Magnitude-Contrast MR-ARFI (Mag-ARFI): Subtraction-free MR-ARFI with inherently fused ultrasound focus and anatomy

Motivation: MR-ARFI visualizes an ultrasound focus based on the micron-level displacement it produces in tissue, and is presently a phase-contrast method. Its phase subtraction makes it sensitive to phase errors that obscure the focus, and it further requires registration to separately acquired anatomic images, which introduces geometric errors. Goal(s): To develop a subtraction-free MR-ARFI method that produces inherently fused ultrasound focus and anatomical images. Approach: A subtraction-free magnetization-preparation MR-ARFI sequence was developed that converts displacement-induced phase shifts into longitudinal magnetization modulation, readable by any imaging sequence. Results: Phantom and head imaging results demonstrate single-acquisition MR-ARFI anatomical images containing ultrasound foci that match phase-contrast MR-ARFI. Impact: MR-ARFI suffers from phase errors that obscure the ultrasound focus, and requires separate anatomical imaging to display the focus overlaid with anatomy. We present a single-acquisition method to produce physiological motion-robust MR-ARFI images with inherently fused ultrasound focus and anatomy.