Variable velocity range imaging of the choroid with dual-beam optical coherence angiography
ABSTRACT In this study, we present dual-beam Doppler optical coherence angiography with variable beam separation. Altering beam distance, independently of the scanning protocol, provides a flexible way to select the velocity range of detectable blood flow. This system utilized a one-micrometer wavelength light source to visualize deep into the posterior eye, i.e., the choroid. Two-dimensional choroidal vasculature maps of a human subject acquired with different beam separations, and hence with several velocity ranges, are presented. Combining these maps yields a semi-quantitative visualization of axial velocity of the choroidal circulation. The proposed technique may be useful for identifying choroidal abnormalities that occur in pathological conditions of the eye.
- SourceAvailable from: Rainer A Leitgeb
- "Enhanced and flexible velocity sensitivity has been achieved by employing dual beam setups. Two beams are laterally offset, and scan the same spot after an adjustable time interval, given by the lateral displacement and the scanning speed (Jaillon et al., 2011, 2012; Zotter et al., 2011). Furthermore post processing algorithms to filter vessel structures out of intensity tomograms work well in the retina. "
Article: Doppler Optical Coherence Tomography[Show abstract] [Hide abstract]
ABSTRACT: Optical Coherence Tomography (OCT) has revolutionized ophthalmology. Since its introduction in the early 1990s it has continuously improved in terms of speed, resolution and sensitivity. The technique has also seen a variety of extensions aiming to assess functional aspects of the tissue in addition to morphology. One of these approaches is Doppler OCT (DOCT), which aims to visualize and quantify blood flow. Such extensions were already implemented in time domain systems, but have gained importance with the introduction of Fourier domain OCT. Nowadays phase-sensitive detection techniques are most widely used to extract blood velocity and blood flow from tissues. A common problem with the technique is that the Doppler angle is not known and several approaches have been realized to obtain absolute velocity and flow data from the retina. Additional studies are required to elucidate which of these techniques is most promising. In the recent years, however, several groups have shown that data can be obtained with high validity and reproducibility. In addition, several groups have published values for total retinal blood flow. Another promising application relates to non-invasive angiography. As compared to standard techniques such as fluorescein and indocyanine-green angiography the technique offers two major advantages: no dye is required and depth resolution is required is provided. As such Doppler OCT has the potential to improve our abilities to diagnose and monitor ocular vascular diseases.Progress in Retinal and Eye Research 07/2014; 41(100). DOI:10.1016/j.preteyeres.2014.03.004 · 9.90 Impact Factor
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- "The limited thickness of this layer limits a nice visualization but a fine mesh-like structure seems to emerge. The blood flow of the choroid is given in Fig. 4(F) and shows a dense network of large vessels similar as observed in previous studies [22,38]. "
ABSTRACT: 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 consequently reduced the phase-noise, thereby enabling the detection of slower blood flows by extending the inter-B-scan time interval. In addition, eye tracking enabled the easy compounding of multiple data sets from the fovea of a healthy volunteer to create high-quality eye motion artifact-free angiograms. High-quality images are presented of two distinct layers of vasculature in the retina and the dense vasculature of the choroid. Additionally we present, for the first time, a phase-resolved OCT angiogram of the mesh-like network of the choriocapillaris containing typical pore openings.Biomedical Optics Express 01/2013; 4(1):51-65. DOI:10.1364/BOE.4.000051 · 3.50 Impact Factor
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ABSTRACT: Ability of a new version of one-micrometer dual-beam optical coherence angiography (OCA) based on Doppler optical coherence tomography (OCT), is demonstrated for choroidal vasculature imaging. A particular feature of this system is the adjustable time delay between two probe beams. This allows changing the measurable velocity range of moving constituents such as blood without alteration of the scanning protocol. Since choroidal vasculature is made of vessels having blood flows with different velocities, this technique provides a way of discriminating vessels according to the velocity range of their inner flow. An example of choroid imaging of a normal emmetropic eye is here given. It is shown that combining images acquired with different velocity ranges provides an enhanced vasculature representation. This method may be then useful for pathological choroid characterization.Proceedings of SPIE - The International Society for Optical Engineering 02/2012; DOI:10.1117/12.907718 · 0.20 Impact Factor