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Vivek Jay Srinivasan, Tingwei Zhang, Jun Zhu; Averaging strategies to improve imaging of the rodent choriocapillaris with OCT angiography. Invest. Ophthalmol. Vis. Sci. 2019;60(9):3071.
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© ARVO (1962-2015); The Authors (2016-present)
The choriocapillaris is a microvascular bed which supplies the metabolically active photoreceptors and outer retina. However, due to its location beyond the retinal pigment epithelium, the choriocapillaris has been especially challenging to study in vivo. Here, we take advantage of a long wavelength OCT angiography system and a very stable rodent ocular preparation to investigate averaging strategies for improving visualization of the choriocapillaris.
Retinal imaging of anesthetized Long Evans (pigmented) and Sprague Dawley (unpigmented) rats was performed with a 1310 nm spectral / Fourier domain OCT system with 7.5 micron transverse resolution. The longer infrared wavelengths improved penetration and resolution beyond the retinal pigment epithelium (RPE). Different protocols were investigated to improve image quality through averaging. Protocol 1 consisted of 5120 y locations x 512 axial scans per frame x 2 frames per y location acquired in a single volume scan. Protocol 2 consistent of ~100 repeated OCT angiography volumes with 128 y locations x 256 axial scans per frame x 2 frames per y location, acquired sequentially. Angiography was performed by complex subtraction of repeated frames at the same y location. For protocol 1, consecutive frames were corrected for motion prior to sliding window averaging in y. For protocol 2, volumes were corrected for axial and transverse motion, registered, and then averaged. Finally, the choriocapillaris was segmented and displayed as an en face image.
Images of the choriocapillaris are shown in the Figure. The long image acquisition time enables averaging to reduce speckle, which reveals the characteristic lobular pattern. Both protocol 1 and 2 yielded similar image quality, with protocol 1 having the advantage of simpler data processing.
Averaging to reduce speckle significantly improves visualization of the choriocapillaris in pigmented and unpigmented rats. While a single, slow angiography volume scan (protocol 1) may be possible in highly stabilized animal preparations, rapid multi-volume scans (protocol 2) with motion correction prior to averaging are more practical in scenarios with significant motion.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
Image of the Sprague Dawley rat choriocapillaris, acquired via protocol 1.
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