2. Artifacts
• Artifacts are features that appear on a reconstructed image but are
not part of the original anatomy.
• They may make the image unclear and harder to interpret, or they
can mimic the appearance of pathology.
• The radiographer’s aim is to minimize artifacts. However, some
artifacts have clinical/diagnostic uses.
3. Movement/Physiological Artifacts
• Motion artifact due to physical movements
• Motion artifact in MRI refers to the image degradation caused by
patient or object motion during image acquisition. It can result in
blurred, distorted, or ghosted images, and can significantly affect
image quality and diagnostic accuracy.
4.
5. CORRECTION
• Give clear instructions to patient before the scan
• Constantly communicate to claustrophobic patients
• Make the patient comfortable
• Use immobilization equipment or paddings
• Feed and wrap the infants
• Use oral or IV sedation
• Perform the scans under GA
• reduce scan time using fast scan techniques
• Adjust phase and frequency encoding directions to project artifact
away from anatomy
• Use compressed sensing techniques
6. Aliasing / Wrap around artifact
• Aliasing, also known as wrap-around artifact, is a common artifact
that can occur in magnetic resonance imaging (MRI) when the field of
view (FOV) is smaller than the actual object being imaged.
• Spatial localisation is determined by the frequency of the spins
within a selected sample of tissue.
• In 3D imaging phase encoding is used to select sections of tissue. If
the anatomy extends beyond the FOV, a similar process may cause
wrap-over in the slab select direction between slices at either end of
the volume.
9. MRI Zipper Artifact
• Zipper artifact is a type of artifact in MRI images that appears as a
series of bright and dark stripes that run parallel to the phase-
encoding direction.
• It is caused by a timing error in the gradient system that causes the
gradient to switch on too early or too late, leading to phase errors in
the acquired signals.
• There can be a range of hardware and software problems that could
contribute to the zipper artifact in MRI scans
10. • One common factor is inadequate RF shielding within the scanner
room, which could result from factors such as a door being left open,
a faulty door seal, or interference from electrical equipment like a
satellite monitor. Additionally, the zipper artifact could arise from
faults in the MRI system itself or issues related to the mains electricity
supply.
11. • Effect on image: Zipper artifact is characterized by the presence of
stripes or bands across the image that appear as bright and dark lines
that resemble the teeth of a zipper.
• These stripes or bands can appear parallel or oblique to the imaging
plane and can affect image quality and diagnostic accuracy.
12.
13. CORRECTION
• Check door is closed, check door seal is intact, remove electrical
equipment, check for blown bulbs in scanner room
• Use MRI compatible monitoring equipment
• Call engineer if no obvious solution is found
• Regularly perform quality control tests to identify and address any
issues with the scanner’s hardware.
14. Blooming Artifact
• Blooming artifact is a type of artifact that occurs in magnetic
resonance imaging (MRI) when there are regions of high magnetic
susceptibility differences.
• It appears as signal spreading or blooming beyond the actual
boundaries of an object
15.
16. • Susceptibility Weighted Imaging (SWI) is a sequence that is
particularly sensitive to magnetic susceptibility differences, making it
useful for visualizing blood products, including hemorrhages.
However, SWI can be susceptible to blooming artifact, which occurs
when the signal from blood products spreads beyond their actual
boundaries, leading to signal loss and distortion in surrounding
structures.
17. CORRECTION
• Sequence selection: Choosing the appropriate MRI sequence is
crucial. Gradient-echo sequences, such as susceptibility-weighted
imaging (SWI) or T2*-weighted sequences, are commonly used to
detect hemorrhages due to their sensitivity to blood products.
However, they are also more susceptible to blooming artifact. Spin-
echo sequences, such as T1-weighted or T2-weighted sequences, may
be preferred when blooming artifact is a concern.
18. Flow Artifacts
• Flow artifacts in MRI refer to distortions or signal changes in the images
caused by the movement of fluids, such as cerebrospinal fluid (CSF) and
blood flow.
• These artifacts can result in blurring, ghosting, or signal loss in the images,
making it challenging to accurately interpret the anatomical structures.
19.
20. CORRECTION
• Lower TE can also be used, which will reduce the time between the
90° and 180° pulses and decrease the likelihood of spins moving in
and out of the slice, thereby reducing the occurrence of flow void.
• NEX (Number of Excitations): NEX refers to the number of times the
MRI scan is repeated to acquire multiple signal averages. Increasing
the NEX can help improve the signal-to-noise ratio (SNR) by reducing
random noise. This, in turn, can enhance image quality and reduce
flow artifacts.
