Ultrasound power deposition model for the chest wall

An ultrasound power deposition model for the chest wall was developed based on secondary-source and plane-wave theories, The anatomic model consisted of a muscle-ribs-lung volume, accounted for wave reflection and refraction at muscle-rib and muscle-lung interfaces, and computed power deposition due to the propagation of both reflected and transmitted waves. Lung tissue wa s assumed to be air-equivalent. The parts of the theory and numerical progr am dealing with reflection were experimentally evaluated by comparing simul ations with acoustic field measurements using several pertinent reflecting materials. Satisfactory agreement was found. A series of simulations were p erformed to study the influence of angle of incidence of the beam, frequenc y, and thickness of muscle tissue overlying the ribs on power deposition di stributions that may be expected during superficial ultrasound (US) hyperth ermia of chest wall recurrences. Both reflection at major interfaces and at tenuation in bone were the determining factors affecting power deposition, the dominance of one vs, the other depending on the angle of incidence of t he beam. Sufficient energy is reflected by these interfaces to suggest that improvements in thermal doses to overlying tissues are possible with adequ ate manipulation of the sound field (advances in ultrasonic heating,devices ) and prospective treatment planning. (C) 1999 World Federation for Ultraso und in Medicine & Biology.