Kathy Beaudette

Laser tissue coagulation and concurrent optical coherence tomography through a double-clad fiber coupler.

Double-clad fiber (DCF) is herein used in conjunction with a double-clad fiber coupler (DCFC) to enable simultaneous and co-registered optical coherence tomography (OCT) and laser tissue coagulation. The DCF allows a single channel fiber-optic probe to be shared: i.e. the core propagating the OCT signal while the inner cladding delivers the coagulation laser light. We herein present a novel DCFC designed and built to combine both signals within a DCF (>90% of single-mode transmission; >65% multimode coupling). Potential OCT imaging degradation mechanisms are also investigated and solutions to mitigate them are presented. The combined DCFC-based system was used to induce coagulation of an ex vivo swine esophagus allowing a real-time assessment of thermal dynamic processes. We therefore demonstrate a DCFC-based system combining OCT imaging with laser coagulation through a single fiber, thus enabling both modalities to be performed simultaneously and in a co-registered manner. Such a system enables endoscopic image-guided laser marking of superficial epithelial tissues or laser thermal therapy of epithelial lesions in pathologies such as Barretts esophagus.

Optical coherence tomography for the identification of musculoskeletal structures of the spine: a pilot study

Adolescent idiopathic scoliosis (AIS) is a complex three-dimensional deformity of the spine requiring in severe cases invasive surgery. Here, we explore the potential of optical coherence tomography (OCT) as a guiding tool for novel fusionless minimally invasive spinal surgeries on an ex vivo porcine model. We show that OCT, despite its limited penetration depth, may be used to precisely locate structures such as growth plate, bone and intervertebral disk using relative attenuation coefficients. We further demonstrate a segmentation algorithm that locates growth plates automatically on en-face OCT reconstructions.

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

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.

Intraoperative imaging of pediatric vocal fold lesions using optical coherence tomography.

Abstract. Optical coherence tomography (OCT) has been previously identified as a promising tool for exploring laryngeal pathologies in adults. Here, we present an OCT handheld probe dedicated to imaging the unique geometry involved in pediatric laryngoscopy. A vertical cavity surface emitting laser-based wavelength-swept OCT system operating at 60 frames per second was coupled to the probe to acquire three-dimensional (3-D) volumes in vivo. In order to evaluate the performance of the proposed probe and system, we imaged pediatric vocal fold lesions of patients going under direct laryngoscopy. Through this in vivo study, we extracted OCT features characterizing each pediatric vocal fold lesion, which shows a great potential for noninvasive laryngeal lesion discrimination. We believe OCT vocal fold examination in 3-D will result in improved knowledge of the pediatric anatomy and could aid in managing pediatric laryngeal diseases.

Tissue-like phantoms for quantitative birefringence imaging

Birefringence imaging, including polarization sensitive optical coherence tomography (PS-OCT), can provide valuable insight into the microscopic structure and organization of many biological tissues. In this paper, we report on a method to fabricate tissue-like birefringence phantoms for such imaging modalities. We utilize the photo-elastic effect, wherein birefringence is induced by stretching a polymer sample after heating it above its glass-transition temperature. The cooled samples stably exhibit homogeneous birefringence, and were assembled into phantoms containing multiple well-defined regions of distinct birefringence. We present planar slab phantoms for microscopy applications and cylindrical phantoms for catheter-based imaging and demonstrate quantitative analysis of the birefringence within individual regions of interest. Birefringence phantoms enable testing, validating, calibrating, and improving PS-OCT acquisition systems and reconstruction strategies.

Non-invasive imaging of zebrafish with spinal deformities using optical coherence tomography: a preliminary study

A zebrafish model has recently been introduced to study various genetic mutations that could lead to spinal deformities such as scoliosis. However, current imaging techniques make it difficult to perform longitudinal studies of this condition in zebrafish, especially in the early stages of development. The goal of this project is to determine whether optical coherence tomography (OCT) is a viable non-invasive method to image zebrafish exhibiting spinal deformities. Images of both live and fixed malformed zebrafish (5 to 21 days postfertilization) as well as wild-type fish (5 to 29 days postfertilization) were acquired non-invasively using a commercial SD-OCT system, with a laser source centered at 930nm (λ=100nm), permitting axial and lateral resolutions of 7 and 8μm respectively. Using two-dimensional images and three-dimensional reconstructions, it was possible to identify the malformed notochord as well as deformities in other major organs at different stages of formation. Visualization of the notochord was facilitated with the development of a segmentation algorithm. OCT images were compared to HE histological sections and images obtained by calcein staining. Because of the possibility of performing longitudinal studies on a same fish and reducing image processing time as compared with staining techniques and histology, the use of OCT could facilitate phenotypic characterization in studying genetic factors leading to spinal deformities in zebrafish and could eventually contribute to the identification of the genetic causes of spinal deformities such as scoliosis.

