Ultrasound imaging velocimetry with interleaved images for improved pulsatile arterial flow measurements: a new correction method, experimental and in vivo validation

Abstract

Blood velocity measurements are important in physiological science and clinical diagnosis. Doppler ultrasound is the most commonly used method but can only measure one velocity component. Ultrasound imaging velocimetry (UIV) is a promising technique capable of measuring two velocity components; however, there is a limit on the maximum velocity that can be measured with conventional hardware which results from the way images are acquired by sweeping the ultrasound beam across the field of view. Interleaved UIV is an extension of UIV in which two image frames are acquired concurrently, allowing the effective interframe separation time to be reduced and therefore increasing the maximum velocity that can be measured. The sweeping of the ultrasound beam across the image results in a systematic error which must be corrected: in this work, we derived and implemented a new velocity correction method which accounts for acceleration of the scatterers. We then, for the first time, assessed the performance of interleaved UIV for measuring pulsatile arterial velocities by measuring flows in phantoms and in vivo and comparing the results with spectral Doppler ultrasound and transit-time flow probe data. The velocity and flow rate in the phantom agreed within 5-10% of peak velocity, and 2-9% of peak flow, respectively, and in vivo the velocity difference was 9% of peak velocity. The maximum velocity measured was 1.8 m s 21 , the highest velocity reported with UIV. This will allow flows in diseased arteries to be investigated and so has the potential to increase diagnostic accuracy and enable new vascular research.

Ventricular Flow Field Visualization During Mechanical Circulatory Support in the Assisted Isolated Beating Heart

“…The B-mode images were analyzed using a previously validated iterative PIV algorithm. 18,41 The algorithm consisted of two stages: First, a region of interest was selected in the LV outflow tract and a simple 2D crosscorrelation was applied on this region for all image pairs from 3 cardiac cycles. This cross-correlation was used to give a rough estimate for the velocity magnitude in that region, which also provided a periodic signal with the same periodicity as the cardiac cycle.…”

“…Calibration of dimensions was based on the scaling factor (image resolution 800 by 600 pixels, spatial resolution 0.15-0.26 mm/px) in the DICOM data header. A sweep correction algorithm 18 was additionally applied to compensate for errors resulting from the echo-image creation by sweeping the echo beam through the imaging plane.…”

Ultrasound Imaging Velocimetry: a review

“…Zhou et al also predicted that for transient flows additional corrections are needed. Recently, Fraser et al (2016) showed that in pulsatile flow in a rabbit aorta this correction was indeed essential to obtain agreement with reference values. It is unclear whether the studies that do not mention the sweep effect perform a correction for it or not.…”

“…Studies of blood flow have been reported in rats ) and in rabbits Fraser et al 2016). So far these were primarily proof-of-principle experiments to show that the mean flow statistics match with reference (Doppler) data.…”

“…Note that UCAs in UIV applications are used in a much lower concentration than in its original intended use: for contrast-enhanced ultrasound imaging, typically a highlyconcentrated bolus is injected to get an optimal visualisation of blood flow. Using a more diluted, continuous feed (infusion) it is possible to obtain much better data quality for UIV purposes (Cimino et al 2012;Fraser et al 2016). The effect of the concentration of contrast microbubbles was studied by Kim et al (2004a).…”