Theoretical study of temperature elevation at muscle/bone interface during ultrasound hyperthermia

Abstract

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 flat boundary to partition the energy of the ultrasound beam, and the analytical solution of temperature distribution is based on the steady-state bio-heat transfer equation. The parameters considered are the incident angle of ultrasound beam, the ultrasound frequency, the acoustic attenuation coefficients of refracted longitudinal and shear waves in bone, and the blood perfusion in 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 the bone region beyond the interface. A muscle with lower perfusion or a bone with higher acoustic attenuation results in the shifting of the temperature peak closer to the interface. It is more difficult to heat a higher perfused muscle in front of a bone using a lower frequency ultrasound since the temperature elevation for bone relative to muscle is greater.

Prostate thermal therapy with high intensity transurethral ultrasound: The impact of pelvic bone heating on treatment delivery

“…When ultrasound is aimed directly at bone, $65% of the incident energy is transmitted into the bone in the form of longitudinal waves [28,62]. As the incident angle of ultrasound on bone increases, the transmission of longitudinal waves decreases but shear waves with a higher attenuation coefficient than longitudinal waves are generated [66].…”

“…The absorption, reflection, and transmission of ultrasound energy at a soft-tissue/bone interface is complex [28,32,33,62,[64][65][66]. When ultrasound is aimed directly at bone, $65% of the incident energy is transmitted into the bone in the form of longitudinal waves [28,62].…”

“…The pubic bones have acoustic and thermal properties similar to cortical bone, but unlike soft tissue, the attenuation and perfusion of bone remain unchanged during heating. The acoustic and thermal properties used for the prostate, bone, rectum, and periprostatic tissue within this model are shown in Table I [26,28,29,52,55,[59][60][61][62][63].…”

Preliminary study of Pseudoarthrosis ultrasonic characterization

“…As expected, average TSAB value for pseudoarthrosis (2.2 ± 1.0 dB/µs) was higher than for bone. Pseudoarthrosis is similar to soft tissue and thus, produces less absorption and attenuation than bone [15].…”

Software didático para modelagem do padrão de aquecimento dos tecidos irradiados por ultra-som fisioterapêutico

“…The software was developed with the use of LabVIEW 7.1 (National Instruments ), implementing these layers (according to tissue properties, as in Table 1 19,20 ), and simulating the passage of a flat wave according to the equations previously described. The software allows the user to define the following parameters of each layer: thickness (x), attenuation coefficient ( ), acoustic impedance (Z), density ( ), specific heat (c), and thermal conductivity (k).…”