ARTIFACTS IN IMAGING MODALITIES. power ptx

ARTIFACTS
MASHHUD HADI GWADABE
DEPT. OF RADIOLOGY,
AKTH, KANO.
March ,2023.
7/18/2024 1

OUTLINE
• INTRODUCTION
• IMAGING MODALITIES
• ARTIFACTS IN VARIOUS IMAGING MODALITIES
• SUMMARY
• CONCLUSION
7/18/2024 2

Introduction
• Artifacts in radiology refer to something seen
on an image that are not present in reality but
appear due to peculiarity of the modality
itself.
• Artifacts could also mean findings that are due
to things outside the patients anatomy that
may obscure or distort the image.
• As such they may affect the quality of the
exam or may be confused with a pathology.
7/18/2024 3

Introduction cont….
Historical background
• First used by the English poet Samuel Taylor
Coleridge in 1821
• Artifact was derived from the word ‘Artificial’
• Latin word …meaning
– Arte (art)
– Factus (to make)
• ‘Artefact’ was formerly used….
• Artefacts vs Artifacts
• The English word Artifact became in use in 1884
7/18/2024 4

Imaging modalities
• Radiography
• Ultrasound Scan
• Computed Tomographic scan (CT)
• Magnetic Resonance imaging (MRI)
• Nuclear imaging (PET)
NB : The commonest form of artifact in all imaging
modalities is NOISE.
• It can be Mitigated but never Eliminated
7/18/2024 5
PET= positron Emission Tomography

Artifacts in Radiography (x-rays)
• X-ray artifacts can present in a variety of forms
– Abnormal shadows on the image
– Degraded image quality
• Result from……
– Hardware failure
– Operator failure
– Software failure (post-processing)
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Radiography
Plain Film
Radiography
Computed
Radiography
(CR)
Digital
Radiography
(DR)
7/18/2024 7
Artifacts in Radiography (x-rays)…cont
1. Finger marks
2. Static electricity
3. Clear film
4. Black film
5. Clear spots
6. Crescent shaped white lines
7. Crescent shaped black lines
1. Ghosting
2. Incorrect detector orientation
3. Backscatter
4. Stitching artifact
5. Over exposure
6. Dead pixel artifact
7. Signal dropout
8. Speckled radio-opaque spots
9. Detector calibration limitation
10. Failure of detector offset
correction
11. Electronic shutter failure
12. Values of interest misread
13. Mid grey clipping
14. Grid line suppression failure
1. Motion artifact
2. Image composition
3. Grid-cutoff
4. Debris In the housing

Common artifacts
• Motion artifact
– Due to patient movement
• Image composition artifact
(twin/double exposure)
– Superimposition of two
structures from different
locations due to double
exposure of same film/plate
• Radio-opaque objects
external to the patient
– Clothing, jewelry, hair
• Grid cut-off
– Lateral decentring
• Debris in the housing
– caused by the collimator
tube
– May appear as small
trapezoidal regions,
indicative of lead shavings
7/18/2024 8

Plain Film radiography
1. Finger marks
– Improper handling with
hands
2. Static electricity
– Films forcibly unwrapped or
excessive flexing of the film
3. Clear film
– Malfunction of the machine
or placing the film in the fixer
before development
4. Black film
– Complete exposure to light
5. Clear spots
– Air bubbles sticking to film
during processing
– Fixer splashed on the film
prior to developing
– Dirt on the intensifying
screen
6. Crescent shaped white
lines
– Cracked intensifying screen
7. Crescent shaped black
lines
– Finger nail pressure on the
film
7/18/2024 9

7/18/2024 10
(A) Motion A.
(B) Double E.
(C) Foreign body
(D) Grid cutoff (E) Debris
(B) Double exposure

7/18/2024 11
(F) Finger marks (G) Static electricity (H) Grid cutoff
(I) watermark
(J) Radiolucent crescent lines

