Erica Su

Long-range Fourier domain optical coherence tomography of the pediatric subglottis

BACKGROUND Acquired subglottic stenosis (SGS) most commonly results from prolonged endotracheal intubation and is a diagnostic challenge in the intubated child. At present, no imaging modality allows for in vivo characterization of subglottic microanatomy to identify early signs of acquired SGS while the child remains intubated. Fourier domain optical coherence tomography (FD-OCT) is a minimally invasive, light-based imaging modality which provides high resolution, three dimensional (3D) cross-sectional images of biological tissue. We used long-range FD-OCT to image the subglottis in intubated pediatric patients undergoing minor head and neck surgical procedures in the operating room. METHODS A long-range FD-OCT system and rotary optical probes (1.2mm and 0.7mm outer diameters) were constructed. Forty-six pediatric patients (ages 2-16 years) undergoing minor upper airway surgery (e.g., tonsillectomy and adenoidectomy) were selected for intraoperative, trans-endotracheal tube FD-OCT of the subglottis. Images were analyzed for anatomical landmarks and subepithelial histology. Volumetric image sets were rendered into virtual 3D airway models in Mimics software. RESULTS FD-OCT was performed on 46 patients (ages 2-16 years) with no complications. Gross airway contour was visible on all 46 data sets. Twenty (43%) high-quality data sets clearly demonstrated airway anatomy (e.g., tracheal rings, cricoid and vocal folds) and layered microanatomy of the mucosa (e.g., epithelium, basement membrane and lamina propria). The remaining 26 data sets were discarded due to artifact, high signal-to-noise ratio or missing data. 3D airway models were allowed for user-controlled manipulation and multiplanar airway slicing (e.g., sagittal, coronal) for visualization of OCT data at multiple anatomic levels simultaneously. CONCLUSIONS Long-range FD-OCT produces high-resolution, 3D volumetric images of the pediatric subglottis. This technology offers a safe and practical means for in vivo evaluation of lower airway microanatomy in intubated pediatric patients. Ultimately, FD-OCT may be applied to serial monitoring of the neonatal subglottis in long-term intubated infants at risk for acquired SGS.

Intraoperative long range optical coherence tomography as a novel method of imaging the pediatric upper airway before and after adenotonsillectomy

BACKGROUND/OBJECTIVES While upper airway obstruction is a common problem in the pediatric population, the first-line treatment, adenotonsillectomy, fails in up to 20% of patients. The decision to proceed to surgery is often made without quantitative anatomic guidance. We evaluated the use of a novel technique, long-range optical coherence tomography (LR-OCT), to image the upper airway of children under general anesthesia immediately before and after tonsillectomy and/or adenoidectomy. We investigated the feasibility of LR-OCT to identify both normal anatomy and sites of airway narrowing and to quantitatively compare airway lumen size in the oropharyngeal and nasopharyngeal regions pre- and post-operatively. METHODS 46 children were imaged intraoperatively with a custom-designed LR-OCT system, both before and after adenotonsillectomy. These axial LR-OCT images were both rendered into 3D airway models for qualitative analysis and manually segmented for quantitative comparison of cross-sectional area. RESULTS LR-OCT images demonstrated normal anatomic structures (base of tongue, epiglottis) as well as regions of airway narrowing. Volumetric rendering of pre- and post-operative images clearly showed regions of airway collapse and post-surgical improvement in airway patency. Quantitative analysis of cross-sectional images showed an average change of 70.52mm(2) (standard deviation 47.87mm(2)) in the oropharynx after tonsillectomy and 105.58mm(2) (standard deviation 60.62mm(2)) in the nasopharynx after adenoidectomy. CONCLUSIONS LR-OCT is an emerging technology that rapidly generates 3D images of the pediatric upper airway in a feasible manner. This is the first step toward development of an office-based system to image awake pediatric subjects and thus better identify loci of airway obstruction prior to surgery.

Real-Time Subglottic Stenosis Imaging Using Optical Coherence Tomography in the Rabbit

