Capabilities of fully populated multi-element ultrasound phased arrays for noninvasive surgical destruction of deep brain structures using shock waves

Three models of multi-element ultrasound phased arrays for shock-wave surgical destruction of deep brain structures through an intact skull are proposed. The arrays contain 256, 512, and 1024 elements and have the maximum dense filling of their surface with the elements. Unlike the existing systems of ultrasound neurosurgery, these arrays can realize not a thermal but a mechanical mechanism of tissue ablation (boiling histotripsy). Such approach permits to avoid undesirable overheating and damage to the skull bones. The proposed arrays are much more compact as compared to the existing systems. The arrays have the shape of a spherical segment with an aperture of 200 mm, whereas existing arrays have the shape of a hemispherical bowl with a diameter of 300 mm. Comparative analysis of focus steering capabilities is performed and the possibility of creating volumetric lesions larger than 20 mm in each dimension is shown for all proposed arrays. Nonlinear simulation demonstrated the possibility of reaching focal waveforms with developed shock fronts higher than 70 MPa, required for boiling histotripsy method. Taking into account energy losses when focusing through the skull bones and brain tissues, the intensity at the elements of the arrays does not exceed maximum permissible value of 40 W/cm2.