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Effect of mode conversion on ultrasonic heating at tissue interfaces.
B A Haken1, L A Frizzell, E L Carstensen
1Department of Electrical and Computer Engineering, University of Illinois, Urbana 61801.
Summary
Localized ultrasound heating near tissue interfaces is explained by mode conversion to shear waves. Shear waves in bone significantly contribute to heating, while muscle shear waves have a negligible effect.
Area of Science:
- Biomedical engineering
- Acoustics
- Tissue interaction
Background:
- Localized heating observed near tissue impedance discontinuities during ultrasound exposure.
- Previous hypothesis suggested mode conversion to shear waves and rapid absorption as the cause.
Purpose of the Study:
- To present a mathematical model for mode conversion at viscoelastic interfaces.
- To quantify mode conversion at muscle-air and muscle-bone interfaces.
Main Methods:
- Developed a mathematical model for mode conversion at a plane interface.
- Utilized longitudinal and shear properties of viscoelastic media.
- Calculated mode conversion at muscle-air and muscle-bone interfaces.
Main Results:
- Mode conversion to shear waves occurs at impedance discontinuities.
- Shear waves in bone are identified as a significant source of localized heating.
- Shear waves in muscle contribute negligibly to heating at the interface.
Conclusions:
- The mathematical model explains localized ultrasound heating at tissue interfaces.
- Bone-related shear waves are a primary driver of observed heating phenomena.
- Muscle shear waves do not significantly influence heating at these interfaces.