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Raksha Urs, Jeffrey A Ketterling, Inez Nelson, Xiangjun Yang, Gulgun Tezel, Ronald H Silverman; Contrast-Enhanced Ultrasound Imaging of Blood-Flow in the Rat Eye. Invest. Ophthalmol. Vis. Sci. 2020;61(7):1873.
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© ARVO (1962-2015); The Authors (2016-present)
Preclinical imaging, especially of rodent models, plays a major role in experimental ophthalmology. The goal of this study was to determine if ultrasound can be used to visualize and measure flow dynamics in the retrobulbar vessels supplying and draining the eye and the potential of contrast microbubbles to provide image and measurement enhancement.
Ultrafast plane-wave imaging of the eyes of Sprague Dawley rats was performed with a Verasonics Vantage 128 ultrasound system using an 18 MHz linear array probe with 128 elements. Compound images were acquired by emitting unfocused wavefronts at multiple angles and combining echo data from all angles to form individual B-scans. Three imaging sequences were utilized, compounding up to six angles, with imaging rates of 50, 500 and 3,000 compound B-scans per second and sequence durations of 3 minutes, 30 seconds and 1.5 seconds respectively. Data were acquired before and after intravenous introduction of contrast microbubbles (USphere Prime contrast agent, Trust Bio-sonics, Taiwan, ROC). USphere Prime consists of perfluorcarbon gas-filled, phospholipid-shelled microbubbles averaging approximately 1 µm in diameter.
The total power of the Doppler signal in the image plane increased approximately 20 fold after injection of contrast, followed by an exponential decay to baseline in about 90 seconds (best-fit time constant ~38 sec) (Figure 1). While major vessels and the retinal/choroidal complex were evident pre-contrast, they were dramatically enhanced with contrast present, with details such as choroidal arterioles seen only with contrast (Figure 2). Ocular arteriovenous transit time determined from comparative enhancement curves in arteries and veins was approximately 0.2 sec.
Plane-wave ultrasound, especially with enhancement by contrast microbubbles, offers a means for the study of ocular hemodynamics using the rat eye as a model for ocular diseases such as Glaucoma. While this report focused on the use of contrast in experimental preclinical models, it should be noted that microbubble contrast agents are commonly used in clinical specialties other than ophthalmology, especially in cardiovascular imaging. Given its advantages, contrast-enhanced plane-wave ultrasound may ultimately find clinical application in ophthalmology as well.
This is a 2020 ARVO Annual Meeting abstract.
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