1. Articles from Koenraad A. Vermeer

    1-15 of 15
    1. Parafoveal Microvascular Alterations in Ocular and Non-Ocular Behҫet's Disease Evaluated With Optical Coherence Tomography Angiography

      Parafoveal Microvascular Alterations in Ocular and Non-Ocular Behҫet's Disease Evaluated With Optical Coherence Tomography Angiography

      Purpose: To compare quantitative optical coherence tomography angiography (OCT-A) measurements of the parafoveal microvasculature in retinal capillary plexuses among Behҫet uveitis (BU) patients, non-ocular Behҫet's disease (NOBD) patients, and healthy volunteers (HVs). Methods: Sixty-eight subjects were enrolled in this prospective observational cross-sectional study. OCT-A imaging was performed using the Heidelberg Engineering Spectralis OCT. A custom algorithm was developed to calculate the vessel density (VD) in three retinal vascular layers: deep capillary plexus, intermediate capillary plexus, and superficial vascular plexus. The foveal avascular zone (FAZ) and acircularity index were calculated for the whole retinal vascular complex. Results: We analyzed one ...

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    2. Intra- and Intergrader Agreement for Detection of OCT Angiographic Characteristics Associated With Type 3 Neovascularization

      Intra- and Intergrader Agreement for Detection of OCT Angiographic Characteristics Associated With Type 3 Neovascularization

      Purpose: To examine the intra- and intergrader agreement on morphologic characteristics of type 3 neovascularization on optical coherence tomography angiography (OCT-A). Methods: OCT-A images of 22 eyes from 21 patients with a new-onset, treatment-naive type 3 neovascularization were included in this cross-sectional retrospective agreement study. Each image was graded three times by two independent medical retina specialists to assess intra- and intergrader agreement. The graders scored the presence or absence of the following vascular and structural features: intraretinal neovascularization (IRN), subretinal neovascularization, sub-retinal pigment epithelium (RPE) neovascularization (SRPEN), retinal choroidal anastomosis (RCA), intraretinal cysts, subretinal fluid, and pigment epithelial detachment ...

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    3. Analysis of attenuation coefficient estimation in Fourier-domain OCT of semi-infinite media

      Analysis of attenuation coefficient estimation in Fourier-domain OCT of semi-infinite media

      The attenuation coefficient (AC) is an optical property of tissue that can be estimated from optical coherence tomography (OCT) data. In this paper, we aim to estimate the AC accurately by compensating for the shape of the focused beam. For this, we propose a method to estimate the axial PSF model parameters and AC by fitting a model for an OCT signal in a homogenous sample to the recorded OCT signal. In addition, we employ numerical analysis to obtain the theoretical optimal precision of the estimated parameters for different experimental setups. Finally, the method is applied to OCT B-scans obtained ...

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    4. Detailed optical coherence tomography angiographic short‐term response of type 3 neovascularization to combined treatment with photodynamic therapy and intravitreal bevacizumab

      Detailed optical coherence tomography angiographic short‐term response of type 3 neovascularization to combined treatment with photodynamic therapy and intravitreal bevacizumab

      Purpose To explore the short‐term vascular and structural changes of type 3 neovascularization using optical coherence tomography angiography (OCT‐A) when treated with a combination of photodynamic therapy (PDT) and intravitreal bevacizumab (IVB), and to evaluate the course of different sequences of the combined therapies. Methods Thirty eyes of 29 treatment‐naïve patients with a type 3 neovascularization were included in this prospective observational cohort study. They were all treated with PDT and IVB 2 weeks apart, starting either with PDT (PDT‐first group) or IVB (IVB‐first group). Optical coherence tomography angiography (OCT‐A) imaging was performed ...

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    5. Classification and treatment follow-up of a juxtapapillary retinal hemangioblastoma with optical coherence tomography angiography

      Classification and treatment follow-up of a juxtapapillary retinal hemangioblastoma with optical coherence tomography angiography

      Purpose Only an endophytic growth pattern in juxtapapillary retinal hemangioblastoma (JRH) is an indication for surgical treatment, but classification of growth types is difficult using conventional imaging techniques. This case report describes the use of optical coherence tomography angiography (OCT-A) features for classification and treatment follow-up in a case with JRH. Observations The JRH of this patient was easily detected with two different OCT-A methods in both en-face and cross-sectional B-scan images, and was classified as a sessile growth type. This growth type excluded the treatment option of vitreoretinal surgery with excision of the lesion or ligation of the feeder ...

