Aberration-inducing body wall phantom for high-intensity focused ultrasound applications

Aberrations induced by soft tissue inhomogeneities distort acoustic fields and often complicate HIFU therapies. An aberration-generating phantom was designed and fabricated to mimic the acoustic effects of a porcine body wall. A rippled surface pattern replicating inhomogeneities of size scales relevant to the porcine body wall was transferred to a large phantom made of fat-like and muscle-like gel materials. The acoustic distortions produced by the phantom and an ex vivo porcine body wall were characterized by hydrophone measurements with a 256-element 1.5 MHz focused ultrasound array (diameter = 144 mm, F# = 0.83). Insertion of the phantom generated large distortions for both linear and nonlinear beam focusing including displacement of the focus (up to 0.3 mm transversely), enlargement of the focal region, and reduction in focal pressures due to aberration (up to 2.5-fold peak positive pressure reduction). The phantom and porcine body wall produced similar levels of aberration and attenuation effects. An aberration correction approach was leveraged to isolate the quantitative effect of aberration and to restore shocks in nonlinear waveforms in the focus. Boiling histotripsy treatments through the phantom or body wall were subsequently demonstrated in a hematoma sample. [This work was supported by NIH R01EB7643 and R01EB25187, and RSF 20-12-00145.]