Magnitude preparation-based MR-acoustic radiation force imaging

Area of Science:

• Medical Imaging
• Acoustic Radiation Force Imaging
• Magnetic Resonance Imaging

Background:

• Conventional phase contrast-ARFI is sensitive to motion and respiration artifacts.
• Visualizing ultrasonic foci and anatomy simultaneously is challenging.

Purpose of the Study:

• To visualize ultrasonic foci in tissue without phase subtraction, reducing motion and respiration sensitivity.
• To achieve fused depiction of anatomy and ultrasonic foci across various image contrasts.

Main Methods:

• Implemented a magnitude-contrast MR-acoustic radiation force imaging (Mag-ARFI) sequence.
• Converted displacement-induced phase shifts into modulated longitudinal magnetization.
• Compared Mag-ARFI with conventional phase contrast-ARFI in phantom and in vivo experiments, including head imaging with simulated breathing motion.

Main Results:

• Mag-ARFI showed strong agreement with phase contrast-ARFI in displacement quantification (R=0.88).
• Mag-ARFI images fused focus and background anatomy, correlating well with phase contrast-ARFI (R=0.87 for T1-weighted, R=0.79 for T2-weighted).
• Mag-ARFI demonstrated significantly reduced breathing motion artifacts (3.5x lower coefficient of variation).

Conclusions:

• Mag-ARFI enables ultrasound focus localization with reduced motion artifacts.
• This technique provides fused anatomical and focus information on T1- and T2-weighted magnitude images.