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Justin V Migacz, Iwona Gorczynska, Ravi Sankar Jonnal, Robert J Zawadzki, John S Werner; For OCT angiography images of choriocapillaris, how fast is too fast?. Invest. Ophthalmol. Vis. Sci. 2017;58(8):5431. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Optical coherence tomography angiography (OCTA) acquisition rates are increasing as new light sources and detection systems are developed. This potentially reduces eye motion artifacts, but image contrast decreases as the capture rate increases. We attempt to estimate an upper limit on the speed of retinal OCTA systems through the quantitative testing of the factors affecting angiogram quality.
We acquired OCTA volumetric datasets on 3 normal human subjects (31-43 years). The custom imaging system used a commercial swept-source laser with a sweep repetition rate of 1.7MHz, which is considerably faster than available clinical systems. Retinal volumes were acquired at full (1.7MHz) and reduced (170kHz) rates. We simulated a speed increase of up to 3.9Mhz by adding noise to the full-rate images which corresponds to the reduced acquisition time.En face images of choriocapillaris (CC) were segmented from the volumes, and radially averaged power spectra of these were computed. The resulting spectra contained distinct peaks indicating the spatial frequency and contrast of the vessel structure.
En face CC images acquired at the 1.7MHz and simulated 3.9MHz imaging rate are shown in Figure 1a, and 1b, respectively. As expected, the increased noise from an increased imaging rate reduces the clarity of the CC image. The log-log plot of the radial power spectra is shown in figure 2a, and a clear peak in the range of 50 cycles/mm to 200 cycles/mm can be seen, the height of which represents the contrast of the CC network. The trend of decreased angiogram contrast with increased simulated speed intersects the zero level (figure 2b) at a 2.6 MHz acquisition rate, which is the upper practical limit on OCTA imaging for this instrument.
OCTA imaging of retinal and choroidal vessel morphology may potentially impact our understanding of the vascular component of blinding diseases such as diabetic retinopathy and age related maculopathy. We have developed a way to estimate the upper limit on OCTA imaging of the CC, which can optimize OCTA instrument design.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
(A) OCTA image of the CC of normal subject taken at 6° nasal. (B) Same location simulated at 3.9MHz.
(A) Radial power spectrum of images with simulated noise. (B) Contrast change as a function of simulated increase speed.
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