Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

KL Boards > Artifacts > Flashcards

Artifacts Flashcards

1
Q

Name the artifact in the image on the left (improved appearance on the right)

What is the cause of the artifact? How can you fix it?

A

Speckle: interference of echoes from the distribution of scatter in tissue, causing a granular appearance of the image

FIX: increase frequency, spatial compounding, THI

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Name the artifact in the image on the left (improved image on the right).

What is the cause of the artifact? How would you (try to) fix it?

A

Clutter artifact: Acoustic noise arising from side-lobes, grating-lobes, and multipath reverberation. Typically seen in fluid-filled structures.

FIX: spatial compounding, THI

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Name this artifact.

What is the cause of the artifact?

A

Reverberation: Occurs at highly reflective surfaces (e.g., tissue-gas interface). Some echoes are reflected back and forth between gas and transducer, then interpreted to exist at twice the depth of the original interface.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Name this artifact.

What is the cause of the artifact?

A

Comet tail artifact: a form of reverberation artifact with reflections occurring from two closely spaced reflective surfaces (calculi, surgical clips, etc)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Name this artifact.

What is the cause of the artifact?

A

Acoustic shadowing artifact: Structures that are strong reflectors or attenuators cause reduction in the beam intensity distal to them, resulting in a dark shadow.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is refraction and in what situation is it most likely to occur? Which specific artifacts arise from refraction phenomenon?

A

Refraction: Occurs when the beam strikes a highly oblique interface, such as the lateral aspect of a curved surface, and with interfaces between substances such as fat and muscle with disparate speeds of sound

Includes: misregistration, ghosting, and edge-shadowing

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Name this artifact.

What is the cause of the artifact? How would you (try to) fix it?

A

Edge shadowing artifact: Refractive artifact that occurs at the edge of a large curved boundary with a different speed of sound than that of the surrounding tissues

FIX: spatial compounding, change angle of insonation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Name this artifact.

What is the cause of the artifact?

A

Misregistration artifact: The actual location of an object is altered by refraction of the beam at an interface superficial to it; object appears to be in a different place than it actually is.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Name this artifact.

What is the cause of the artifact? How would you (try to) fix it?

A

Side lobe artifact:

  • off axis beams at the edge of US beam (side lobe beam) bounces of strong reflector and goes back to the transducer
  • incorrectly placed as if the echo originated from the main beam

Usually too low energy to make a big difference, however in an anechoic structure, can appear to be sludge in the GB or urinary bladder

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the difference between side lobe and grating lobe artifact?

A

Grating lobe artifact: same concept but occur at more oblique angles and higher amplitude than side lobe

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Name this artifact (image on the right)

What is the cause of the artifact? How would you (try to) fix it?

A

Anisotropy artifact: angle of insonation alters reflective pattern. Normal or hyperchoic when perpendicular; hypoechoic appearance (‘false lesion’) when off angle.

To fix: change the angle of the transducer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Name this artifact.

What is the cause of the artifact?

A

Distal enhancement (through transmission): As sound passes through low-attenuating structure, there is less attenuation than expected and the returning echo will be stronger.

CAUTION: a homogeneous solid lesion with a lower attenuation than the adjacent tissues will also exhibit increased through transmission.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Name this artifact.

What is the cause of the artifact?

A

Mirror image artifact: Created when sound reflects off a strong reflector and is redirected toward a second structure (target), where it then reflects back to the first reflector, then back up to probe. This creates a second image of the target in the path of the original beam and deeper than the actual target

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Name this artifact.

What is the cause of the artifact?

A

Electronic noise artifact: Stray electric signal from electric equipment such as lights, clippers, and electrocautery units may cause artifacts to appear that remain when the transducer is not in contact with the animal.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Name this artifact.

What is the cause of the artifact?

A

Slice thickness/Volume Averaging Artifact – if two structures of differing attenuation are present in the same slice width, their intensities are averaged

Example: pseudosludge

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Name this artifact.

What is the cause of the artifact? How would you (try to) fix it?

