The Influence of Harmonic Ratio on HIFU-Induced Thermal Lesion Formation in Biological Tissue

High-Intensity Focused Ultrasound (HIFU) is a non-invasive therapeutic technique, widely used for thermal ablation of tumors and other pathological tissues. The formation of thermal lesions during HIFU therapy is influenced by nonlinear acoustic effects, including the generation of harmonics and harmonic ratios.

This study aimed to investigate the influence of the harmonic ratio on HIFU-induced thermal lesion formation in biological tissue. A coupled acoustic-thermal model is developed to simulate HIFU wave propagation and temperature elevation, incorporating nonlinear acoustic effects and dynamic tissue properties.

This numerical study investigates the influence of the harmonic ratio (R^* =(P₃ +P₄ )/P₂ ) on HIFU-induced thermal lesion formation in liver tissue. A coupled acoustic-thermal model was developed to simulate the propagation of HIFU waves and the resulting temperature elevation in tissue. The model incorporates nonlinear acoustic effects and dynamic tissue properties. The relationship between harmonic ratio, focal temperature, and thermal lesion size was analyzed through numerical simulation.

The results demonstrate that the harmonic ratio significantly affects the spatial distribution of acoustic energy deposition and the resulting thermal lesion size. Specifically, below 50 °C, the harmonic ratio decreases with rising focal temperature; above 50 °C, the harmonic ratio increases, indicating a turning point at the thermal denaturation threshold of liver tissue. Furthermore, higher harmonic ratio values correlate with larger thermal lesions, suggesting that higher-harmonic components enhance energy deposition in the focal region.

These findings provide insights into optimizing HIFU therapy by controlling harmonic ratio generation, thereby improving treatment efficacy and safety.