Theoretical study of concave spherical ultrasonic and high focused ultrasound for hyperthermia(1)

Heating tumor tissue has become one of the important methods for treating tumors. Ultrasound has become an important heating treatment because of its characteristics of easy to produce,it is focusable and invasive. In recent years, HIFU piezo for thermoplastic weight heating therapy technology has developed so rapidly. Because of the difference in the damage of normal tissue and diseased tissue at high temperature, the selection of focused piezo is very important. Adding the piston sound source to the acoustic lens and grinding piezoelectric ceramic into a concave surface are commonly used for acoustic focusing methods. When the vibration velocity of piezoelectric ceramic on the concave spherical acoustic lens focusing piezo is Gaussian, the focused sound source is called on focused Gaussian sound source. In this paper, the concepts of thermal focal length and temperature field 3 dB are introduced. The differential heat method of HIFU piezo ceramic is used to solve the bioheat transfer equation. The heating effects of these focused ultrasound on biological tissues are studied. Different conditions are analyzed by isotherms, assuming focused Gaussian sound and The acoustic focal spot of the concave spherical self-focusing sound has the same size, geometric focal length, half aperture, and frequency are respectively 3cm, 10cm, 10MHz.

The results show that the sound field and temperature field distribution in the biological tissue are different when the concave spherical self-focusing HIFU ultrasound piezo ceramic and the focused Gaussian sound source are heated. When the concave spherical surface is heated by the focusing source, the sound pressure at the near source fluctuates; when the Gaussian source is heated, the sound pressure distribution is smoother. When the concave spherical surface is heated by the self-focusing sound source, the isotherm is formed into a heart shape, and the near source is laterally wider; when the Gauss source is heated, the isotherm is similar to an ellipse, and the long axis is along the direction of sound propagation. When the acoustic intensity of the concave end of the HIFU piezo transducer is the same, the effective treatment area corresponding to the concave spherical self-focusing sound source is wider, the effective treatment area corresponding to the focused Gaussian sound source is concentrated, and the temperature at the sound focus can be stabilized more quickly. Comparing the main characteristics of the sound field and steady-state temperature field generated by the two focused ultrasound sources, the focal length and thermal focal length of the HIFU ultrasound for weight loss are larger, which is closer to the geometric focal length, and the deviation between the acoustic focal length and the thermal focal length is more obvious; the sound field and temperature The field axial 3 d B width is larger, and the difference between the two is also greater.