Monitoring lesion formation of HIFU-treatment from radiated shear waves

To ensure the success of high-intensity focused ultrasound (HIFU) treatment, lesion formation and focus dislocation has to be monitored online. For an automatic and immediate stop of HIFU exposure in case of irregularities of the lesion formation a monitoring technique allowing real time feedback is needed. For this purpose, we propose the analysis of shear waves which are radiated from treated tissue when the exposure with HIFU is intermitted. By A-scans close to the focal region the changes in time-of-flight and magnitude of shear waves are investigated. It is shown that dislocation of the focus can be detected by a decrease of shear wave magnitude in regions below the original focus. Deformation of lesion comes along with considerable changes in magnitude and time-of-flight of the shear wave.