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Feasibility of real-time motion correction for H.I.F.U applications

Though HIFU may offer a practical alternative to conventional surgery for a range of abdominal tumors, patient motion (particularly respiratory motion) should be monitored and corrected. We propose here a new generation of multi-channel HIFU systems able to track and correct in real time 3D motion of tissues. The feasibility of a 3D real time motion tracking and feedback for the H.I.F.U. beam focal spot location is demonstrated. The process is based on an accurate ultrasonic speckle tracking method for following and compensating the 3D motion of the tumor. Experiments were conducted with an electronically focused phased array made of 200 elements. This unique system is used both for motion tracking and feedback electronic steering of the HIFU beam. The displacement estimation is based on the correlation of the RF signals at two different times. A pulse-echo sequence is performed for a set of transmit transducers of the phased array. The complete 3D motion estimation requires to use at least three sub-apertures on the large phased array. This motion tracking technique has been experimentally validated in phantoms moving as fast as 50 mm/s. The motion tracking sequences are interleaved with HIFU sequences at high frame rate. The HIFU sonication is interrupted every 100 ms in order to allow motion estimation performed in a few ms. This provides a real time feedback for the HIFU beam steering correction. A maximum duty cycle of about 80 % was performed experimentally. HIFU experiments combined with 3D real time motion correction conducted in fresh tissues samples will be presented.