1. Articles from martin villiger

    1-24 of 34 1 2 »
    1. Depth-resolved birefringence imaging of collagen fiber organization in the human oral mucosa in vivo

      Depth-resolved birefringence imaging of collagen fiber organization in the human oral mucosa in vivo

      Stromal collagen organization has been identified as a potential prognostic indicator in a variety of cancers and other diseases accompanied by fibrosis. Changes in the connective tissue are increasingly considered for grading dysplasia and progress of oral squamous cell carcinoma, investigated mainly ex vivo by histopathology. In this study, polarization-sensitive optical coherence tomography (PS-OCT) with local phase retardation imaging is used for the first time to visualize depth-resolved (i.e., local) birefringence of healthy human oral mucosa in vivo . Depth-resolved birefringence is shown to reveal the expected local collagen organization. To demonstrate proof-of-principle, 3D image stacks were acquired at labial ...

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    2. Balloon catheter-based radiofrequency ablation monitoring in porcine esophagus using optical coherence tomography

      Balloon catheter-based radiofrequency ablation monitoring in porcine esophagus using optical coherence tomography

      We present a microscopic image guidance platform for radiofrequency ablation (RFA) using a clinical balloon-catheter-based optical coherence tomography (OCT) system, currently used in the surveillance of Barrett’s esophagus patients. Our integrated thermal therapy delivery and monitoring platform consists of a flexible, customized bipolar RFA electrode array designed for use with a clinical balloon OCT catheter and a processing algorithm to accurately map the thermal coagulation process. Non-uniform rotation distortion was corrected using a feature tracking-based technique, which enables robust, frame-to-frame analysis of the temporal fluctuation of the complex OCT signal. With proper noise calibration, precise delineation of the thermal ...

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    3. Robust reconstruction of local optic axis orientation with fiber-based polarization-sensitive optical coherence tomography

      Robust reconstruction of local optic axis orientation with fiber-based polarization-sensitive optical coherence tomography

      It is challenging to recover local optic axis orientation from samples probed with fiber-based polarization-sensitive optical coherence tomography (PS-OCT). In addition to the effect of preceding tissue layers, the transmission through fiber and system elements, and imperfect system alignment, need to be compensated. Here, we present a method to retrieve the required correction factors from measurements with depth-multiplexed PS-OCT, which accurately measures the full Jones matrix. The correction considers both retardation and diattenuation and is applied in the wavenumber domain, preserving the axial resolution of the system. The robustness of the method is validated by measuring a birefringence phantom with ...

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    4. Optic axis mapping with catheter-based polarization-sensitive optical coherence tomography

      Optic axis mapping with catheter-based polarization-sensitive optical coherence tomography

      Birefringence offers an intrinsic contrast mechanism related to the microstructure and arrangement of fibrillary tissue components. Here we present a reconstruction strategy to recover not only the scalar amount of birefringence, but also its optic axis orientation as a function of depth in tissue from measurements with catheter-based polarization-sensitive optical coherence tomography. A polarization symmetry constraint, intrinsic to imaging in the backscatter direction, facilitates the required compensation for wavelength-dependent transmission through the system elements, the rotating catheter, and overlying tissue layers. Applied to the intravascular imaging of coronary atherosclerosis in human patients, the optic axis affords refined interpretation of plaque ...

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    5. Quantitative depolarization measurements for fiber‐based polarization‐sensitive optical frequency domain imaging of the retinal pigment epithelium

      Quantitative depolarization measurements for fiber‐based polarization‐sensitive optical frequency domain imaging of the retinal pigment epithelium

      A full quantitative evaluation of the depolarization of light may serve to assess concentrations of depolarizing particles in the retinal pigment epithelium and to investigate their role in retinal diseases in the human eye. Optical coherence tomography (OCT) and optical frequency domain imaging (OFDI) use spatial incoherent averaging to compute depolarization. Depolarization depends on accurate measurements of the polarization states at the receiver but also on the polarization state incident upon and within the tissue. Neglecting this dependence can result in artifacts and renders depolarization measurements vulnerable to birefringence in the system and in the sample. In this work, we ...

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    6. Robust wavenumber and dispersion calibration for Fourier-domain optical coherence tomography

      Robust wavenumber and dispersion calibration for Fourier-domain optical coherence tomography

      Many Fourier-domain optical coherence tomography (FD-OCT) systems sample the interference fringes with a non-uniform wavenumber ( k ) interval, introducing a chirp to the signal that depends on the path length difference underlying each fringe. A dispersion imbalance between sample and reference arms also generates a chirp in the fringe signal which, in contrast, is independent of depth. Fringe interpolation to obtain a signal linear in k and compensate dispersion imbalance is critical to achieving bandwidth-limited axial resolution. In this work, we propose an optimization-based algorithm to perform robust and automated calibration of FD-OCT systems, recovering both the interpolation function and the ...