Birefringence phantoms for polarization sensitive optical coherence tomography (Conference Presentation)

Polarization sensitive optical coherence tomography (PS-OCT) is increasingly used in a range of applications, both in bench-top and catheter-based imaging configurations. Reconstruction of tissue birefringence is subject to many system and processing-dependent artifacts. However, methods for the calibration and validation of PS-OCT are missing. Here, we report on a method to fabricate tissue-like imaging phantoms exhibiting clearly defined regions with controllable amounts of birefringence. We employed the photoelastic effect to enable the generation of controllable amounts of stress-induced birefringence in rubber samples, verified with polarized light microscopy. Pigmented ink was added to liquid latex solution to mold and cure rubber bands with controlled backscattering and transparency. Differently stretched segments were embedded in a stress-free background matrix to generate clearly defined areas with high birefringence contrast in an area of homogenous backscatter intensity. Arranged in planar geometry or on the outside of a glass capillary, the stretched rubber bands defined phantoms for bench-top and catheter-based imaging, respectively. Segmentation of the defined regions of interest in the reconstructed volumetric birefringence tomograms enabled assessing measurement consistency, between repeated imaging with a single system, or between independent imaging systems. Consistent and durable imaging phantoms are crucial for advancing PS-OCT imaging technology. Our tissue-like imaging phantoms exhibit clearly defined regions with controlled amounts of birefringence and facilitate testing, calibration, and validation of imaging systems and reconstruction strategies.

Towards in vivo laser coagulation and concurrent optical coherence tomography through double-clad fiber devices

There is a strong clinical need for an optical coherence tomography (OCT) system capable of delivering concurrent coagulation light enabling image-guided dynamic laser marking for targeted collection of biopsies, as opposed to a random sampling, to reduce false-negative findings. Here, we present a system based on double-clad fiber (DCF) capable of delivering pulsed laser light through the inner cladding while performing OCT through the core. A previously clinically validated commercial OCT system (NVisionVLE, Ninepoint Medical) was adapted to enable in vivo esophageal image-guided dynamic laser marking. An optimized DCF coupler was implemented into the system to couple both modalities into the DCF. A DCF-based rotary joint was used to couple light to the spinning DCF-based catheter for helical scanning. DCF-based OCT catheters, providing a beam waist diameter of 62μm at a working distance of 9.3mm, for use with a 17-mm diameter balloon sheath, were used for ex vivo imaging of a swine esophagus. Imaging results using the DCF-based clinical system show an image quality comparable with a conventional system with minimal crosstalk-induced artifacts. To further optimize DCF catheter optical design in order to achieve single-pulse marking, a Zemax model of the DCF output and its validation are presented.

Image-guided dynamic laser coagulation using a double-clad fiber-based system (Conference Presentation)

Optical coherence tomography (OCT) used in combination with laser coagulation to mark selected regions of interest could efficiently guide the collection of biopsies. This would reduce false-negative findings, and have a significant impact on the management of Barrett’s esophagus. Here, we present a system based on double-clad fiber (DCF) capable of delivering marking laser light through the inner cladding while performing OCT through the core. A previously clinically validated commercial OCT system (NVisionVLE, Ninepoint Medical) was adapted in order to perform in vivo esophageal image-guided dynamic laser marking. A dedicated DCF coupler (core signal transmission: ~95%; inner cladding coupling: ~75%) was implemented into the system to combine both modalities into the DCF. The original rotary junction, necessary for helical scanning with a side-looking fiber probe, was replaced by a custom DCF-based optical rotary junction (Princetel Inc.). This rotary junction was optimized to provide low insertion loss and crosstalk to preserve imaging quality (effective dynamic range of up to 52dB). DCF-based OCT catheters were designed to have a beam waist diameter of 62±4µm at a working distance of 9.3±0.4mm, for use with a 17-mm diameter balloon sheath. Our previous ex vivo marking experiments demonstrate that, based on the characterization of these DCF components, the system is capable of single-pulse laser marking at 1436 nm. This enables further in vivo experiments to demonstrate image-guided dynamic laser marking and potentially other therapeutic applications.

Intraoperative handheld probe for 3D imaging of pediatric benign vocal fold lesions using optical coherence tomography (Conference Presentation)

Excessive and repetitive force applied on vocal fold tissue can induce benign vocal fold lesions. Children affected suffer from chronic hoarseness. In this instance, the vibratory ability of the folds, a complex layered microanatomy, becomes impaired. Histological findings have shown that lesions produce a remodeling of sup-epithelial vocal fold layers. However, our understanding of lesion features and development is still limited. Indeed, conventional imaging techniques do not allow a non-invasive assessment of sub-epithelial integrity of the vocal fold. Furthermore, it remains challenging to differentiate these sub-epithelial lesions (such as bilateral nodules, polyps and cysts) from a clinical perspective, as their outer surfaces are relatively similar. As treatment strategy differs for each lesion type, it is critical to efficiently differentiate sub-epithelial alterations involved in benign lesions. In this study, we developed an optical coherence tomography (OCT) based handheld probe suitable for pediatric laryngological imaging. The probe allows for rapid three-dimensional imaging of vocal fold lesions. The system is adapted to allow for high-resolution intra-operative imaging. We imaged 20 patients undergoing direct laryngoscopy during which we looked at different benign pediatric pathologies such as bilateral nodules, cysts and laryngeal papillomatosis and compared them to healthy tissue. We qualitatively and quantitatively characterized laryngeal pathologies and demonstrated the added advantage of using 3D OCT imaging for lesion discrimination and margin assessment. OCT evaluation of the integrity of the vocal cord could yield to a better pediatric management of laryngeal diseases.