Aberration correction using nonlinear backscattered signals from the focus of an ultrasound beam

High intensity focused ultrasound (HIFU) therapies are often affected by aberrations, which can severely limit treatments. For multi-element arrays, applying phase corrections for each element could mitigate these effects. Here, an aberration correction method based on cross-correlation of nonlinear HIFU waves, backscattered from the focus is proposed and tested. A spherically focused 1.5 MHz 256-element HIFU array powered by Verasonics system was used for both emitting and receiving backscattered ultrasound waves. A short (3-cycle) high-amplitude pulse was transmitted through an aberrating layer into an ex vivo clotted bovine blood sample. The backscattered signal was recorded by individual array elements and high-pass filtered at 4 MHz. The layer introduced different acoustic path lengths for individual elements leading to a decrease in the peak-positive pressure of ~70%. The time delay required for each element to restore the nonlinear waveform at the focus was calculated based on the cross-correlation between the backscattered filtered signals. The results were confirmed by replacing the sample with a hydrophone. Using the corrected time delays, peak-positive focal pressure increased over 75% from uncorrected aberrated levels. These results demonstrate that the proposed focal “nonlinear beacon” can be used for phase correction feedback in HIFU treatments of soft tissue. [Work supported by NIH R01GM122859, R01EB007643, and RSF19-12-00148.]