Optimal Ultrasonic Focusing Through Strongly Aberrating Media Using Radiation Force Magnetic Resonance Guidance

Benoit Larrat¹, Mathieu Pernot², Laurent Marsac³, Benjamin Robert³, Gabriel Montaldo¹, Jean-Franois Aubry¹, Mathias Fink¹, Mickael Tanter²

The non invasive correction of phase aberrations of ultrasonic waves is mandatory in the framework of human transcranial brain High Intensity Focused Ultrasound (HIFU) therapy at relatively high frequency (> 500 kHz). This study proposes an adaptive focusing technique based on the measurement of the acoustic intensity at the focus via MRI. The main objective is here to demonstrate the ability of acoustic radiation force MR imaging to learn experimentally how to correct strong medium aberrations with a few ultrasonic transmissions. Sharp focal spots and optimal acoustic energies are restored through several aberrating layers.