CR/DR Radiography
1. Ghosting ( detector-
image lag)
– Latent image on previous
exposure present on
current exposure
2. Failure of detector offset
correction
– Similar to ghosting &
occurs when the digital
detector is not calibrated
when being promoted
3. Backscatter
– Electronics are visible on
the exposed image
4. Stitching artifact
– Occurs when two separate
DR/CR images are merged
into a single image
5. Incorrect detector
orientation (upside down
cassette)
– Spoke-like radiopaque lines
6. Signal dropout
– Large areas of signal loss
due to detector drop
7/18/2024 12

CR/DR Radiography
1. Speckled radio-opaque spots
– Occurs due to detector drop
2. Detector calibration limitation
– Faint radiopaque stripping in the background of
an image
3. Electronic shutter failure
– The digital image will have obscurely shaped,
tight collimation that defies logic
7/18/2024 13

CR/DR Radiography
4. Values of interest misread
– Image appears washed out and underexposed
– Occurs due to a largely collimated area of smaller
anatomy
5. Mid grey clipping
– Loss of contrast in areas of different pixel density yet
no change in density can be seen
6. Grid line suppression failure
– Faint grid lines present on an image with no grid cut-
off
7/18/2024 14

7/18/2024 15
CR/DR Radiography

ARTIFACTS IN USS
• Artifacts in the
ultrasound image are
echoes that do not
correspond to an
anatomic structure.
• They result from the
physical properties of
ultrasound propagation
in tissues.
7/18/2024 16
• Noise
– Is the appearance of
grainy echoes, especially
in the proximal portion
of cystic areas. It is
caused mainly by
excessive gain in the
near field.
– Noise can be reduced by
lowering the gain
setting.

ARTIFACTS IN USS...cont
7/18/2024 17
• Acoustic shadowing
– is an echo-free area
located behind an
insonated structure
– It is caused by total
reflection (e.g., by air)
or absorption(bone,
gallstones) of the
sound energy.

7/18/2024 18
• Posterior acoustic
enhancement
– the area behind an echo-free
structure
– appears more echogenic than
its surroundings.
– When the sound passes
through the echo-free
structure, typically a cyst, it
undergoes very little energy
loss and attenuation. Because
of this, the area behind the
cyst appears brighter in
relation to the surrounding
tissues.
ARTIFACTS IN USS…cont

• Reverberation A.
– Reverberations occur at the
interfaces of adjacent
media that differ greatly in
their acoustic impedance.
– Sets up repetitive back-and
forth reflections that either
appear as
• Distinct parallel bands or,
• Very strong reflectors, blend
into a narrow streak
resembling a comet tail.
7/18/2024 19

• Beam width artifact
– Appears as a collection of fine
grainy echoes distributed along the
inside of cystic structures whose
wall is struck by ultrasound beam
obliquely
– The main beam emitted by the
transducer has a definitive width,
when it encounters an oblique
interface, the beam width overlaps
both the echo-free interior of the
cyst and its highly reflective wall.
– Because the echogenicities of
these different structures are
averaged together electronically to
form an image, smudgy echoes
appear to line the cyst wall
(pseudosludge).
7/18/2024 20

• Side-lobe artifact
– Side-lobe artifacts are bright, curved
lines that are usually seen in
hypoechoic or echo-free structures.
– They are caused by side lobes, which
are secondary oblique
concentrations of energy located off
the main beam axis.
– When the echo from a side lobe
reaches the receiver with sufficient
energy, it is assigned to the main
beam and is therefore displayed at a
false location.
– Due to the low energy of the side
lobe, a strong reflector (e.g., air) and
hypoechoic or echo-free
surroundings (gallbladder, large
vessels) must be present in order for
the artifact to be seen.
7/18/2024 21

• Mirror-image artifact
– A mirror-image artifact is
the virtual image of a real
object that forms behind
a highly reflective
interface.
– It is caused by deflection
of the beam at the
“specular” reflector.
– The virtual image appears
behind the interface in
the path of the main
beam.
7/18/2024 22

