1. Articles from Dierck Hillmann

    1-20 of 20
    1. OCT on a chip aims at high-quality retinal imaging

      OCT on a chip aims at high-quality retinal imaging

      Optical coherence tomography (OCT) has become one of the most important techniques in ophthalmic diagnostics, as it is the only way to three-dimensionally visualize morphological changes in the layered structure of the retina at a high resolution. In addition, OCT is applied for countless medical and technical purposes. Recent developments pave the way for small-footprint OCT systems at significantly reduced costs, thereby extending possible use cases. Now, it appears increasingly likely that, in the near future, OCT will find its way into many more industrial and medical applications, including disease monitoring at home. Currently, ophthalmologic clinics and doctor’s offices ...

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    2. Determination and correction of aberrations in full field OCT using phase gradient autofocus by maximizing the likelihood function

      Determination and correction of aberrations in full field OCT using phase gradient autofocus by maximizing the likelihood function

      A method for numerical estimation and correction of aberrations of the eye in fundus imaging with optical coherence tomography (OCT) is presented. Aberrations are determined statistically by using the estimate based on likelihood function maximization. The method can be considered as an extension of the phase gradient autofocusing algorithm in synthetic aperture radar imaging to 2D optical aberration correction. The efficacy of the proposed method has been demonstrated in OCT fundus imaging with 6λ aberrations. After correction, single photoreceptors were resolved. It is also shown that wavefront distortions with high spatial frequencies can be determined and corrected.

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    3. 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 optics—in 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 apertures, we improved aberration correction. Since these modifications only slightly increase the run time of the correction, we believe this method can become the algorithm of choice for many ...

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    4. 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 and axial motion are explained. It is shown that speckle tracking and multi-aperture Doppler OCT are equally affected by the artifact, which has a considerable effect, even for a defocus ...

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    5. 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 demonstrated. Our implementation of full-field optical coherence tomography combines a low technical complexity with the possibility for computational image correction.

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    6. 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 to different computational subapertures. These are used to calculate all three components of the motion vector with interferometric precision. As known from conventional Doppler OCT for axial motion only, the ...

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    7. 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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    8. 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 first give a short overview of recent advances in techniques and applications of parallelized OCT and finally present an iterative and statistical algorithm that estimates and corrects motion-induced phase errors ...

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    9. In-vivo retinal imaging with off-axis full-field time-domain optical coherence tomography

      In-vivo retinal imaging with off-axis full-field time-domain optical coherence tomography

      With a simple setup, mainly composed of a low coherence light source and a camera, full-field optical coherence tomography (FF-OCT) allows volumetric tissue imaging. However, fringe washout constrains its use in retinal imaging. Here, we present a novel motion-insensitive approach to FF-OCT, which introduces path-length differences between the reference and the sample light in neighboring pixels using an off-axis reference beam. The temporal carrier frequency in scanned time-domain OCT is replaced by a spatial carrier frequency. Volumetric in-vivo FF-OCT measurements of the human retina were acquired in only 1.3 s, comparable to the acquisition times of current clinically used ...

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    10. Feature Of The Week 10/25/2015: Imaging Pulse Wave Propagation in Human Retina using Full-Field Swept-Source OCT

      Feature Of The Week 10/25/2015: Imaging Pulse Wave Propagation in Human Retina using Full-Field Swept-Source OCT

      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 the frequency-dependent pulse propagation through the capillary bed, are determined. For the first time, imaging speed and motion sensitivity are sufficient for a direct measurement of pulse waves propagating with ...

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    11. 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 the frequency-dependent pulse propagation through the capillary bed, are determined. For the first time, imaging speed and motion sensitivity are sufficient for a direct measurement of pulse waves propagating with ...

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    12. Efficient holoscopy image reconstruction

      Efficient holoscopy image reconstruction

      Holoscopy is a tomographic imaging technique that combines digital holography and Fourier-domain optical coherence tomography (OCT) to gain tomograms with diffraction limited resolution and uniform sensitivity over several Rayleigh lengths. The lateral image information is calculated from the spatial interference pattern formed by light scattered from the sample and a reference beam. The depth information is obtained from the spectral dependence of the recorded digital holograms. Numerous digital holograms are acquired at different wavelengths and then reconstructed for a common plane in the sample. Afterwards standard Fourier-domain OCT signal processing achieves depth discrimination. Here we describe and demonstrate an optimized ...

