1. Articles from Andreas Wartak

    1-25 of 25
    1. Optical design, optimization and validation of an extended-depth-of-field optical coherence tomography probe based on mirror-tunneling

      Optical design, optimization and validation of an extended-depth-of-field optical coherence tomography probe based on mirror-tunneling

      We present results from optimizing mirror-tunnel based optical coherence tomography probes, achieving extended depth of field at high resolution. We achieved 6 µm spot diameter over 1 mm depth in simulations and validated experimentally.

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    2. Advances in Imaging of Subbasal Corneal Nerves With Micro–Optical Coherence Tomography

      Advances in Imaging of Subbasal Corneal Nerves With Micro–Optical Coherence Tomography

      Purpose: To investigate the most peripheral corneal nerve plexus using high-resolution micro-optical coherence tomography (µOCT) imaging and to assess µOCT's clinical potential as a screening tool for corneal and systemic diseases. Methods: An experimental high-resolution (1.5 × 1.5 × 1 µm) µOCT setup was applied for three-dimensional imaging of the subbasal nerve plexus in nonhuman primates (NHPs) and swine within 3 hours postmortem. Morphologic features of subbasal nerves in µOCT were compared to β3 tubulin-stained fluorescence confocal microscopy (FCM). Parameters such as nerve density, nerve distribution, and imaging repeatability were evaluated, using semiautomatic image analysis in form of a ...

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    3. Dual-modality optical coherence tomography and fluorescence tethered capsule endomicroscopy

      Dual-modality optical coherence tomography and fluorescence tethered capsule endomicroscopy

      OCT tethered capsule endomicroscopy (TCE) is an emerging noninvasive diagnostic imaging technology for gastrointestinal (GI) tract disorders. OCT measures tissue reflectivity that provides morphologic image contrast, and thus is incapable of ascertaining molecular information that can be useful for improving diagnostic accuracy. Here, we introduce an extension to OCT TCE that includes a fluorescence (FL) imaging channel for attaining complementary, co-registered molecular contrast. We present the development of an OCT-FL TCE capsule and a portable, plug-and-play OCT-FL imaging system. The technology is validated in phantom experiments and feasibility is demonstrated in a methylene blue (MB)-stained swine esophageal injury model ...

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    4. Modeling, optimization, and validation of an extended-depth-of-field optical coherence tomography probe based on a mirror tunnel

      Modeling, optimization, and validation of an extended-depth-of-field optical coherence tomography probe based on a mirror tunnel

      The diagnostic capability of high-resolution optical coherence tomography (OCT) may be enhanced by using extended depth-of-field (EDOF) imaging that retains high transverse resolution over long depths. A recently developed mirror-tunnel optical probe design (single-mode fiber to multimode fiber to lens structure) that generates coaxially focused modes has been previously shown to enable EDOF for endoscopic OCT applications. Here, we present ray-tracing optical modeling of this optical configuration, which has the potential to guide performance improvement through optimization. The Huygens wave propagation of the field was traced through probe components with initial lengths. The irradiance along the

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    5. Micro-optical coherence tomography for high-resolution morphologic imaging of cellular and nerval corneal micro-structures

      Micro-optical coherence tomography for high-resolution morphologic imaging of cellular and nerval corneal micro-structures

      We demonstrate the highest resolution (1.5×1.5×1 µm) micrometer optical coherence tomography (µOCT) imaging of the morphologic micro-structure of excised swine and non-human primate corneas. Besides epithelial, stromal, and endothelial cell morphology, this report focuses on investigating the most peripheral corneal nerve fibers, the nerve fibers of the subbasal plexus (SBP). Alterations of SBP nerve density and composition are reportedly linked to major neurologic disorders, such as diabetic neuropathy, potentially indicating earliest onsets of denervation. Here, the fine, hyperreflective, epithelial nerve structures located just above Bowman’s membrane, are i) visualized using our µOCT prototype, ii) validated ...