• Lateral edge shadow
– A lateral edge shadow is a
thin acoustic shadow that
appears distal to the lateral
edges of a cystic structure .
– It is caused by the refraction
and scattering of sound
striking the cyst wall at a
tangential angle.
– Due to the energy loss that
occurs, the sound does not
propagate to deeper levels,
and an acoustic shadow is
formed.
7/18/2024 23

Artifacts in Computed Tomography (CT)
CT Artifacts
Patient based
artifacts
Physics based
artifacts
Hardware based
artifacts
7/18/2024 24
1. Motion artifact
2. Clothing/jewelry artifact
3. Transient interruption
of contrast (TIC)
1. Beam hardening artifact
2. Partial volume averaging
3. Quantum mottle(noise)
4. Photon starvation
5. Aliasing
6. Truncation artifact
1. Ring artifact
2. Tube artifact
3. Out of field artifact
4. Air bubble artifact
5. Helical & multichannel
artifact

Artifacts in Computed Tomography
(CT)…patient based artifact
• Motion artifact
– Occurs due to voluntary or
involuntary patient
movement during image
acquisition
– Results in misregistration
appearing as blurring,
streaking or shading on the
image
– Voluntary motion may be
mitigated by immobilization
or sedation
– Involuntary motion by using
fast imaging techniques or
cardiac gating for
examinations of the
Mediastinum
7/18/2024 25

7/18/2024 26
• Clothing Artifact
– Results from clothing worn by the patient
– Could be jewelry, button etc
– Can be corrected by asking patient to simply
remove those in the filed of interest.

• Transient interruption of
contrast (TIC)
– Is an artifact seen in CTPA
– Suboptimal opacification of
the pulmonary arteries
despite adequate contrast
administration.
– Results from increased flow
of unopacified blood from
the IVC to the right side of
the heart during deep
inspiration.
– Adequate timing of contrast
administration mitigates the
artifact.
7/18/2024 27
CTPA=CT pulmonary angiography

(CT)…Physics based artifact
• Beam Hardening
– occurs when a polychromatic X-
ray beam passes through an
object resulting in selective
attenuation of lower energy
photons.
– This results in increase in the
mean beam energy.
– It appears in two characteristic
forms
• Streaking (dark bands)
• Cupping artifact
7/18/2024 28

(CT)…Physics based artifact
7/18/2024 29
• Method of reduction
– Most CT scanners utilize filters in an attempt to overcome
beam hardening. The attenuating substance (usually metallic)
is appropriated to harden the beam before it reaches the
patient.
– Calibration with vendor specific phantoms reduces beam
hardening (cupping)
– Streak artifacts can sometimes be effectively reduced by
increasing tube voltage
– Metal reduction algorithms that utilize iterative reconstruction
to limit beam hardenings

(CT)…cont
• Partial volume averaging
– Occurs when tissues of widely different
absorption are encompassed on the
same CT voxel producing a beam
attenuation proportional to the
average value of these tissues.
– It is particularly problematic in CT
angiography (e.g. misdiagnosis of an
apparent contrast filling defect caused
by the artifact as PE.
– Use of thin section reconstructions (1-
1.5mm) are recommended where the
impact of this artifact is negligible.
– Newer generation CT scanners with an
associated reduction in the volume of a
voxel has substantially reduced the
occurrence of this artifact.
7/18/2024 30

(CT)…cont
• Photon Starvation artifact
– Is a cause of streak artifact
commonly seen in CT
– It is seen in high attenuation areas
particularly behind metal implants.
– Because of high attenuation,
insufficient photons reach the
detector.
– During reconstruction process, the
noise is greatly magnified in these
areas leading to characteristic
streaks in the image.
– Can be reduced by
• increasing tube voltage
• Use of iterative reconstruction
techniques.
7/18/2024 31

