Real-time imaging and control of boiling histotripsy lesion formation using Doppler ultrasound

Abstract

In boiling histotripsy (BH), millisecond-long HIFU bursts with shocks are used to mechanically liquefy tissue. Most BH studies have been performed under real-time B-mode ultrasound imaging of bubbles generated at the treatment site. However, such approach does not allow quantitative assessment of the degree of tissue liquefaction. In addition, aberration and clutter often limit the echogenicity introduced by bubbles. In this work, plane wave Doppler followed by B-mode imaging were implemented immediately after each BH pulse to visualize residual bubble motion during volumetric BH treatments in ex vivo bovine liver. The changes in the Doppler power and speed were used as metrics to assess the degree of tissue liquefaction. An ATL P6-3 imaging probe connected to a Verasonics Ultrasound Engine (VUE) was mounted in the central opening of a 256-element 1.5 MHz HIFU array driven by another VUE with 1.2 kW external power source enhanced by a capacitor bank. The proposed imaging sequence improved BH targeting and bubble visualization. As tissue liquefaction progressed from partial to full (single versus five BH pulses per focal spot), both Doppler power and residual bubble velocity directed away from the transducer increased (7-fold and 10 cm/s to 20 cm/s, correspondingly) and then saturated. [Work supported by NIH R01EB7643.]