RATE OF TEMPERATURE INCREASE IN HUMAN MUSCLE DURING 1 MHZ AND 3 MHZ CONTINUOUS ULTRASOUND

To achieve the thermal effects of ultrasound, the tissue temperature m ust be raised from 1 to greater than or equal to 4 degrees C, dependin g on the desired outcome of the treatment. In the past 25 years, there have been no in vivo studies that have measured rate of change in tem perature during 1-MHz ultrasound treatments, and none have ever been p erformed with the 3-MHz frequency. Thus, we are left to pure speculati on regarding how long to administer an ultrasound treatment We perform ed this study to plot the rate of temperature increase during ultrasou nd treatments delivered at various intensities and frequencies. We ins erted two 23-gauge thermistors into each subjects' medial triceps sura e at the following depths: 1 MHz at depths of 2.5 and 5.0 cm (12 subje cts) and 3 MHz at depths of .8 and 1.6 cm (12 subjects). Each subject received a total of four 10-minute treatments, one each at .5, 1.0, 1. 5, and 2.0 W/cm(2), and temperature was measured every 30 seconds. No significant difference was found in the rate of heating at the two dep ths (p = .987) within the same frequency and dose levels. The 3-MHz fr equency heated significantly faster than the 1-MHz frequency at all do ses tested (p < .001). On average, the rate of temperature increase pe r minute at the two depths of the 1-MHz frequency was: .04 degrees C a t .5 W/cm(2); .16 degrees C at 1.0 W/cm(2); .33 degrees C at 1.5 W/cm( 2); and .38 degrees C at 2.0 W/cm(2). The rate of temperature increase per minute at the two depths of the 3-MHz frequency was: .3 degrees C at .5 W/cm(2); .58 degrees C at 1.0 W/cm(2); .89 degrees C at 1.5 W/c m(2); and 1.4 degrees C at 2.0 W/cm(2). The results of this research s hould enable clinicians to choose the correct frequency, intensity, an d treatment time when using thermal ultrasound.