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Hasan Ul Banna, Joel Palko; Measurement of posterior ciliary artery perfusion velocity with super-resolution ultrasound localization microscopy. Invest. Ophthalmol. Vis. Sci. 2021;62(8):1846.
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We evaluated the potential of super-resolution ultrasound localization microscopy (ULM) as a method to measure perfusion velocity in absolute metrics within the posterior ciliary arteries and their anastomoses.
Porcine ocular tissue from a local abattoir was dissected immediately following the sacrifice of the animal. The ophthalmic artery was further dissected and cannulated with micro-tubing attached to a microvolume syringe pump and in-line pressure transducer. A dilute microbubble (MB) ultrasound contrast agent (Vevo Micromarker) in 10% dextran and heparin was used to perfuse the whole globe. The anterior chamber was cannulated to manometrically maintain IOP at 25 mm Hg. Using a 50-MHz ultrasound transducer (Vevo2100, FUJIFILM VisualSonics) at a frame rate of 100 Hz, 3 sec of continuous image data was recorded with a mean arterial pressure of 60 mm Hg. Singular value decomposition was applied to separate tissue signal from the microbubble flow signals. A sparse recovery process was used to estimate the center position of the MB onto a high-resolution grid using knowledge of the MB point spread function and signal intensity. Multi-Hypothesis tracking in combination with Kalman filtering were used to incorporate the position and velocity information from prior frames to predict the position of each microbubble in each frame. The accuracy of the algorithm was validated using controlled velocity experiments in a 230 µm inner diameter tubing system and by manually tracking MBs in the long posterior ciliary arteries (figure 1).
Validation studies in controlled velocity tube experiments resulted in a root-mean-square error of 0.28 mm/s (controlled velocity range of 1.0 to 10.0 mm/s). The mean velocity within the long posterior ciliary artery was 4.18 mm/s using the tracking algorithm and 4.06 mm/s with manual MB tracking.
Super-resolution ULM provides spatial resolution beyond the acoustic diffraction limit. This technique has the potential to measure vascular perfusion in absolute metrics within regions of the globe that cannot currently be measured using conventional optical techniques.
This is a 2021 ARVO Annual Meeting abstract.
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