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    6. Joint Segmentation of Retinal Layers and Focal Lesions in 3-D OCT Data of Topologically Disrupted Retinas

      Joint Segmentation of Retinal Layers and Focal Lesions in 3-D OCT Data of Topologically Disrupted Retinas

      Accurate quantification of retinal structures in 3-D optical coherence tomography data of eyes with pathologies provides clinically relevant information. We present an approach to jointly segment retinal layers and lesions in eyes with topology-disrupting retinal diseases by a loosely coupled level set framework. In the new approach, lesions are modeled as an additional space-variant layer delineated by auxiliary interfaces. Furthermore, the segmentation of interfaces is steered by local differences in the signal between adjacent retinal layers, thereby allowing the approach to handle local intensity variations. The accuracy of the proposed method of both layer and lesion segmentation has been evaluated ...

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    7. Automatic estimation of retinal nerve fiber bundle orientation in SD-OCT images using a structure-oriented smoothing filter

      Automatic estimation of retinal nerve fiber bundle orientation in SD-OCT images using a structure-oriented smoothing filter

      Optical coherence tomography (OCT) yields high-resolution, three-dimensional images of the retina. A better understanding of retinal nerve fiber bundle (RNFB) trajectories in combination with visual field data may be used for future diagnosis and monitoring of glaucoma. However, manual tracing of these bundles is a tedious task. In this work, we present an automatic technique to estimate the orientation of RNFBs from volumetric OCT scans. Our method consists of several steps, starting from automatic segmentation of the RNFL. Then, a stack of en face images around the posterior nerve fiber layer interface was extracted. The image showing the best visibility ...

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    8. Loosely coupled level sets for simultaneous 3D retinal layer segmentation in optical coherence tomography

      Loosely coupled level sets for simultaneous 3D retinal layer segmentation in optical coherence tomography

      Optical coherence tomography (OCT) yields high-resolution, three-dimensional images of the retina. Reliable segmentation of the retinal layers is necessary for the extraction of clinically useful information. We present a novel segmentation method that operates on attenuation coefficients and incorporates anatomical knowledge about the retina. The attenuation coefficients are derived from in-vivo human retinal OCT data and represent an optical property of the tissue. Then, the layers in the retina are simultaneously segmented via a new flexible coupling approach that exploits the predefined order of the layers. The accuracy of the method was evaluated on 20 peripapillary scans of healthy subjects ...

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    9. Fiber-based polarization-sensitive OCT of the human retina with correction of system polarization distortions

      Fiber-based polarization-sensitive OCT of the human retina with correction of system polarization distortions

      In polarization-sensitive optical coherence tomography (PS-OCT) the use of single-mode fibers causes unpredictable polarization distortions which can result in increased noise levels and erroneous changes in calculated polarization parameters. In the current paper this problem is addressed by a new Jones matrix analysis method that measures and corrects system polarization distortions as a function of wavenumber by spectral analysis of the sample surface polarization state and deeper located birefringent tissue structures. This method was implemented on a passive-component depth-multiplexed swept-source PS-OCT system at 1040 nm which was theoretically modeled using Jones matrix calculus. High-resolution B-scan images are presented of the ...

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    10. Angiography of the retina and the choroid with phase-resolved OCT using interval-optimized backstitched B-scans

      Angiography of the retina and the choroid with phase-resolved OCT using interval-optimized backstitched B-scans

      In conventional phase-resolved OCT blood flow is detected from phase changes between successive A-scans. Especially in high-speed OCT systems this results in a short evaluation time interval. This method is therefore often unable to visualize complete vascular networks since low flow velocities cause insufficient phase changes. This problem was solved by comparing B-scans instead of successive A-scans to enlarge the time interval. In this paper a detailed phase-noise analysis of our OCT system is presented in order to calculate the optimal time intervals for visualization of the vasculature of the human retina and choroid. High-resolution images of the vasculature of ...

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    11. Challenges in estimating the accuracy of imaging-based detection methods for glaucomatous progression

      Challenges in estimating the accuracy of imaging-based detection methods for glaucomatous progression

      The accuracy of glaucoma diagnosis by imaging devices that are commonly used in clinical practice, such as the GDx, the Heidelberg retinal tomograph and optical coherence tomography (OCT) is at a very high level, often surpassing the accuracy of trained ophthalmologists. 1 Because glaucoma specialists are considered to be the gold standard that imaging devices are tested against, the interobserver and intraobserver agreement of these specialists impose a limit on the possibilities to further improve the diagnostic accuracy of these imaging devices. Even if these devices perform better than clinicians, our estimates of their accuracy will not reflect this because ...

