1C-2 An All-Ultrasound System for Sonication and Real-Time Monitoring of Temperature and Ablation

Over the past years, researchers have investigated the potential of focused ultrasound surgery for non-invasive or minimally invasive modalities for cancer treatment. Focus ultrasound (FUS) transducer induces a high acoustic intensity at the localized focus for a short time period while the temperature at the focus rises significantly and reaches a thermal dose that causes local irreversible cell damage (coagulation necrosis). The key limitations of FUS surgery are the difficulty of monitoring temperature and tissue mechanical properties as well as potential requirement of interrupting the FUS exposure during surgery. Amplitude-Modulated Harmonic Motion Imaging (AM-HMI) technique for simultaneous monitoring and generation of ultrasound surgery using a single-element FUS transducer was formerly introduced [Maleke, C, et al., 2006]. The uniqueness of this technique is that the focused transducer is driven by a low AM wave with high modulation index. This produces a stable harmonic radiation force oscillating at a low modulation frequency (25 Hz). This paper presents the effect of thermal ablation using the AM-HMI technique in in vitro bovine liver. The temperature and RF echoes were recorded during FUS ablation. The tissue displacement was estimated using a speckle tracking technique based on the one-dimensional cross-correlation to estimate the resulting axial tissue displacement. The temperature elevation at the focal zone throughout sonication was over 50degC that produced tissue damage. During FUS ablation, the temperature rose significantly while the tissue stiffness decreased resulting in higher tissue displacements. The results show a linear relationship between the temperature and tissue displacements during lesion formation (<53degC). The AM-HMI technique was able to accurately detect the protein-denatured lesion according to variation in the tissue displacement. In this conclusion, the technique could be potentially used for realtime monitoring of the te- mperature and mechanical properties of tissues during FUS surgery