Motion and ghosting
Patient motion can create blurring, phase-direction ghosting or inconsistent data across k-space. Physiologic motion from respiration, pulsation and flow can produce structured artifacts. Mitigation may involve communication, immobilization, gating, faster acquisitions, altered phase direction or sequence-specific strategies.
Aliasing and wrap
Aliasing occurs when anatomy outside the sampled field of view is mapped back into the image. It is commonly associated with insufficient FOV in the phase direction. Oversampling, phase-FOV changes, coil sensitivity methods and positioning choices can affect the result.
Chemical shift
Fat and water resonate at slightly different frequencies. In frequency-encoded imaging this can displace fat relative to water by a number of pixels that depends on field strength, receiver bandwidth and pixel bandwidth. Increasing bandwidth typically reduces the displacement while lowering SNR.
Susceptibility and field inhomogeneity
Local magnetic-field variations can cause dephasing, distortion and signal loss, especially in gradient-echo and echo-planar techniques. Air-tissue interfaces, metal and imperfect shimming can amplify these effects. Sequence choice, TE, bandwidth, voxel size and shimming can influence severity.
Other recognizable patterns
Gibbs ringing relates to finite sampling of sharp transitions. Zipper artifacts can reflect RF interference entering the system. Flow can create signal loss, enhancement or ghosting depending on sequence and direction. Correct identification is the first step toward an efficient troubleshooting strategy.