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Variations in the output power and surface heating effects of transducers in therapeutic ultrasound
Christian Kollmann1, Gerda Vacariu, Othmar Schuhfried
1Center for Biomedical Engineering and Physics, Medical University of Vienna, Vienna, Austria. christian.kollmann@meduniwien.ac.at
Objective:
To determine the real emitted output power and maximum surface heating of commercial therapeutic ultrasound transducers emitting in air for various therapeutic regimens.
Design:
Surface temperatures of ultrasound transducers with frequencies of .05 to 3 MHz were detected over 5 minutes by using a calibrated infrared thermographic camera; additionally, the indicated output power was checked with a radiation force balance.
Setting:
University center for biomedical engineering and physics and medical school for physical medicine and rehabilitation.
Participants:
Not applicable.
Interventions:
Not applicable.
Main Outcome Measures:
Power variations and surface temperatures of clinical devices were analyzed to determine whether they comply with obligatory limits given in International Electrotechnical Commission standard 60601-2-5.
Results:
Depending on the operation mode and the output power, surface temperatures ranged between 24.2 degrees to 80 degrees C within 5 minutes. Differences between measured and displayed power output (limit, +/-20%) ranged between -32% and 28%.
Conclusions:
The effectiveness of treatment is lowered if the value of emitted power is not known reliably. In the worst case, damage or irritation of the skin is possible, particularly in patients with sensory compromised skin. Damage may be caused by hot surfaces if the threshold level required to activate the device is lowered or if the device is defective. Improved thermal control units are necessary to prevent potential thermal hazards. Regular checks of transducer emission should be obligatory to ensure correct and precise function of the clinical devices.
