Artifacts

Question 1

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

Answer 1

Large coil with a small FOV

Question 2

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

Answer 2

TRUE

Question 3

What are common causes of aliasing

Answer 3

-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

Question 4

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

Answer 4

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.

Question 5

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

Answer 5

Truncation/Gibbs artifact
Common in sagittal spine imaging

Question 6

Truncation/ Gibbs artifacts mimic what in the sagittal cervical spine

Answer 6

Syrinxes

Question 7

Truncation/Gibbs artifact are caused by

Answer 7

Undersampling

Question 8

Truncation artifacts can be compensated for by increasing what

Answer 8

NEX or Phase encoding matrix

Question 9

As magnetic field strength ________, Chemical shift artifact ________

Answer 9

Increases / Increases

Question 10

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

Answer 10

Increases / Increases

Question 11

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

Answer 11

147 Hz

220 @ 1.5T
440@ 3T

Question 12

As receive bandwidth _______, chemical shift artifact _________.

Answer 12

Narrows / Increases

Question 13

Chemical Shift artifact can be compensated for by

Answer 13

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

Question 14

Another name for chemical misregistration artifact is

Answer 14

Out of phase artifact

Question 14

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

Answer 14

Chemical misregistration artifact

Question 14

Chemical misregisration artifacts are caused by

Answer 14

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

Question 14

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

Answer 14

Gradient Echo pulse sequences

Question 14

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

Answer 14

2.1

Question 14

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

Answer 14

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

Question 14

Dixon Technique

Answer 14

Out of phase imaging

Question 14

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

Answer 14

Magnetic susceptibility artifact

Question 14

Magnetic susceptibility artifacts can be caused by

Answer 14

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

Question 15

Magnetic susceptibility artifacts can be compensated for by:

Answer 15

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

Question 16

Radiofrequency/Zipper artifacts occur in _________ direction

Answer 16

Phase direction

Question 17

What imaging artifact appears as a los of spatial resolution

Answer 17

Partial volume averaging Present within all image to some degree

Question 18

Partial volume averaging is caused by

Answer 18

Large FOV Small Matrix Thick slices

Question 19

Partial volume averaging can be compensated by

Answer 19

Small FOV Large Matrix Thin Slices

Question 20

The amount of partial volume averaging is directly related to :

Answer 20

Voxel Volume Size

Question 21

Cross excitation artifacts can be compensated for by

Answer 21

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

Question 22

Moire pattern artifacts are only present in what pulse sequence

Answer 22

Gradient echo pulse sequence

Question 23

Moire pattern artifacts are caused by :

Answer 23

Undersampling

Question 24

Moire pattern artifacts can be compensated for by

Answer 24

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

Question 25

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

Answer 25

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

Question 26

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

Answer 26

Magic Angle Artifact

Question 27

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

Answer 27

55 degrees