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MRI > Artifacts > Flashcards

Artifacts Flashcards

1
Q

Which coil/FOV pairing is more sensative to aliasing artifacts?

A

Large coil with a small FOV

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2
Q

Aliasing in the FREQUENCY direction is compensated for automatically by frequency filtering —- True/False

A

TRUE

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3
Q

What are common causes of aliasing

A

-Undersampling along the phase axis
-Using an active coil that is much larger than the anatomy of interest or in the FOV
-Using a phase FOV smaller than the anatomy of interest or the active Coil

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4
Q

What are common methods for compensating for Aliasing/wrap around artifacts?

A
  1. Enlarge FOV
  2. Applying phase over sampling (no wrap)
  3. Properly center anatomy to the RF coil
  4. Disengage RF coils that are not needed
  5. Avoid the use of oversized coils
  6. Place pre saturation pulses over unwated anatomy.
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5
Q

What imaging artifact appears as bands of high and low signal intensities running parallel to tissue interfaces?

A

Truncation/Gibbs artifact
Common in sagittal spine imaging

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6
Q

Truncation/ Gibbs artifacts mimic what in the sagittal cervical spine

A

Syrinxes

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7
Q

Truncation/Gibbs artifact are caused by

A

Undersampling

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8
Q

Truncation artifacts can be compensated for by increasing what

A

NEX or Phase encoding matrix

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9
Q

As magnetic field strength ________, Chemical shift artifact ________

A

Increases / Increases

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10
Q

As magnetic field strength ________, the processional frequency difference between fat and water ____________

A

Increases / Increases

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11
Q

At 1T, the precessional frequency difference between fat and water is:

A

147 Hz

220 @ 1.5T
440@ 3T

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12
Q

As receive bandwidth _______, chemical shift artifact _________.

A

Narrows / Increases

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13
Q

Chemical Shift artifact can be compensated for by

A
  1. Increasing the receive bandwidth
  2. Decreasing the pixel size
  3. Scanning at lower field strengths
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14
Q

Another name for chemical misregistration artifact is

A

Out of phase artifact

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14
Q

What image artifact appears as rings of dark signal around organs where fat and water interface within the same voxels?

A

Chemical misregistration artifact

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14
Q

Chemical misregisration artifacts are caused by

A

Fat and water precessing at different frequencies where they are out of phase with eachother at certain intervals

14
Q

Chemical misregistration artifact or out-of-phase artifact is common during what pulse sequences

A

Gradient Echo pulse sequences

14
Q

TE Values in intervals of ______ ms can results in chemical misregisration artifacts

A

2.1

14
Q

Chemical mis registration artifacts can be compensated for by _________ or __________.

A

Using SE sequence / Applying a TE in intervals of 4.2ms

14
Q

Dixon Technique

A

Out of phase imaging

14
Q

What artifact appears as dark signal void image distortions near the presence of metallic objects?

A

Magnetic susceptibility artifact

14
Q

Magnetic susceptibility artifacts can be caused by

A
  1. Metallic/ferromagnetic objects
  2. Iron content from hemorrhages
  3. Areas of air-tissue interface
15
Q

Magnetic susceptibility artifacts can be compensated for by:

A
  1. Using a FSE sequence with a long ETL
  2. Decreasing the TE
  3. Removing all metallic/ferromagnetic objects

Can be decreased by FSE/TSE pulse sequences

16
Q

Radiofrequency/Zipper artifacts occur in _________ direction

A

Phase direction

17
Q

What imaging artifact appears as a los of spatial resolution

A

Partial volume averaging
Present within all image to some degree

18
Q

Partial volume averaging is caused by

A

Large FOV
Small Matrix
Thick slices

19
Q

Partial volume averaging can be compensated by

A

Small FOV
Large Matrix
Thin Slices

20
Q

The amount of partial volume averaging is directly related to :

A

Voxel Volume Size

21
Q

Cross excitation artifacts can be compensated for by

A

Using a gap space of at least 30% / Using the interleaving imaging option

22
Q

Moire pattern artifacts are only present in what pulse sequence

A

Gradient echo pulse sequence

23
Q

Moire pattern artifacts are caused by :

A

Undersampling

24
Q

Moire pattern artifacts can be compensated for by

A
  1. Using a spine echo pulse sequence
  2. Keeping patient anatomy away from the walls of the bore
  3. Making sure that all anatomy fits within the FOV
25
Q

Parallel imaging artifacts can be compensated for by _________ or __________.

A

Reducing the R factor / the proper use of a calibration scan

26
Q

What imaging artifact appears as areas of high signal intensity near collagen dense anatomy

A

Magic Angle Artifact

27
Q

Magic angle artifacts can sometimes occur around tendons positioned at what angle to the main magnetic field

A

55 degrees

MRI (8 decks)

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