Artefacts

Question 1

How does Phase mismapping (motion) appear?

Answer 1

Ghosting. Replicates anatomy along the image.

This always happens in the phase direction

Question 2

What causes phase mismapping (motion)

Answer 2

Motion

Question 3

What are some remedies for phase mismapping?

Answer 3

1. Swap phase/frequency
2. Use pre-sat pulses
3. Respiratory compensation
4. Cardiac gating
5. Gradient motion re-phasing
6. Immobilization
7. Communication with patient
8. Sedation

Question 4

How does the aliasing (wrap-around) artifact appear on the image?

Answer 4

Anatomy outside of FOV wraps inside of FOV.

Appears on opposite side of image.

Can be in frequency or phase direction

Question 5

What causes aliasing?

Answer 5

Anatomy outside of FOV produces signal. This signal is encoded and placed inside FOV

Question 6

How can you remedy aliasing?

Answer 6

1. Increase FOV.
2. Use pre-saturation bands.
3. Oversampling.

Question 7

How does the truncation artefact appear on an image?

Answer 7

Banding at the interface of high and low signal. High and low intensity bands.

Question 8

What causes the artefact truncation?

Answer 8

Under-sampling of data (too few lines of k-space)

Question 9

How can you remedy truncation artefacts?

Answer 9

1. Increase matrix size.
2. Decrease pixel size

Question 10

How does the RF artefact (zipper artefact)

Answer 10

RF lines will run parallel to the phase direction, perpendicular to the frequency direction.

Looks like a zipper. Alternating light and dark.

Happens in frequency direction

Question 11

What causes RF (zipper) artefact?

Answer 11

RF interference entering room

Question 12

How do you remedy RF artefact?

Answer 12

1. Remove electronic objects
2. Maintain proper humidity in room
3. Call engineer

Question 13

How does magnetic susceptibility artefact appear?

Answer 13

Distortion of image and voids of signal.

Frequency and phase direction.

Question 14

What causes magnetic susceptibility artefact?

Answer 14

Ferromagnetic metal such as braces, screws, or pins.

Natural iron of a haemorrhage.

Question 15

How can you remedy magnetic susceptibility artefact?

Answer 15

1. Thorough screening
2. Use SE or TSE (rather than GRE)
3. increase bandwidth

Question 16

What does the partial volume effect look like?

Answer 16

Inhomogenous signal. More pronounced in area of body where large difference in signals.

Question 17

What causes partial volume effect?

Answer 17

Different anatomical structures with different signals in same pixel

Question 18

How do you remedy partial volume effect?

Answer 18

Reduce pixel size

Question 19

What artifact is seen in this image?

Answer 19

crosstalk

Dark bands of signal loss are seen crossing horizontally through the axial acquisition

Question 20

What artifact is seen in this image?

Answer 20

magic angle artifact

Question 21

What artifact is seen in this image?

Answer 21

aliasing

Question 22

What artifact is seen in this image?

Answer 22

gibbs/ truncation

Question 23

What artifact is seen in this image?

Answer 23

Zipper artifact

Question 24

What artifact is seen in this image?

Answer 24

Phase mismapping (motion)

Question 25

What artifact is seen in this image?

Answer 25

Magnetic susceptibility artifact