[Ultrasound control of thermal tissue therapy]

As alternatives to surgical resection and/or supportive to radio- or chemo-therapy of tumors and metastases minimal invasive interstitial thermal treatment procedures by which the tissue is heated up locally to temperatures up to 100 degrees C are used. However beside nuclear magnetic resonance tomography there is no economical, by routine applicable procedure for non invasive therapy control at present disposal. In this work the possibility of non invasive control of thermal therapies by means of temporal and spectral analysis of radio frequency ultrasound signals are evaluated. Two different ultrasonic procedures, the first beeing based on the analysis of local modifications in the time of flight of the ultrasound signal for determination of the temperature distribution in the tissue, the second beeing based on the physical attenuation characteristics of biological tissue and their dependence on the tissue structure are proposed and evaluated for therapy control. With in vitro experiments the possibilities and limitations of both procedures and preliminary results of a prototype control system are demonstrated.