B-scan ultrasound imaging of thermal coagulation in bovine liver: frequency shift attenuation mapping

Thermal therapy is an experimental procedure to treat localised tumours in, for example, the prostate, liver, kidney or breast. Following work that demonstrated a marked increase in the ultrasound (US) attenuation of tissues heated above 65 degrees C, US attenuation estimation is proposed as a method to monitor the progression and extent of thermal therapy. In this study, B-scan attenuation mapping techniques, based on the shift in centre frequency of the US signal, are examined. A simple technique based on the change of phase of the quadrature-demodulated signal is presented and analysed. Autoregressive analysis is also examined. It is shown with simulated data that these methods are effective at differentiating and localizing the attenuation change associated with tissue coagulation, but that, in the analysis of phantom or ex vivo bovine liver data, electronic noise severely limits the effectiveness of these techniques.