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    7. Prediction of scar size in rats six months after burns based on early post injury polarization-sensitive optical frequency domain imaging

      Prediction of scar size in rats six months after burns based on early post injury polarization-sensitive optical frequency domain imaging

      Hypertrophic scars remain a major clinical problem in the rehabilitation of burn survivors and lead to physical, aesthetic, functional, psychological, and social stresses. Prediction of healing outcome and scar formation is critical for deciding on the best treatment plan. Both subjective and objective scales have been devised to assess scar severity. Whereas scales of the first type preclude cross-comparison between observers, those of the second type are based on imaging modalities that either lack the ability to image individual layers of the scar or only provide very limited fields of view. To overcome these deficiencies, this work aimed at developing ...

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    8. Depolarization signatures map gold nanorods within biological tissue

      Depolarization signatures map gold nanorods within biological tissue

      Owing to their electromagnetic properties, tunability and biocompatibility, gold nanorods are being investigated as multifunctional probes for a range of biomedical applications. However, detection beyond the reach of traditional fluorescence and two-photon approaches and quantitation of their concentration in biological tissue remain challenging tasks in microscopy. Here, we show how the size and aspect ratio that impart gold nanorods with their plasmonic properties also make them a source of entropy. We report on how depolarization can be exploited as a strategy to visualize gold nanorod diffusion and distribution in biologically relevant scenarios ex vivo, in vitro and in vivo. We ...

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    9. Intravascular optical coherence tomography [Invited]

      Intravascular optical coherence tomography [Invited]

      Shortly after the first demonstration of optical coherence tomography for imaging the microstructure of the human eye, work began on developing systems and catheters suitable for intravascular imaging in order to diagnose and investigate atherosclerosis and potentially to monitor therapy. This review covers the driving considerations of the clinical application and its constraints, the major engineering milestones that enabled the current, high-performance commercial imaging systems, the key studies that laid the groundwork for image interpretation, and the clinical research that traces intravascular optical coherence tomography (OCT) from early human pilot studies to current clinical trials.

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    10. Extended bandwidth wavelength swept laser source for high resolution optical frequency domain imaging

      Extended bandwidth wavelength swept laser source for high resolution optical frequency domain imaging

      Improving the axial resolution by providing wider bandwidth wavelength swept lasers remains an important issue for optical frequency domain imaging (OFDI). Here, we demonstrate a wide tuning range, all-fiber wavelength swept laser at a center wavelength of 1250 nm by combining two ring cavities that share a single Fabry-Perot tunable filter. The two cavities contain semiconductor optical amplifiers with central wavelengths of 1190 nm and 1292 nm, respectively. To avoid disturbing interference effects in the overlapping spectral region, we modulated the amplifiers in order to obtain consecutive wavelength sweeps in the two spectral regions. The two sweeps were fused together ...

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    11. Optimal selection of laser modulation parameters in photothermal optical coherence tomography

      Optimal selection of laser modulation parameters in photothermal optical coherence tomography

      Photothermal optical coherence tomography (PT-OCT) employs a secondary intensity-modulated photothermal laser to create modulated thermal strains that cause variations of the refractive index in the proximity of absorbing chromophores. These variations are directly detected with phase-sensitive OCT and offer insight to the molecular composition and thermo-elastic properties of the sample. Here, we define optimal PT laser modulation parameters by investigating the effect of PT laser power and modulation frequency on the ensuing thermal waves and thermal waves’ impact on the spatial resolution of PT-OCT imaging based on numerical simulations of PT-OCT and samples containing point absorbers.

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    12. Birefringence microscopy platform for assessing airway smooth muscle structure and function in vivo

      Birefringence microscopy platform for assessing airway smooth muscle structure and function in vivo

      The inability to visualize airway smooth muscle (ASM) cells in vivo is a major obstacle in understanding their role in normal physiology and diseases. At present, there is no imaging modality available to assess ASM in vivo. Confocal endomicroscopy lacks the penetration depth and field of view, and conventional optical coherence tomography (OCT) does not have sufficient contrast to differentiate ASM from surrounding tissues. We have developed a birefringence microscopy platform that leverages the micro-organization of tissue to add further dimension to traditional OCT. We have used this technology to validate ASM measurements in ex vivo swine and canine studies ...

