MRI MRI Artifacts

Question 1

Which MRI artifact appears as a ghosting or smearing of bright structures in the phase-encoding direction?

Accepted Answer

Motion (ghosting) artifact

Answer

Motion artifact manifests as ghost images displaced in the phase-encoding direction because phase-encoding samples data over many TR intervals while frequency encoding is instantaneous.

Question 2

Chemical shift artifact of the first kind occurs at interfaces between fat and water and manifests as:

Accepted Answer

A bright band and a dark band at the fat-water interface in the frequency-encoding direction

Answer

First-kind chemical shift artifact creates a bright rim on one side and a dark void on the other side at fat-water interfaces in the frequency-encoding direction due to the 3.5 ppm resonance frequency difference.

Question 3

Gibbs (truncation) artifact is caused by:

Accepted Answer

Undersampling of k-space — insufficient high-frequency data to represent sharp tissue interfaces

Answer

Gibbs artifact arises from the Fourier series representation of sharp edges when high spatial-frequency k-space data is truncated, producing ringing lines parallel to the interface.

Question 4

Wraparound (aliasing) artifact in MRI is caused by:

Accepted Answer

Structures outside the FOV contributing signal that is folded back into the image

Answer

When anatomy extends beyond the selected FOV in the phase-encode direction, it is aliased and appears superimposed on the opposite side of the image.

Question 5

Which technique is most effective for reducing susceptibility artifact from a metallic implant in MRI?

Accepted Answer

Use a spin-echo or fast spin-echo (FSE) sequence with narrow bandwidth

Answer

Spin-echo and FSE sequences use 180° refocusing pulses that compensate for susceptibility-induced dephasing, and a narrow bandwidth reduces chemical shift but a wide bandwidth reduces susceptibility — MARS protocols use high bandwidth FSE.

MRI - Magnetic Resonance Imaging Practice Test

MRI - Magnetic Resonance Imaging Practice Test

MRI MRI Artifacts