1. Articles from Bernd Hofer

    1-24 of 31 1 2 »
    1. Non-Invasive Detection of Early Retinal Neuronal Degeneration by Ultrahigh Resolution Optical Coherence Tomography

      Non-Invasive Detection of Early Retinal Neuronal Degeneration by Ultrahigh Resolution Optical Coherence Tomography

      Optical coherence tomography (OCT) has revolutionises the diagnosis of retinal disease based on the detection of microscopic rather than subcellular changes in retinal anatomy. However, currently the technique is limited to the detection of microscopic rather than subcellular changes in retinal anatomy. However, coherence based imaging is extremely sensitive to both changes in optical contrast and cellular events at the micrometer scale, and can generate subtle changes in the spectral content of the OCT image. Here we test the hypothesis that OCT image speckle (image texture) contains information regarding otherwise unresolvable features such as organelle changes arising in the early ...

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    2. Measurement of Tear Film Thickness Using Ultrahigh Resolution Optical Coherence Tomography

      Measurement of Tear Film Thickness Using Ultrahigh Resolution Optical Coherence Tomography

      Purpose: To visualize the pre-corneal tear film with high resolution spectral domain optical coherence tomography, enabling quantification of tear film thickness in healthy subjects. Methods: A custom built spectral domain optical coherence tomography system comprising a broad band Ti:Sapphire laser operating at 800 nm and a high speed CCD camera with a read out rate of 47 kHz was used for measurement of pre-corneal tear film thickness. The system provides an axial resolution of 1.2 µm in tissue. A total of 26 healthy subjects were included in this study. Measurement was started immediately after blinking and averaged over ...

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    3. Graphics processing unit-based dispersion encoded full-range frequency-domain optical coherence tomography

      Graphics processing unit-based dispersion encoded full-range frequency-domain optical coherence tomography

      Dispersion encoded full-range (DEFR) frequency-domain optical coherence tomography (FD-OCT) and its enhanced version, fast DEFR, utilize dispersion mismatch between sample and reference arm to eliminate the ambiguity in OCT signals caused by non-complex valued spectral measurement, thereby numerically doubling the usable information content. By iteratively suppressing asymmetrically dispersed complex conjugate artifacts of OCT-signal pulses the complex valued signal can be recovered without additional measurements, thus doubling the spatial signal range to cover the full positive and negative sampling range. Previously the computational complexity and low processing speed limited application of DEFR to smaller amounts of data and did not allow ...

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    4. Graphics processing unit based dispersion encoded full-range frequency domain OCT

      Graphics processing unit based dispersion encoded full-range frequency domain OCT

      Standard FD-OCT systems suffer from a limited useful depth range due to the inherent complex conjugate artifacts and continuous fall-off in sensitivity with distance from the zero delay. The techniques of dispersion encoded full range (DEFR) frequency-domain optical coherence tomography (FD-OCT) and its enhanced version fast DEFR use the dispersion mismatch between sample and reference arm to double the imaging depth range by iteratively suppressing complex conjugate artifacts. Previously the computational complexity of DEFR prevented its application to fields where real-time visualization or large volumetric datasets are needed. A graphics processing unit (GPU) with hundreds of processing cores provides highly ...

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    5. 3D optical coherence tomography for clinical diagnosis of nonmelanoma skin cancers

      3D optical coherence tomography for clinical diagnosis of nonmelanoma skin cancers

      High-resolution frequency domain optical coherence tomography (OCT) stands out amongst a range of novel dermatologic imaging technologies, with its good detection sensitivity around -100 dB, high measurement speeds allowing real-time image acquisition and its ability to acquire high definition cross-sectional and 3D tomograms of regions greater than 1 cm2, providing tissue information comparable to conventional histopathology without the need for any contrast agents. Typical axial and transverse resolutions of state-of-the-art OCT systems range between 1–10 µm and approximately 20 µm, respectively, depending on the employed wavelength region. This review investigates the significant progress accomplished in the field of dermatologic ...

