High-Frequency Ultrasound Case Studies with the Vantage System
Recently, Dr. Daniel Rohrbach joined Verasonics and will support new software developments for high-frequency applications of the Vantage systems. Prior to joining Verasonics, Dr. Rohrbach worked at the Lizzi Center for Biomedical Engineering at the Riverside Research Institute as a principal investigator where he collaborated with some Verasonics’ customers. These customers included Dr. Jeffrey A. Ketterling from the Lizzi Center for Biomedical Engineering at the Riverside Research Institute and Dr. Ronald H. Silverman from the Department of Ophthalmology at the Harkness Eye Institute Columbia University in New York City. Dr. Ketterling and Dr. Silverman are both considered leading researchers that have successfully used the high-frequency-ultrasound capabilities offered with the Vantage system for research.
Dr. Ketterling and team uses vector-flow analysis methods to study blood-flow patterns in the mouse embryo. Imaging blood flow in the hearts of embryonic mice, in utero, can be challenging due to the small size of the heart and rapid heart rate. High-frequency ultrasound systems using single-element and linear-array transducers have been used for many years to obtain local Doppler-flow estimates in embryos. However, these systems are limited and unable to estimate the instantaneous flow at high temporal and spatial resolution over a large area. Additionally, they are not able to portray the complex nature of blood-flow patterns in the heart.
Together with collaborators at the NYU School of Medicine and the University of Waterloo, the group and Dr. Ketterling performed initial experiments applying plane-wave, high-speed imaging and vector-flow estimate approaches to blood flow in mouse embryos. An 18-MHz, L22-14v linear array was used to acquire plane-wave data from a 16.5 day old embryo at an absolute frame rate of 20 kHz using a set of five fixed transmission angles. After beamforming, vector-flow processing and image compounding, the effective frame rate was 4 kHz. The vector-flow analysis revealed the complex nature of the blood flow patterns in the embryo and umbilical cord. Figure 2 demonstrates different phases of the cardiac cycle: (a) early systolic phase, (b) late diastole to early systole, and (c) the flow in the heart chambers while the umbilical artery reveals an increased flow after the earlier heart contractions. These initial results indicate that high-frequency, plane-wave imaging has the potential to simultaneously resolve complex cardiac motion and blood-flow patterns throughout a full image frame at sub-millisecond temporal resolution.
 Ketterling JA, Aristizábal O, Yiu BYS, Turnbull DH, Phoon CKL, Yu ACH, Silverman RH. High-speed, high-frequency ultrasound, in utero vector-flow imaging of mouse embryos. Sci Rep. 2017 Nov 30;7(1):16658.
In another case study under IRB approval, Dr. Silverman and Dr. Raksha Urs (Harkness Eye Institute, Columbia University) used the Vantage system with an L22-14v linear array probe to study blood flow in the eye,. Plane-wave imaging methods are particularly advantageous in ophthalmology because acoustic intensity may be significantly lower than it is by using conventional Doppler methods.
Scans centered on the optic nerve head are typically acquired for 3 seconds, allowing capture of several cardiac cycles. In this example, two angled plane-waves were transmitted at ±9 degrees at a 6 kHz PRF after compounding. In Figure 3, the leftmost image is the structural B-scan showing the mostly anechoic vitreous (V), the vitreo-retinal interface (R), and the optic nerve (ON). The center image shows a directionally color-coded power Doppler image, derived from the same data. On the right is a spectrogram portraying flow velocities in the region of interest (box) in the power Doppler image capturing flow velocities from both the central retinal artery and vein.
 Urs R, Ketterling JA, Yu ACH, Lloyd HO, Yiu BYS, Silverman RH. Ultrasound imaging and measurement of choroidal blood flow. TVST 2018;7(5);1-8.
 Urs R, Ketterling JA, Silverman RH. Ultrafast ultrasound imaging of ocular anatomy and blood flow. Invest Ophthalmol Vis Sci. 2016:57(8):3810-6.