MRI Artefacts

This lecture explores common MRI artifacts, explains their mathematical origins using Fourier Transform principles, and provides strategies for mitigation. Key topics include aliasing (wraparound) caused by a small field of view, ghosting from motion or signal fluctuations, and geometric distortions arising from magnetic field inhomogeneities. The lecture also details chemical shift effects between water and fat, susceptibility artifacts from metal or substances such as hair gel, and various motion correction techniques, including prospective adjustment and the PROPELLER sequence. Finally, the lecture emphasizes that while artifacts can hinder diagnostics, they also provide valuable information about the imaging environment that advanced reconstruction models can potentially exploit.

Learning objectives:
By the end of this lecture, students will be able to:

• Recognize artifacts such as aliasing (wraparound), ghosting, geometric distortions, chemical shifts, and motion-related errors
• Explain why these artifacts occur using the principles of the Fourier Transform and magnetic field (B0) inhomogeneities
• Apply mitigation strategies, such as oversampling to reduce aliasing, using "topup" to correct geometric distortions, and implementing prospective motion correction or the PROPELLER sequence to correct motion.
• Understand that artifacts are not just "errors" but can also provide useful information about the imaging environment that advanced reconstruction models can exploit