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    6. Mapping Choroidal and Retinal Thickness Variation in Type 2 Diabetes using Three-Dimensional 1060-nm Optical Coherence Tomography

      Mapping Choroidal and Retinal Thickness Variation in Type 2 Diabetes using Three-Dimensional 1060-nm Optical Coherence Tomography
      Purpose. To map choroidal (ChT) and retinal thickness (RT) in healthy subjects and patients with diabetes with and without maculopathy using three dimensional 1060-nm optical coherence tomography (3D-1060nm-OCT). Methods. Sixty-three eyes from 42 diabetic subjects (41–82 years of age; 11 females) grouped according to a custom scheme using Early Treatment Diabetic Retinopathy Study definitions for pathology within 1 disc-diameter of fovea (without pathology [NDR], microaneurysms [M1], exudates [M2], clinically significant macular edema [CSME]) and 16 eyes from 16 healthy age matched subjects (38–79 years of age; 11 females) were imaged by 3D-1060nm-OCT performed over a 36° × 36° field ...
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    7. Multimodal photoacoustic and optical coherence tomography scanner using an all optical detection scheme for 3D morphological skin imaging

      Multimodal photoacoustic and optical coherence tomography scanner using an all optical detection scheme for 3D morphological skin imaging

      A noninvasive, multimodal photoacoustic and optical coherence tomography (PAT/OCT) scanner for three-dimensional in vivo (3D) skin imaging is described. The system employs an integrated, all optical detection scheme for both modalities in backward mode utilizing a shared 2D optical scanner with a field-of-view of ~13 × 13 mm2. The photoacoustic waves were detected using a Fabry Perot polymer film ultrasound sensor placed on the surface of the skin. The sensor is transparent in the spectral range 590-1200 nm. This permits the photoacoustic excitation beam (670-680 nm) and the OCT probe beam (1050 nm) to be transmitted through the sensor head ...

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    8. Heritability of ocular component dimensions in mice phenotyped using depth-enhanced swept source optical coherence tomography

      Heritability of ocular component dimensions in mice phenotyped using depth-enhanced swept source optical coherence tomography
      The range of genetic and genomic resources available makes the mouse a powerful model for the genetic dissection of complex traits. Because accurate, high-throughput phenotypic characterisation is crucial to the success of such endeavours, we recently developed an optical coherence tomography (OCT) system with extended depth range scanning capability for measuring ocular component dimensions in mice. In order to test whether the accuracy and reproducibility of our OCT system was sufficient for gene mapping studies, we carried out an experiment designed to estimate the heritability of mouse ocular component dimensions. High-resolution, two dimensional tomograms were obtained for both eyes of ...
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    9. Artefact reduction for cell migration visualization using spectral domain optical coherence tomography

      Artefact reduction for cell migration visualization using spectral domain optical coherence tomography
      Visualization of cell migration during chemotaxis using spectral domain optical coherence tomography (OCT) requires non-standard processing techniques. Stripe artefacts and camera noise floor present in OCT data prevent detailed computer-assisted reconstruction and quantification of cell locomotion. Furthermore, imaging artefacts lead to unreliable results in automated texture based cell analysis. Here we characterize three pronounced artefacts that become visible when imaging sample structures with high dynamic range, e.g. cultured cells: (i) time-varying fixed-pattern noise; (ii) stripe artefacts generated by background estimation using tomogram averaging; (iii) image modulations due to spectral shaping. We evaluate techniques to minimize the above mentioned artefacts ...
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    10. Three-Dimensional 1060-nm OCT: Choroidal Thickness Maps in Normal Subjects and Improved Posterior Segment Visualization in Cataract Patients

      Three-Dimensional 1060-nm OCT: Choroidal Thickness Maps in Normal Subjects and Improved Posterior Segment Visualization in Cataract Patients
      Purpose. To evaluate the performance and potential clinical role of three-dimensional (3D) 1060-nm OCT by generating choroidal thickness (ChT) maps in patients of different ages with different degrees of ametropia and axial lengths and to investigate the effect of cataract grade on OCT retinal imaging quality. Methods. Axial lengths (ALs) and 45° fundus photographs were acquired from 64 eyes (34 healthy subjects, 19 to 80 years, ametropia +3 to –10 D). 3D 1060-nm OCT was performed over a 36° x 36° field of view with 7-µm axial resolution and up to 70 frames/s (512 A-scans/frame). ChT maps between ...
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    11. Highly reproducible swept-source, dispersion-encoded full-range biometry and imaging of the mouse eye