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    6. Corneal optical density in Fuchs endothelial dystrophy determined by anterior segment optical coherence tomography

      Corneal optical density in Fuchs endothelial dystrophy determined by anterior segment optical coherence tomography

      Purpose: In this study, we propose a method to grade corneal stromal opacity using optical density measurements by anterior segment optical coherence tomography (AS-OCT) and validate the approach in Fuchs endothelial corneal dystrophy (FECD). Methods: A retrospective analysis of human corneal OCT scans was performed on 48 eyes of 32 patients with FECD and 33 control eyes of 21 patients using the Carl Zeiss Cirrus HD-OCT 5000. In addition, corneal edema in fresh rabbit cadaver eyes was artificially induced by distilled water and imaged with the Thorlabs TELESTO-II spectral domain OCT at different time points during saturation. The increase of ...

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    7. Stromal Nerve Imaging and Tracking Using Micro-Optical Coherence Tomography

      Stromal Nerve Imaging and Tracking Using Micro-Optical Coherence Tomography

      urpose : To image, track and map the nerve fiber distribution in excised rabbit corneas over the entire stromal thickness using micro-optical coherence tomography (µOCT) to develop a screening tool for early peripheral neuropathy. Methods : Excised rabbit corneas were consecutively imaged by a custom-designed µOCT prototype and a commercial laser scanning fluorescence confocal microscope. The µOCT images with a field of view of approximately 1 × 1 mm were recorded with axial and transverse resolutions of approximately 1 µm and approximately 4 µm, respectively. In the volumetric µOCT image data, network maps of hyper-reflective, branched structures traversing different stromal compartments were segmented ...

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    8. Investigating spontaneous retinal venous pulsation using Doppler optical coherence tomography

      Investigating spontaneous retinal venous pulsation using Doppler optical coherence tomography

      We demonstrate the advantages of optical coherence tomography (OCT) imaging for investigation of spontaneous retinal venous pulsation (SRVP). The pulsatile changes in venous vessel caliber are analyzed qualitatively and quantitatively using conventional intensity-based OCT as well as the functional extension Doppler OCT (DOCT). Single-channel and double-channel line scanning protocols of our multi-channel OCT prototype are employed to investigate venous pulsatile caliber oscillations as well as venous flow pulsatility in the eyes of healthy volunteers. A comparison to recordings of scanning laser ophthalmoscopy (SLO) – a standard en-face imaging modality for evaluation of SRVP – is provided, emphasizing the advantages of tomographic image ...

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    9. Synthetic subaperture-based angle-independent Doppler flow measurements using single-beam line field optical coherence tomography in vivo

      Synthetic subaperture-based angle-independent Doppler flow measurements using single-beam line field optical coherence tomography in vivo

      We demonstrate a synthetic subaperture-based angle-independent Doppler flow calculation, using a line field spectral domain optical coherence tomography system. The high speed of the system features a high phase stability over the volume, which is necessary to apply synthetic subapertures in the aperture plane. Thus, the flow component for each subaperture can be reconstructed in postprocessing. Capillary phantom and in vivo retinal imaging experiments were performed to validate and demonstrate angle-independent Doppler flow calculation

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    10. Mapping of Corneal Layer Thicknesses With Polarization-Sensitive Optical Coherence Tomography Using a Conical Scan Pattern

      Mapping of Corneal Layer Thicknesses With Polarization-Sensitive Optical Coherence Tomography Using a Conical Scan Pattern

      Purpose : We demonstrate segmentation and mapping of corneal layers (epithelium, Bowman's layer, and stroma) across the entire cornea (limbus to limbus), using additional contrast provided by polarization-sensitive optical coherence tomography (PS-OCT) and analyze the reproducibility of the procedure. Methods : A custom built PS-OCT system operating at 1045 nm central wavelength with conical scanning was used for image acquisition. Conical scanning allows for almost perpendicular beam incidence on the corneal surface and provides good signal quality over the entire field of view. Epithelium, Bowman's layer, and stroma were segmented using the additional contrast provided by PS-OCT. Thickness maps were ...