(CT)…cont
• Aliasing Artifact/under-
sampling artifact
– Refers to an error in the
accuracy proponent of
analogue to digital
converter (ADC) during
image digitization.
– It results from lack of
enough sampling from the
pixels during quantization.
– It has the appearance of
Moirés patterns
7/18/2024 32

(CT)…cont
• Truncation Artifact
– This is an apparently
increased curvilinear band of
attenuation along the edge of
the image.
– It results when part of the
body to be imaged remain
outside the field of view. (e.g.
due to the patients body
habitus resulting in inaccurate
measurement of attenuation
along the edge of the image.
– This can be reduced by using
• an extended FOV
• reconstruction of the affected
region.
7/18/2024 33

(CT)…cont
• Ring Artifact
– Results from mis-calibration or
failure of one or more detector
elements in a CT scanner.
– It can also be caused less
frequently by insufficient radiation
dose or contrast material
contamination of the detector
cover.
– They occur close to the isocentre
of the scan and are usually visible
on multiple slices at the same
location.
– Recalibration of the scanner will
rectify the artifact.
– Replacement of the detector
elements
7/18/2024 34

(CT)…cont
• OUT OF FIELD ARTIFACT
– This also known as incomplete
projection artifact
– It is due to the part of the
patient existing peripheral to the
field of view of the CT scanner.
– The lack of data from these out
of field tissue interferes with the
ability of the software to
generate a correct image leading
to streaking and areas of
unusual increased or decreased
density.
– This artifact can be prevented by
ensuring that the body of the
patient lies wholly within the
scan field.
7/18/2024 35

(CT)…cont
• Air bubble artifact
– This is due to the presence of
abnormal gas in the oil coolant which
surrounds the X-ray tube.
– The artifact manifests as subtle low
density which has only been described
on brain scans.
– The abnormal bubbles of air/gas in the
system subtly modify the transmission
of the primary x-ray beam decreasing
its attenuation by up to 3HU
– The number and precise location of
the bubbles may vary
– The effect of attenuation of the x-ray
beam is very mild & are only seen
when narrow window widths are used
e.g. brain CT scans
7/18/2024 36

• The air bubbles get into the coolant oil via several
mechanisms
– During CT service/repair e.g. oil changes or top ups
– Loss of integrity of the tube envelope/heat exchanger
– Spontaneous formation of gas within the oil when in
situ, due to vaporization in the system which increases
as the tube ages.
– This artifact can be removed by replacing the oil and
treating any underlying defect in the system.
7/18/2024 37
(CT)…cont

(CT)…cont
• Helical and multichannel artifact
– Windmill artifact
– Cone beam effect
– Multiplanar reconstruction artifact
7/18/2024 38

(CT)…cont
• Windmill artifact
– Is an image distortion in
the axial plane
encountered during helical
multidetector acquisitions
– The characteristic
appearance is that of
equally distanced bright
streaks diverging from a
focal high density structure
– The streaks seemingly
rotate while scrolling back
and forth through the
affected slices
7/18/2024 39

• Caused by inadequate data sampling in the z-
plane due to multi-detector rows intersecting
the reconstruction plane during rotation of
the gantry
– The number of detector rows intersecting the
same image planes increases as the helical pitch
increases
• It can be ameliorated by either decreasing the
pitch or using axial acquisition technique
7/18/2024 40
(CT)…cont

(CT)…cont
• Cone beam artifact
– Are seen in multidetector row
CT (cone beam CT) acquisitions
– Modern CT scanners use more
detector arrays to increase the
number of sections acquired
per rotation
– This will cause the x-ray beams
to become cone-shaped as
opposed to fan-shaped.
7/18/2024 41

• As a result instead of collecting data that
corresponds to a flat plane, each detector collects
data that corresponds to the volume contained
between two cones which can lead to under
sampling in the cone angle dimension
• This will result into noise, streaks and stair-step
artifacts
7/18/2024 42
(CT)…cont

