Theoretical study of temperature elevation at muscle/bone interface duringultrasound hyperthermia

This paper examines the distributions of the SAR (specific absorption rate) ratio and temperature elevation when an ultrasound beam propagates through the interface of muscle and bone. This interface is regarded as a Rat boun dary to partition the energy of the ultrasound beam, and the analytical sol ution of temperature distribution is based on the steady-state bio-heat tra nsfer equation. The parameters considered are the incident angle of ultraso und beam, the ultrasound frequency, the acoustic attenuation coefficients o f refracted longitudinal and sheer waves in bone, and the blood perfusion i n muscle. The results show that the peak of the SAR ratio is always at the interface of muscle and bone, while the peak of temperature is located in t he bone region beyond the interface. A muscle with lower perfusion or a bon e with higher acoustic attenuation results in the shifting of the temperatu re peak closer to the interface. It is more difficult to heat a higher perf used muscle in front of a bone using a lower frequency ultrasound since the temperature elevation for bone relative to muscle is greater. (C) 2000 Ame rican Association of Physicists in Medicine. [S0094-2405(00)01005-1].