IMPORTANCE Subglottic stenosis (SGS) is a severe, acquired, potentially life-threatening disease that can be caused by endotracheal tube intubation. Newborns and neonates are particularly susceptible to SGS owing to the small caliber of their airway. OBJECTIVE To demonstrate optical coherence tomography (OCT) capabilities in detecting injury and scar formation using a rabbit model. Optical coherence tomography may provide a noninvasive, bedside or intensive care unit modality for the identification of early airway trauma with the intention of preventing progression to SGS and can image the upper airway through an existing endotracheal tube coupled with a small fiber-optic probe. DESIGN Rabbits underwent suspension laryngoscopy with induction of of SGS via epithelial injury. This model was used to test and develop our advanced, high-speed, high-resolution OCT imaging system using a 3-dimensional microelectromechanical systems-based scanning device integrated with a fiber-optic probe to acquire high-resolution anatomic images of the subglottic epithelium and lamina propria. SETTING All experiments were performed at the Beckman Laser Institute animal operating room. INTERVENTION OR EXPOSURE: Optical coherence tomography and endoscopy was performed with suspension laryngoscopy at 6 different time intervals and compared with conventional digital endoscopic images and histologic sections. Fifteen rabbits were killed at 3, 7, 14, 21, and 42 days after the induction of SGS. The laryngotracheal complexes were serially sectioned for histologic analysis. MAIN OUTCOME AND MEASURE Histologic sections, endoscopic images, and OCT images were compared with one another to determine if OCT could accurately delineate the degree of SGS achieved. RESULTS The rabbit model was able to reliably and reproducibly achieve grade I SGS. The real-time OCT imaging system was able to (1) identify multiple structures in the airway; (2) delineate different tissue planes, such as the epithelium, basement membrane, lamina propria, and cartilage; and (3) detect changes in each tissue plane produced by trauma. Optical coherence tomography was also able demonstrate a clear picture of airway injury that correlated with the endoscopic and histologic images. With subjective review, 3 patients had high correlation between OCT and histologic images, 10 demonstrated some correlation with histologic images, and 2 showed little to no correlation with histologic images. CONCLUSIONS AND RELEVANCE Optical coherence tomography, coupled with a fiber-optic probe, identifies subglottic scarring and can detect tissue changes in the rabbit airway to a depth of 1 mm. This technology brings us 1 step closer to minimally invasive subglottic airway monitoring in the intubated neonate, with the ultimate goal of preventing SGS and better managing the airway.

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

The upper airway is a complex tissue structure that is prone to collapse. Current methods for studying airway obstruction are inadequate in safety, cost, or availability, such as CT or MRI, or only provide localized qualitative information such as flexible endoscopy. Long range optical coherence tomography (OCT) has been used to visualize the human airway in vivo, however the limited imaging range has prevented full delineation of the various shapes and sizes of the lumen. We present a new long range OCT system that integrates high speed imaging with a real-time position tracker to allow for the acquisition of an accurate 3D anatomical structure in vivo. The new system can achieve an imaging range of 30 mm at a frame rate of 200 Hz. The system is capable of generating a rapid and complete visualization and quantification of the airway, which can then be used in computational simulations to determine obstruction sites.

Long-Range Optical Coherence Tomography of the Neonatal Upper Airway for Early Diagnosis of Intubation-related Subglottic Injury.

RATIONALE Subglottic edema and acquired subglottic stenosis are potentially airway-compromising sequelae in neonates following endotracheal intubation. At present, no imaging modality is capable of in vivo diagnosis of subepithelial airway wall pathology as signs of intubation-related injury. OBJECTIVES To use Fourier domain long-range optical coherence tomography (LR-OCT) to acquire micrometer-resolution images of the airway wall of intubated neonates in a neonatal intensive care unit setting and to analyze images for histopathology and airway wall thickness. METHODS LR-OCT of the neonatal laryngotracheal airway was performed a total of 94 times on 72 subjects (age, 1-175 d; total intubation, 1-104 d). LR-OCT images of the airway wall were analyzed in MATLAB. Medical records were reviewed retrospectively for extubation outcome. MEASUREMENTS AND MAIN RESULTS Backward stepwise regression analysis demonstrated a statistically significant association between log(duration of intubation) and both laryngeal (P < 0.001; multiple r(2) = 0.44) and subglottic (P < 0.001; multiple r(2) = 0.55) airway wall thickness. Subjects with positive histopathology on LR-OCT images had a higher likelihood of extubation failure (odds ratio, 5.9; P = 0.007). Longer intubation time was found to be significantly associated with extubation failure. CONCLUSIONS LR-OCT allows for high-resolution evaluation and measurement of the airway wall in intubated neonates. Our data demonstrate a positive correlation between laryngeal and subglottic wall thickness and duration of intubation, suggestive of progressive soft tissue injury. LR-OCT may ultimately aid in the early diagnosis of postintubation subglottic injury and help reduce the incidences of failed extubation caused by subglottic edema or acquired subglottic stenosis in neonates. Clinical trial registered with www.clinicaltrials.gov (NCT 00544427).

Quantitative Evaluation of Adult Subglottic Stenosis Using Intraoperative Long-range Optical Coherence Tomography.

