A Comparison of Human Muscle Temperature Increases During 3-MHz Continuous and Pulsed Ultrasound With Equivalent Temporal Average Intensities

Abstract

Study Design: A repeated-measure crossover design was used. The independent variable was the type of ultrasound (pulsed or continuous) and the dependent variable was intramuscular temperature. Objective: To compare changes in intramuscular temperature resulting from the use of pulsed ultrasound versus continuous ultrasound with an equivalent spatial average temporal average (SATA) intensity. Background: There is a lack of research on the heat-generating capabilities of pulsed ultrasound within human muscle. Methods and Measures:The subjects were 16 healthy volunteers (mean age ± SD, 21.3 ± 2.5 years). Each subject was treated with pulsed ultrasound (3 MHz, 1.0 W/cm 2 , 50% duty cycle, for 10 minutes) and continuous ultrasound (3 MHz, 0.5 W/cm 2 , for 10 minutes) during a single testing session. Tissue temperature returned to baseline and stabilized between treatments and treatment order was randomized. Tissue temperature was measured every 30 seconds using a 26-gauge needle microprobe inserted at a depth of 2 cm in the left medial gastrocnemius muscle. Data were analyzed using a linear mixed model. Results: Treatment with continuous ultrasound produced a mean (±SD) temperature increase of 2.8°C ± 0.8°C above baseline. Treatment with pulsed ultrasound produced a mean (±SD) temperature increase of 2.8°C ± 0.7°C above baseline. Statistical analysis revealed no significant differences in either the extent or rate of temperature increases between the 2 modes of ultrasound application. Conclusion: Pulsed ultrasound (3 MHz, 1.0 W/cm 2 , 50% duty cycle, for 10 minutes) produces similar intramuscular temperature increases as continuous ultrasound (3 MHz, 0.5 W/cm 2 , for 10 minutes) at a 2-cm depth in the human gastrocnemius. Spatial average temporal average intensity is an important consideration when selecting pulsed ultrasound parameters intended to deliver nonthermal effects.

Ultrasound-Induced Thermal Elevation in Clotted Blood and Cranial Bone

“…A temperature increase of 2.8° C was noted in these in-vivo experiments. Using eqn (10) and using the exposure parameters of Gallo et al (2004) and the absorption coefficient of 0.26 Np/cm for human skeletal muscle, the predicted temperature increase is 2.5° C, which is consistent with their measured value of 2.8°C . Similarly, Carstensen et al (1990) measured the temperature elevation in rat liver exposed to 2.0-MHz continuous wave ultrasound with an I SATA of 0.57 W/cm 2 .…”

“…In one study, temperature rise was quantified in human muscle exposed to 3.0-MHz pulsed ultrasound with a spatial average, temporal average intensity of 0.5 W/cm 2 for 10 min (Gallo et al 2004). A temperature increase of 2.8° C was noted in these in-vivo experiments.…”

Common Clinical Treatment of Plantar Fasciitis: A Survey of Physical Therapists Practicing in the Northeast Region of the United States

“…Many clinicians chose a pulsed setting with the idea that it offers non-thermal tissue healing benefits, and no increase the tissue temperature. As stated by Gallo et al [10] the association of a pulsed ultrasound as strictly a non-thermal modality is an "oversimplification", and "is likely to be problematic in establishing appropriate dosages of pulsed ultrasound in clinical practice." Gallo et al has shown that a pulsed ultrasound does not always result in a non-thermal effect.…”

“…Gallo et al has shown that a pulsed ultrasound does not always result in a non-thermal effect. He and his colleagues have indicated that ultrasound parameters set to 3MHz with a 50% duty cycle and a 1.0 W/cm 2 intensity for a period of 10 minutes had an equal effect on heating the tissue as did a 3MHz frequency with a 100% duty cycle and 0.5 W/cm 2 intensity, applied for 10 minutes [10]. In this example, the tissue was heated to approximately 3°C above baseline with both the continuous duty cycle and at 50%.…”

“…Hayes et al suggests that a 1 MHz ultrasound transducer will have a therapeutic effect on tissue up to 5 cm in depth. A 3 MHz is then best suited for tissues up to 2.5 cm in depth [9][10][11]. The plantar fascia is a broad band of non-contractile tissue that remains relatively superficial.…”