Contrast imaging with chirped excitation

Area of Science:

• Ultrasound imaging
• Acoustic wave propagation
• Biomedical engineering

Background:

• Coded excitation enhances ultrasound imaging by increasing signal-to-noise ratio (SNR) and penetration depth.
• Wideband signals are hypothesized to improve contrast-to-tissue ratio (CTR) with contrast agents.
• Nonlinear contrast agent properties complicate coded excitation in contrast imaging.

Purpose of the Study:

• To propose and evaluate two chirped excitation methods for contrast agent imaging.
• To assess the impact of chirped excitation on contrast-to-tissue ratio (CTR) and tissue rejection.
• To compare chirped excitation with conventional tone burst insonation at low mechanical index (MI).

Main Methods:

• Two chirped excitation methods: single chirp and chirp sequence, with mechanical index (MI) from 0.05 to 0.34.
• Clutter filter and matched filter for single chirp; echo subtraction for chirp sequence to reject tissue echoes.
• Acoustic experiments comparing CTR and tissue rejection ratio (TRR) for chirp vs. tone burst at constant spatial peak temporal averaged intensity (I(SPTA)).

Main Results:

• Chirped excitation increased CTR by 4 dB to 8 dB compared to tone burst.
• Achieving a 15 dB CTR required 6 dB lower spatial peak pulse averaged intensity (I(SPPA)) with chirped excitation.
• Chirp sequence achieved over 10 dB higher tissue rejection ratio (TRR) than tone burst phase inversion.
• Axial resolution difference between chirp and tone burst was approximately 220 micrometers.

Conclusions:

• Chirped excitation offers significant advantages for ultrasound contrast imaging.
• Improved CTR and TRR allow for reduced acoustic intensity, enhancing safety.
• Deconvolution techniques can recover spatial resolution lost due to microbubble response.