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Jan Philip Kolb, Thomas Klein, Kathrin J. Mohler, Wolfgang Wieser, Aljoscha S. Neubauer, Marcus Kernt, Anselm Kampik, Armin Wolf, Robert Huber; Single volume widefield retinal and choroidal OCT angiography of patients with MHz-OCT over 45° field of view. Invest. Ophthalmol. Vis. Sci. 2016;57(12):443.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate single volume OCT angiography of the retina and choroid in patients over a wide field of view of 45° (~13.5mm) with data captured by a MHz-OCT.
45 patients diagnosed with various diseases including but not limited to AMD, diabetic retinopathy and macula edema were imaged with an OCT angiography protocol of a widefield MHz-OCT. This is a custom swept-source OCT device based on a Fourier-domain mode-locked laser source with 1050nm central wavelength and a depth scan rate of 1.68MHz, which is about 16 times faster than even the latest commercial swept-source OCT devices. Therefore, an OCT angiography protocol with 5x(1600x320) A-scans over 45° field of view took only 2.18s total acquisition time. In post processing, the RPE was automatically detected and angiograms of the retina (see fig. 1B) and the upper 40µm of the choroid (see fig. 1C) were computed by calculating the speckle variance of five consecutive B-scans taken at the same location. The optical nerve head (ONH) was assigned to the retina as RPE segmentation is not possible in this region.
Single volume OCT angiography over a 45° field of view in patients is feasible and highlights retinal vessels, which are not visible in a regular enface images. Still, there are some challenges remaining: Shadowing due to eye lids and lashes and the pupil require careful alignment of the patient. B-scans with involuntary motion of the patient need to be filtered, but due to the high acquisition speed of the MHz-OCT this should be less critical than with a standard OCT. Moreover, the resolution in y-direction of 42µm given by density of B-scans seems to be too low to resolve very fine vessels.
OCT angiography with a MHz-OCT over 45° field of view with single volume acquisition in patients could be demonstrated for the first time. For future measurements the scan protocol should include a larger number of B-scans to improve the resolution in y-direction. Additionally, a more advanced processing of the data like SSADA could enhance the vessel contrast further.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
A) EnFace projection of OCT dataset from a 43 year old male patient showing 45° field of view. B) OCT Angiogram from the same dataset as A of the retina and ONH.C) OCT angiogram of the same dataset as A of the upper 40µm of the choroid.
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