Artifacts Flashcards
the superimposition of a signal that occurs when a LRGE FOV is acquired is known as
partial volume averaging
the superimposition that occurs when a SMALL FOV is used known as
wrap around
fold over
aliasing
motion is seen as a smearing in the
phase encoding direction
aliasing occurs because tissue outsied the selcted FOV is
undersampled
in order to compensate for aliasing
the FOV can be changed
an oversampling technique can be employed
GIbbs or truncation artifact is seen as
high and low signal intensity bands
chemical shift occurs because the
fat and water precess at different frequencies
chemical shift is more obvious as the
receiver bandwidth is decreases
magnetic susceptibility effects are more prominent with
gradient echo sequences
magnetic susceptibility effects can be reduced by
reducing FOV
reducing the TE
a leak in the RF shielding can appear as a
zipper artifact int he frequency direction
flow artifacts can be reduced by
gradient moment nulling
spatial presaturation pulses
shortening the TE
a decrease in voxel volume leads to a decrease in
chemical shift
partial volume averaging
as FOV increases partial volume averaging
increases
as slice thickness increases partial volume averaging
increases
a matrix increases partial volume averages
decreases
as TR increases partial volume averaging
is not affected
respiratory artifacts can be reduced by
respiratory gating
respiratoy triggering
increasing the number of signals averaged
motion artifact occurs due to period and or aperiodic motion whereby respiraoty motion is an example of
periodic
motion artifact occurs due to periodic and or aperiodic motion whereby cardia motin is an example of
periodic motion
motion artifact occurs due to periodic and or aperiodic motion whereby patient movement is an example of
aperiodic motion
motion artifact occurs due to periodic and or aperiodic motion whereby peristaltic motion is an example of
aperiodic
