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Harriet O Lloyd, Alfred Yu, Raksha Urs, Billy Yiu, Jeffrey Ketterling, Ronald H Silverman; Superresolution Ultrasound Imaging of the Rat Eye Vasculature. Invest. Ophthalmol. Vis. Sci. 2018;59(9):5841. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
While optical coherence tomography angiography offers excellent depiction of the retinal and choroidal vasculature, the orbital vessels supplying the eye are optically inaccessible. We have used ultrafast plane-wave imaging to assess human choroidal and orbital flow, but the resolution provided by Doppler ultrasound is inadequate for imaging flow in the rat eye, which would be crucial if the rat is to be utilized as an animal model of glaucoma or other disease. We therefore now demonstrate superresolution (SRI) imaging of the rat eye.
We implemented ultrafast plane-wave imaging on a Verasonics Vantage 128 ultrasound system. An 18 MHz linear array with 128 elements was used. We injected 0.1ml of 1/20 diluted Definity microbubble contrast agent as a bolus through a catheter into the tail vain of the anesthetized rat which was stabilized to limit respiratory or other motions. The ultrasound probe was held and positioned with a 3-axis positioner. We immediately acquired compound plane wave data emitting plane waves at two angles (±5°) which were then coherently compounded for a final rate of 6000 compound images/sec for 2 sec. SRI images were produced by forming persistence images of the tracks of the centroids of individual microbubbles (3 µm diameter) as they moved through the vasculature.
We compared conventional power Doppler images, power Doppler with contrast and SRI images of the rat vasculature. The addition of contrast improved sensitivity for depiction of flow in the choroidal and orbital vessels. SRI provided resolution of approximately 70 µm in depiction of orbital vessels versus approximately 125 µm in power Doppler with contrast and about 150 µm in power Doppler without contrast.
SRI offers a means to obtain high resolution depiction of the orbital vessels in pre-clinical models. We will soon increase the sample rate to further improve resolution. In this experiment, we focused on imaging, but are now developing methods for quantifying flow velocities and propose to utilize this approach for gaining understanding of how ocular blood flow is altered in experimental glaucoma.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
Comparative 18 MHz ultrafast compound coherent plane wave (CPWI) (left) and superresolution (SRI) (right) images of retrobulbar blood-flow in the rat eye after intravenous injection of Definity ultrasound contrast agent.
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