A method to determine the bandwidth of imaging pulses for chirp-coded excitation imaging of histotripsy bubble clouds

Abstract

Histotripsy is a noninvasive focused ultrasound therapy that utilizes bubble cloud activity for tissue ablation. Real-time ultrasound imaging is used to guide histotripsy, and subharmonic imaging with chirp-coded excitation has been shown to provide effective bubble cloud contrast for targets at depth (>5 cm). Choice of appropriate parameters for the chirped imaging pulse are dependent on a number of factors, including the imaging probe bandwidth. In this study, an analytic method was developed and tested to design chirped imaging pulses for fundamental and subharmonic imaging. In silico studies were conducted to estimate received signal based on the frequency response of a curvilinear imaging probe (C5-2v, Verasonics, Inc., Kirkland, WA). To enable assessment of both bubbles and anatomic information, criteria were set to maximize the probe sensitivity for both fundamental and contrast-specific signals. Based on these analyses, in vitro studies were conducted using a scattering tissue phantom for sequences that highlight fundamental, subharmonic, or equally between the two for bubble cloud visualization. Good qualitative agreement was observed between insilico prediction and in vitro assessment of bubble cloud generation, indicating the formalism developed here is a promising approach for the development of imaging sequences for histotripsy guidance.