A Comparison of Temperature Rise in Human Calf Muscles following Applications of Underwater and Topical Gel Ultrasound

trasound is one of the most widely used therapeutic modalities for treating soft tissue injuries. In 1987, 4 million ultrasound treatments were performed in Canada (1 7). Many of its uses have been documented, including wound healing (4), reabsorp tion of calcium deposits (2). increasing tendon extensibility (6), pain relief (9, 18), and treatment of plantar warts (1, 8 , 13, 16). Ultrasound treatment of sports injuries is on the rise. It is the treatment of choice when tissue temperature rise is indicated for a variety of soft tissue dysfunctions (1 1, 12). Ultrasound is a sound wave generator that operates above the audible threshold of humans. Therapeutic ultrasound is administered a t a frequency in the range of 800,000 to 3 million Hz. These sound waves cause molecular vibration and collision, and the increase in molecular activity results in heat (7). T h e therapeutic benefits of ultrasound are derived from the transfer of mechanical to thermal energy. T h e therapeutic benefits of ultrasound are classified as thermal o r nonthermal. T h e majority of ultrasound treatments are administered to obtain thermal benefits. Thermal effects of For ultrasound to be effective, a conducting medium must be placed between the soundhead and the skin. Little research has been performed to test whether or not these mediums actually work. The purpose of this study was to compare the effect of tap water immersion and ultrasound gel conducting mediums on tissue temperature rise in the human leg. A 23-gauge hypodermic needle microprobe was inserted 3 cm deep into the medial portion of the gastrocnemius muscle of 20 subjects. Each subject participated in two random order treatments using tap water immersion and topical gel conducting mediums. Each treatment consisted of continuous ultrasound delivered topically at 1.5 W/cm2 for 10 minutes. During both treatments, the soundhead was moved at a speed of 4 cm per second, and the temperature was recorded every 30 seconds. A significant difference was found between the two treatment methods Tt(19) = 9.18, p < .001]. The !apical gel increased tissue temperature 4.8 C, whereas the underwater treatment increased tissue temperature only 2.1 C. Therefore, at a tissue depth of 3 cm, ultrasound gel is a better conducting medium than water. Also, the authors discovered that it took nearly 8 minutes for the temperature to reach therapeutic levels during the gel technique. These findings should be of clinical significance to clinicians who regularly use ultrasound.