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Original Article |

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

Jennifer L. Lin, MD; Amy Y. Yau, MD; Jonathon Boyd, MD; Ashley Hamamoto, BS; Erica Su, BS; Lauren Tracy, BS; Andrew E. Heidari, BS; Alex H. Wang, BS; Gurpreet Ahuja, MD; Zhongping Chen, MD; Brian J. Wong, MD, PhD
JAMA Otolaryngol Head Neck Surg. 2013;139(5):502-509. doi:10.1001/jamaoto.2013.2643.
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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.

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Figures

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Figure 1. Schematics of the optical coherence tomography system built by University of California, Irvine, department of biomedical engineering in conjunction with Beckman Laser Institute used in this current rabbit model. DSP indicates digital signal processing; OCT, optical coherence tomography.

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Figure 2. The area of scar as seen by optical coherence tomography (OCT) and histologic examination was evaluated by blinded investigators. The x-axis shows the rabbit numbers. Airway scarring measured by fractional airway area measurements ranged from 9% to 34% as identified by OCT, and 23% to 43% by histologic images. Among OCT experts, the area of stenosis was consistently identified within a standard error of 2.8%, and among histology experts, the area of stenosis was consistently identified within a standard error of 3.2%. Error bars indicate standard errors.

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Figure 3. Histologic images (A-C) and optical coherence tomographic (OCT) images (D-F) of a control rabbit. A, An axial slice of the airway at the most inferior edge of the cricoid cartilage and the first tracheal ring. B, The cricoid cartilage. C, The most superior aspect of the cricoid cartilage. D-F, The level of the airway can be gauged based on the shape change of the airway as demonstrated by these figures. The classic sideways “D” is seen with the tracheal rings, a circular shape at the level of the cricoid and the ovoid shape at the immediate subglottic. The missing data at the 5-o’clock position are a shadow caused by the motor wire of the OCT probe.

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Figure 4. Images of the subglottic region of rabbits studied. Endoscopic (A), histologic (B), and optical coherence tomographic (OCT) (C) images of the subglottic region of a control rabbit. Endoscopic (D), histologic (E), and OCT (F) images of the subglottic region of a rabbit 3 days after mucosal injury. In all 3 images, there is a clear area of mucosal abnormality from the 4-o’clock to 8-o’clock positions, with a clear demarcation between intact epithelium and damaged epithelium. Histologic images confirm the presence of granulation tissue, early blood vessel formation, hemorrhage, and abundant lymphocytes. The arrows point to a clear area of demarcation for normal epithelium and damaged epithelium

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Figure 5. A rabbit killed 14 days after mucosal injury. A scar on endoscopy (A), a scar on histologic images (B), and a scar on optical coherence tomography (OCT) (C) images. All 3 modalities show significant circumferential scarring in the airway. On OCT, the tissue penetration is limited, and therefore the entire thickness of the scar is not visualized; however, clear evidence of reepitheliazation is seen at the 11-o’clock position as indicated by the arrows and correlates with histology. Submucosal tissue injury is evident.

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Figure 6. A rabbit killed 21 days after mucosal injury. Endoscopic (A), histologic (B), and optical coherence tomographic (C) images. Circumferential scarring with reepithelialization are seen in all imaging modalities.

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Figure 7. A rabbit killed 42 days after mucosal injury. Histologic (A) and optical coherence tomographic (OCT) (B) images show a single area of fibrous scarring at the 11-o’clock position. The OCT image very clearly demonstrates changes in both surface and submucosal anatomy that correlates well with histologic images.

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