P3P-8 Strongly Curved Short Focus Annular Array For Therapeutic Applications

Strongly focused transducers are widely used in medical therapeutic applications. Radiators with a short focal length, utilized in treatments of subcutaneous tissues, have particular safety requirements to provide a delivery of high intensity ultrasound inside the tissue, yet not harming the overlaid layers and the skin. Numerical simulations can be employed to carefully design the system, however strongly focused transducers are difficult to model at high intensity levels of excitation. Full field diffraction method is time consuming for modeling of nonlinear waves, and the conventional parabolic approximation, proven to be very effective for low aperture sources, is not valid in this case. A novel parabolic approach modified for modeling strongly curved high intensity annular arrays transducers is developed in this work and validated by comparison of the linear solutions for strongly curved single element radiator with those of the full diffraction model, and nonlinear solutions for lower focusing radiator with those available in literature. The approach is applied for designing 16 element annular array of 1 MHz frequency, 100 mm aperture and 60 mm focal length. The results of simulations of nonlinear ultrasound field for different focusing depth along the acoustic axis are presented. They show that very high peak pressure levels, significantly higher than those generated by low-aperture radiators, is possible to obtain in strongly curved short focus fields due to better focusing and lower nonlinear saturation effects