Ultrasound Pixel-Based Beamforming With Phase Alignments of Focused Beams

Abstract

We previously developed unified pixel-based (PB) beamforming to generate high-resolution sonograms, based on field pattern analysis. In this framework, we found that the transmit waveshape away from the focus could be characterized by two spherical pulses. These correspond to the maximal and minimal distances from the imaging point to the active aperture. The beamformer uses this model to select the highest energy signals from backscattered data. A spatiotemporal interpolation formula is used to provide a smooth transition in regions near the focal depth where there is no dominant reflected pulse. In this paper, we show that the unified PB approach is less robust at lower center frequencies. The interpolated data is suboptimal for a longer transmit waveshape. As a result, the spatial resolution at the focal depth is lower than that in other regions. By further exploring the field pattern, we propose a beamformer that is more robust to variations in beamwidth. The new method, named coherent PB beamforming, aligns and compounds the pulse data directly in the transition regions. In simulation and phantom studies, the coherent PB approach is shown to outperform the unified PB approach in spatial resolution. It helps regain optimal resolution at the focal depth while still maintaining good image quality in other regions. We also demonstrate the new method on in vivo data where its improvements over the unified PB method are demonstrated on scanned objects with a more complicated structure.

A Spatial Coherence Approach to Minimum Variance Beamforming for Plane-Wave Compounding

“…the pulse-echo beam is generated with both transmit and receive focussing over the entire imaging region [3]. Such systems include synthetic aperture imaging [10], coherent plane-wave compounding [11], and pixel-based beamforming with focused beams [12], [13]. In these approaches, the transmit focusing is synthesized by accumulating data from a large number of pulse-echo sequences.…”

A Spatial Compounding Method for Non-Delayed Sequential Beamforming

“…where β i is associated with R max . Equations ( 7) and (8) show that the transmit wave shape can be characterized by three spherical waves. The total field is a combination of the three pulses with differen transmit origins and different time delays.…”

“…Improved resolution is obtained for areas away from the focus. For linear array, similar algorithms have been introduced [3][4][5][6][7][8].…”

Sub-wavelength lateral detection of tissue-approximating masses using an ultrasonic metamaterial lens

“…Delay-and-sum (DAS) beamforming methods comprise the bulk of applied techniques with maximum MSD of~2.1λ and FWHM commonly approaching 4:6λ 2,5,10 . Other developing techniques include the synthetic aperture (SA) 6,11,12 , minimum variance (MV) 10 , Bessel beams 13 , and pixel-based beamformer (PBB) approaches 14,15 . All provide superior resolution to DAS under ideal conditions with resolutions reaching as high as λ/12 for FWHM using MV.…”

“…All provide superior resolution to DAS under ideal conditions with resolutions reaching as high as λ/12 for FWHM using MV. However, in more practical settings, these techniques result in much smaller improvements over DAS with FWHM (MSD) of 0.38λ (0.91λ) for MV 10 , 3.3λ(2λ) for SA 11 , and 1.02λ (1.43λ) for PBB 15 . The maximum resolution of each technique occurs at the focal point, varies strongly with applied frequency, and must be within the acoustic near-field of the emitters.…”