Simple and robust calibration procedure for k-linearization and dispersion compensation in optical coherence tomography

In Fourier-domain optical coherence tomography (FD-OCT), proper signal sampling and dispersion compensation are essential steps to achieve optimal axial resolution. These calibration steps can be performed through numerical signal processing, but require calibration information about the system that may require lengthy and complex measurement protocols. We report a highly robust calibration procedure that can simultaneously determine correction vectors for nonlinear wavenumber sampling and dispersion compensation. The proposed method requires only two simple mirror measurements and no prior knowledge about the system's illumination source or detection scheme. This method applies to both spectral domain and swept-source OCT systems. Furthermore, it may be implemented as a low-cost fail-safe to validate the proper function of calibration hardware such as k-clocks. We demonstrate the method's simple implementation, effectiveness, and robustness on both types of OCT systems

Combined optical coherence tomography and hyperspectral imaging using a double-clad fiber coupler

This work demonstrates the combination of optical coherence tomography (OCT) and hyperspectral imaging (HSI) using a double-clad optical fiber coupler. The single-mode core of the fiber is used for OCT imaging, while the inner cladding of the double-clad fiber provides an efficient way to capture the reflectance spectrum of the sample. The combination of both methods enables three-dimensional acquisition of the sample morphology with OCT, enhanced with complementary molecular information contained in the hyperspectral image. The HSI data can be used to highlight the presence of specific molecules with characteristic absorption peaks or to produce true color images overlaid on the OCT volume for improved tissue identification by the clinician. Such a system could be implemented in a number of clinical endoscopic applications and could improve the current practice in tissue characterization, diagnosis, and surgical guidance

Advancements in Multimodal Endoscopic Optical Coherence Tomography: Novel Hardware, Software, and Optical Strategies

RÉSUMÉ: Le cancer de l'oesophage (CO) est une maladie dangereuse, principalement en raison de sa nature asymptomatique jusqu'à un stade avancé de son développement. Actuellement, la vidéo-endoscopie en lumière blanche combinée à des biopsies aléatoires constituent l'étalon-or pour la détection du CO. Cependant, ces méthodes sont invasives, manquent de sensibilité et ne sont pas rentables. La tomographie par cohérence optique (OCT) est une technique interférométrique qui permet d'obtenir une imagerie 3D de tissus biologiques en haute résolution et en profondeur. Son implémentation endoscopique est très prometteuse pour la détection précoce des CO. Cependant, à ce jour, l'OCT endoscopique n'a jamais atteint les performances requises pour remplacer complètement les protocoles standard de vidéo-endoscopie et biopsies aléatoires. Dans cette thèse doctorale, nous émettons l'hypothèse que la combinaison de l'OCT à des techniques d'imagerie spectroscopique, offrant un sensibilité accrue à la composition moléculaire des échantillons biologiques, pourrait améliorer le pouvoir diagnostique pour la détection précoce du cancer de l'oesophage. Nous présentons tout d'abord une analyse critique de la littérature qui expose le principe de fonctionnement fondamental de l'OCT et de l'imagerie spectroscopique. Nous examinons ensuite les méthodes existantes pour augmenter le contraste de l'OCT, par le biais d'extensions fonctionnelles ou de combinaisons avec d'autres techniques et nous étudions leur compatibilité avec le format endoscopique. Nous présentons la fibre à double gaine (DCF) et les coupleurs de fibre à double gaine (DCFC), des technologies permettant le développement de systèmes multimodaux. De plus, ces technologies fibrées ont un haut potential de miniaturisation et pourraient être adaptées dans des sondes endoscopiques. La fibre DCF possède un coeur monomode (SM) et une gaine interne multimode (MM) qui peuvent chacun transporter un signal optique. L'on peut accéder à ces deux canaux efficacement par le biais d'un DCFC, qui permet de combiner ou séparer les signaux. Dans les systèmes OCT multimodaux à base de DCFC, l'imagerie OCT est réalisée par le coeur tandis que l'imagerie avec la modalité supplémentaire est réalisée pas la gaine interne. Dans la première partie de cette thèse, nous présentons trois systèmes qui combinent l'OCT avec différentes variantes de l'imagerie spectroscopique, en utilisant de la DCF et des DCFC. Ces systèmes sont progressivement de plus en plus compatibles avec l'imagerie dans un milieu clinique. ABSTRACT: Esophageal cancer (EC) is a deadly disease, primarily because of its asymptomatic nature until advanced stages in its development. Currently, white light video-endoscopy combined with random biopsies is the gold standard for the detection of EC. However, such methods are invasive and lack sensitivity and cost-effectiveness. Optical coherence tomography (OCT) is an interferometric technique that allows depth-resolved, high-resolution 3D imaging of biological tissue. Its endoscopic implementation for esophageal imaging has shown great promise for the early detection of EC but has, to this day, always fallen short of the required performance to replace video-endoscopy and biopsies outright. We hypothesize that combining OCT with spectroscopic imaging techniques that provide enhanced sensitivity to the molecular composition may enhance diagnostic performance for early esophageal cancer detection. We first present a critical literature review that outlines the fundamental operating principle of OCT and spectroscopic imaging. We delve into existing methods for expanding OCT contrast through functional extensions or combinations with other techniques and consider their compatibility with endoscopic applications. We present double-clad fiber (DCF) and double-clad fiber couplers (DCFC) as viable candidates for developing fiber-based multimodal systems with the potential for miniaturization into endoscopic devices. DCF possesses a single-mode (SM) core and a multimode (MM) inner-cladding that can each transport complementary optical signals. These two channels may be efficiently accessed through a DCFC, which can combine or separate the signals. In DCF-based multimodal OCT systems, OCT is carried out through the fiber core and the additional modality through the inner cladding. In the first part of this thesis, we present three systems that combine OCT with different implementations of spectroscopic imaging, using DCF and DCFCs and with progressive levels of compatibility with clinical imaging. The first system combines OCT with hyperspectral imaging (HSI) by utilizing an external broadband source to illuminate the sample and collecting the reflected signal through the inner cladding for spectroscopic analysis. This system was the first demonstration of combined OCT and HSI through a single fiber. However, this implementation suffered from low imaging speed and low lateral resolution for HSI. In the second system, we used multiple single-wavelength lasers to perform multispectral imaging (MSI)

Calibration procedure for enhanced mirror artifact removal in full-range optical coherence tomography using passive quadrature demultiplexing

SignificancePassive quadrature demultiplexing allows full-range optical coherence tomography (FR-OCT). However, imperfections in the wavelength- and frequency-response of the demodulation circuits can cause residual mirror artifacts, which hinder high-quality imaging on both sides of zero delay.AimWe aim at achieving high mirror artifact extinction by calibrated postprocessing of the FR-OCT signal.ApproachWe propose a mathematical framework for the origin of the residual mirror peaks as well as a protocol allowing the precise measurement and correction of the associated errors directly from mirror measurements.ResultsWe demonstrate high extinction of the mirror artifact over the entire imaging range, as well as an assessment of the method's robustness to time and experimental conditions. We also provide a detailed description of the practical implementation of the method to ensure optimal reproducibility.ConclusionThe proposed method is simple to implement and produces high mirror artifact extinction. This may encourage the adoption of FR-OCT in clinical and industrial systems or loosen the performance requirements on the optical demodulation circuit, as the imperfections can be handled in postprocessing