An MRI artifact is image information that does not faithfully represent the underlying anatomy. It may blur a structure, conceal a finding, or resemble disease. Recognizing the pattern helps narrow the cause—and decide what to check before repeating a sequence.
The same pattern can have different causes. Check it against the sequence, scanner, patient, and clinical question before changing the acquisition. The deciding issue is whether it limits diagnostic interpretation.
For deeper practice, these three resources complement the guide.
Quick recognition guide
| What you see | Likely mechanism | First useful check |
|---|---|---|
| Repeated anatomy or smearing, often along phase encoding | Patient or physiologic motion | Review movement, breathing, gating, and phase direction |
| Anatomy from outside the field of view appears on the opposite side | Wraparound / aliasing | Check phase FOV, oversampling, and coverage |
| Adjacent bright and dark bands at fat–water boundaries | Chemical shift (type 1) | Check frequency direction and receiver bandwidth |
| Local signal loss, blooming, or geometric distortion | Magnetic susceptibility differences | Check nearby air or metal and sequence sensitivity |
| A narrow line or band crossing the image | Possible RF interference / zipper artifact | Check RF door and approved in-room equipment |
| Fine alternating bands beside a sharp edge | Gibbs / truncation ringing | Check acquired matrix and sharp tissue boundaries |
| Patchy fat suppression or uneven image brightness | B0 / B1 nonuniformity or coil/positioning factors | Check shimming, positioning, and fat-suppression method |
Motion and ghosting
Appearance: Blurred edges, duplicated structures, or regularly spaced “ghosts.” The ghosts typically propagate in the phase-encoding direction; the patient’s movement does not have to be in that direction. Respiratory motion, pulsatile flow, swallowing, bowel movement, and changes in patient position can all contribute.
What to check: Was the patient comfortable and well supported? Did the sequence require a breath-hold, and was it understood? Is the pattern consistent with a vessel or CSF pulsation rather than gross motion? Depending on the protocol, appropriate options may include clearer coaching, positioning support, respiratory or cardiac synchronization, motion-robust acquisition, or changing the phase direction to move the ghosts away from anatomy of interest. The trade-offs vary by method and may affect scan time, SNR, or coverage.
Wraparound (aliasing)
Appearance: A body part outside the prescribed field of view is folded into the image, commonly across the phase-encoding boundary. In 3D imaging, wrapping can also occur along the slice-encoding direction.
What to check: Confirm the planned FOV covers the relevant anatomy, then review phase oversampling / no-phase-wrap settings and the acquisition direction. Increasing phase FOV or using oversampling can help; neither is automatically free of scan-time or resolution trade-offs.
Chemical shift and India-ink boundaries
Type 1 chemical shift: Because fat and water precess at different frequencies, fat signal can be displaced relative to water along the frequency-encoding axis. The result is a bright border on one side of a fat–water interface and a dark border on the other. Increasing receiver bandwidth can reduce this displacement, although it commonly reduces SNR. Fat suppression or a different readout strategy may be useful when appropriate.
India-ink (type 2) effect: On opposed-phase gradient-echo images, fat and water within the same voxel can cancel, producing a dark outline at an interface. This is a distinct mechanism; increasing bandwidth is not the general solution. Interpret it in the context of echo time and in-phase/opposed-phase behavior.
Susceptibility and metal-related distortion
Appearance: Signal voids, blooming, and spatial distortion near tissue–air interfaces or metallic objects. Gradient-echo and echo-planar sequences are often more sensitive than spin-echo-based acquisitions.
What to check: Review the chosen sequence and TE; consider an approved less susceptibility-sensitive sequence or metal-artifact-reduction option where available. The presence of an artifact does not establish an implant’s MR safety status. Implant screening and conditions of use must be resolved independently under the institution’s MR safety process.
RF interference and zipper artifacts
Appearance: A conspicuous linear or band-like signal across the image. Unwanted radiofrequency energy reaching the receive chain is an important cause, but not every zipper-like line shares the same mechanism.
What to check: Confirm the RF-shielded room door is properly closed. Follow established checks for permitted monitoring equipment and other electronic sources; do not bring in, remove, or manipulate devices contrary to MR safety procedures. If it persists across patients or sequences, record the affected acquisitions and involve the responsible physicist, applications specialist, or service team. Avoid assuming that repeating the scan will correct a recurring RF or hardware problem.
Gibbs (truncation) ringing
Appearance: Thin, alternating light and dark lines near a sharply defined, high-contrast edge, such as the interface between CSF and spinal cord. In some settings these lines can mimic a lesion.
What to check: Look for a regular pattern aligned with a sharp boundary. Increasing the acquired spatial sampling can reduce ringing, but may alter SNR and acquisition time. Interpolating a displayed image is not equivalent to acquiring additional high-frequency k-space information.
Uneven fat suppression and shading
Appearance: Fat is suppressed in one region but remains bright elsewhere, or the image shows broad signal variation. Static-field (B0) inhomogeneity, RF transmit-field (B1) variation, off-isocenter positioning, and coil-related factors can contribute.
What to check: Review positioning and shimming, confirm the selected fat-suppression method suits the anatomy, and check applicable coil or calibration warnings. An approved Dixon-based approach may be more robust than frequency-selective fat saturation in some settings, but it is not universally interchangeable with the prescribed sequence.
Before repeating an acquisition
- Decide what is affected. Does the artifact obscure the diagnostic target or compromise a required sequence? Compare other planes or sequences; do not judge from one slice alone.
- Identify the pattern. Is it repeated anatomy, fold-over, a boundary shift, local distortion, or a line of RF-like noise?
- Check the simple causes first. Look at motion history, phase direction, prescribed coverage, patient position, and relevant scanner messages.
- Consider the trade-off. A larger FOV, higher bandwidth, different acquisition, or gating method may improve one problem while affecting resolution, SNR, or scan duration.
- Escalate when necessary. If the artifact prevents interpretation or recurs across patients, document the pattern and involve the responsible radiologist, physicist, or service team before continuing with an uncertain workaround.
This is an educational recognition guide, not a substitute for facility-approved protocols, device-specific MR safety conditions, vendor instructions, or a radiologist’s assessment of diagnostic adequacy.