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    13. Automatic classification of atherosclerotic plaques imaged with intravascular OCT

      Automatic classification of atherosclerotic plaques imaged with intravascular OCT

      Intravascular optical coherence tomography (IV-OCT) allows evaluation of atherosclerotic plaques; however, plaque characterization is performed by visual assessment and requires a trained expert for interpretation of the large data sets. Here, we present a novel computational method for automated IV-OCT plaque characterization. This method is based on the modeling of each A-line of an IV-OCT data set as a linear combination of a number of depth profiles. After estimating these depth profiles by means of an alternating least square optimization strategy, they are automatically classified to predefined tissue types based on their morphological characteristics. The performance of our proposed method ...

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    14. Laser thermal therapy monitoring using complex differential variance in optical coherence tomography

      Laser thermal therapy monitoring using complex differential variance in optical coherence tomography

      Conventional thermal therapy monitoring techniques based on temperature are often invasive, limited by point sampling, and are indirect measures of tissue injury, while techniques such as magnetic resonance and ultrasound thermometry are limited by their spatial resolution. The visualization of the thermal coagulation zone at high spatial resolution is particularly critical to the precise delivery of thermal energy to epithelial lesions. In this work, an integrated thulium laser thermal therapy monitoring system was developed based on complex differential variance (CDV), which enables the 2D visualization of the dynamics of the thermal coagulation process at high spatial and temporal resolution with ...

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    15. Deep tissue volume imaging of birefringence through fibre-optic needle probes for the delineation of breast tumour

      Deep tissue volume imaging of birefringence through fibre-optic needle probes for the delineation of breast tumour

      Identifying tumour margins during breast-conserving surgeries is a persistent challenge. We have previously developed miniature needle probes that could enable intraoperative volume imaging with optical coherence tomography. In many situations, however, scattering contrast alone is insufficient to clearly identify and delineate malignant regions. Additional polarization-sensitive measurements provide the means to assess birefringence, which is elevated in oriented collagen fibres and may offer an intrinsic biomarker to differentiate tumour from benign tissue. Here, we performed polarization-sensitive optical coherence tomography through miniature imaging needles and developed an algorithm to efficiently reconstruct images of the depth-resolved tissue birefringence free of artefacts. First ex ...

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    16. Feature of the Week 03/26/2016: Longitudinal, 3D Imaging of Collagen Remodeling in Murine Hypertrophic Scars In Vivo Using Polarization-Sensitive Optical Frequency Domain Imaging

      Feature of the Week 03/26/2016: Longitudinal, 3D Imaging of Collagen Remodeling in Murine Hypertrophic Scars In Vivo Using Polarization-Sensitive Optical Frequency Domain Imaging

      This work is the result of the collaboration between the Center for Biomedical OCT Research and Translation, Center for Engineering in Medicine at Massachusetts General Hospital (MGH) and Shriners Burn Hospital, Division of Plastic and Reconstructive Surgery at MGH, and Program in Dermatopathology at Brigham and Women’s Hospital. The goal of this study is to develop a noninvasive, label-free technique for monitoring scars over time to facilitate studies of scar etiology and treatment. In fact, hypertrophic scars (HTS) are very commonly seen after traumatic injuries and surgery, especially in burn victims. HTS remain a major clinical challenge because of ...

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

      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 ...

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    18. Longitudinal, 3D Imaging of Collagen Remodeling in Murine Hypertrophic Scars In Vivo Using Polarization-Sensitive Optical Frequency Domain Imaging

      Longitudinal, 3D Imaging of Collagen Remodeling in Murine Hypertrophic Scars In Vivo Using Polarization-Sensitive Optical Frequency Domain Imaging

      Hypertrophic scars (HTS), frequently seen after traumatic injuries and surgery, remain a major clinical challenge because of the limited success of existing therapies. A significant obstacle to understanding HTS etiology is the lack of tools to monitor scar remodeling longitudinally and noninvasively. We present an in vivo, label-free technique using polarization-sensitive optical frequency domain imaging for the 3D, longitudinal assessment of collagen remodeling in murine HTS. In this study, HTS was induced with a mechanical tension device for 4–10 days on incisional wounds and imaged up to 1 month after device removal; an excisional HTS model was also imaged ...