      Highly reproducible swept-source, dispersion-encoded full-range biometry and imaging of the mouse eye
      We report a high-speed, dispersion-encoded, full-range (DEFR) swept-source optical coherence tomography system for in vivo ocular imaging and biometry of small animals. The fast DEFR algorithm removes the depth ambiguity, gives access to objects located at the zero delay position, and doubles the sampling depth to 2×5.0 mm (at −101 to −71 dB sensitivity) in a single scan using 2048 samples/depth scan 0.43 nm line width of a light source operating at 1056 nm with 70 nm tuning range. The acquisition speed (frames of 512 depth scans in 18.3 ms) permits precise on-line monitoring during ...
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    12. Robust segmentation of intraretinal layers in the normal human fovea using a novel statistical model based on texture and shape analysis

      Robust segmentation of intraretinal layers in the normal human fovea using a novel statistical model based on texture and shape analysis
      A novel statistical model based on texture and shape for fully automatic intraretinal layer segmentation of normal retinal tomograms obtained by a commercial 800nm optical coherence tomography (OCT) system is developed. While existing algorithms often fail dramatically due to strong speckle noise, non-optimal imaging conditions, shadows and other artefacts, the novel algorithm’s accuracy only slowly deteriorates when progressively increasing segmentation task difficulty. Evaluation against a large set of manual segmentations shows unprecedented robustness, even in the presence of additional strong speckle noise, with dynamic range tested down to 12dB, enabling segmentation of almost all intraretinal layers in cases previously ...
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    13. In Vivo, In Situ Imaging of Microneedle Insertion into the Skin of Human Volunteers Using Optical Coherence Tomography

      In Vivo, In Situ Imaging of Microneedle Insertion into the Skin of Human Volunteers Using Optical Coherence Tomography

      Purpose  To gather sub-surface in situ images of microneedle-treated human skin, in vivo, using optical coherence tomography (OCT). This is the first study to utilise OCT to investigate the architectural changes that are induced in skin following microneedle application. Methods  Steel, silicon and polymer microneedle devices, with different microneedle arrangements and morphologies, were applied to two anatomical sites in human volunteers following appropriate ethical approval. A state-of-the-art ultrahigh resolution OCT imaging system operating at 800 nm wavelength and <3 µm effective axial resolution was used to visualise the microneedle-treated area during insertion and/or following removal of the device, without ...

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    14. Three-dimensional 1060nm OCT: Choroidal thickness maps in normals and improved posterior segment visualization in cataract patients

      Three-dimensional 1060nm OCT: Choroidal thickness maps in normals and improved posterior segment visualization in cataract patients
      Purpose. To evaluate the performance and potential clinical role of 3D-1060nm-OCT by generating choroidal thickness (ChT) maps in patients of different age, ametropia and axial lengths and to investigate the effect of cataract grade on OCT retinal imaging quality. Methods. Axial lengths (AL) and 45° fundus photographs were acquired from 64 eyes (34 healthy subjects, 19-80 years, ametropia +3 to -10D). 3D-1060nm-OCT was performed over 36°x36° field of view with ~7µm axial resolution and up to 70 frames/second (512 A-scans/frame). ChT-maps between retinal pigment epithelium and the choroidal/scleral-interface, were generated and statistically analyzed. A further thirty ...
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    15. Multispectral in vivo three-dimensional optical coherence tomography of human skin

      Multispectral in vivo three-dimensional optical coherence tomography of human skin

      The capability of optical coherence tomography (OCT) to perform “optical biopsy” of tissues within a depth range of 1 to 2 mm with micron-scale resolution in real time makes it a promising biomedical imaging modality for dermatologic applications. Three high-speed, spectrometer-based frequency-domain OCT systems operating at 800 nm (20,000 A-scans/s), 1060 nm, and 1300 nm (both 47,000 A-scans/s) at comparable signal-to-noise ratio (SNR), SNR roll-off with scanning depth, and transverse resolution (<15 μm) were used to acquire 3-D tomograms of glabrous and hairy human skin in vivo. Images obtained using these three systems were compared in ...