• The artifacts are more pronounced at the
periphery of the field of view and worsen with
an increasing number of detector rows
• These artifacts have been addressed by use of
cone beam reconstruction techniques instead
of standard reconstruction
• It can also be minimized by ensuring a well-
sampled environment.
7/18/2024 43
(CT)…cont

(CT)…cont
• Zebra stripes/zebra
artifacts
– Appear as alternating
bright and dark bands in
an image.
– Result from 3D
reconstructions
– Other artifacts described
as zebra artifacts are the
• Moiré fringes
• Spike in K space
• Zero-fill artifact
7/18/2024 44

(CT)…cont
• CT Stair-step artifact
– Is found in structures which are
oriented obliquely with respect to
movement of the table and appear
around the edges of sagittal and
coronal reformatted images when
wide collimations and non-overlapping
reconstruction intervals are used
– It is also seen in coronary CT
angiography when step-wise
reconstructions are from different
cardiac phases
– It can be minimized by using smaller
collimation and overlapping
reconstruction in helical imaging
– In coronary CT 256 and 320 detector
CT scanners avoid this artifact.
7/18/2024 45

MRI ARTIFACTS
MRI
Artifacts
Hardware &
Room shielding
Software
Patient &
physiologic
Motion
Tissue
heterogeneity
& foreign body
Fourier
transform &
Nyquist sampling
theorem
7/18/2024 46
1.Zipper artifact
2.Zebra artifact
3.Moire Fringes
4. Shading artifact
5. Aliasing artifact
6. Starry sky artifact
7.Central point artifact
8. RF overflow artifact
9. Herringbone A.
10. Inhomogeneity A.
1.Slice overlap
2. Cross excitation
1.Phase-encoded
motion artifact
2. Entry slice
phenomenon
1.Magic angle
2. Black boundary
3.Chemical shift
4.Dielectric effect
5.Magnetic
susceptibility A.
(blooming A.)
1.Gibbs A.
2. zero-fill A
3.Aliasing/wrap
around A.

MRI ARTIFACTS….Hardware/Room
shielding
• Zipper artifact
– Result when one or more spurious
bands of electronic noise extends
across the image.
– They can be from hardware or
software problem or the shielding
itself.
– A common cause is spurious
radiofrequency signal
contaminating the received imaging
data.
– Appears at right angles to the
frequency encoding direction
– This results in an abnormal black
and white signal band across the
entire image corresponding to that
frequency
7/18/2024 47

• Zipper Artifact cont….
– If the signal is from only one frequency then only
one band will occur. An if multiple frequencies
then multiple bands will be present.
– The zipper artifacts that can be easily controlled
are those that occur when the door is open during
the acquisition of images due to RF entering the
scanning room from electronic equipment.
– Differential- Herringbone artifact
7/18/2024 48
shielding

shielding
• Herringbone Artifact..
– Also known as spike artifact,
crisscross artifact or corduroy
artifact
– Related to one or few aberrant
data points in k-space.
– The regularly spaced stripes
resemble the appearance of a
fabric with a herringbone
pattern. The artifact covers the
entire image in a single slice or
multiple slices.
– Caused by – electromagnetic
spikes by gradient coils,
fluctuating power supply and RF
pulse discrepancies
– Differential- zipper artifact
7/18/2024 49

shielding
• Zebra Artifact /stripes
– Appear as alternating bright
and dark bands in MRI image.
– Aliasing artifacts combined with
field Inhomogeneity artifact can
lead to zebra artifact
– It is caused by phase shift
across an image due to poor
shimming & image wrap of
signal-producing tissues.
– The phase difference In the
selected FOV & tissues
wrapping into the image results
in the light & dark banding
7/18/2024 50

shielding
• Zebra Artifact /stripes
• Changing the number of saturation bands
• Decreasing the TSE factor
• Using an even number of signal averages
(Philips, 2004).
• Manipulating the position of the saturation
bands in 3D TSE can be an effective alternative.
7/18/2024 51

