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Leo Puyo, Mathias Fink, Michel Paques, Jose Alain Sahel, Michael Atlan; Laser Doppler holography reveals retinal blood flow in humans. Journal of Vision 2017;17(15):30. doi: 10.1167/17.15.30.
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We report on laser Doppler perfusion imaging of human retinas using off-axis holography with near infrared light. Holograms were computed from optical interferograms recorded in the two output channels of a Mach-Zehnder interferometer by a video-rate and a high-speed camera. In the first channel, a sCMOS camera was used for real-time narrowband measurements; in the second channel, a CMOS camera was used for wideband measurements. The first channel enabled real-time monitoring of retinal holograms from an input stream of 16-bit, 512 by 512 pixels interferograms at 80 frames per second. The holograms were numerically reconstructed by the angular spectrum propagation method with 64-bit single-precision floating-point complex values using a computer on a single graphics processing unit (GPU). A short-time Fourier transformation along the temporal dimension of an input stream of 12-bit, 512 by 512 pixels interferograms acquired at 39,000 frames per second in the second channel was computed, high-pass filtered, and the Doppler signal was drawn from the first moments of the envelope of the result, yielding images with a temporal resolution of about 13 ms, a spatial resolution of about 20 microns and a field of view approximately 2*2 mm, on which tissue perfusion contrasts are related to both the local speed and concentration of blood cells. The cardiac cycle of retinal vessels is apparent, and choroidal vasculature can also be observed. Further analysis of the vessels frequency signature allowed for the discrimination of retinal and choroidal vessels, at low and high frequencies, respectively.
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