Therapy monitoring and assessment using quantitative ultrasound

Quantitative ultrasound (QUS) techniques have demonstrated the ability to detect changes in tissue microstructure following the application of cancer therapy. In this chapter, QUS techniques, i.e., spectral-based analysis and envelope statistics, are examined for their ability to detect, image and quantify the therapeutic response of diseased and normal tissues ex vivo and in vivo. Specifically, high frequency QUS (>20 MHz) techniques were used to detect changes in the tumor microstructure of cancer mouse models following radiation therapy and changes in ex vivo liver tissue following thermal therapy. QUS parameter estimates were correlated with changes observed in photomicrographs of histological slides of stained tissues. Mouse tumors treated with radiation therapy demonstrated an increase in the ultrasound integrated backscatter of 6–8 dB in the treated regions compared to untreated regions. The treated regions can be clearly distinguished in ultrasound images as hyperechoic areas. When liver tissues were treated with heat, a change in the slope of the frequency dependence of the backscatter coefficient versus thermal dose was observed. QUS changes were examined versus transient elevations in temperature using a thermocouple in order to guide the application of thermal therapies in these samples. It was observed that some QUS parameters were capable of tracking changes in the temperature. This work provides means of using QUS to monitor and guide therapy application, and rapidly assess the response of tissues to different therapies.