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MRI > 12: MRI Artifacts > Flashcards

12: MRI Artifacts Flashcards

1
Q

Aliasing artifact is also called…

A

Wrap artifact

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2
Q

Wrap or Aliasing artifact: Cause -

A

when the area of anatomy exceeds the FOV margins in the phase direction with no/limited oversampling and no phase wrap option off

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3
Q

Wrap or Aliasing artifact: Appearance:

A

area of slice that would be cut would be folded back into the image in the phase direction

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4
Q

Wrap or Aliasing artifact: Compensation:

A

1: select “no phase wrap/ oversampling” before scanning
2: increase FOV to extend past anatomy in the phase direction
3: Place Saturation pulse on anatomy extending past FOV (least effective)

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5
Q

Adding “no phase wrap” adds….

A

time

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6
Q

Truncation artifact is also called

A

Ringing artifact

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7
Q

Ringing / Truncation artifact:

A

Incomplete sampling of high contrast borders

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8
Q

Ringing / Truncation artifact: Appearance-

A

Oscillating waves parallel with high contrast border
Commonly found on SAG T2 of C spine due to high contrast edges between the thecal sac and spinal cord

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9
Q

Ringing / Truncation artifact: Compensation:

A

1: Increase matrix ( increase matrix = decrease truncation )
2: Select a raw data filler ( 2D Sequential Filling ) to smooth out incomplete sampling
3: Fat Suppression ( if high contrast border is due to fat )

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10
Q

Gibbs Artifact:

A

When Fourier transform samples phase and frequency separate from another

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11
Q

Gibbs Artifact: Appearance:

A

Dark circumference surrounding anatomy followed by brighter circumference surrounding the dark circumference

Imagine a dark circle surrounded by a white circle on the edge of an image

Differs from Truncation by that is does NOT have a wave light appearance and is present along the entire circumference of an image

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12
Q

Gibbs Artifact: Compensation

A

Does not warrant the need to fix and repeat

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13
Q

Chemical Shift artifact:

A

Lack of resonant frequency in hydrogen atoms in fat compared to hydrogen atoms in water

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14
Q

Chemical Shift artifact: Appearance

A

Shifting of fat based tissue over water based tissue in the FREQUENCY direction

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15
Q

Chemical Shift artifact: Compensation

A

Increase bandwidth (indirect relationship with chemical shift)

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16
Q

Magnet shift = Magnet strength (T) x Hertz/T

149 Hertz/T in 1.0 Tesla Magnet = Increase Chemical Shift
224 Hertz/T in 1/5 Tesla Magnet = Decrease Chemical Shift

A
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17
Q

Magnetic Susceptibility:

A

Extreme localized dephasing due to different areas being magnetized

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18
Q

Magnetic Susceptibility: Appearance

A

1: extreme signal loss
2: Geometric distortion

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19
Q

Magnetic Susceptibility: Compensation

A

1: Remove metallic object (hairpins, bra, glasses, etc. )
2: Metal protocol (increase bandwidth + increase FOV + tailored RF)
3: Metal Suppression sequences (MAVRIC - GE; WARP - Seimens)

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20
Q

RF Zipper Artifact

A

Stray RF waves entering the room from mobile or navigation devices

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21
Q

RF Zipper Artifact: Appearance:

A

severe distortion with signal disorientation (zipper lines) in the phase direction

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22
Q

RF Zipper Artifact: Compensation

A

1: closing the scanner door completely
2: removing any mobile devises from vicinity of control room

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23
Q

Motion Artifact: Flow/movement:

A

movement of the image being sampled by either patient motion or blood flow

24
Q

Motion Artifact: Flow/movement: Appearance:

A

Flow - pulsation artifact along the phase direction
motion - blurry anatomy in the phase direction

25
Q

Motion Artifact: Flow: Compensation:

A

Saturation band inferior or superior to area of interest
select “flow compensation option”

26
Q

Motion Artifact: Movement: Compensation

A

Sponges to keep patient still
motion correction imaging techniques such as Propeller/BLADE

27
Q

Partial Volume Averaging:

A

With thick slices, more area gets sampled and also gets averaged which drops signal contrast in certain pieces of anatomy

28
Q

Partial Volume Averaging: Appearance

A

decrease signal contrast on thicker slices

29
Q

Partial Volume Averaging: Compensation

A

Use thinner slices

30
Q

Crosstalk Artifact:

A

Multiple overlapping slices or acquisitions

31
Q

Crosstalk Artifact: Appearance

A

loss of signal in area of overlapping slices or acquisitions

32
Q

Crosstalk Artifact: Compensation:

A

Separate acquisitions
increasing spaces of slices

33
Q

Moire Pattern:

A

too large of a FOV while using a gradient pulse sequence and magnet body coil

34
Q

Moire Pattern: Apprearance

A

Severe banding or wave-line pattern at the periphery of image

35
Q

Moire Pattern: Compensation

A

Use a different pulse sequence for a localizer rather than a gradient

use a dedicated coil rather than the body coil

36
Q

Annefact:

A

direction of signals being generated outside of desired FOV

Commonly found when scanning thoracic spine and your coil elements are tuned on outside the FOV

37
Q

Annefact: Appearance

A

bright, ghosting signals smeared across the phase direction of an image

38
Q

Annefact: Compensation

A

Proper selection of the receiver coil

verify the phase/frequency directions

39
Q

IDEAL Artifact *NOT ON REGISTRY *

A

too large of a FOV with too high of an acceleration rate

40
Q

IDEAL Artifact: Apprearance

A

moire pattern on the periphery with a mid-sagittal pixelations

41
Q

IDEAL Artifact: Compensation

A

Decrease FOV and decrease ACCL rate

use another sequence such as inversion recovery

42
Q

Imperfect Fat Saturation:

A

range of frequencies exceed the FOV selected for fat saturation or anatomy in direct contact with coil

43
Q

Imperfect Fat Saturation: Appearance

A

immediate fat saturation drop at the periphery of the FOV

44
Q

Imperfect Fat Saturation: Compenstion

A

use traditional IR Recovery (STIR)

45
Q

Corduroy Artifact

A

K space corruption in a particular data point which causes an error during fourier transformation

46
Q

Corduroy Artifact: Appearance

A

Narrow angular lines throughout the entire sequence resulting in a corduroy appearance

47
Q

Corduroy Artifact: Compensation

A

choose another sequence from protocol management; this sequence may be corruption

48
Q

Dielectric Effect:

A

when a patient’s body diameter measures wider than the RF pulse wavelength be distributed

49
Q

Dielectric Effect: Appearance:

A

Results in a drastic decrease in signal resulting in a dark shadowing in the center of the image

Can also happen in people very skinny, Low fat high water

Normally found in 3T Body MR

50
Q

Dielectric Effect is normally found on__________________

A

3T Body MR

51
Q

Dielectric Effect: Compensation

A

Move to a lower field magnet (most effective)

Use of dielectric pads

Drainage of ascites or other body fluids

52
Q

Wrap occurs in the ________ direction.

A

Phase

53
Q

Wrap folds the image back into the ____________ direction.

A

Phase direction

54
Q

A 8mm slice will have _________ partial volume averaging artifact than a slice with a 4mm slice thickness.

A

more

NOT HALF

55
Q

By turning “No Phase Wrap” and increasing FOV to cover anatomy, your scan time will be _________.

A

shorter

MRI (14 decks)

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