Abstract
Purpose :
Plane-wave (PW) ultrasound with a linear array probe is capable of visualizing and measuring retrobulbar blood flow. Because the retrobulbar vessels have a complex arrangement and are not situated in one plane, 2D images cannot capture their anatomic arrangement. The goal of this study was to determine if PW ultrasound could be used to visualize and measure flow dynamics in 3D in the retrobulbar vessels in a rat model.
Methods :
Ultrafast PW imaging on the eyes of Sprague Dawley rats was performed with a Verasonics Vantage 128 ultrasound system using an 18 MHz linear array probe. Compound images were acquired by emitting unfocused wavefronts at multiple angles and combining echo data from all angles to form individual B-scans. 3D data were acquired by moving the probe on a linear translation stage over 2.5 mm at 1.5 mm/s, imaging at the rate of 3000 images/s. Plane thickness was approximately 0.5 mm, allowing sufficient dwell time in overlapping planes to both capture anatomy and measure flow dynamics in 3D data sets. A Singular Value Decomposition (SVD) filter was used to detect blood flow and produce power Doppler images. Velocity was measured using spectrogram analysis.
Results :
3D images were produced in ImageJ from the stack of image planes. By applying the SVD filter to overlapping sets of scan planes (i.e., within a beamwidth), we were able to visualize pulsatile flow of vessels. Figure 1 shows a projection image of grey-scale structural backscatter and blood-flow from a 3D scan set. Figure 2 (a) and (b) show spectrograms of the two arteries marked in Figure 1. Cosine-corrected peak-velocities (47.7 and 32.2 mm/s) can be seen at depths of 1.2 and 0.9 mm, corresponding to the locations of the arteries in the 2.5 mm translation axis, velocities which are comparable to observed values in Doppler B-scans (39.9±14.4, n=20).
Conclusions :
While 3D ultrasound imaging is not new, 3D capture combining structural and functional information is novel. Although the axial and lateral resolution of the array are on the order of 0.1 mm, out-of-plane resolution is ~0.5 mm, which is disadvantageous in terms of interplane spatial resolution This weakness is turned to advantage by SVD processing sets of overlapping data from regions approximating slice thickness to obtain both structural and functional data.
This is a 2021 ARVO Annual Meeting abstract.