Coupling agents in therapeutic ultrasound: Acoustic and thermal behavior

Casarotto RA, Adamowski JC, Fallopa F, Bacanelli F. Coupling agents in therapeutic ultrasound: acoustic and thermal behavior. Arch Phys Med Rehabil 2004;85:162-5. Objective: To compare transmissivity data and thermal behavior of 4 coupling media. Design: Experimental. Setting: Postgraduate rehabilitation program in Brazil. Specimens: Four coupling media: gel, mineral oil, white petrolatum, and degassed water. Interventions: Not applicable. Main Outcome Measures: The transmission, attenuation, reflection coefficient, and acoustic impedance of gel, mineral oil, white petrolatum, and degassed water were measured with a density measurement cell. The temperature variation in the therapeutic ultrasound transducer was measured with a thermocouple. Results: The transmissivity data showed that the water and gel presented the highest transmission coefficient, the lowest reflection, and an attenuation coefficient and acoustic impedance close to that of the skin. The thermal data revealed the highest heating in the transducer during the insonation with white petrolatum and mineral oil, resulting from the thermal conductivity features of each medium. Conclusions: Transmissivity data obtained showed that water and-gel present the best acoustic features. In ultrasound therapy, with the direct contact technique using thin layers of coupling agents, any product may be used, because the effect of the attenuation coefficient does not play a significant role when layers are as thin as those used in this experiment.