Rate of Temperature Change in Human Fat during External Ultrasound: Implications for Liposuction

This paper will introduce a third type of ultrasonically assisted liposuction. This is a surface-applied technique, but instead of using only the mechanical effects of ultrasound, it focuses on thermal effects to heat fat prior to liposuction of small pockets of fat, such as those in the upper arm or under the chin. This information would be valuable to cosmetic surgeons, who recently have been using external ultrasound prior to liposuction. Previous data have been published regarding the rate of ultrasound heating in muscle and tendon; however, this rate has not been recorded for fat tissue. This study was performed to determine if ultrasound could vigorously heat fat and to note the frequency, intensity, and treatment duration required. Ten females (mean age of 38 ± 1.4 years) volunteered to participate in the investigation and signed informed consent waivers. The left tricep was cleansed with a Betadine scrub while the subject was supine. A 1-cc injection of 1% lidocaine (Xylocaine) buffered with sodium bicarbonate was administered subcutaneously to anesthetize the area. Next, a 23-gauge thermistor micro-probe connected to a monitor was inserted into the adipose tissue covering the left tricep muscle belly. After ultrasound gel was applied to the area, we administered ultrasound at the following parameters: continuous mode; 3-MHz frequency; 1 W/cm²; 10-minute duration; and treatment size = 2 times the size of the effective radiating area. Temperature was recorded every 60 seconds. At the end of each 10-minute application, we recorded the per-minute rate at which the temperature dropped for 10 minutes. The rounded mean baseline temperature was 33°C, and the temperature peaked at 40.5°C (average increase from baseline to peak = 7.5°C). The fat temperature dropped 4.0°C and 5.5°C, respectively, at 5 and 10 minutes postinsonation. Our protocol resulted in vigorous heating of adipose tissue.