technical Review

Diagnosis of inhalation injury has been clinically challenging. Currently, assessment of inhalation injury relies on subjective clinical exams and bronchoscopy, which provides little understanding of tissue conditions and results in limited prognostics. Endoscopic Optical coherence tomography (OCT) technology has been recently utilized in the airway for direct assessment of respiratory tract disorders and injuries. Endoscopic OCT is capable of capturing high-resolution images of tissue morphology 1-3 mm beneath the surface as well as the complex 3D anatomical shape. Previous studies indicate that changes in airway histopathology can be found in the OCT image almost immediately after inhalation of smoke and other toxic chemicals, which correlates well with histology and pulmonary function tests. This review summarizes the recent development of endoscopic OCT technology for airway imaging, current uses of OCT for inhalation injury, and possible future directions.

Automatic three-dimensional segmentation of endoscopic airway OCT images

Automatic delineation and segmentation of airway structures from endoscopic optical coherence tomography (OCT) images improve image analysis efficiency and thus has been of particular interest. Conventional two-dimensional automatic segmentation methods, such as the dynamic programming approach, ensures the edge-continuity in the xz-direction (intra-B-scan), but fails to preserve the surface-continuity when concerning the y-direction (inter-B-scan). To solve this, we present a novel automatic three-dimensional (3D) airway segmentation strategy. Our segmentation scheme includes an artifact-oriented pre-processing pipeline and a modified 3D optimal graph search algorithm incorporating adaptive tissue-curvature adjustment. The proposed algorithm is tested on endoscopic airway OCT image data sets acquired by different swept-source OCT platforms, and on different animal and human models. With our method, the results show continuous surface segmentation performance, which is both robust and accurate.

Combined anatomical optical coherence tomography and intraluminal pressure reveal viscoelasticity of the in vivo airway

It is hypothesized that the local, viscoelastic (time-dependent) properties of the airway are important to accurately model and ultimately predict dynamic airway collapse in airway obstruction. Toward this end, we present a portable, endoscopic, swept-source anatomical optical coherence tomography (aOCT) system combined with a pressure catheter to capture local airway dynamics in vivo during respiration. aOCT scans were performed in the airways of a mechanically ventilated pig under paralysis with dynamic and static ventilation protocols. Validation of dynamic aOCT luminal cross-sectional area (CSA) measurements against Cine CT, obtained during the same exam, showed an aggregate difference of 15  %    ±  3  %  . aOCT-derived CSA obtained in the in vivo trachea also exhibited hysteresis as a function of pressure, depicting the viscoelastic nature of the airway wall. The volumetric imaging capabilities were validated by comparing aOCT- and CT-derived geometries of the porcine airway spanning nine generations from the trachea to the bronchioles. The ability to delineate regional differences in airway viscoelastic properties, by measuring airway deformation using aOCT combined with intraluminal pressure, paves the way to patient-specific models of dynamic airway collapse.

Upper airway reconstruction using long-range optical coherence tomography: Effects of airway curvature on airflow resistance

OBJECTIVES

Adenotonsillectomy (AT) is commonly used to treat upper airway obstruction in children, but selection of patients who will benefit most from AT is challenging. The need for diagnostic evaluation tools without sedation, radiation, or high costs has motivated the development of long-range optical coherence tomography (LR-OCT), providing real-time cross-sectional airway imaging during endoscopy. Since the endoscope channel location is not tracked in conventional LR-OCT, airway curvature must be estimated and may affect predicted airway resistance. The study objective was to assess effects of three realistic airway curvatures on predicted airway resistance using computational fluid dynamics (CFD) in LR-OCT reconstructions of the upper airways of pediatric patients, before and after AT.

METHODS

Eight subjects (five males, three females, aged 4-9 years) were imaged using LR-OCT before and after AT during sedated endoscopy. Three-dimensional (3D) airway reconstructions included three airway curvatures. Steady-state, inspiratory airflow simulations were conducted under laminar conditions, along with turbulent simulations for one subject using the k-ω turbulence model. Airway resistance (pressure drop/flow) was compared using two-tailed Wilcoxon signed rank tests.

RESULTS

Regardless of the airway curvatures, CFD findings corroborate a surgical end-goal with computed post-operative airway resistance significantly less than pre-operative (P < 0.01). The individual resistances did not vary significantly for different airway curvatures (P > 0.25). Resistances computed using turbulent simulations differed from laminar results by less than ∼5%.

