Real-time motion correction combined with electronic beam steering strategies optimized for large tumors: First in-vitro HIFU experiments in large moving targets

Abstract

A method for tracking in realtime the 3D motion of tissues is combined with a 2D high-intensity focused ultrasound (HIFU) multichannel system in order to correct for respiratory motion during HIFU therapy. Displacements estimation is based on an accurate 3D ultrasonic speckle tracking technique. A correction is achieved in real time by adjusting the transmit delays of each channel of the HIFU system. In vitro HIFU experiments combined with motion correction are performed in fresh biological tissues. The accuracy of the HIFU targeting is clearly improved. Moreover, this technique permits an important reduction of the treatment time for moving tumors. To generate large thermal lesions, the focus is scanned electronically over a large region. Different heating strategies are investigated in moving tissues: the shot-by-shot treatment interleaved with cooling periods, and the continuously scanned treatment of the whole region. The temperature distribution and the thermal dose are computed using a 3D thermal diffusion code combined with a 3D wave diffraction algorithm and compared to experimental results. Using motion correction, the necrosis threshold is achieved 3 times faster than without motion correction. This should lead to an important time reduction for the treatment of abdominal tumors.