Which MRI sequence is most affected by the chemical shift artifact?

• A. Spin echo
• B. Fast spin echo
• C. Gradient echo
• D. Inversion recovery

Answer: (C)

The gradient echo sequence is most affected by chemical shift artifacts because of its reliance on changes in the magnetic field. In MRI, chemical shift artifacts occur due to the difference in resonant frequency between fat and water protons. Since gradient echo sequences use variable magnetic field gradients, they are more sensitive to these frequency differences compared to other sequences.

Gradient echo imaging captures images based on the T2* relaxation times, which are influenced by local field inhomogeneities and chemical shifts more so than T1 or spin echo techniques. In this context, when fat and water are present in the same voxel, their slight frequency difference can lead to misregistration of signals and, consequently, visible artifacts.

Other sequences like spin echo and fast spin echo use a refocusing pulse which tends to mitigate the effects of magnetic field inhomogeneities, thereby reducing the impact of chemical shift artifacts. Inversion recovery, while it may experience various types of artifacts, is not particularly influenced by chemical shift in the same way as gradient echo sequences.