Investigation of ultrasonic fields produced by HIFU transducers used in cancer therapy

Ultrasonic fields induced by HIFU (High Intensity Focused Ultrasound) have been studied. Effect of input electrical power, harmonics and nonlinear propagation of the ultrasound fields has been quantized. Asymmetric waveforms with peak (+) pressures and peak (-) pressures were obtained both numerically and experimentally. Nonlinear propagation with harmonics output was dominant at higher intensities that leads to an increase of the compressional wave and a decrease of rarefactional wave. All measurements have been realized in the constructed system at National Metrology Institute of Turkey, TÜBİTAK UME. Set up includes a water reservoir, positioning system, HIFU transducers, needle hydrophone, power amplifier, signal generator, measurement and control devices which are all controlled by LabVIEW 8.1 software. P+, P- and P pressures have been determined theoretically for each waveform. Wave behaviors generated by the Khoklov-Zabolotskaya-Kuznetsov model (KZK model) and from experiments match in general. Decrease in size of focus point was shown in 3rd harmonic.