Improving Spatial Resolution Using Incoherent Subtraction of Receive Beams Having Different Apodizations

Area of Science:

• Medical Imaging
• Ultrasound Technology
• Signal Processing

Background:

• Lateral sidelobe reduction is crucial for improving image quality in ultrasonic imaging, minimizing distortion and artifacts.
• Conventional apodization techniques lower sidelobes but often decrease lateral resolution by widening the main lobe.

Purpose of the Study:

• To evaluate Null Subtraction Imaging (NSI) as a nonlinear technique for reducing sidelobes and enhancing lateral resolution in ultrasonic imaging.
• To compare NSI performance against conventional rectangular apodization and minimum variance beamforming.

Main Methods:

• NSI utilizes multiple receive apodizations on identical RF data to achieve low sidelobes and improved lateral resolution.
• Experiments involved imaging wire targets for lateral resolution and anechoic/hyperechoic targets for contrast using an ATS539 phantom.
• Image quality was assessed via -6-dB receive beamwidth, main-lobe-to-sidelobe ratio, and contrast-to-noise ratio (CNR).

Main Results:

• NSI demonstrated a significant improvement in apparent lateral resolution, exceeding a 35x increase compared to rectangular apodization.
• The -6-dB beamwidth was reduced to 0.03λ with NSI, versus 2.79λ for rectangular apodization.
• Sidelobes were reduced by 32.9 dB using NSI, but contrast-to-noise ratio decreased for both anechoic and hyperechoic targets.

Conclusions:

• NSI effectively reduces sidelobes and enhances lateral resolution in ultrasonic imaging.
• While NSI improves resolution, there is a trade-off with reduced contrast performance for certain targets.