Chirp-Coded Subharmonic Imaging With Volterra Filtering: Histotripsy Bubble Cloud Assessment In Vitro and Ex Vivo

Area of Science:

• Medical Imaging
• Biomedical Engineering
• Acoustic Medicine

Background:

• Histotripsy is a noninvasive focused ultrasound therapy that uses bubble activity to liquefy tissue.
• Current clinical monitoring of histotripsy relies on conventional ultrasound imaging.
• There is a need for improved imaging metrics to assess treatment success.

Purpose of the Study:

• To investigate nonlinear imaging techniques for assessing histotripsy ablation zones in vitro.
• To evaluate the feasibility of enhancing bubble cloud contrast in ex vivo tissue using these techniques.

Main Methods:

• Histotripsy bubble clouds were generated in phantoms and ex vivo porcine kidney.
• Chirp-coded subharmonic imaging with and without Volterra filtering was employed.
• Ablation zones were assessed using digital cameras and compared with bubble cloud areas via statistical analysis.

Main Results:

• Nonlinear imaging with Volterra filtering significantly enhanced contrast-to-tissue ratio (CTR) by up to 40.06 dB in vitro and 26.95 dB ex vivo.
• Bubble cloud areas estimated using subharmonic imaging and Volterra filtering closely matched actual ablation zone areas.
• The developed imaging approach demonstrated high accuracy in assessing treatment zones.

Conclusions:

• Nonlinear ultrasound imaging, particularly with Volterra filtering, offers a promising method for monitoring histotripsy.
• This technique can provide accurate assessment of ablation zones, advancing image guidance for histotripsy.
• The findings support the development of improved surrogate imaging metrics for successful histotripsy treatment.