Rapid MR-ARFI Method for Focal Spot Localization During Focused Ultrasound Therapy

MR-guided focused ultrasound (FUS) is a noninvasive therapy for treating various pathologies. MR-based acoustic radiation force imaging (MR-ARFI) measures tissue displacement in the focal spot due to acoustic radiation force. MR-ARFI also pro-vides feedback for adaptive focusing algorithms that could correct for phase aberrations caused by the skull during brain treatments. This work developed a single-shot echo-planar imaging–based MR-ARFI method that reduces scan time and ultrasound energy deposition. The new method was imple-mented and tested in a phantom and ex vivo brain tissue. The effect of the phase aberrations on the ultrasound focusing was studied using displacement maps obtained with echo-planar imaging and two-dimensional spin-warp MR-ARFI. The results show that displacement in the focal spot can be rap-idly imaged using echo-planar imaging–based MR-ARFI with high signal-to-noise ratio efficiency and without any measura-ble tissue heating. Echo-planar imaging–based displacement images also demonstrate sufficient sensitivity to phase aber-rations and can serve as rapid feedback for adaptive focusing in brain treatments and other applications. Magn Reson Me