Measuring the surface-heating of medical ultrasonic probes

Abstract

Due to converting losses the probe's surface itself is heated up, especially whenemitting into air. Possible temperature increases in an ensemble of 15 different diagnostic andtherapeutic ultrasound probes from 7 manufacturers in the frequency range between 0.05–7.5MHz have been examined. Surface temperatures were detected by means of a calibrated IR-thermographiccamera using a scheme of various power and pulse settings, as well as differentimaging modalitites as used in clinical routine. Depending on the setup and the output power,the absolute surface temperatures of some of the probes emitting in air can be beyond 43 °Cwithin 5–7 min.; a maximum surface temperature of 84 °C has been detected. Continuous modeor high pulse repetition frequencies on the therapeutic system side, small focused Doppler modeson the diagnostic system side combined with increased emitted acoustic intensities result inhigh surface temperatures. Within a worst case scenario a potential risk of negative skin changes(heat damage) or non-optimal therapeutic effects seems to be possible if a therapeutic systemis used very often and if its emission continues unintentionally. In general the user shouldbe aware that low emission intensities of e.g. 50 mW cm-2 could already produce hot surfaces.