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    11. Feature Of The Week 07/01/2018: Endoscopic Optical Coherence Tomography with a Flexible Fiber Bundle

      Feature Of The Week 07/01/2018: Endoscopic Optical Coherence Tomography with a Flexible Fiber Bundle

      We demonstrate in vivo endoscopic optical coherence tomography (OCT) imaging in the forward direction using a flexible fiber bundle (FB). In comparison to current conventional forward-looking probe schemes, our approach simplifies the endoscope design by avoiding the integration of any beam steering components in the distal probe end due to two-dimensional scanning of a focused light beam over the proximal FB surface. We describe the challenges that arise when OCT imaging with an FB is performed, such as multimoding or cross coupling. The performance of different FBs varying in parameters, such as numerical aperture, core size, core structure, and flexibility ...

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    12. Endoscopic optical coherence tomography with a flexible fiber bundle

      Endoscopic optical coherence tomography with a flexible fiber bundle

      We demonstrate in vivo endoscopic optical coherence tomography (OCT) imaging in the forward direction using a flexible fiber bundle (FB). In comparison to current conventional forward-looking probe schemes, our approach simplifies the endoscope design by avoiding the integration of any beam steering components in the distal probe end due to two-dimensional scanning of a focused light beam over the proximal FB surface. We describe the challenges that arise when OCT imaging with an FB is performed, such as multimoding or cross coupling. The performance of different FBs varying in parameters, such as numerical aperture, core size, core structure, and flexibility ...

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    13. Beyond backscattering: optical neuroimaging by BRAD

      Beyond backscattering: optical neuroimaging by BRAD

      Optical coherence tomography (OCT) is a powerful technology for rapid volumetric imaging in biomedicine. The bright field imaging approach of conventional OCT systems is based on the detection of directly backscattered light, thereby waiving the wealth of information contained in the angular scattering distribution. Here we demonstrate that the unique features of few-mode fibers (FMF) enable simultaneous bright and dark field (BRAD) imaging for OCT. As backscattered light is picked up by the different modes of a FMF depending upon the angular scattering pattern, we obtain access to the directional scattering signatures of different tissues by decoupling illumination and detection ...

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    14. Adaptable switching schemes for time-encoded multichannel optical coherence tomography

      Adaptable switching schemes for time-encoded multichannel optical coherence tomography

      We introduce the approach of variable time encoding for multichannel optical coherence tomography (OCT). High-speed fiber optical switches are applied for sequential sample arm switching to enable quasisimultaneous image acquisition from three different orientation angles. In comparison with previous multichannel OCT (using simultaneous sample illumination), time-encoded multichannel OCT has no need for division of illumination power among the respective channels to satisfy laser safety requirements. Especially for ophthalmic applications—in particular retinal imaging, which the presented prototype was developed for—this advantage strongly influences image quality through an enhanced sensitivity. Nevertheless, time encoding comes at the cost of a decrease ...

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    15. Compact akinetic swept source optical coherence tomography angiography at 1060 nm supporting a wide field of view and adaptive optics imaging modes of the posterior eye

      Compact akinetic swept source optical coherence tomography angiography at 1060 nm supporting a wide field of view and adaptive optics imaging modes of the posterior eye

      Imaging of the human retina with high resolution is an essential step towards improved diagnosis and treatment control. In this paper, we introduce a compact, clinically user-friendly instrument based on swept source optical coherence tomography (SS-OCT). A key feature of the system is the realization of two different operation modes. The first operation mode is similar to conventional OCT imaging and provides large field of view (FoV) images (up to 45° × 30°) of the human retina and choroid with standard resolution. The second operation mode enables it to optically zoom into regions of interest with high transverse resolution using adaptive ...

