SignificanceEsophageal cancer is becoming increasingly prevalent in Western countries. Early detection is crucial for effective treatment. Multimodal imaging combining optical coherence tomography (OCT) with complementary optical imaging techniques may provide enhanced diagnostic capabilities by simultaneously assessing tissue morphology and biochemical content.AimWe aim to develop a tethered capsule endoscope (TCE) that can accommodate a variety of point-scanning techniques in addition to OCT without requiring design iterations on the optical or mechanical design.ApproachWe propose a TCE utilizing exclusively reflective optics to focus and steer light from and to a double-clad fiber. Specifically, we use an ellipsoidal mirror to achieve finite conjugation between the fiber tip and the imaging plane.ResultsWe demonstrate a functional all-reflective TCE. We first detail the design, fabrication, and assembly steps required to obtain such a device. We then characterize its performance and demonstrate combined OCT at 1300 nm and visible spectroscopic imaging in the 500- to 700-nm range. Finally, we discuss the advantages and limitations of the proposed design.ConclusionsAn all-reflective TCE is feasible and allows for achromatic high-quality imaging. Such a device could be utilized as a platform for testing various combinations of modalities to identify the optimal candidates without requiring design iterations.
Single fiber reflectance spectroscopy can measure tissue optical properties and analyze physiological state. However, the standard implementation of SFR comprises several sources of instabilities that are typically not accounted for. These are fiber modal content, instabilities in the illumination spectrum, and bend losses. These instabilities lead to reduced reproducibility and reliability. We propose a new SFR system design with dynamic correction of source fluctuations and bend losses. Furthermore, we replace the traditional bifurcated fiber with a wideband multimode circulator for improved light transmission and reduced modal sensitivity. We demonstrate the enhanced stability in a one-to-one comparison with a standard system.
We demonstrate an all-reflective tethered capsule endoscope (RTCE) utilizing double-clad fiber and reflective optics for achromatic multimodal imaging of the esophagus. This device uses a custom ellipsoidal mirror to focus the light from the fiber tip onto the sample. In this work, we first describe key design parameters and highlight important assembly steps. We then demonstrate several data processing/analysis methods for signal multiplexing, rotation stabilization, and image analysis. Finally, we demonstrate the implementation of the capsule by performing combined OCT and spectral imaging in ex-vivo biological samples.
We demonstrate a tethered capsule endoscope (TCE), which uses double-clad fiber and reflective optics for multimodal imaging in the esophagus without undesirable chromatic effects, such as focal shifts or back-reflections. We use a single, custom ellipsoidal mirror to focus the light from the fiber tip onto the sample. We describe the mechanical and optical designs and the fabrication and assembly protocols necessary for optimal performance. We demonstrate the implementation of the capsule by performing combined optical coherence tomography and spectral imaging in ex-vivo esophagus.
KEYWORDS: Mirrors, Calibration, Colorimetry, Optical coherence tomography, Range imaging, Demodulation, Signal attenuation, Optical coherence, Signal to noise ratio, Signal analyzers
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.
In its standard implementation, OCT suffers from the well-known “mirror artifact” around the zero-delay plane. Full-range OCT enables imaging on both sides of zero-delay by measuring the interference signal’s in-phase and quadrature components. These signals can be accessed passively using polarization demultiplexing or optical hybrids. However, such optical systems present imperfections, including chromatic and RF variations in phase and amplitude, which result in residual mirror artifacts. In this work, we propose a calibration methodology that relies solely on simple mirror measurements to correct the imperfections of the demultiplexing system and achieve high extinction of the mirror artifacts.
We present a bi-modal bench-top system combining OCT with broadband, single-fiber reflectance spectroscopy. This combination aims to address the limited molecular sensitivity of standard OCT imaging in order to obtain co-registered morphological and molecular information. We present various technical innovations for this work, including an all-reflective scanner head with adaptive optic components for focus scanning and reduction of field curvature. Furthermore, we demonstrate the use of specialty fiber components to obtain multiple illumination schemes for the spectroscopic channel and enhance the spatially resolved reconstruction of optical properties.
We present here an all-fiber Few-Mode OCT system making use of a modally specific photonic lantern to simultaneously de-multiplex light exciting the first two propagation modes of a few-mode fiber. Each mode collects a distinct projection of the scattering phase function from light backscattered by the sample. This implementation is mechanically more robust, has an optimal interferometric contrast and is compatible with commercially available OCT systems. We present a proof-of-concept through the imaging of micro-beads generating varying contrast depending on their relative size. Such a system offers an additional means of intrinsic contrast for OCT.
We present a system combining optical coherence tomography (OCT) and multispectral imaging (MSI) for coregistered structural imaging and surface color imaging. We first describe and numerically validate an optimization model to guide the selection of the MSI wavelengths and their relative intensities. We then demonstrate the integration of this model into an all-fiber bench-top system. We implement frequency-domain multiplexing for the MSI to enable concurrent acquisition of both OCT and MSI at OCT acquisition rates. Such a system could be implemented in endoscopic practices to provide multimodal, high-resolution imaging of deep organ structures that are currently inaccessible to standard video endoscopes.
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.
Previous works have demonstrated feasibility of combining optical coherence tomography (OCT) and hyper-spectral imaging (HSI) through a single double-clad fiber (DCF). In this proceeding we present the continued development of a system combining both modalities and capable of rapid imaging. We discuss the development of a rapidly scanning, dual-band, polygonal swept-source system which combines NIR (1260-1340 nm) and visible (450-800 nm) wavelengths. The NIR band is used for OCT imaging while visible light allows HSI. Scanning rates up to 24 kHz are reported. Furthermore, we present and discuss the fiber system used for light transport, delivery and collection, and the custom signal acquisition software. Key points include the use of a double-clad fiber coupler as well as important alignments and back-reflection management. Simultaneous and co-registered imaging with both modalities is presented in a bench-top system
In this proceeding we demonstrate a system combining optical coherence tomography (OCT) and hyper-spectral imaging (HSI) into a single dual-clad fiber (DCF). Combining these modalities gives access to the sample morphology through OCT and to its molecular content through HSI. Both modalities have their illumination through the fiber core. The OCT is then collected through the core while the HSI is collected through the inner cladding of the DCF. A double-clad fiber coupler (DCFC) is used to address both channels separately. A scanning spectral filter was developed to successively inject narrow spectral bands of visible light into the fiber core and sweep across the entire visible spectrum. This allows for rapid HSI acquisition and high miniaturization potential.
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.
This proceedings shows the combination of Optical Coherence Tomography (OCT) and Hyper-Spectral Imaging
(HSI) using a double-clad optical fiber. The single mode core of the fiber is used to transmit OCT signals,
while the cladding, with its large collection area, provides an efficient way to capture the reflectance spectrum
of the sample. The combination of both methods enables three-dimensional acquisition of sample morphology
with OCT, enhanced by the molecular information contained in its hyper-spectral image. We believe that the
combination of these techniques could result in endoscopes with enhanced tissue identification capability.
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