1. Articles from Andreas Wartak

    1-16 of 16
    1. 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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    2. 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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    3. 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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    4. 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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    5. 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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    6. 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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    7. 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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    8. 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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    9. 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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    10. 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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    11. 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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    12. 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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    13. 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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    14. 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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    15. 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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    16. 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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    1-16 of 16
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  2. Topics in the News

    1. (16 articles) Medical University of Vienna
    2. (10 articles) Michael Pircher
    3. (10 articles) Christoph K. Hitzenberger
    4. (9 articles) Bernhard Baumann
    5. (5 articles) Rainer A. Leitgeb
    6. (4 articles) Lara M. Wurster
    7. (3 articles) Abhishek Kumar
    8. (1 articles) Harvard University
    9. (1 articles) Massachusetts General Hospital
    10. (1 articles) Antonia Lichtenegger
    11. (1 articles) University of Tsukuba
    12. (1 articles) Federal University of Pernambuco
    13. (1 articles) University of Rochester
    14. (1 articles) Jannick P. Rolland
    15. (1 articles) Cláudia Cristina Brainer Oliveira Mota
    16. (1 articles) Anderson S. L. Gomes
    17. (1 articles) Yoshiaki Yasuno
    18. (1 articles) Bioptigen
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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 Depth encoded three-beam swept source Doppler optical coherence tomography Conical scan pattern for enhanced visualization of the human cornea using polarization-sensitive OCT 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 Remineralizing Potential of Nano-Silver-Fluoride for Tooth Enamel: An Optical Coherence Tomography Analysis Clinical Features and Multi-Modality Imaging of Isolated Retinal Astrocytic Hamartoma