Characterization of high intensity focused ultrasound induced thermal lesions from changes in ultrasound backscatter.

Abstract

Although good results have already been obtained, notably in urology, ultrasound-guided HIFU devices lack a real time monitoring system different from conventional B-mode ultrasound imaging to check the efficacy of the treatment procedures. This presentation describes the development and assessment of several noninvasive procedures developed in our laboratory for making local measurements of attenuation variations, strain changes, and/or temperature increases during HIFU treatment procedures. The techniques to characterize lesions generated by HIFU are based on estimation of relative changes in tissue properties derived from backscattered rf data. Our recent work has demonstrated good agreements between ultrasound backscattering changes versus temperature increase and thermocouple measurements. In ex vivo liver samples, a linear relationship between changes in the radiofrequency signal and temperature was found for temperatures up to 90 °C. Using differential imaging, any issues related to the heterogeneity of the medium is eliminated, since only changes in attenuation, strain, and temperature of tissue are taken into account. These ultrasound techniques can be used during in vivo treatment procedures and they can be easily implemented in real time.