Comparison of tissue heating between manual and hands-free ultrasound techniques.

The objective of this single-factor repeated-measures design was to examine the effectiveness of tissue heating with a hands-free ultrasound (US) technique compared to a hand-held US transducer using the Rich-Mar AutoSound unit. US is a therapeutic modality often used to provide deep tissue heating. Recently, a "hands-free" US unit was introduced by Rich-Mar Incorporated. This unit allows the clinician to choose the mode of US delivery, using either a handheld (manual) transducer or a hands-free device that pulses the US beam through the transducer. However, the Center for Medicare and Medicaid Services has deemed delivery of US via a hands-free unit to be investigational. Forty volunteers over 18 years of age participated. Treatment was provided at a 3-MHz US frequency. Muscle temperature was measured with 26-gauge, 4-cm Physiotemp thermistors placed in the triceps surae muscle. The depth of thermistor placement was at 1 - and 2-cm deep. One calf was treated with a manual transducer (5-cm(2) US head at three times the effective radiating area [ERA]), and one calf was treated with the hands-free transducer (14-cm(2) [ERA]). Both methods used a 1.5 W/cm(2) intensity for 10 minutes. The manual technique used an overlapping circular method at 4 cm/sec, and the hands-free method used a sequential pulsing at 4 cm/sec. Tissue temperatures were recorded at baseline and every 30 seconds. The hands-free technique resulted in a tissue temperature increase from 33.68 to 38.7 degrees C and an increase from 33.45 to 40.1 degrees C using the manual technique at 1-cm depth. The tissue temperature increase at the 2-cm depth was from 34.95 to 35.44 degrees C for the hands-free device and 34.44 to 38.42 degrees C for the manual device. Thus, there was a significant difference between the hands-free and the manual mode of US delivery for the 3-MHz frequency (5.02 degrees C vs. 6.65 degrees C at 1 cm and 1.49 degrees C vs. 3.98 degrees C at 2 cm). In this study, the "hands-free" device did not result in the same level of tissue heating as the manual technique. The hands-free device has the advantage of not needing a clinician present to deliver the modality but a therapeutic level of heating was not achieved at the 2-cm tissue depth. Thus, the efficacy of the "hands-free" treatment is in question.