Fast 3-D Velocity Estimation in 4-D Using a 62 + 62 Row–Column Addressed Array

Abstract

This paper presents an imaging scheme capable of estimating the full 3-D velocity vector field in a volume using rowcolumn addressed (RCA) arrays at a high volume rate. A 62+62 RCA array is employed with an interleaved synthetic aperture sequence. It contains repeated emissions with rows and columns interleaved with B-mode emissions. The sequence contains 80 emissions in total and can provide continuous volumetric data at a volume rate above 125 Hz. A transverse oscillation crosscorrelation estimator determines all three velocity components. The approach is investigated using Field II simulations and measurements using a specially built 3 MHz 62+62 RCA array connected to the SARUS experimental scanner. Both the B-mode and flow sequences have a penetration depth of 14 cm when measured on a tissue mimicking phantom (0.5 dB/[MHz•cm] attenuation). Simulations of a parabolic flow in a 12 mm diameter vessel at a depth of 30 mm, beam-to-flow angle of 90 • , and xyrotation of 45 • gave a standard deviation (SD) of (3.3, 3.4, 0.4)% and bias of (-3.3, -3.9, -0.1)%, for (v v v x x x , v v v y y y , v v v z z z ). Decreasing the beam-to-flow angle to 60 • gave a SD of (8.9, 9.1, 0.8)% and bias of (-7.6, -9.5, -7.2)%, showing a slight increase. Measurements were carried out using a similar setup, and pulsing at 2 kHz yielded comparable results at 90 • with a SD of (5.8, 5.5, 1.1)% and bias of (1.4, -6.4, 2.4)%. At 60 • the SD was (5.2, 4.7 1.2)% and bias (-4.6, 6.9, -7.4)%. Results from measurements across all tested settings showed a maximum SD of 6.8% and a maximum bias of 15.8%, for a peak velocity of 10 cm/s. A tissue mimicking phantom with a straight vessel was used to introduce clutter, tissue motion, and a pulsating flow. The pulsating velocity magnitude was estimated across 10 pulse periods and yielded an SD of 10.9%. The method was capable of estimating transverse flow components precisely, but underestimated the flow with small beam-to-flow angles. The sequence provided continuous data in both time and space throughout the volume, allowing for retrospective analysis of the flow. Moreover, B-mode planes can be selected retrospectively anywhere in the volume. This shows that tensor velocity imaging (full 3-D volumetric vector flow imaging) can be estimated in 4-D (x x x

3D Volumetric Tensor Velocity Imaging with Low Computational Complexity Using a Row-Column Addressed Array

“…Full 3D velocity vector field in a volume by row-column addressed array was presented by Schou el al. [24]. They also used an interleaved sequence and SA imaging, which requires beamforming of the entire volume for all emissions.…”

“…However, the small RSD enables compensating for the RB. [24] to add motion correction to improve the velocity estimation. However, due the motion correction the SA beamforming needs to be done multiple times for each estimate.…”

“…Holbek et al, demonstrated 3D VFI in a plane [22] and in a volume [23] for stationary, laminar flow, but with a very low aliasing limit of a few cm/s in the axial direction. Schou et al [24] demonstrated volumetric 4D (3D+time) VFI without this aliasing limit by using a computationally very expensive synthetic aperture (SA) imaging sequence, making real-time implementation extremely difficult at best. Also, Schou et al presented volumetric flow in 4D with RC addressed array by using SA.…”

Anatomic and Functional Imaging Using Row–Column Arrays

“…The VFI approach gives consistent results for flow in the 2-D plane, but neglects the out-of-plane component. The approach has therefore been translated to RC arrays for both traditionally focused emissions [69,70] and for a fast SA based approach [71,72] using interleaved SA imaging [73,74]. Here, the full 3-D blood velocity is estimated in the volume for each time instance for full tensor velocity imaging (TVI).…”

Ultrafast 3-D Ultrasound Imaging Using Row–Column Array-Specific Frame-Multiply-and-Sum Beamforming

“…As this study is concentrating on fast 3-D ultrasound imaging only, the plane wave reconstruction technique will be considered. Since RCA probes were first introduced much work has been done to demonstrate the benefits of RCA probes [19]- [23], along with development of apodisation schemes to account for ghost echos and other artefacts [18], [24], high frame rate RCA imaging for flow estimation [25]- [28] and recently super resolution has been demonstrated using RCA probes [29].…”