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    16. Fast dispersion encoded full range optical coherence tomography for retinal imaging at 800 nm and 1060 nm

      Fast dispersion encoded full range optical coherence tomography for retinal imaging at 800 nm and 1060 nm

      The dispersion mismatch between sample and reference arm in frequency-domain optical coherence tomography (OCT) can be used to iteratively suppress complex conjugate artifacts and thereby increase the imaging range. In this paper, we propose a fast dispersion encoded full range (DEFR) algorithm that detects multiple signal components per iteration. The influence of different dispersion levels on the reconstruction quality is analyzed experimentally using a multilayered scattering phantom and in vivo retinal tomograms at 800 nm. Best results have been achieved with 30 mm SF11, with neglectable resolution decrease due to finite resolution of the spectrometer. Our fast DEFR algorithm achieves ...

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    17. Multimodal simultaneous photoacoustic tomography, optical resolution microscopy, and OCT system

      Multimodal simultaneous photoacoustic tomography, optical resolution microscopy, and OCT system

      A novel combined photoacoustic tomography (PAT), optical resolution photoacoustic microscopy (ORPAM) and optical coherence tomography (OCT) instrument has been developed for imaging biological tissues. The system is based on the use of a Fabry-Perot (FP) polymer film ultrasound sensor. This is designed to be transparent to wavelengths between 590nm and 1200nm so that photoacoustic excitation laser pulses in this spectral range can be transmitted through the sensor into the underlying tissue to allow backward mode operation. The dual PAT-ORPAM capability of the system was demonstrated by imaging a tissue phantom composed of 7µm diameter carbon fibres immersed in an ...

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    18. Mutant and wild type cell chemotaxis in 3D and 4D with ultrahigh- resolution optical coherence tomography

      Mutant and wild type cell chemotaxis in 3D and 4D with ultrahigh- resolution optical coherence tomography

      Conventionally, cell chemotaxis is studied on two-dimensional (2D) transparent surfaces due to limitations in optical and image data-collection techniques. However, substrates which more closely mimic the natural environment of cells are often opaque or three-dimensional (3D). The non-invasive label-free imaging technique of frequency domain optical coherence tomography (OCT) has high axial and transverse resolution of >4µm, comparatively high penetration depth and the ability to acquire volumes in a few seconds, therefore offering the potential to visualize moving cells in 3D (2D+time) and 4D (3D+time). Cell migration is demonstrated in 3D on opaque surfaces, and in 4D within ...

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    19. Method For Image Range Extension In Optical Coherence Tomography (Wo 2010/007025)

      Method For Image Range Extension In Optical Coherence Tomography (Wo 2010/007025)
      A method of generating a tomogram of a sample (18) wherein an analysis beam (Ed) is subject to dispersion distortion, the method comprising: a) detecting the analysis beam (Ed) b) generating a signal (s) representative of the intensity of wavelengths in the analysis beam (Ed); c) generating (46, 48) a first spatial domain signal (S) representative of the signal (s) so generated; d) detecting (50) a desired signal component of the first spatial domain signal (S) and outputting (70) the desired signal component for use in generating a depth scan which can be used to create a line of the ...
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    20. Spectroscopic measurements with dispersion encoded full range frequency domain optical coherence tomography in single- and multilayered weakly scattering phantoms

      Spectroscopic measurements with dispersion encoded full range frequency domain optical coherence tomography in single- and multilayered weakly scattering phantoms
      In this study, depth resolved measurements of absorption profiles in the wavelength range of 800 nm with a bandwidth of 140 nm are demonstrated using high speed spectroscopic frequency domain OCT(SOCT) and a full range reconstruction algorithm (dispersion encoded full range, DEFR). The feasibility of the algorithm for SOCT is tested in simulation and experiment. With proper calibration, SOCT with DEFR is able to extract absolute, depth resolved absorption profiles over the whole wavelength range at once without the need of tuning and performing measurements at single wavelengths sequentially. The superior acquisition speed and better phase stability in frequency ...
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    21. Adaptive optics optical coherence tomography at 120,000 depth scans/s for non-invasive cellular phenotyping of the living human retina

      Adaptive optics optical coherence tomography at 120,000 depth scans/s for non-invasive cellular phenotyping of the living human retina