A

Range ambiguity artifact: Occurs when the echo from a distant structure reaches the transducer after a second pulse has been emitted. Transducer thinks that this echo is associated with the second pulse and therefore in the near field instead of the far field.

FIX: reduce number of focal zone, especially when imaging fluid-filled structures

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Name this artifact.

What is the cause of the artifact?

A

Registration/propagation speed error: distance is calculated based on speed of sound through tissue. In fluid-filled structures, this may mean that the distal wall is actually farther from transducer than is displayed. In more dense objects, the distal wall may be closer than it appears.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Name this artifact.

What is the cause of the artifact? How would you (try to) fix it?

A

Aliasing artifact: occurs when the doppler shift frequency exceeds the Nyquist limit (1/2 PRF) –> information is mapped to the wrong side of baseline.

FIX: increase PRF, move baseline, decrease frequency, increase Doppler angle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What are the four general types of artifacts encountered in CT?

A
  1. Streaking
  2. Shading
  3. Rings
  4. Distortion

Barrett, J.F. & Keat, N. (2004) Artifacts in CT: Recognition and Avoidance. RadioGraphics 24, 1679–1691

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q
  • Name this artifact.
  • What is the cause?
  • What are the two subtypes of this artifact?
A
  • Beam Hardening: as the beam passes through an object, its mean energy increases because lower- energy photons are absorbed more rapidly than the higher-energy photons
  • Subtypes:
    • Cupping – occurs with round/cylindrical objects (Figure 3)
    • Streaks and dark bands – occurs when beam passes between two very dense structures
      • Beam is more attenuated when it passes through both dense structures than when it is only passing through one (at a different angle)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is this artifact and how do we fix it?

What was the technique for reducing this artifact as suggested by Mosenco et. al (2004) for dogs and horses?

A
  • Beam hardening (streaks/dark bands) in the interpetrous space.
  • FIX/REDUCTION:
    • ​Thick-section reconstructions of thin slices reduces this artifact.
    • Built-in software (filtration, calibration and BH correction)
  • Canine: five contiguous 1-mm slices added to create reformatted images of 5mm section thickness and interval
  • Equine: five contiguous 2-mm slices added to create images of 10mm section thickness

Porat-Mosenco, Y., Schwarz, T. & Kass, P.H. (2004) Thick-section reformatting of thinly collimated computed tomography for reduction of skull-base-related artifacts in dogs and horses. Veterinary Radiology and Ultrasound 45, 131–135

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is this artifact and how is it fixed?

A
  • Photon starvation: photons travelling through extremely dense structures are attenuated to the point that an insufficient number of photons reach the detector –> this leads to increased noise, which gets magnified during reconstruction
  • FIX:
    • Automatic tube current modulation
    • Adaptive filtration
      *
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is this artifact? How do we fix it?

A
  • Undersampling: occurs when there is too large of an interval between projections, resulting in misregistration, which leads to view aliasing
    • View aliasing = fine stripes appear to be radiating from the edge of, but at a distance from, a dense structure
  • FIX: increase projections (often means increasing rotating time)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is this artifact? How is it reduced?

A
  • Metal artifact: attenuation higher than the upper limit the computer can read (incomplete attenuation profile)
  • FIX:
    • ​Gantry angulation
    • Software correction
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What is this artifact and how can it be addressed?

A
  • Motion artifact
  • FIX:
    • Stabilize the patient
    • Overscanning/underscanning modes
    • Software correction
    • Gating
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Name this artifact. How is it fixed?

A
  • Out of field: incomplete information about the portion out of the FOV
  • FIX:
    • Reposition the patient and/or remove detritus
    • Use a larger DFOV
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What is this artifact? Fix?

A
  • Stair step artifact: appears around the edges of structures in multiplanar and three-dimensional reformatted images when wide collimations and non-overlapping reconstruction intervals are used.
  • Fix:
    • Thin slices
    • Use 50% overlap on recon slices incrementation
28
Q

Name this artifact. How do we fix it?

A
  • Apparent thickening occurring due to blurring (backprojection reconstruction), increased modulation transfer associated with lower spatial frequency objects, and partial volume average artifact
  • Fix:
    • Decrease slice thickness
    • