In vivo phase aberration correction for high intensity focused ultrasound therapy with a 256-element spiral array

One of the challenges of transcutaneous high intensity focused ultrasound therapies, especially ones relying on shock formation such as boiling histotripsy (BH), is the deterioration of focusing from phase aberration induced by soft tissue heterogeneities within the acoustic path. Here, a methodology to perform phase aberration correction in vivo is proposed. A custom BH system consisting of a 1.5 MHz phased array of 256 elements connected to Verasonics V1 system was used in pulse/echo mode targeting liver and kidneys in swine. Phase shift on each element needed to correct for aberration was estimated by maximizing the value of the coherence factor on the backscattered signals received from the focal region and iteratively repeating the pulse emission with corrected phases. The process required 3 to 10 iterations to converge to a solution, which necessitated the implementation of tracking the moving target via additional pulse/echo sequences. The performance of the method was evaluated by comparing the transducer driving voltage needed for shock-forming conditions to generate a boiling bubble at the target with and without aberration correction. Results show that aberration correction effectively lowers the voltage required to reach boiling by 8%–25%. [Work supported by NIH R01EB007643, R01GM122859, R01EB25187, P01DK043881, and RSF 20-12-00145.]