Intramuscular Heating Characteristics of Multihour Low-Intensity Therapeutic Ultrasound.
BACKGROUND
The heating characteristics of a stationary device delivering sustained acoustic medicine with low-intensity therapeutic ultrasound (LITUS) are unknown.


OBJECTIVE
To measure intramuscular (IM) heating produced by a LITUS device developed for long-duration treatment of musculoskeletal injuries.


METHODS
Controlled laboratory study.


METHODS
University research laboratory.


METHODS
A total of 26 healthy volunteers (16 men, 10 women; age = 23.0 ± 2.1 years, height = 1.74 ± 0.09 m, mass = 73.48 ± 14.65 kg).


METHODS
Participants were assigned randomly to receive active (n = 20) or placebo (n = 6) LITUS at a frequency of 3 MHz and an energy intensity of 0.132 W/cm(2) continuously for 3 hours with a single transducer or dual transducers on the triceps surae muscle. We measured IM temperature using thermocouples inserted at 1.5- and 3-cm depths into muscle. Temperatures were recorded throughout treatment and 30 minutes posttreatment.


METHODS
We used 2-sample t tests to determine the heating curve of the LITUS treatment and differences in final temperatures between depth and number of transducers.


RESULTS
A mild IM temperature increase of 1 °C was reached 10 ± 5 minutes into the treatment, and a more vigorous temperature increase of 4 °C was reached 80 ± 10 minutes into the treatment. The maximal steady-state IM temperatures produced during the final 60 minutes of treatment at the 1.5-cm depth were 4.42 °C ± 0.08 °C and 3.92 °C ± 0.06 °C using 1 and 2 transducers, respectively. At the 3.0-cm depth, the maximal steady-state IM temperatures during the final 60 minutes of treatment were 3.05 °C ± 0.09 °C and 3.17 °C ± 0.05 °C using 1 and 2 transducers, respectively. We observed a difference between the temperatures measured at each depth (t78 = -2.45, P = .02), but the number of transducers used to generate heating was not different (t78 = 1.79, P = .08).


CONCLUSIONS
The LITUS device elicited tissue heating equivalent to traditional ultrasound but could be sustained for multiple hours. It is a safe and effective alternative tool for delivering therapeutic ultrasound and exploring dosimetry for desired physiologic responses.
Department of Human Performance and Health Promotions, Weber State University, Ogden, UT;
Justin H
JH
Rigby
Advanced Health Products Research Lab, Trumbull, CT;
Rebecca M
RM
Taggart
Advanced Health Products Research Lab, Trumbull, CT;
Kelly L
KL
Stratton
Advanced Health Products Research Lab, Trumbull, CT;
George K
GK
Lewis
Department of Exercise Science, Brigham Young University, Provo, UT. Dr Rigby is now with the Department of Athletic Training and Nutrition, Weber State University.
David O
DO
Draper
D001831:Body Temperature / Q000502:physiology*; D018592:Cross-Over Studies; D004867:Equipment Design; D005260:Female; D064368:Healthy Volunteers; D006361:Heating; D006801:Humans; D007866:Leg; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D013821:Thermometers; D013997:Time Factors; D014464:Ultrasonic Therapy / Q000295:instrumentation / Q000379:methods*; D055815:Young Adult
rehabilitation; therapeutic modalities; tissue temperature