shielding
• Moiré fringes
– Are an interference pattern
most commonly seen when
acquiring gradient echo
images using the body coil.
– Aliasing of one side of the
body to the other results in
superimposition of signals of
different phases that
alternatively add and cancel.
– This causes the banding
appearance.
7/18/2024 52

shielding
• Moiré fringes cont..
• Increasing the frequency matrix and decreasing the
slice thickness
• Using wide beam width techniques thus increasing
gradient strength
7/18/2024 53

shielding
• Aliasing/ wrap around artifact
– It occurs when the field of view (FOV)
is smaller than the body part being
imaged.
– The part of the body that lies beyond
the edge of the FOV is projected onto
the other side of the image
– correction
• This can be corrected by oversampling
the data.
• Sampling twice as fast in the frequency
direction
• Increasing the number of phase
encoding steps in the phase direction
7/18/2024 54

shielding
• Shading artifact
– Refers to loss of signal intensity in one part
of the image leading to dark shading in this
portion of the image
– Causes
• Uneven excitation of nuclei within the field
• Abnormal loading of coil or coupling of coil at
a point
• Inhomogeneity in the magnetic field
• Overflow of analogue to digital converter
– Correction
• Use of proper scanning parameters
• Load the coil correctly
• Use the proper coil for the patient size and
part examined
• Prevent the patient from touching the coil
• Shimming to reduce Inhomogeneity of the
magnetic field
7/18/2024 55

shielding
• Starry sky artifact
– Refers to non-uniform
distribution of image noise
typically affecting the
centre part of the image
more than the superficial
tissues.
– This can be reduced by
downward adjustment of
the R factor (acceleration
factor) at the expense of
increased scan time.
7/18/2024 56

shielding
• Central point artifact
– Is a focal dot of increased signal in
the centre of an image.
– It is caused by a constant offset of
the DC voltage in the receiver.
– After Fourier transformation, this
constant offset gives the bright dot in
the centre of the image.
– Correction
• Repeating the sequence
• Maintain a constant temperature in
scanner and equipment room for
receiver amplifiers
• Software to estimate DC offset and
adjust the data in K-space
• Call a service engineer for
recalibration.
7/18/2024 57

shielding
• RF overflow artifact
– Causes a non-uniform, washed
out appearance to an image
– It occurs when the signal
received by the scanner from the
patient is too intense to be
accurately digitized by the ADC.
– Correction
• Auto rescanning usually adjusts
the receiver gain to prevent this
from occurring
• The receiver gain can be reduced
manually
7/18/2024 58

shielding
• Inhomogeneity Artifact
– It occurs as a result of multiple factors;
• Irregular anatomical area
• Presence of metallic objects
• Inhomogeneity in the main field
– It appears as hyperintense or high signal
in some fat suppressed sequences that
depend on the main field (i.e. SPIR or
SPAIR)
– The main concern with this artifact is
that it can simulate edema or
subcutaneous cellulitis.
– Correction
• Can be fixed by using shimming coils
• Removing all metallic elements with
magnetic susceptibility
• Using STIR sequences instead of fat
saturation techniques
7/18/2024 59
SPIR= spectral presaturation with inversion recovery
SPAIR= spectral attenuated inversion n recovery

MRI ARTIFACTS….software related
• Slice overlap Artifact
– It is also known as cross-talk artifact
– Is the loss of signal seen in an image
from a multi-angle, multi-slice
acquisition as is obtained commonly
in the lumbar spine.
– If the slices obtained at different disk
spaces are not parallel they may
overlap
– If two levels are acquired at the same
time, e.g. L4/L5 & L5/S1 the level
acquired second will include spins
that have already been saturated.
7/18/2024 60

