Output intensity measurement on a diagnostic ultrasound machine using a calibrated thermoacoustic sensor

Abstract

Thermal ultrasound intensity sensors: concept and prototype calibration V Wilkens-Thermal ultrasound intensity sensors: application to exposimetry V Wilkens-Beam profile measurement on HITU transducers using a thermal intensity sensor technique V Wilkens, S Sonntag and K-V Jenderka-Abstract. A thermoacoustic measurement technique based on the transformation of the incident ultrasonic energy into heat inside a cylindrical absorber is investigated. To enable quantitative acoustic intensity measurements, a thermoacoustic sensor with an absorber 3 mm in diameter is calibrated in the far field of a planar source transducer. For ultrasound frequencies in the range from 1 to 9 MHz, the time-averaged intensities are derived from pressure field measurements using a membrane hydrophone. In a second run, measurements are performed with the thermoacoustic sensor at the same position in the acoustic field and under the same excitation conditions. The equilibrium temperature enhancement at the rear side of the absorber is determined at each frequency, and the transfer function of the sensor is given by the temperature enhancement per ultrasound intensity averaged over the sensor cross section. The calibrated thermoacoustic sensor is then applied to acoustic output measurements on a diagnostic ultrasound machine at various parameter settings. The results for M-mode and pulse Doppler mode, i. e. for non-scanning beams, are compared with the intensities derived from additional hydrophone measurements. If the spatial averaging effect of the thermoacoustic sensor is taken into consideration, agreement can be observed between the results of both methods.