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12 Cards in this Set

  • Front
  • Back
What artifact is this?
What artifact is this?
Susceptibility artifact

Common in T2*, GRE, Echo planar sequences
Occur near boundaries between tissues with different magnetic susceptibility, and when metals are present.

Remedy: remove metals and try to use non gradient echo sequences
I...
Susceptibility artifact

Common in T2*, GRE, Echo planar sequences
Occur near boundaries between tissues with different magnetic susceptibility, and when metals are present.

Remedy: remove metals and try to use non gradient echo sequences
Increase bandwidth, matrix, slice thickness
What are 3 classes of substances that contribute to magnetic susceptibiltiy?
Diamagnetic -small internal magnetic field opposite direction of external field (most tissues/wood)
Paramagnetic- small internal magnetic field parallel direction of external field (deoxygenated blood)
Ferromagentic - strong (steel
What artifact is this?
What artifact is this?
Aliasing (wrap around artifact)

occurs in phase encoding (2D: occurs in 1 direction; 3D: occurs in 2 directions)
Field of view too small for excited tissue

Remedy: Orient the thinnest axis of anatomy along the phase-encoding direction
Enla...
Aliasing (wrap around artifact)

occurs in phase encoding (2D: occurs in 1 direction; 3D: occurs in 2 directions)
Field of view too small for excited tissue

Remedy: Orient the thinnest axis of anatomy along the phase-encoding direction
Enlarge FOV
Exclude all anatomy from the top few slices (3D head exam)
Use spatial saturation bands to null tissue outside FOV
What is this artifact?
What is this artifact?
Ghosting (Nyquist ghost)

Phase encoding
Results from motion
Also results from sequences that require rapid on and off of phase gradient (EPI sequences) This causes Nyquist ghost with anatomy shifted 1/2 field of view
Pulsatile flow

Remedy...
Ghosting (Nyquist ghost)

Phase encoding
Results from motion
Also results from sequences that require rapid on and off of phase gradient (EPI sequences) This causes Nyquist ghost with anatomy shifted 1/2 field of view
Pulsatile flow

Remedy: Apply eddy current correction
Switch PE and FE directions
Apply saturation bands
Motion resistant sequences
respiratory/cardiac gating
ask patient to be still.
What is this artifact?
What is this artifact?
Truncation Artifact

Occurs 2/2 nature of Fourier reconstruction which are most inacureate around sharp boundaries (CSF/tissue, Cysts/edema) - results in alternating bright and dark lines (ringing)

Decreases with increased matrix
Pre and pos...
Truncation Artifact

Occurs 2/2 nature of Fourier reconstruction which are most inacureate around sharp boundaries (CSF/tissue, Cysts/edema) - results in alternating bright and dark lines (ringing)

Decreases with increased matrix
Pre and post reconstruction filters
What is this artifact?
What is this artifact?
Chemical Shift Type 1(left) and Type 2 (right)

Type 1 Misregistration of fat and water tissue resulting in shift in the Frequency encoding direction (small receiver bandwidth)

Type 2 Fat and water in the same voxel negate each other resultin...
Chemical Shift Type 1(left) and Type 2 (right)

Type 1 Misregistration of fat and water tissue resulting in shift in the Frequency encoding direction (small receiver bandwidth)

Type 2 Fat and water in the same voxel negate each other resulting in no signal at fat/water interfaces (india ink)

Remedy:
Type 1: Increase bandwidth
Type 2: Image in phase 4.6 msec (1.5T) and 2.3 msec (3T)
or lengthen TE greater than 30 msec and apply shimming over FOV
What is this artifact?
What is this artifact?
Spikes in K-space

Noise spikes during acquisition produces corrugated sinusoidal pattern.
NOT in phase or frequency encoding direction

Remedy: Repeat
Spikes in K-space

Noise spikes during acquisition produces corrugated sinusoidal pattern.
NOT in phase or frequency encoding direction

Remedy: Repeat
What is this artifact?
What is this artifact?
Zippers

Form of noise artifact related to spurious RF signal from malfunctioning equipment or breach in MR faraday cage

Remedy: Close scan room door
Chech for RF emissions from equipment in scan room. Find RF leak
Zippers

Form of noise artifact related to spurious RF signal from malfunctioning equipment or breach in MR faraday cage

Remedy: Close scan room door
Chech for RF emissions from equipment in scan room. Find RF leak
What is this artifact?
What is this artifact?
Fat saturation failure
Occurs when a fat sat pulse fails to supress due to resonant frequency of fat not being uniform in the image, poosrly shimmed magnetic field, anatomy distant from isocenter

Remedy: 
Apply shimming within ROI
Move anato...
Fat saturation failure
Occurs when a fat sat pulse fails to supress due to resonant frequency of fat not being uniform in the image, poosrly shimmed magnetic field, anatomy distant from isocenter

Remedy:
Apply shimming within ROI
Move anatomy to isocenter
For finger, have patient hold them together.
What is this artifact?
What is this artifact?
Dielectric effect

In large patients where torso = or > RF pulse size, causes central signal void, worse with higher field strength

Remedy: 
Use dielectric pads
Engage multichannel transmission
Dielectric effect

In large patients where torso = or > RF pulse size, causes central signal void, worse with higher field strength

Remedy:
Use dielectric pads
Engage multichannel transmission
What is this artifact?
What is this artifact?
Zipper artifact in a noncartesian readout (like filtered backprojection)
Zipper artifact in a noncartesian readout (like filtered backprojection)
What is this artifact?
What is this artifact?
T2 shine through

Inherent T2 in DWI
T2 shine through

Inherent T2 in DWI