Changes in bubble-cloud dissolution throughout the application of histotripsy pulses.

Area of Science:

• Biomedical Engineering
• Acoustic Physics
• Medical Imaging

Background:

• Histotripsy uses focused ultrasound to create bubble clouds for tissue ablation.
• Understanding bubble cloud dynamics is crucial for optimizing histotripsy efficacy and safety.
• Material damage from cavitation is a key consideration in pressure-field applications.

Purpose of the Study:

• To investigate the relationship between bubble cloud evolution and tissue damage during histotripsy.
• To compare bubble cloud behavior in agarose gel versus water under histotripsy exposure.
• To correlate acoustic emissions with bubble dynamics and tissue damage.

Main Methods:

• Utilized ultrafast ultrasound imaging to track bubble cloud dissolution periods in water and agarose gel.
• Quantified the damage area in agarose gel and correlated it with exposure duration.
• Employed passive acoustic imaging to monitor acoustic emissions during histotripsy.
• Extended a bubble-dynamics model to simulate bubble expansion in agarose gel.

Main Results:

• Bubble cloud dissolution period increased in agarose gel, reaching steady-state after approximately 555 pulses.
• Damage area and bubble dissolution period in agarose gel showed equivalent changes with exposure duration (p > 0.05).
• Acoustic emissions exhibited a different functional form compared to bubble dissolution and damage area.
• No significant changes in imaging markers were observed when bubble clouds were generated in water.

Conclusions:

• Bubble cloud dynamics and tissue damage in agarose gel exhibit similar trends during histotripsy.
• The observed bubble dynamics in agarose gel may differ from model predictions due to complex late-stage behavior.
• Histotripsy shows distinct bubble cloud responses in different media, highlighting the importance of material properties.