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      Mentions: Thorlabs
    13. Common approach for compensation of axial motion artifacts in swept-source OCT and dispersion in Fourier-domain OCT

      Common approach for compensation of axial motion artifacts in swept-source OCT and dispersion in Fourier-domain OCT

      Swept-source optical coherence tomography (SS-OCT) is sensitive to sample motion during the wavelength sweep, which leads to image blurring and image artifacts. In line-field and full-field SS-OCT parallelization is achieved by using a line or area detector, respectively. Thus, approximately 1000 lines or images at different wavenumbers are acquired. The sweep duration is identically with the acquisition time of a complete B-scan or volume, rendering parallel SS-OCT more sensitive to motion artifacts than scanning OCT. The effect of axial motion on the measured spectra is similar to the effect of non-balanced group velocity dispersion (GVD) in the interferometer arms. It ...

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    14. Holoscopy—holographic optical coherence tomography

      Holoscopy—holographic optical coherence tomography
      Scanning optical coherence tomography (OCT) is limited in sensitivity and resolution by the restricted focal depth of the confocal detection scheme. Holoscopy, a combination of holography and Fourier-domain full-field OCT, is proposed as a way to detect photons from all depths of a sample volume simultaneously with uniform sensitivity and lateral resolution, even at high NAs. By using the scalar diffraction theory, as frequently applied in digital holographic imaging, we fully reconstruct the object field with depth-invariant imaging quality. In vivo imaging of human skin is demonstrated with an image quality comparable to conventionally scanned OCT.
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    15. Real-time volumetric optical coherence tomography OCT imaging with a surgical microscope

      Real-time volumetric optical coherence tomography OCT imaging with a surgical microscope
      Optical coherence tomography is a unique technique to visualize subsurface tissue structures with a resolution below 10μm during microsurgery without tissue contact. Since it was introduced more than 15 years ago imaging speed was boosted by more than three orders of magnitude, from less than 100 to more than 300,000 A-scans per second. Instead of taking only still images of anatomical structures, the increased speed of OCT allows now to image volumes nearly in real time. This enables not only the scanning of larger tissue surfaces, but also opens new application beyond simple diagnosis. A noncontact volumetric imaging with ...
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    16. Optical coherence tomography with online visualization of more than seven rendered volumes per second

      Optical coherence tomography with online visualization of more than seven rendered volumes per second
      Nearly real-time visualization of 3-D volumes is crucial for the use of optical coherence tomography (OCT) during microsurgery. With an ultrahigh speed spectral domain OCT coupled to a surgical microscope, on-line display of 7.2 rendered volumes at 87 megapixels per second is demonstrated. Calculating the A-scans from the spectra is done on a quad-core personal computer (PC), while dedicated software for the 3-D rendering is executed on a high performance video card. Imaging speed is practically only limited by the readout of the camera. First experiments show the feasibility of real-time 3-D OCT for guided interventions.
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    1-20 of 20
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  2. Topics in the News

    1. (15 articles) University of Lübeck
    2. (11 articles) Thorlabs
    3. (1 articles) Institute of Applied Physics
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    Optical coherence tomography with online visualization of more than seven rendered volumes per second Real-time volumetric optical coherence tomography OCT imaging with a surgical microscope Holoscopy: holographic optical coherence tomography Holoscopy—holographic optical coherence tomography Common approach for compensation of axial motion artifacts in swept-source OCT and dispersion in Fourier-domain OCT 3D OPTICAL IMAGING: Holoscopy makes ultrafast lensless imaging of scattering tissues possible Efficient holoscopy image reconstruction Method For Optical Tomography Imaging pulse wave propagation in human retinal vessels using full-field swept-source optical coherence tomography Feature Of The Week 10/25/2015: Imaging Pulse Wave Propagation in Human Retina using Full-Field Swept-Source OCT Post-Doctoral and Graduate Student Research Positions at the University of Illinois Urbana-Champaign Multiscale correlation of microvascular changes on optical coherence tomography angiography with retinal sensitivity in diabetic retinopathy