Objectives: To determine the feasibility of long-range optical coherence tomography (LR-OCT) as a tool to intraoperatively image and measure the subglottis and trachea during suspension microlaryngoscopy before and after endoscopic treatment of subglottic stenosis (SGS). Methods: Long-range optical coherence tomography of the adult subglottis and trachea was performed during suspension microlaryngoscopy before and after endoscopic treatment for SGS. The anteroposterior and transverse diameters, cross-sectional area (CSA), distance from the vocal cords, and length of the SGS were measured using a MATLAB software. Pre-intervention and postintervention airway dimensions were compared. Three-dimensional volumetric airway reconstructions were generated using medical image processing software (MIMICS). Results: Intraoperative LR-OCT imaging was performed in 3 patients undergoing endoscopic management of SGS. Statistically significant differences in mean anteroposterior diameter (P < .01), transverse diameter (P < .001), and CSA (P < .001) were noted between pre-intervention and postintervention data. Three-dimensional airway models were viewed in cross-sectional format and via virtual “fly through” bronchoscopy. Conclusions: This is the first report of intraoperative LR-OCT of the subglottic and tracheal airway before and after surgical management of SGS in humans. Long-range optical coherence tomography offers a practical means to measure the dimensions of SGS and acquire objective data on the response to endoscopic treatment of SGS.

Constructing 3D models of the pediatric upper airway from long range optical coherence tomography images

Long-range optical coherence tomography has been developed to image the upper airway, obtaining high resolution, cross-sectional images of the hollow structure. The information obtained from the anatomical structure of the airway is important to objectively identify regions of airway obstruction. This paper describes a technique to create 3D reconstructions of the upper airway from LR-OCT images. Herein we outline the necessary steps to generate these 3D models, including image processing techniques, manual tissue segmentation in Mimics, anatomical curvature bending, and the final STL model rendition. These 3D models were used to qualitatively analyze structural changes before and after surgical interventions. The reconstructions could also be used for further computational fluid dynamics analysis.

Analysis and digital 3D modeling of long-range fourier-domain optical coherence tomography images of the pediatric subglottis

In neonatal and pediatric patients who require long-term endotracheal intubation, the subglottic mucosa is most susceptible to injury from the endotracheal tube. At present, there is no diagnostic modality to identify early signs of subglottic mucosal pathology. Fourier-domain optical coherence tomography (FD-OCT) is a minimally-invasive imaging modality which acquires high-resolution, 3D cross-sectional images of biological tissue. FD-OCT of the neonatal and pediatric airways was conducted to evaluate subglottic microanatomy and histopathologic changes associated with prolonged intubation. FD-OCT of the larynx, subglottis and proximal trachea was conducted in pediatric and neonatal patients. OCT image sets were analyzed by anatomic categorization (airway level), tissue segmentation and mucosa micrometry in MATLAB. Subsequently, OCT data sets were rendered into digital 3D airway models in Mimics software. We report original methods for subglottic OCT image processing and analysis.

Preclinical investigations of articular cartilage ablation with femtosecond and pulsed infrared lasers as an alternative to microfracture surgery

Abstract. Microfracture surgery is a bone marrow stimulation technique for treating cartilage defects and injuries in the knee. Current methods rely on surgical skill and instrumentation. This study investigates the potential use of laser technology as an alternate means to create the microfracture holes. Lasers investigated in this study include an erbium:YAG laser (λ=2.94  μm), titanium:sapphire femtosecond laser system (λ=1700  nm), and Nd:glass femtosecond laser (λ=1053  nm). Bovine samples were ablated at fluences of 8 to 18  J/cm2 with the erbium:YAG laser, at a power of 300±15  mW with the titanium:sapphire femtosecond system, and at an energy of 3  μJ/pulse with the Nd:glass laser. Samples were digitally photographed and histological sections were taken for analysis. The erbium:YAG laser is capable of fast and efficient ablation; specimen treated with fluences of 12 and 18  J/cm2 experienced significant amounts of bone removal and minimal carbonization with saline hydration. The femtosecond laser systems successfully removed cartilage but not clinically significant amounts of bone. Precise tissue removal was possible but not to substantial depths due to limitations of the systems. With additional studies and development, the use of femtosecond laser systems to ablate bone may be achieved at clinically valuable ablation rates.

Long‐term in vivo electromechanical reshaping for auricular reconstruction in the New Zealand white rabbit model

To demonstrate the dosimetry effect of electromechanical reshaping (EMR) on cartilage shape change, structural integrity, cellular viability, and remodeling of grafts in an in vivo long‐term animal model.