Artifacts

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Author:
Dianna
ID:
32364
Filename:
Artifacts
Updated:
2010-09-01 22:50:13
Tags:
radiology MRI CT US
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Description:
artifacts
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  1. MRI: chemical shift artifact
    light & dark bands at water/fat interphase d/t difference in Lamour Freq - usually in frequency encoding direction
  2. MRI barrel distortion
    Image distortion caused by gradient nonlinearities (the peripheral FOV has a tendency of lower field strength, esp with bigger FOV) causing compression of the anatomy
  3. MRI: center-point artifact
    a bright spot in the center of the image for imbalanced amplifiers (from RF quadrature coils - coils that simultaneously measured the signal from orthogonal views, have 2 separate amplifiers and gain controls to compensate for signal dropoff.)
  4. MRI herringbone artifacts
    caused by braodband RF noise disrupt the image over a much larger area than zipper artifact. Reduce w proper site planning and FT shielding (i.e. a Faraday cage)
  5. MRI Ringing artifacts/ Gibbs phenomenon/ truncation artifacts
    near sharp boundaries/ high contrast transitions, appear as multiple regularly spaced parallel bands; more conspicuous with low frequency.
  6. MRI: wraparound artifacts [AKA aliasing]
    • mismapping of anatomy lies outside of the FOV of a gradient (with sampling rate less than twice the maximal frequency in the object) => high freq assigned to a lower frequency value.
    • Reduce in freq encode direction: low pass filter
    • Reduce in phase encode direction: increase number of phase encode steps.
  7. MRI: partial volume artifacts.
    heterogeneous signal in a voxel => loss of detail and spatial resolution.
  8. MRI: Motion ghosts
    low intensity "ghosts" in the phase encoding direction d/t motion.
  9. MRI: cross talk ghosts
    faint images of bright structures outside of the slice.

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