Artifacts Flashcards
A superimposition of signal that occurs when a LARGE FOV is acquired is known as
A) wrap around
B) fold over
C) aliasing
D) partial voluming
d
the superimposition of signal that occurs when a small FOV is acquired is known as all of the following except
A) wrap around
B) aliasing
C) fold over
D) partial voluming
d
motion is seen as a smearing in the
A) frequency encoding direction
B) phase encoding direction
C) slice selection direction
D) z axis direction
b
aliasing occurs because the tissue outside the FOV is
A) undersampled
B) oversampled
C) not sampled
D) too large
a
in order to compensate for aliasing
A) the scan can be shortened
B) the FOV can be enlarged
C) an oversampling technique can be employed
D) b and c
d
Gibbs or truncation artifact is seen as
A) tissue that looks very similar to aliased tissue
B) a bright pixel in the centre of the image
C) dark lined between fat and water interfaces within the image
D) high and low signal intensity bands
d
to correct for Gibbs artifact the
A) # of PE’s is decreased
B) # of PE’s is increased
C) FOV is increased
D) TE is increased
b
chemical shift occurs because the
A) system is undersampling the fat and water molecules
B) SNR is too low
C) fat and water precess at different frequencies
D) tissue is undersampled in the frequency direction
c
chemical shift becomes more obvious as the
A) transmitter BW is increased
B) receiver BW is decreased
C) receiver BW is increased
D) field strength of the magnet decreases
b
magnetic susceptibility effects are more prominent with
A) GE sequences
B) SE sequences
C) FSE sequences
D) IR sequences
A
magnetic susceptibility effects are less prominent with
A) GE sequences
B) SE sequences
C) FSE sequences
D) IR sequences
c. multiple 180˚ pulses correct for the susceptibility effects
susceptibility effects can be reduced by
A) reducing FOV
B) reducing TR
C) reducing TE
D) a and c
d
a leak in the RF shielding can appear as
A) a bright spot in the centre of the image
B) zipper artifact in the ƒ encoding direction
C) wet spot on the image
D) ghost along the images edge
b
flow artifacts can be reduced by
A) gradient moment nulling
B) spatial presaturation pulses
C) shortening the TE
D) all of the above
d
a decrease in voxel volume can lead to a decrease in
A) chemical shift
B) aliasing
C) partial volume averaging
D) a and c
d
