Self-heating of Diagnostic Ultrasound Transducers in Air and in Contact with Tissue Mimics

Abstract

The temperature rises at the surface of diagnostic ultrasound transducers in air and in contact with a tissue-equivalent phantom have been compared. Twenty-five transducers from seven different manufacturers were studied in imaging and pulsed Doppler modes. Comparisons were made between the temperature rise at 200 s 'in air' and 'on phantom' using two standard tissue mimicking materials (TMMs). Temperature rises in contact with the phantom (ΔTp) were always lower than those in air (ΔTa). Using a phantom that included a 1·5-mm silicone rubber layer to mimic the skin, the relative temperature rises ΔTp/ΔTa varied from 43 to 87 % with an average of 60%. The two TMMs gave comparable temperature rises despite their different compositions. Relative temperature rise depended slightly on frequency (2·5% MHz−1) and was higher on average in imaging mode than in pulsed Doppler mode. Linear relationships were observed between temperature rise and acoustic power, and relative temperature rise and silicone rubber thickness (∼11.5% mm−1). The phantoms gave rise to broadly similar temperature rises to those on skin, although the 1·5-mm silicone rubber skin-mimic layer may give a slight over-estimate of temperature rise for some transducers.