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    16. Large field of view adaptive optics scanning laser ophthalmoscopy and optical coherence tomography

      Large field of view adaptive optics scanning laser ophthalmoscopy and optical coherence tomography

      Adaptive Optics (AO) retinal imaging is revealing microscopic structures of the eye in a non-invasive way. Due to anisoplanatism, conventional AO systems are efficient on small 1°x1° field of view (FoV). We present a lens-based AO scanning laser ophthalmoscope (SLO) set-up with 2 deformable mirrors (DM), providing high-resolution retinal imaging on a 4°x4° FoV, for an eye pupil diameter of 7 mm. The first DM is in a pupil plane and is driven using a Shack-Hartmann (SH). The second DM is conjugated to a plane located 0.7 mm in front of the retina, to correct for aberrations ...

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    17. Endoscopic optical coherence tomography with a flexible fiber bundle

      Endoscopic optical coherence tomography with a flexible fiber bundle

      We demonstrate in vivo endoscopic optical coherence tomography (OCT) imaging in the forward direction using a flexible fiber bundle. In comparison to current conventional forward looking probe schemes, our approach simplifies the endoscope design by avoiding the integration of any beam steering components in the distal probe end due to 2D scanning of a focused light beam over the proximal fiber bundle surface. We describe the challenges that arise when OCT imaging with a fiber bundle is performed, such as multimoding or cross-coupling. The performance of different fiber bundles with varying parameters such as numerical aperture, core size and core ...

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    18. Multi-channel optical coherence tomography for retinal imaging (Thesis)

      Multi-channel optical coherence tomography for retinal imaging  (Thesis)

      Optical coherence tomography (OCT) is a three-dimensional imaging modality using the interferometric principle to probe transparent or translucent samples non-invasively, at high-speed and with high resolution. Conventional OCT instruments employ a single imaging channel to obtain real-time cross-sectional images of micrometer scale resolution in vivo. However, the addition of supplementary imaging channels proved successful for a variety of OCT sub-modalities or extensions. Ophthalmology, and in particular retinal imaging, rapidly evolved into OCTs most distinguished medical field of application. Since its introduction in the early 1990s, ophthalmic disease detection and monitoring of treatment response both experienced a revolutionary surge of advancement ...

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    19. Beyond backscattering: Optical neuroimaging by BRAD

      Beyond backscattering: Optical neuroimaging by BRAD

      Optical coherence tomography (OCT) is a powerful technology for rapid volumetric imaging in biomedicine. The bright field imaging approach of conventional OCT systems is based on the detection of directly backscattered light, thereby waiving the wealth of information contained in the angular scattering distribution. Here we demonstrate that the unique features of few-mode fibers (FMF) enable simultaneous bright and dark field (BRAD) imaging for OCT. As backscattered light is picked up by the different modes of a FMF depending upon the angular scattering pattern, we obtain access to the directional scattering signatures of different tissues by decoupling illumination and detection ...

      Read Full Article
    20. Multi-directional optical coherence tomography for retinal imaging

      Multi-directional optical coherence tomography for retinal imaging

      We introduce multi-directional optical coherence tomography (OCT), a technique for investigation of the scattering properties of directionally reflective tissue samples. By combining the concepts of multi-channel and directional OCT, this approach enables simultaneous acquisition of multiple reflectivity depth-scans probing a mutual sample location from differing angular orientations. The application of multi-directional OCT in retinal imaging allows for in-depth investigations on the directional reflectivity of the retinal nerve fiber layer, Henle’s fiber layer and the photoreceptor layer. Major ophthalmic diseases (such as glaucoma or age-related macular degeneration) have been reported to alter the directional reflectivity properties of these retinal layers ...

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    21. Conical scan pattern for enhanced visualization of the human cornea using polarization-sensitive OCT

      Conical scan pattern for enhanced visualization of the human cornea using polarization-sensitive OCT

      Conventional imaging of the human cornea with optical coherence tomography (OCT) relies on telecentric scanning optics with sampling beams that are parallel to the optical axis of the eye. Because of the shape of the cornea, the beams have in some areas considerable inclination to the corneal surface which is accompanied by low signal intensities in these areas and thus an inhomogeneous appearance of corneal structures. In addition, alterations in the polarization state of the probing light depend on the angle between the imaging beam and the birefringent axis of the sample. Therefore, changes in the polarization state observed with ...

