Fast lesion mapping during HIFU treatment using harmonic motion imaging guided focused ultrasound (HMIgFUS) in vitro and in vivo

The successful clinical application of high intensity focused ultrasound(HIFU) ablation depends on reliable monitoring of the lesionformation. Harmonic motion imaging guided focused ultrasound (HMIgFUS) is an ultrasound-based elasticity imaging technique, which monitors HIFU ablation based on the stiffness change of the tissue instead of the echo intensity change in conventional B-mode monitoring, rendering it potentially more sensitive to lesiondevelopment. Our group has shown that predicting the lesionlocation based on the radiation force-excited region is feasible during HMIgFUS. In this study, the feasibility of a fast lesionmapping method is explored to directly monitor the lesionmap during HIFU. The harmonic motion imaging (HMI) lesionmap was generated by subtracting the reference HMI image from the present HMI peak-to-peak displacement map, as streamed on the computer display. The dimensions of the HMIgFUS lesionswere compared against gross pathology. Excellent agreement was found between the lesiondepth (r 2 = 0.81, slope = 0.90), width (r 2 = 0.85, slope = 1.12) and area (r 2 = 0.58, slope = 0.75). In vivo feasibility was assessed in a mouse with a pancreatic tumor. These findings demonstrate that HMIgFUS can successfully map thermal lesionsand monitor lesiondevelopment in real time in vitro and in vivo. The HMIgFUS technique may therefore constitute a novel clinical tool for HIFU treatment monitoring.