– This will result in horizontal band of signal loss
crossing the image which is most pronounce
posteriorly
– As long as the saturated area stays posterior to the
spinal canal, it causes no meaningful degradation to
the image
– Correction
• Simply not to overlap the slices in a single acquisition
• Or if they must be overlapped, to do so in separate
acquisitions (to obtain the oblique images in
concatenated rather than sequential acquisition mode)
7/18/2024 61
Slice overlap…cont

• Cross-excitation Artifact
– It refers to the loss of signal within a
slice due to pre-excitation from RF
pulse meant for an adjacent slice
– The frequency profile of the RF pulse
is imperfect and means during slice
selection there is some degree of
excitation of the adjacent slices as
well.
– If that adjacent slice is imaged during
the same TR or soon after, it will be
partially saturated to begin with and
the resulting signal will be reduced
– This phenomenon is more
pronounced in inversion recovery
sequences
7/18/2024 62

• Correction-
– By leaving a minimum gap of 1/3 slice thickness when
imaging contiguous slices
– Interleaving between slices
– Employing 3D imaging if volume imaging is required
– Using optimized pulse sequences that have a time
penalty of a higher minimum TE and reduced number
of slices for a given TR.
– Differential –
• cross-talk artifact similar in causation but it is due to angled
images, e.g. lumbar spine imaging
7/18/2024 63

MRI ARTIFACTS….patient and
physiologic motion
• Phase encoded motion
artifact
– Occurs as a result of tissue/fluid
moving during the scan.
– It manifests as ghosting in the
direction of phase encoding, usually
in the direction of the short axis of
the image.
– They can also be seen from arterial
pulsations, swallowing, breathing,
peristalsis and physical patient
movement.
– When it is projected over the
patients anatomy can mimic
pathology
7/18/2024 64

• Phase encoded motion artifact
– Periodic motion such as respiratory or cardiac/vascular
pulsation, produces discrete, well defined ghosts.
– Phase artifacts can be identified by
• By identifying known moving/flowing structures and noting
that the artifact is in line with them.
• Matching shape of ghost to that of flowing vessel
• Wide windowing to see repetitive ghost beyond confines of
anatomy
• They can be distinguished from Gibbs or Truncation artifact
because they extend across the entire field of view ,unlike with
truncation artifacts that diminish quickly away from the
boundary causing them.
7/18/2024 65
physiologic motion

• Remedy to phase mismapping
– Cardiac/respiratory gating
– Scanning prone to reduce abdominal excursion
– Shorten the scan time when motion is from patient
movement
– Spatial presaturation bands placed over moving tissues
– Spatial presaturation bands placed outside the FOV,
especially before the entry or after the exit slice for reducing
ghosting from vascular flow
– Switching phase and frequency directions
– Increasing the number of signal averages.
7/18/2024 66
physiologic motion

MRI ARTIFACTS….Tissue heterogeneity
and foreign bodies
• Chemical shift
artifact/Misregistration
– Is a type of artifact seen
commonly in MR spectroscopy
– It occurs in the frequency
encoding direction and results
from spatial misregistration of
fat & water molecules
– It occurs due to the
differences between
resonance frequency of fat
and water.
7/18/2024 67

and foreign bodies
• Black boundary artifact
– Also known as India ink/Type 2 chemical
shift/Chemical shift artifact of the 2nd kind/
phase cancellation/Edging artifact or Black
line artifact.
– It is an artificially created black line located at
fat-water interfaces such as those between
muscle and fat.
– This results in sharp delineation of the
muscle-fat boundary lending the image an
appearance of an interface outlined with an
ink
– It occurs in gradient echo sequences as a
result of selecting an echo time (TE) in which
the fat and water spins are out of phase
cancelling each other
– The artifact does not occur with spin echo
sequences (SE)
7/18/2024 68

