The impact of the central opening on nonlinear effects in ultrasound fields generated by Sonalleve V1 and V2 MR-HIFU systems

Abstract

Previous studies have shown that the Sonalleve MR-HIFU clinical system can generate shocks of 80–105 MPa at the focus, which is sufficient for boiling histotripsy. Two versions of the system (V1 and V2) have therapeutic transducers that differ in focusing angle, arrangement of elements, and the size of a central opening. The goal here was to reveal the impact of different array geometries on shock amplitudes at the focus. Nonlinear modeling of the array’s field in water using boundary conditions reconstructed from holography shows that at the same power output, the V2 array generates 10–15 MPa lower shock amplitudes at the focus. Although this difference is mainly caused by the smaller focusing angle of the V2 array, the larger central opening of the V2 array has a nontrivial impact. By suppressing a direct wave, the central opening produces a somewhat higher shock amplitude. Axisymmetric equivalent source models were constructed for both arrays and the importance of including the central opening was demonstrated. These models can be used in the “HIFU beam” software for simulating nonlinear fields of the Sonalleve V1 and V2 systems in water and flat-layered biological tissues. [Work supported by RSF-22-72-00047 and NIH R01EB025187.]