Histotripsy Bubble Cloud Contrast With Chirp-Coded Excitation in Preclinical Models

Area of Science:

• Medical Imaging
• Acoustic Physics
• Biomedical Engineering

Background:

• Histotripsy uses focused ultrasound for noninvasive tissue ablation via bubble cloud generation.
• Sensitive and specific bubble imaging is crucial for guiding histotripsy procedures.
• Standard plane-wave ultrasound imaging faces signal reduction challenges with deep-seated organs.

Purpose of the Study:

• To evaluate the effectiveness of chirp-coded excitation for enhancing histotripsy bubble contrast.
• To compare chirp-coded excitation with standard plane-wave imaging in scattering phantoms and in vivo.
• To assess the impact of different imaging pulse durations on bubble visualization.

Main Methods:

• Chirp-coded excitation pulses of varying durations were tested and compared to standard plane-wave pulses.
• Received signals were processed using matched filters to isolate fundamental and subharmonic frequencies.
• Contrast-to-tissue ratio (CTR) was measured in scattering gel phantoms and a subcutaneous mouse tumor model.

Main Results:

• The longest-duration chirp-coded pulse significantly improved subharmonic contrast-to-tissue ratio (CTR) in scattering media.
• Subharmonic CTR was enhanced by 4.25 dB ± 1.36 dB in phantoms and 3.84 dB ± 6.42 dB in vivo compared to fundamental contrast.
• Bubble cloud size and dissolution rates remained consistent across imaging sequences, indicating maintained image resolution.

Conclusions:

• Chirp-coded excitation is a feasible technique for specific visualization of histotripsy bubble clouds.
• This method enhances imaging contrast, particularly at depth, crucial for effective histotripsy guidance.
• The findings support the use of chirp-coded excitation for improved noninvasive ultrasound-guided tissue ablation.