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Rainer A. Leitgeb, Cedric Blatter, Thomas Klein, Wolfgang Wieser, Christoph M. Eigenwillig, Robert Huber, Tilman Schmoll; Ultrahigh-speed wide-field Microangiography in a Single Patch. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2196.
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To visualize comprehensively the retinal and choroidal microvascular network over a large field of view using MHz optical coherence tomography at 1060nm as a non-invasive complement to fluorescein angiography.
The method is based on functional Swept source OCT using speckle variance as vessel contrasting technique. This highly sensitive technique detects small changes in the speckle pattern between successive intensity tomograms caused by tissue blood flow and is insensitive to trigger timing artifacts of phase sensitive techniques. The use of Megahertz A-Scan rate FDML laser at 1050nm allows for wide-field angiography of the inner retina as well as of the choroidal vasculature acquired in a single recording within only a few seconds. Typically 5 tomograms are recorded at each vertical location to calculate the corresponding variance image. High lateral sampling is maintained and permits resolving the vessel network down to the capillary level. The axial resolution is 18μm at 1.4MHz A-scan rate.
We present wide field angiographic maps of healthy volunteers over a field of 30x30degree that has been obtained in a single volume recording without patching. The recording of a single volume takes only 5sec covering 30x30deg. Since the method uses changes between successive tomograms recorded at 500Hz the speckle variance technique is on the one hand sensitive to flow velocities of only 70µm per second typical for the smallest capillaries in the parafoveal bed. On the other hand larger velocities will immediately give rise to speckle decorrelation and large variance signatures. Thus the velocity range is covering the full vascular system. The center wavelength of the FDML laser of 1060nm allows for better penetration to visualize also the outer choroidal vasculature.
The ultra-high imaging speed offers a completely new perspective for imaging the retinal vascular network from a large field of view in a single recording down to the smallest capillaries in the parafoveal region. The fact that a large field of view can be obtained without patching several recordings marks a major step towards non-invasive retinal vascular imaging as a complement to fluorescein angiography. Further improvement in speed could be obtained by employing multi-beam approaches to scan the retina.
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