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    22. Active-passive path-length encoded (APPLE) Doppler OCT

      Active-passive path-length encoded (APPLE) Doppler OCT

      We present a novel active-passive path-length encoded (APPLE) swept source Doppler optical coherence tomography (DOCT) approach, enabling three-dimensional velocity vector reconstruction of moving particles without prior knowledge of the orientation of motion. The developed APPLE DOCT setup allows for non-invasive blood flow measurements in vivo and was primarily designed for quantitative human ocular blood flow investigations. The system’s performance was demonstrated by in vitro flow phantom as well as in vivo retinal vessel bifurcation measurements. Furthermore, total retinal blood flow – a biomarker aiding in diagnosis and monitoring of major ocular diseases such as glaucoma, diabetic retinopathy or central/branch ...

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    23. Depth encoded three-beam swept source Doppler optical coherence tomography

      Depth encoded three-beam swept source Doppler optical coherence tomography

      A novel approach for investigation of human retinal and choroidal blood flow by the means of multi-channel swept source Doppler optical coherence tomography (SS-D-OCT) system is being developed. We present preliminary in vitro measurement results for quantification of the 3D velocity vector of scatterers in a flow phantom. The absolute flow velocity of moving scatterers can be obtained without prior knowledge of flow orientation. In contrast to previous spectral domain (SD-) D-OCT investigations, that already proved the three-channel D-OCT approach to be suitable for in vivo retinal blood flow evaluation, this current work aims for a similar functional approach by ...

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    24. Total retinal blood flow and reproducibility evaluation by three beam optical Doppler tomography

      Total retinal blood flow and reproducibility evaluation by three beam optical Doppler tomography

      We present a three beam optical Doppler tomography (ODT) technique suitable for 3-D velocity and flow measurements to evaluate total retinal blood circulation from and to the optic nerve head (ONH). The system consists of three independent ODT channels. Superluminescent diodes with a central wavelength of 840 nm and a spectral bandwidth of 50 nm were used. The sources are coupled to collimators resting in a specially designed mount to ensure a well-defined beam geometry, necessary for the full reconstruction of the three dimensional velocity vector. The reconstruction works without prior knowledge on the vessel geometry, which is normally required ...

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    25. Total retinal blood flow measurement by three beam Doppler optical coherence tomography

      Total retinal blood flow measurement by three beam Doppler optical coherence tomography

      We present measurements of total retinal blood flow in healthy volunteers using a three beam Doppler optical coherence tomography (D-OCT) technique. This technology has the advantage of a precise determination of the flow vector without the use of any a-priori information on the vessel geometry. Circular D-OCT scans around the optic disc were recorded and venous as well as arterial total blood flow was determined and compared for each subject. The reproducibility of the method was assessed in 6 subjects by repeated measurements. Only small deviations of around 6% between the measurements were found which indicates the high precision of ...

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    1-25 of 25
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    Total retinal blood flow measurement by three beam Doppler optical coherence tomography Total retinal blood flow and reproducibility evaluation by three beam optical Doppler tomography Conical scan pattern for enhanced visualization of the human cornea using polarization-sensitive OCT Multi-directional optical coherence tomography for retinal imaging Beyond backscattering: Optical neuroimaging by BRAD Endoscopic optical coherence tomography with a flexible fiber bundle Compact akinetic swept source optical coherence tomography angiography at 1060 nm supporting a wide field of view and adaptive optics imaging modes of the posterior eye Adaptable switching schemes for time-encoded multichannel optical coherence tomography Endoscopic optical coherence tomography with a flexible fiber bundle Feature Of The Week 07/01/2018: Endoscopic Optical Coherence Tomography with a Flexible Fiber Bundle The truth about invisible posterior vitreous structures Increased Macrophage-like Cell Density in Retinal Vein Occlusion as Characterized by en Face Optical Coherence Tomography