1. Hendrik Spahr

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    1. Mentioned In 8 Articles

    2. Computational adaptive optics for optical coherence tomography using multiple randomized subaperture correlations

      Computational adaptive optics for optical coherence tomography using multiple randomized subaperture correlations
      Computational adaptive optics (CAO) is emerging as a viable alternative to hardware-based adaptive opticsin particular when applied to optical coherence tomography of the retina. For this technique, algorithms are required that detect wavefront errors precisely and quickly. Here we propose an extension of the frequently used subaperture image correlation. By applying this algorithm iteratively and, more importantly, comparing each subaperture not to the central subaperture but to several randomly selected ...
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    3. Artifacts in speckle tracking and multi-aperture Doppler OCT imaging of lateral motion

      Artifacts in speckle tracking and multi-aperture Doppler OCT imaging of lateral motion
      In optical coherence tomography (OCT), lateral motion is determined either by speckle tracking or by multi-aperture Doppler OCT. Here we show that both methods may provide incorrect results because, outside the focal plane, non-uniform axial motion is misinterpreted as lateral motion. First, we demonstrate the existence of this artifact by means of a simulation for speckle tracking. Then the physical origin of the artifact and its mathematical relation to defocus ...
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    4. Simple approach for aberration-corrected OCT imaging of the human retina

      Simple approach for aberration-corrected OCT imaging of the human retina
      Aberration-corrected imaging of human photoreceptor cells, whether hardware or software based, presently requires a complex and expensive setup. Here we use a simple and inexpensive off-axis full-field time-domain optical coherence tomography (OCT) approach to acquire volumetric data of an in vivo human retina. Full volumetric data are recorded in 1.3 s. After computationally correcting for aberrations, single photoreceptor cells were visualized. In addition, the numerical correction of ametropia is ...
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    5. Interferometric detection of 3D motion using computational subapertures in optical coherence tomography

      Interferometric detection of 3D motion using computational subapertures in optical coherence tomography
      Doppler optical coherence tomography (OCT) quantifies axial motion with high precision, whereas lateral motion cannot be detected by a mere evaluation of phase changes. This problem was solved by the introduction of three-beam Doppler OCT, which, however, entails a high experimental effort. Here, we present the numerical analogue to this experimental approach. Phase-stable complex-valued OCT datasets, recorded with full-field swept-source OCT, are filtered in the Fourier domain to limit imaging ...
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    6. Retinal pulse wave velocity measurement using spectral-domain optical coherence tomography

      Retinal pulse wave velocity measurement using spectral-domain optical coherence tomography
      In their latest publication on retinal pulse wave velocity measurement using optical co-herence tomography (OCT), Qian Li et al. propose a method to determine the pulse wave velocity in retinal arteries and veins [1]. This should enable a non-invasive determination of biomechanical properties of the vessel network, particularly the elasticity of the vessel walls [2].
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    7. Reduction of frame rate in full-field swept-source optical coherence tomography by numerical motion correction [Invited]

      Reduction of frame rate in full-field swept-source optical coherence tomography by numerical motion correction [Invited]
      Full-field swept-source optical coherence tomography (FF-SS-OCT) was recently shown to allow new and exciting applications for imaging the human eye that were previously not possible using current scanning OCT systems. However, especially when using cameras that do not acquire data with hundreds of kHz frame rate, uncorrected phase errors due to axial motion of the eye lead to a drastic loss in image quality of the reconstructed volumes. Here we ...
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    8. Imaging pulse wave propagation in human retinal vessels using full-field swept-source optical coherence tomography

      Imaging pulse wave propagation in human retinal vessels using full-field swept-source optical coherence tomography
      We demonstrate a new noninvasive method to assess biomechanical properties of the retinal vascular system. Phase-sensitive full-field swept-source optical coherence tomography (PhS-FF-SS-OCT) is used to investigate retinal vascular dynamics at unprecedented temporal resolution. The motion of retinal tissue that is induced by expansion of the vessels therein is measured with an accuracy of about 10 nm. The pulse shapes of arterial and venous pulsations, their temporal delays, as well as ...
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  2. About Hendrik Spahr

    Hendrik Spahr

    Hendrik Spahr is with the Institute of Biomedical Optics, University of Lübeck, Germany and the Medical Laser Center Lübeck GmbH, Lübeck, Germany.