MRI MRI Artifacts 2

Question 1

Pulsatile flow artifact from a vessel typically appears as ghost images displaced in which direction?

Accepted Answer

Phase-encoding direction

Answer

Pulsatile flow ghosts appear in the phase-encoding direction because pulsatile variations in spin phase occur between TR intervals during phase-encode data collection.

Question 2

Which of the following best describes the 'magic angle' artifact and at what angle it occurs?

Accepted Answer

Artifactual T1/PD signal increase in ordered collagen structures at ~55° to B0

Answer

When ordered collagen fibers (tendons, ligaments) are oriented at ~55° to B0, dipole-dipole interactions average to zero, artifactually increasing signal on short TE sequences.

Question 3

A 'DC offset' or 'center dot' artifact seen as a bright spot in the center of the image is related to:

Accepted Answer

A small DC current offset in the receiver causing a spike in the center of k-space

Answer

A DC offset artifact occurs when a constant voltage offset in the MR receiver chain introduces a spike at the origin of k-space (DC component), appearing as a bright dot at image center.

Question 4

EPI (echo planar imaging) sequences are particularly prone to which artifact caused by off-resonance spins accumulating phase during the long readout?

Accepted Answer

Chemical shift (N/2 ghost or Nyquist ghost) and geometric distortion

Answer

EPI's long readout makes it sensitive to field inhomogeneity, causing geometric distortion along the phase-encode direction and N/2 ghosting from alternating echo phase inconsistencies.

Question 5

Which artifact appears as parallel bright and dark bands in the phase-encoding direction when the FOV is too small and the patient extends beyond it?

Accepted Answer

Aliasing (wraparound)

Answer

When anatomy outside the FOV is phase-encoded, it aliases (wraps around) and appears as a superimposed copy on the opposite edge of the image, sometimes appearing as bands.

MRI - Magnetic Resonance Imaging Practice Test

MRI - Magnetic Resonance Imaging Practice Test

MRI MRI Artifacts 2