Focused ultrasound ablation using electronically scanned grating lobes with real-time echo decorrelation imaging feedback

Focused ultrasound can successfully treat tumors by thermal ablation, but treatments using mechanical or electronic scanning of single foci can be prohibitively long. This study investigated a proposed approach to increase ablation efficiency by creating multiple foci as grating lobes of a coarse ultrasound aperture, then electronically scanning these grating lobes by applying phase rotations to shift their positions. A 64-element, 5.4 MHz linear image-ablate array performed weakly focused ablation (380 W/cm
²
spatial-peak, temporal peak intensity [I
_SPTP
]) using a virtual 32-element aperture (2.5λ pitch) as well as real-time ablation monitoring and control by echo decorrelation imaging. Phase shifts were applied to treat a planar tissue region by employing five symmetrically arranged grating lobe patterns. Treatments were assessed in ex vivo bovine liver. Lesion dimensions and treatment durations were compared with uncontrolled and unfocused ablation treatments. Results demonstrate that electronic grating lobe scanning with control by echo decorrelation imaging can ablate tissue more efficiently than uncontrolled or unfocused approaches.