Delay-Encoded Harmonic Imaging (DE-HI) in Multiplane-Wave Compounding.

Area of Science:

• Medical Imaging
• Ultrasound Technology
• Signal Processing

Background:

• Ultrafast ultrasound imaging offers advancements in techniques like shear wave elastography and Doppler imaging.
• Compounding multiple ultrasound images improves quality but involves trade-offs in signal-to-noise ratio (SNR), resolution, and frame rate.
• Multiplane wave (MW) imaging enhances SNR using Hadamard encoding but introduces reverberation artifacts and cannot encode the second harmonic.

Purpose of the Study:

• To propose and evaluate a novel delay-encoded harmonic imaging (DE-HI) technique.
• To overcome limitations of MW imaging by enabling second harmonic encoding.
• To suppress reverberation artifacts and improve image quality in ultrafast ultrasound.

Main Methods:

• Developed DE-HI encoding the second harmonic using a quarter-period delay, distinct from MW imaging's polarity reversal.
• Signals are decoded in the frequency domain to recover fundamental and second harmonic components.
• Experimental validation using a point target, phantom studies, and in-vivo human liver imaging.

Main Results:

• DE-HI demonstrated significant improvements in contrast-to-noise ratio (CNR) and lesion-signal-to-noise ratio (lSNR) compared to standard plane wave compounding, MW imaging, and standard harmonic imaging.
• Maximal improvements of 116% in CNR and 115% in lSNR were observed in phantom studies at a depth of 55 mm.
• DE-HI showed stable encoding/decoding processes and potential for high frame rates.

Conclusions:

• DE-HI effectively encodes the second harmonic component, enhancing SNR and image quality.
• The technique successfully suppresses reverberation artifacts and clutter noise.
• DE-HI shows promise for diverse high-frame-rate ultrasound imaging applications.