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    12. Real-time eye motion correction in phase-resolved OCT angiography with tracking SLO

      Real-time eye motion correction in phase-resolved OCT angiography with tracking SLO

      In phase-resolved OCT angiography blood flow is detected from phase changes in between A-scans that are obtained from the same location. In ophthalmology, this technique is vulnerable to eye motion. We address this problem by combining inter-B-scan phase-resolved OCT angiography with real-time eye tracking. A tracking scanning laser ophthalmoscope (TSLO) at 840 nm provided eye tracking functionality and was combined with a phase-stabilized optical frequency domain imaging (OFDI) system at 1040 nm. Real-time eye tracking corrected eye drift and prevented discontinuity artifacts from (micro)saccadic eye motion in OCT angiograms. This improved the OCT spot stability on the retina and ...

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    13. Means For Determining DEPTH-RESOLVED Physical AND/OR Optical Properties Of Scattering Media

      Means For Determining DEPTH-RESOLVED Physical AND/OR Optical Properties Of Scattering Media

      In depth-resolved imaging of scattering media, incident light interacts with tissue in a complex way before the signal reaches the detector: Light interacts with media between the light source and a specific depth, then scatters at that depth and the back scattered light again interacts with media, on its way to the detector. The resulting depth-resolved signal therefore likely does not directly represent a physical or optical property of the media at those depths. According to an exemplary embodiment of the present disclosure, systems, methods and computer-accessible medium can be provided to determine physical or optical properties based on such ...

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    14. RPE-normalized RNFL attenuation coefficient maps derived from volumetric OCT imaging for glaucoma

      RPE-normalized RNFL attenuation coefficient maps derived from volumetric OCT imaging for glaucoma

      Purpose: We present spatial retinal nerve fiber layer (RNFL) attenuation coefficient maps for healthy and glaucomatous eyes based on optical coherence tomography (OCT) measurements. Quantitative analyses of differences between healthy and glaucomatous eyes were performed. Methods: Peripapillary volumetric images of 10 healthy and 8 glaucomatous eyes were acquired by a Spectralis OCT system (Heidelberg Engineering, Germany). Per A-line, the RNFL's attenuation coefficient was determined based on a method that utilizes the retinal pigment epithelium as a reference layer. The attenuation coefficient describes the attenuation of light in tissue due to scattering and absorption. En-face maps were constructed and visually ...

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    15. Phase-stabilized optical frequency domain imaging at 1-µm for the measurement of blood flow in the human choroid

      Phase-stabilized optical frequency domain imaging at 1-µm for the measurement of blood flow in the human choroid
      In optical frequency domain imaging (OFDI) the measurement of interference fringes is not exactly reproducible due to small instabilities in the swept-source laser, the interferometer and the data-acquisition hardware. The resulting variation in wavenumber sampling makes phase-resolved detection and the removal of fixed-pattern noise challenging in OFDI. In this paper this problem is solved by a new post-processing method in which interference fringes are resampled to the exact same wavenumber space using a simultaneously recorded calibration signal. This method is implemented in a high-speed (100 kHz) high-resolution (6.5 µm) OFDI system at 1-µm and is used for the removal ...
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    1-15 of 15
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  2. Topics in the News

    1. (10 articles) VU University Amsterdam
    2. (2 articles) Delft University of Technology
    3. (1 articles) Massachusetts General Hospital
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    Phase-stabilized optical frequency domain imaging at 1-µm for the measurement of blood flow in the human choroid RPE-normalized RNFL attenuation coefficient maps derived from volumetric OCT imaging for glaucoma Means For Determining DEPTH-RESOLVED Physical AND/OR Optical Properties Of Scattering Media Real-time eye motion correction in phase-resolved OCT angiography with tracking SLO Challenges in estimating the accuracy of imaging-based detection methods for glaucomatous progression Angiography of the retina and the choroid with phase-resolved OCT using interval-optimized backstitched B-scans Fiber-based polarization-sensitive OCT of the human retina with correction of system polarization distortions Loosely coupled level sets for simultaneous 3D retinal layer segmentation in optical coherence tomography Automatic estimation of retinal nerve fiber bundle orientation in SD-OCT images using a structure-oriented smoothing filter Joint Segmentation of Retinal Layers and Focal Lesions in 3-D OCT Data of Topologically Disrupted Retinas Quantification of biomechanical properties of human corneal scar using acoustic radiation force optical coherence elastography Longitudinal changes in complete avascular area assessed using anterior segmental optical coherence tomography angiography in filtering trabeculectomy bleb