[Paper Review] Large elements and advanced beamformers for increased field of view in 2-D ultrasound matrix arrays

Mick Gardner, M. L. Oelze|arXiv (Cornell University)|Feb 16, 2026

Ultrasound Imaging and Elastography0 citations

TL;DR

The paper demonstrates that doubling element size in a 2D ultrasound matrix array increases the field of view without adding elements, and shows that advanced beamformers (NSI, DCF, MV) can preserve resolution and image quality, with NSI often yielding the best resolution in simulations and phantom experiments.

ABSTRACT

Three-dimensional (3D) ultrasound promises various medical applications for abdominal, obstetrics, and cardiovascular imaging. However, ultrasound matrix arrays have extremely high element counts limiting their field of view (FOV). This work seeks to demonstrate an increased field-of-view using a reduced element count array design. The approach is to increase the element size and use advanced beamformers to maintain image quality. The delay and sum (DAS), Null Subtraction Imaging (NSI), directional coherence factor (DCF), and Minimum Variance (MV) beamformers were compared. K-wave simulations of the 3D point-spread functions (PSF) of NSI, DCF, and MV display reduced side lobes and narrowed main lobes compared to DAS. Experiments were conducted using a multiplexed 1024-element matrix array on a Verasonics 256 system. Elements were electronically coupled to imitate a larger pitch and element size. Then, a virtual large aperture was created by using a positioning system to collect data in sections with the matrix array. High-quality images were obtained using a coupling factor of two, doubling the FOV while maintaining the same element count in the virtual large aperture as the original matrix array. The NSI beamformer demonstrated the best resolution performance in simulations and on the large aperture, maintaining the same resolution as uncoupled DAS for coupling factors up to 4. Our results demonstrate how larger matrix arrays could be constructed with larger elements, with resolution maintained by advanced beamformers.

Motivation & Objective

• Investigate whether using larger square elements in a periodic 2D matrix array can increase the aperture and field of view without increasing the element count.
• Assess whether advanced beamformers (NSI, DCF, MV) can maintain or improve image quality when element size is increased.
• Compare performance of DAS, NSI, DCF, and MV in simulations and with a virtual large aperture created from a multiplexed matrix probe.
• Evaluate trade-offs between resolution, contrast, and speckle when using large elements and different beamformers.

Proposed method

• Use a commercial 2D matrix array (Verasonics system) with electronic coupling to simulate larger elements and create a virtual large aperture by data collection in quadrants.
• Perform beamforming with DAS, NSI, DCF, and MV to compare resolution and artifact levels.
• Run K-wave simulations to obtain 3D PSFs for NSI, DCF, MV, and DAS to assess side lobes and main-lobe width.
• Create a virtual large aperture by coupling blocks of adjacent elements (coupling factors 1, 2, and 4) and moving the probe to collect sectional data.
• Evaluate image quality using FWHM, contrast (CR), CNR, gCNR, and speckle SNR (sSNR).
• Analyze algorithmic complexities and runtimes for each beamformer to discuss computational feasibility.

Experimental results

Research questions

• RQ1 Can larger element size in a periodic 2D matrix array increase the field of view without increasing the number of active elements?
• RQ2 Which beamformer best preserves resolution and manages side lobes when element size is increased (DAS vs NSI vs DCF vs MV)?
• RQ3 How do coupling factor and virtual aperture configuration affect resolution, contrast, and speckle for the different beamformers?
• RQ4 What are the trade-offs between image quality metrics (resolution, contrast, CNR, gCNR, sSNR) across beamformers under large-element conditions?

Key findings

• NSI yields the best resolution among advanced beamformers in simulations, with lateral/elevational FWHM around 1.22–1.25 mm and main-lobe to side-lobe contrasts up to 41.3 dB.
• DAS shows highest side lobes and lowest contrast but remains the most computationally efficient; MV provides competitive CNR and gCNR but poorer resolution for large elements.
• Combining larger elements (coupling factor 2) with NSI achieves comparable resolution to uncoupled DAS while doubling the FOV, in phantom and virtual-aperture contexts.
• Coupling factor of four degrades resolution and image quality, producing grainy images and larger dead zones, indicating an upper limit to practical element enlargement.
• DC-offset NSI tuning maintains sharp main lobes and suppresses sidelobes, while DCF performance depends on directional coherence projections and can reduce speckle.
• MV performance is less effective for large elements due to reduced apodization weight diversity with low element counts.
• NSI demonstrates favorable runtime efficiency among advanced beamformers (NSI fastest after DAS) for low-element-count virtual apertures.