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    19. Ultrahigh-resolution optical coherence elastography

      Ultrahigh-resolution optical coherence elastography

      Visualizing stiffness within the local tissue environment at the cellular and subcellular level promises to provide insight into the genesis and progression of disease. In this Letter, we propose ultrahigh-resolution optical coherence elastography (UHROCE), and demonstrate 3D imaging of local axial strain of tissues undergoing compressive loading. We combine optical coherence microscopy (OCM) and phase-sensitive detection of local tissue displacement to produce strain elastograms with resolution (

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    20. Degree of polarization (uniformity) and depolarization index: unambiguous depolarization contrast for optical coherence tomography

      Degree of polarization (uniformity) and depolarization index: unambiguous depolarization contrast for optical coherence tomography

      The degree of polarization (uniformity) has attracted increased interest as a functional contrast in optical coherence tomography (OCT). However, its computation from a single polarization state suggests an ambiguity that is strongly dependent on a sample’s orientation. We here propose an improved metric to present depolarization with respect to the optical system rather than the propagating field. Using numerical simulations and optical frequency domain imaging, we evaluate the conventional DOP(U) for different polarization states and compare its performance with the unambiguous depolarization index.

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    21. Functional optical coherent imaging

      Functional optical coherent imaging

      The present invention relates to a functional optical coherent imaging (fOCI) platform comprising at least one active camera unit (ACU) comprising a coherent and/or a partially coherent light source, and means for spectral filtering and imaging a selected body area of interest; an image processing unit (IPU) for pre-processing data received from an ACU; at least one stimulation unit (STU) transmitting a stimulation to a subject; at least one body function reference measurement unit (BFMU); a central clock and processing unit (CCU), with interconnections to the ACU, the IPU, the STU, for collecting pre-processed data from the IPU, stimuli ...

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    22. Feature Of The Week 5/10/2015: Laser Tissue Coagulation and Concurrent Optical Coherence Tomography Through a Double-Clad Fiber Coupler

      Feature Of The Week 5/10/2015: Laser Tissue Coagulation and Concurrent Optical Coherence Tomography Through a Double-Clad Fiber Coupler

      This work is the result of a collaboration between researchers from Professor Caroline Boudoux’s team from Polytechnique Montréal (Canada) and Professor Brett E. Bouma’s team at the Wellman Center for Photomedicine (MGH, Boston). The goal is to assess whether OCT-guided biopsy could benefit from the use of double-clad fiber (DCF). 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 used for laser marking. DCF is herein used in conjunction with a double-clad fiber coupler (DCFC) to enable simultaneous and ...

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    23. Single input state, single-mode fiber-based polarization-sensitive optical frequency domain imaging by eigenpolarization referencing

      Single input state, single-mode fiber-based polarization-sensitive optical frequency domain imaging by eigenpolarization referencing

      Fiber-based polarization-sensitive optical frequency domain imaging is more challenging than free-space implementations. Using multiple input states, fiber-based systems provide sample birefringence information with the benefit of a flexible sample arm but come at the cost of increased system and acquisition complexity, and either reduce acquisition speed or require increased acquisition bandwidth. Here we show that with the calibration of a single polarization state, fiber-based configurations can approach the conceptual simplicity of traditional free-space configurations. We remotely control the polarization state of the light incident at the sample using the eigenpolarization states of a wave plate as a reference, and determine ...

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

      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 ...

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    1-24 of 34 1 2 »
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    1. (34 articles) Martin L. Villiger
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    DUAL BEAM HETERODYNE FOURIER DOMAIN OPTICAL COHERENCE TOMOGRAPHY (WO 2008/087613) Image formation and tomogram reconstruction in optical coherence microscopy Frequency domain multiplexing for speckle reduction in optical coherence tomography Fast three-dimensional imaging of gold nanoparticles in living cells with photothermal optical lock-in Optical Coherence Microscopy Label-Free Imaging of Cerebral β-Amyloidosis with Extended-Focus Optical Coherence Microscopy Single input state, single-mode fiber-based polarization-sensitive optical frequency domain imaging by eigenpolarization referencing Feature Of The Week 5/10/2015: Laser Tissue Coagulation and Concurrent Optical Coherence Tomography Through a Double-Clad Fiber Coupler Longitudinal, 3D Imaging of Collagen Remodeling in Murine Hypertrophic Scars In Vivo Using Polarization-Sensitive Optical Frequency Domain Imaging Feature of the Week 03/26/2016: Longitudinal, 3D Imaging of Collagen Remodeling in Murine Hypertrophic Scars In Vivo Using Polarization-Sensitive Optical Frequency Domain Imaging Deep tissue volume imaging of birefringence through fibre-optic needle probes for the delineation of breast tumour Perimeter Medical Imaging Closes Oversubscribed $C4.4M Financing Time-domain optical coherence tomography system based on moving-optical-wedge interferometer