Superharmonic imaging with chirp coded excitation: filtering spectrally overlapped harmonics

Area of Science:

• Medical Imaging
• Ultrasound Technology
• Signal Processing

Background:

• Superharmonic imaging utilizes higher-order harmonics for enhanced spatial resolution in ultrasound.
• Low energy content of these harmonics leads to poor signal-to-noise ratio (SNR).
• Wideband excitation, while preserving axial resolution, causes spectral overlap of harmonics, increasing artifacts.

Purpose of the Study:

• To improve SNR and image quality in superharmonic imaging.
• To address the challenge of spectrally overlapping harmonics in wideband excitation.
• To introduce and evaluate a novel filtering technique for harmonic isolation.

Main Methods:

• Coded excitation was employed to boost excitation energy.
• Pulse compression with harmonic matched filters was used for SNR improvement.
• The fan chirp transform (FChT) was utilized for isolating higher-order harmonics in a transformed domain.

Main Results:

• Wideband excitation (up to 50% fractional bandwidth) improved resolution but introduced range side lobes up to -23 dB.
• The proposed FChT filtering technique achieved >50 dB range side lobe suppression.
• Image quality was significantly improved without compromising axial resolution.

Conclusions:

• The FChT filtering technique effectively isolates higher-order harmonics in superharmonic imaging.
• This method enhances image quality by suppressing artifacts caused by wideband excitation.
• The approach offers a viable solution for improving superharmonic ultrasound imaging performance.