Figure 8.

Schematic diagram showing the origin of chemical shift artifacts. Fat and water protons resonate at different frequencies within the static magnetic field because of differences in the chemical environment. In the frequency-encoding direction (x-axis), the precession frequency difference between a fat proton (white square) and a water proton (black square) is translated directly into differences in physical position. No chemical shift artifact occurs in the phase-encoding direction (y-axis) for the fat and water protons (gray squares) with conventional pulse sequences. These differences are more pronounced at higher field strengths because the frequency difference is directly proportional to the field strength. MRI = MR imaging, NMR = nuclear magnetic resonance imaging.