Optimal Ultrasonic Focusing through Strongly Aberrating Media using Radiation Force Magnetic Resonance Guidance

When focusing ultrasound through strongly aberrating layers such as bones, adaptive focusing techniques need to be used. They aim at recovering the delays to be applied to each emission channel of the ultrasonic (US) therapeutic array in order to compensate the phase shifts induced by the aberrator. We recently proposed a new energy-based technique requiring the sole knowledge of the acoustic intensity at the desired focus (1). MR-Acoustic Radiation Force Imaging (MR-ARFI) was first proposed in 1998 to map the displacement induced by the radiation force of a focused ultrasound beam (2). When properly acquired, the MR phase signal can be shown to be directly linked to the local acoustic intensity. The use of MR-ARFI for the proposed adaptive focusing technique is demonstrated experimentally in the present work.