A system and method for focusing ultrasound into a target tissue is disclosed. The method calculates a pressure field for an array of transducer elements to generate an unaberrated pressure field matrix and causes the transducer elements to apply focused ultrasound to generate a respective aberrated pressure field at a focus location in a target tissue and surrounding volume. MR-ARFI images are acquired of the focus location and surrounding volume, a magnitude of the aberrated pressure field is measured that is generated by the applied focused ultrasound at respective focus locations in the target tissue and surrounding volume based on the MR-ARFI images, an aberration for the transducer elements is determined from the pressure field matrix and the MR-ARFI images of the focus location and the surrounding volume using a magnitude least-squares method, and a corrective phase/amplitude adjustment is applied to the transducer elements based on the determined aberrations.