Abstract
Purpose :
Current optical techniques to measure ocular blood flow are limited in their depth of penetration. The purpose of this study was to determine the utility of high-frequency ultrasound localization microscopy (ULM) to measure volumetric blood flow in the rat eye.
Methods :
The right eye anterior chamber of the anesthetized rat (n=4) was cannulated for IOP control. The lateral tail vein was cannulated for injection of a microbubble (MB) ultrasound contrast agent. A linear focused array ultrasound probe (38.4 MHz center frequency, Visualsonics Inc) oriented horizontally was used to collect 7,000 frames (1079 fps) of radiofrequency data at each step. A linear motor was used to move the probe at a 90 μm step size across a 2.5 mm range. Frames were collected at an IOP of 10 and 50 mm Hg. The frames were registered and a spatiotemporal singular value decomposition was used as a clutter filter. A spatiotemporal non-local means filtering, and relative intensity thresholding was applied to suppress background noise. A normalized cross-correlation between interpolated frames and a pre-selected microbubble point spread function was performed to isolate microbubbles in each frame. The MB centroids were paired frame to frame using the Kuhn-Munkres algorithm. The accumulated MB tracks for each set of 7,000 frames were linearly interpolated and used to provide perfusion velocity and direction of the posterior in vivo rat eye. A 3-D volume was then created using a vesselness filter [Jerman et al 2016] and volumetric flow was calculated for retinal arteries by combining the planar velocimetry algorithm with the continuity equation.
Results :
The mean volumetric flow for the 1° branches (n=8) of the central retinal artery was 3.0 ± 0.93 µL/min and 1.7 ± 0.93 µL/min at 10 and 50 mm Hg, respectively. This is comparable to volumetric flow of rat retinal vessels measured using optical microangiography [Zhi et al 2011]. Representative 2D and 3D vascular anatomy are seen in Fig 1.
Conclusions :
ULM is capable of measuring volumetric blood flow within the posterior rat eye. Future work will characterize volumetric flow throughout the thickness of the posterior rat eye, which may be beneficial in understanding the pathophysiology of eye diseases such as glaucoma.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.