Why we should care about soft tissue interfaces when applying ultrasonic diathermy: an experimental and computer simulation study.
BACKGROUND
One goal of therapeutic ultrasound is enabling heat generation in tissue. Ultrasound application protocols typically neglect these processes of absorption and backscatter/reflection at the skin/fat, fat/muscle, and muscle/bone interfaces. The aim of this study was to investigate the heating process at interfaces close to the transducer and the bone with the aid of computer simulation and tissue-mimicking materials (phantoms).


METHODS
The experimental setup consists of physiotherapeutic ultrasound equipment for irradiation, two layers of soft tissue-mimicking material, and one with and one without an additional layer of bone-mimicking material. Thermocouple monitoring is used in both cases. A computational model is used with the experimental parameters in a COMSOL® software platform.


RESULTS
The experimental results show significant temperature rise (42 °C) at 10 mm depth, regardless of bone layer presence, diverging 3 °C from the simulated values. The probable causes are thermocouple and transducer heating and interface reverberations. There was no statistical difference in the experimental results with and without the cortical bone for the central thermocouple of the first interface [t(38) = -1.52; 95% CI = -0.85, 0.12;p= 14]. Temperature rise (>6 °C) close to the bone layer was lower than predicted (>21 °C), possibly because without the bone layer, thermocouples at 30 mm make contact with the water bath and convection intensifies heat loss; this factor was omitted in the simulation model.


CONCLUSIONS
This work suggests that more attention should be given to soft tissue layer interfaces in ultrasound therapeutic procedures even in the absence of a close bone layer.
Ultrasound Laboratory, Biomedical Engineering Program/COPPE/Federal University of Rio de Janeiro - UFRJ, Rio de Janeiro, Rio de Janeiro Brazil.
Thaís Pionório
TP
Omena
Ultrasound Laboratory, Biomedical Engineering Program/COPPE/Federal University of Rio de Janeiro - UFRJ, Rio de Janeiro, Rio de Janeiro Brazil.
Aldo José
AJ
Fontes-Pereira
Brazilian National Cancer Institute, INCA, Rio de Janeiro, Rio de Janeiro Brazil.
Rejane Medeiros
RM
Costa
Centre for Informatics and Systems, University of Coimbra, Coimbra, Portugal.
Ricardo Jorge
RJ
Simões
Ultrasound Laboratory, Biomedical Engineering Program/COPPE/Federal University of Rio de Janeiro - UFRJ, Rio de Janeiro, Rio de Janeiro Brazil.
Marco Antônio
MA
von Krüger
Ultrasound Laboratory, Biomedical Engineering Program/COPPE/Federal University of Rio de Janeiro - UFRJ, Rio de Janeiro, Rio de Janeiro Brazil.
Wagner Coelho de Albuquerque
WCA
Pereira
Diathermy; Evidence-based practice; Practice-research gap; Ultrasonic therapy; Ultrasound