Modulation of transcranial focusing thermal deposition in nonlinear HIFU brain surgery by numerical simulation

As the skull induces strong aberrations in phase and amplitude during transcranial treatment of brain surgery, high-intensity focused ultrasound suffers degradation in beam shape and deposits significant heat in the skull which may cause thermal damage to the bone and surrounding tissue. The goal of this study is to optimize the transcranial pressure and thermal fields to reduce thermal damage to the skull and simultaneously concentrate more energy in the focal region and make its size controllable during transcranial brain tumor treatment by modulating the excitation signals of the transducer array (including the phase and amplitude) and superposing the signals used to reduce peak pressure in the skull. A 3D numerical model was developed based on the reconstructed images from high-resolution CT scans of a human skull and a 64-element phased array to simulate acoustic propagation and thermal behavior calculated by the finite-difference time domain method. The simulation showed that more energy was focused at the setting target with little temperature elevation in the skull after correcting phase and amplitude and reducing peak pressure in the skull; through modulating the input intensity of arrays, the volume of focal regions located off-axis could be made equal to the volume achieved with on-axis focusing.