CONCLUSIONS

The results suggest that reconstruction of the upper airways from LR-OCT imaging data may not need to account for airway curvature to be predictive of surgical effects on airway resistance. Lasers Surg. Med. 51:150-160, 2019. © 2018 Wiley Periodicals, Inc.

Automated 3D segmentation of methyl isocyanate-exposed rat trachea using an ultra-thin, fully fiber optic optical coherence endoscopic probe

Development of effective rescue countermeasures for toxic inhalational industrial chemicals, such as methyl isocyanate (MIC), has been an emerging interest. Nonetheless, current methods for studying toxin-induced airway injuries are limited by cost, labor time, or accuracy, and only provide indirect or localized information. Optical Coherence Tomography (OCT) endoscopic probes have previously been used to visualize the 3-D airway structure. However, gathering such information in small animal models, such as rat airways after toxic gas exposure, remains a challenge due to the required probe size necessary for accessing the small, narrow, and partially obstructed tracheas. In this study, we have designed a 0.4 mm miniature endoscopic probe and investigated the structural changes in rat trachea after MIC inhalation. An automated 3D segmentation algorithm was implemented so that anatomical changes, such as tracheal lumen volume and cross-sectional areas, could be quantified. The tracheal region of rats exposed to MIC by inhalation showed significant airway narrowing, especially within the upper trachea, as a result of epithelial detachment and extravascular coagulation within the airway. This imaging and automated reconstruction technique is capable of rapid and minimally-invasive identification of airway obstruction. This method can be applied to large-scale quantitative analysis of in vivo animal models.

Intravascular Optical Coherence Tomography for Characterization of Atherosclerosis with a 1.7 Micron Swept-Source Laser

The main cause of acute coronary events, such as thrombosis, is the rupture of atherosclerotic plaques. Typical intravascular optical coherence tomography (IVOCT) imaging systems that utilize a 1.3 μm swept source laser are often used for identifying fibrous cap thickness of plaques, yet cannot provide adequate depth penetration to resolve the size of the lipid pool. Here, we present a novel  IVOCT system with a 1.7 μm center wavelength swept light source that can readily penetrate deeper into the tissue because of the longer wavelength and allows for better identification of plaques due to the lipid absorption spectrum at 1.7 μm. Using this system, we have imaged a human coronary artery to evaluate the performance of the novel OCT system and verified the results by hematoxylin and eosin (H&E) histology. The significantly improved imaging depth and better identification sensitivity suggest that the 1.7 μm OCT system holds great potential  that can be further translated for in-vivo applications of atherosclerosis characterization.

Dual-beam manually-actuated distortion-corrected imaging (DMDI) with micromotor catheters

We present a new paradigm for performing two-dimensional scanning called dual-beam manually-actuated distortion-corrected imaging (DMDI). DMDI operates by imaging the same object with two spatially-separated beams that are being mechanically scanned rapidly in one dimension with slower manual actuation along a second dimension. Registration of common features between the two imaging channels allows remapping of the images to correct for distortions due to manual actuation. We demonstrate DMDI using a 4.7 mm OD rotationally scanning dual-beam micromotor catheter (DBMC). The DBMC requires a simple, one-time calibration of the beam paths by imaging a patterned phantom. DMDI allows for distortion correction of non-uniform axial speed and rotational motion of the DBMC. We show the utility of this technique by demonstrating en face OCT image distortion correction of a manually-scanned checkerboard phantom and fingerprint scan.

Endoscopic forward-viewing optical coherence tomography and angiography with MHz swept source

Endoscopic optical coherence tomography (OCT) instruments are mostly side viewing and rely on at least one proximal scan, thus limiting accuracy of volumetric imaging and en face visualization. Previous forward-viewing OCT devices had limited axial scan speeds. We report a forward-viewing fiber scanning 3D-OCT probe with 900 μm field of view and 5 μm transverse resolution, imaging at 1 MHz axial scan rate in the human gastrointestinal tract. The probe is 3.3 mm diameter and 20 mm rigid length, thus enabling passage through the endoscopic channel. The scanner has 1.8 kHz resonant frequency, and each volumetric acquisition takes 0.17 s with 2  volumes/s display. 3D-OCT and angiography imaging of the colon was performed during surveillance colonoscopy.