• Black boundary artifact..cont
• Correction
– Choosing TEs close to 4.4ms, 9ms, 13.6ms
– Use of fat saturation
– Use of SE sequences instead of GE
• Applications –
– Aids in the diagnosis of benign conditions
• Lipomatous hypertrophy of the interatrial septum
• Focal pancreatic fat
• Fat-rich renal angiomyolipoma
– Aids in the diagnosis identification of inflammation
• Acute pancreatitis
• Mesenteric panniculitis
• Omental infarction
7/18/2024 69
and foreign bodies

and foreign bodies
• Magic angle effect
– Is an artifact which occurs on
sequences with a short TE (less than
32ms; T1W, PD, and GE sequences)
– It is confined to regions of tightly
bound collagen at 54.740 from the
main magnetic field and appears
hyperintense thus potentially being
mistaken for tendinopathy
• Correction
– Tends to occur only on short TE
sequences
– Longer TE can be used to avoid this
artifact.
7/18/2024 70

and foreign bodies
• MR susceptibility
artifact/susceptibility artifact
– Refer to a variety of MR artifacts
that share distortions or local signal
change due to local magnetic field
inhomogeneities from a variety of
compounds
– They are encountered while
imaging near metallic orthopaedic
hardware or dental work and result
from local magnetic field
inhomogeneities introduced by the
metallic object into the otherwise
homogeneous external magnetic
field B0.
7/18/2024 71

and foreign bodies
– The blooming artifact is
a susceptibility related
artifact deliberately
sought to make small
lesions more
conspicuous
– Susceptibility artifacts
can be diamagnetic,
paramagnetic, super
paramagnetic,
ferromagnetic
7/18/2024 72

and foreign bodies
• Dielectric effect Artifact
– Commonly encountered during body MRI
with 3T units
– At 3T, the RF frequency measures 234cm
in air and the speed & wavelength of the
RF field is shortened to ~ 26cm within the
body as a result of dielectric effect.
– But this 26cm field of view is
approximately the cross-sectional
diameter of most body imaging studies
– Therefore with abdominal diameters that
exceed the RF wavelength…e.g patients
with cirrhosis & ascites or pregnant
women.
– Constructive & deconstructive
interference patterns may emerge
7/18/2024 73

• Dielectric effect Artifact…..cont
– This may lead to darkening/shading at the centre
of the image
– At 7.0T, the RF wavelength in tissue decreases to
~11
• Correction
– Switch imaging to a < 3.0T system
– Reducing the abdominal girth e.g. drainage of
ascites in patient with cirrhosis
7/18/2024 74
and foreign bodies

MRI ARTIFACTS….Fourier transform
and Nyquist sampling artifact
• Gibbs artifact/truncation/ringing
artifact
– It refers to a series of lines in the MR
image parallel to abrupt and intense
changes in the object at this location
such as CSF-spinal cord and the skull-
brain interface.
– Because MR images are constructed
from k-space which is a finite sampling
of the signal subjected to inverse
Fourier transform in order to obtain the
final image.
– At high contrast boundaries, the Fourier
transform corresponds to an infinite
number of frequencies.
7/18/2024 75

– Since MR sampling is finite, the discrepancy is
manifest in the reconstructed image in the form of a
series of lines.
– They can appear in both phase-encode and frequency
encode directions.
– The more the encoding steps, the less intense and
narrower the artifacts
• Correction
– Increasing the matrix size
– Use of smoothing filters
– Use of fat suppression if fat is one of the boundaries.
7/18/2024 76

• Zero fill- artifact
– Is due to data in the k-space
array missing or set to zero
during scanning.
– The abrupt change from signal
to no signal results in artifacts
in the images showing
alternating bands of shading
and darkness often in an
oblique direction.
• Differential
– A spike in k-space as from an
electrostatic spark is another
artifact that causes oblique
stripes
7/18/2024 77

7/18/2024 79
Artifacts in Nuclear imaging
Nuclear imaging Artifacts
Instrumental Radiopharmaceutical Technical
patient Treatment related

ARTIFACTS IN IMAGING MODALITIES. power ptx

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