Do. Draper et al., RATE OF TEMPERATURE INCREASE IN HUMAN MUSCLE DURING 1 MHZ AND 3 MHZ CONTINUOUS ULTRASOUND, The Journal of orthopaedic and sports physical therapy, 22(4), 1995, pp. 142-150
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.