Estimation and correction of ultrasonic wavefront distortion using pulse-echo data received in a two-dimensional...

Area of Science:

• Ultrasound imaging
• Medical acoustics
• Wave propagation and aberration compensation

Background:

• Ultrasound imaging relies on pulse-echo measurements to create images.
• Aberrations in tissue can distort the ultrasound wavefront, degrading image quality.
• Effective compensation techniques are crucial for accurate diagnostic imaging.

Purpose of the Study:

• To quantify the impact of transmitter beam size on ultrasound imaging.
• To evaluate different aberration compensation techniques.
• To determine the isoplanatic patch size in biological tissues.

Main Methods:

• Pulse-echo measurements using single-element transmitters (0.5, 1, 2 inches) focused at 3 inches.
• Utilized a tissue-mimicking phantom and a point target for echo generation.
• Synthesized a 2D aperture by scanning a linear array, with abdominal wall tissue introducing aberrations.

Main Results:

• Decreased transmitter beam size improved time-delay estimation and wavefront coherence.
• Average isoplanatic patch size was 16.7 mm (azimuthal) and 39.0 mm (range), increasing to 19.0 mm and 41.4 mm after backpropagation.
• Backpropagation followed by time-shift compensation yielded higher contrast ratio improvements (2.3-3.5 dB) compared to time-shift compensation alone (2.0-2.8 dB).

Conclusions:

• A tightly focused transmitter beam is essential for accurate time-shift estimation in ultrasound.
• The isoplanatic patch is anisotropic, being longer in the range than azimuthal direction.
• Backpropagation combined with time-shift compensation offers superior aberration correction over time-shift compensation alone.