      This paper presents a successful combination of ultra-high speed (120,000 depth scans/s), ultra-high resolution optical coherence tomography with adaptive optics and an achromatizing lens for compensation of monochromatic and longitudinal chromatic ocular aberrations, respectively, allowing for non-invasive volumetric imaging in normal and pathologic human retinas at cellular resolution. The capability of this imaging system is demonstrated here through preliminary studies by probing cellular intraretinal structures that have not been accessible so far with in vivo, noninvasive, label-free imaging techniques, including pigment epithelial cells, micro-vasculature of the choriocapillaris, single nerve fibre bundles and collagenous plates of the lamina cribrosa ...

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    22. Techniques for extraction of depth-resolved in vivo human retinal intrinsic optical signals with optical coherence tomography

      Purpose To demonstrate acquisition and analysis methods for depth-resolved observation of slow retinal physiology induced changes in infrared backscatter in vivo. Methods A dark-adapted human was briefly subjected to a localized photobleach. For 20 min before and 30 min after the stimulus, volumetric optical coherence tomograms were collected partially overlapping the bleached region. Tomograms were segmented into retinal layers by a newly described algorithm exploiting information in adjacent B-scans. En face fundus images extracted from major intraretinal layers were laterally registered manually. Time series summarizing the observed backscatter in selected layers for the bleached and unbleached areas are shown with ...
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    23. Three- and four-dimensional visualization of cell migration using optical coherence tomography

      Conventionally, cell chemotaxis is studied on two-dimensional (2D) transparent surfaces, due to limitations in optical and image data-collection techniques. However, surfaces that more closely mimic the natural environment of cells are often opaque. Optical coherence tomography (OCT) is a noninvasive label-free imaging technique, which offers the potential to visualize moving cells on opaque surfaces and in three dimensions (3D). Here, we demonstrate that OCT is an effective means of time-lapse videomicroscopy of Dictyostelium cells undergoing 3D (2D+time) cell migration on nitrocellulose substrates and 4D (3D+time) chemotaxis within low-density agarose gels. The generated image sequences are compatible with current ...

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    24. Wide-Field Optical Coherence Tomography of the Choroid In Vivo

      PURPOSE. To demonstrate high-speed, high axial resolution optical coherence tomography (OCT) at 1060 nm with penetration to the sclera. The clinical feasibility of dense, high-speed sampling for higher levels of detail at the macula and optic nerve head is explored with respect to motion artifacts. METHODS. A three-dimensional (3D) OCT system making use of a high-speed camera operating at 47,000 depth scans/s was developed. The 1010- to 1080-nm wavelength band leads to 6.7 µm effective axial resolution and enables the acquisition of retinal and choroidal 130 Megavoxel volumes of human subjects within 7 seconds. Motion artifacts were ...
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    1-24 of 31 1 2 »
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    1. (31 articles) Bernd M. Hofer
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    3. (28 articles) Cardiff University
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    Spectroscopic measurements with dispersion encoded full range frequency domain optical coherence tomography in single- and multilayered weakly scattering phantoms Multimodal simultaneous photoacoustic tomography, optical resolution microscopy, and OCT system Fast dispersion encoded full range optical coherence tomography for retinal imaging at 800 nm and 1060 nm Multispectral in vivo three-dimensional optical coherence tomography of human skin In Vivo, In Situ Imaging of Microneedle Insertion into the Skin of Human Volunteers Using Optical Coherence Tomography Robust segmentation of intraretinal layers in the normal human fovea using a novel statistical model based on texture and shape analysis Highly reproducible swept-source, dispersion-encoded full-range biometry and imaging of the mouse eye Three-Dimensional 1060-nm OCT: Choroidal Thickness Maps in Normal Subjects and Improved Posterior Segment Visualization in Cataract Patients AI-Assisted In Situ Detection of Human Glioma Infiltration Using a Novel Computational Method for Optical Coherence Tomography Motorized capsule for shadow-free OCT imaging and synchronous beam control Notal Vision Diagnostic Clinic reports completion of 6 million ForeseeHome AMD home-monitoring tests Monitoring retinal responses to acute intraocular pressure elevation in rats with visible light optical coherence tomography