Nonlinear effect in fat tissue for high-intensity focused ultrasound

Nonlinearity plays a significant role in high-intensity focused ultrasound (HIFU) treatment since the generation of higher harmonic frequency components enhances absorption and thus heating effects. High-B/A fat layer commonly appears in the propagation path so that HIFU fields could be affected by nonlinearity and attention needs to be paid to the changes since caused for nonlinearity may not be easily perceived by usual linear viewpoint. To gain a more accurate knowledge in the interaction of ultrasound through multi-layered tissue and better control therapeutic outcome, a HIFU simulator software package is used to numerically simulate the axisymmetric ultrasound propagation through water-fat layered medium. Results show that nonlinearity plays a major part in increasing peak acoustic intensity (/peak) and decreasing focus deviation (Δzfocus) for HIFU propagation in fat. Furthermore, sharper focused transducer with higher acoustic power could enhance nonlinear effect.