QA and Artifacts

1. ARTIFACTS & QUALITY CONTROL
WEEK SIX

2. Objective
Identify various types of artifacts
Be able to identify artifact from
other imaging issues
Learn how to correct artifact
issues

3.  “Wrapping” of anatomy outside
the FOV back into the image.
 Can occur along the frequency
or phase encoding axis
Compensation
Techniques
 Increasing FOV as far as the coil
will allow
 Use oversampling in the phase
direction
 Spatial pre saturation pulses
can be placed over the
anatomy

4.  You have patients who
have hip replacements,
etc. and have hardware
in place. This will
cause an artifact to
your image.
Compensation
Techniques
 Increasing bandwidth

5.  The ability or how well a
property can be magnetized.
 Results in signal loss and
dephasing in that structures
boundaries.
 Mostly affected because of
metal in the area.
 Be sure to remove all metal
from patient, use SE or FSE
sequences, decrease TE to
allow for more.

6.  “ringing” artifact at high
and low signals.
 Best seen in cervical
spine and brain
 Occurs when an over
and under estimation of
signal is produced at
high contrast levels.
 Increase the number of
phase encoding steps
to minimize this artifact.

7.  Appears as black or white
band at fat and water
interfaces occurring in the
frequency direction.
 It is impossible to get rid
of this artifact but you can
reduce it.
 Reducing field strength
 Keep FOV lowest as possible
 Reduce the bandwidth on high
field units

8.  Occurs when RF
enters the room
during a scan
 Occurs either
frequency or phase
direction
 To correct this issue
call the engineer.

9.  Respiration, cardiac, blood flow,
CSF fluid, swallowing, peristalsis,
body movements
 “ghosting”
 Corrective measures can include:
 Changing your phase and frequency
directions
 Using pre-saturation bands over that
area
 Incorporate the use of respiratory gating
or asking the patient to hold their
breath.
 Cardiac gating with ECG leads that will

10.  The machine
averages a portion
of tissue in one
slice.
 Results in poor
spatial resolution
and signal intensity
 Use thinner slices

11.  Our image experiences an
increase in T1 weight and
decrease in SNR.
 “slice overlap artifact”
 When your acquisition slices
overlap onto another and more
protons get saturated
 Decreased signal and contrast
 One way to correct this is by
decreasing the angle of the slices

12. RF pulse meant for a
neighboring slice is
pre excited and
results in loss of
signal in a slice.
Leave a gap of 1/3
slice thickness
Alternate the slices
by using interleaving

13.  It can be like
looking through
two window
screens
 Aliasing of one
side the body to
the other
 Make use of the
SE sequence
 Patient keeps
their arms in
FOV

14. Experience the
same artifacts as
routine MR
imaging such as
noise, ghosting
and motion
artifacts

15.  Breath holds by patient or Respiratory
Gating/Triggering
 Suppression imaging techniques
 Cardiac gating
 Increase FOV
 Change direction to or from phase or frequency
 Contact engineer for RF leaks
 Use SE or FSE sequences instead

16. Objective
Learn basic quality control (QA)
measures to correct problems
Learn the importance of regular
quality control in MR
Learn how to care for coils, door
seals, coil cables

17.  Test checks the
accuracy with which
a slice of specified
thickness is reached.
Can affect the image
contrast
Can cause a low
signal to noise ratio.

18.  Test of the scanner’s ability to
correct small objects when the
contrast-to-noise ratio is very high so
that it does not play a role in
completing it’s job.
 Technologist will visually inspect if
the white dots are clear

19.  The
technologist
will visually
inspect how
many dots they
can count to
complete this
test.

20.  ROI denotes areas
where technologist
will test for noise
inside the phantom
around the
phantom.
 A calculation and
comparison with
previous values is
made.

21.  Identify is the magnet
is drifting or RF
instability
 Scanner is
automatically tuned
to water for the
correct slice position
and fat saturation.
 Phantom is scanned
to acquire a reading
for CF

22.  This denotes the
power needed for an
RF pulse
 Must remain
constant
 Available pre and
post scan

23. making length
measurements on the
images from one point
to the other end point.

24.  Always handle coil and cables gently
 Don’t drop coils or slam them
 Don’t’ allow cables to hit the floor
 Some cables have prongs, so be careful when
plugging them in as they can break
 Check door seals for RF shielding compromise
 Inspect coil cables for any separations and
cracks