Identical 3-MHz ultrasound treatments with different devices produce different intramuscular temperatures

A counterbalanced, repeated-measures design with ultrasound device (Omnisound 3000C, Dynatron 950, Excel Ultra III) as the independent variable. The 2 dependent variables were intramuscular (IM) temperature at 6 minutes and at the end of a 10-minute treatment.

To compare IM temperatures produced by identical 3-MHz ultrasound treatments between 3 different ultrasound devices.

Most recent studies prescribing intensity and duration parameters for thermal ultrasound treatments have been performed using an Omnisound device, but have not been verified in other common ultrasound devices.

Six uninjured volunteers (mean age +/- SD, 22 +/- 3.4 y; mean height +/- SD, 171.9 +/- 11.0 cm; mean mass +/- SD, 66.1 +/- 11.1 kg) gave informed consent and served as subjects. Separate ultrasound treatments using identical parameters (3 MHz, 1.5 W/cm2, 10 minutes, treatment area equal to twice transducer surface area) were administered at 24 or 48 hours intervals using a different ultrasound device for each treatment. Left medial calf IM temperature was recorded every 20 seconds using implantable thermocouples at a depth of 1.6 cm below the treatment surface. Data were analyzed using MANOVA with Sidak adjusted multiple comparisons post hoc.

Tissue heating using the Omnisound device was greater than with either the Dynatron or the Excel. The results of treatments using Dynatron or Excel devices did not differ. The Omnisound was the only device to consistently produce IM temperatures above the 40 degrees C therapeutic threshold and did so in less than 6 minutes. The other devices did not reach this threshold within the 10-minute treatment session. Subjects routinely reported heating sensations approaching discomfort when the IM temperature reached the 40 degrees C therapeutic threshold.

Because there are differences in thermal effects between ultrasound devices, our results suggest that recently published parameters for ultrasound intensity and duration parameters will not produce equally therapeutic effects for all ultrasound devices.