In MRI, artifacts are unwanted features in the image that do not represent the true anatomy. These artifacts can be classified as coherent or incoherent, depending on how structured or random they appear.

In a nutshell, incoherent artifact is like noise.

🟩 Coherent Artifacts

  • Definition: Artifacts that appear structured, regular, and predictable.
  • Cause: Usually caused by periodic or consistent errors, such as regular undersampling or periodic motion.
  • Appearance: Clear patterns like ghosting or aliasing (wrap-around).
  • Example: Skipping every other line in k-space (2× undersampling) causes aliasing — a coherent artifact.

Coherent = organized, structured, follows a pattern.

🟥 Incoherent Artifacts

  • Definition: Artifacts that appear random, noisy, or diffuse.
  • Cause: Result from irregular or random errors, such as random undersampling or physiological noise.
  • Appearance: No clear structure; looks like background noise or smearing.
  • Example: Random k-space undersampling in compressed sensing creates incoherent artifacts.

Incoherent = disorganized, noisy, scattered.

🧠 Summary Table

Feature Coherent Artifact Incoherent Artifact
Pattern Regular / Structured Irregular / Random
Cause Periodic errors Random errors
Appearance Ghosting, aliasing Noise, smearing
Example Uniform k-space skipping Random k-space skipping