Abstract
Purpose :
The goal of this study was to utilize ultrasound localization microscopy imaging (ULM) to visualize changes in orbital microvascular flow resulting from elevated intraocular pressure (IOP)
Methods :
Ultrafast plane-wave imaging of the eyes was performed on Sprague Dawley rat eyes with an 18 MHz linear array probe and a Verasonics Vantage 128 ultrasound system. Compounded B-Scans were acquired at 500 Hz for 3 minutes during an intravenous injection of 0.2% contrast microbubble solution (USphere Prime, Trust Bio-sonics, Taiwan, ROC) at a constant infusion rate of 25 µl/min. USphere Prime is a perfluorcarbon gas-filled, phospholipid-shelled microbubble averaging approximately 1 µm in diameter. Data were acquired at normal IOP of 10 mmHg and at 40 and 70 mmHg by cannulation of the anterior chamber. In post-processing, a singular value decomposition spatiotemporal filter was used to suppress signal components related to stationary or slow-moving tissue while retaining signals from moving blood cells and microbubbles. The filtered data was processed to produce power Doppler images. ULM was performed following Couture et al. [IEEE UFFC, 65(8), 2018]. Microbubbles were detected as the brightest local maximas in the image and their positions were extracted using a weighted average approach. A tracking algorithm [Simple Tracker, Tinevez et al] was used to trace their trajectories between frames and a final microbubble density map was displayed as a projection of all microbubble tracks.
Results :
As IOP was increased, there was a significant deficit in flow area. At 40 mmHg, flow area was reduced by 24% relative to normal and at 70 mmHg by 51%. Flow in much of the orbital vasculature had collapsed at 70 mmHg, but the central retinal artery was still visualized.
Conclusions :
We previously reported a 50% decrease in systolic and 60% decrease in diastolic arterial velocities in the rat eye at 60 mmHg IOP. ULM allows for far better visualization of finer vessels versus traditional Doppler methods. Particle velocity was not determined in these experiments and, thus, visualization of the central retinal artery only, at 70 mmHg means some arterial flow remains. However, the images suggest a flow deficit in both the orbit and retina/choroid.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.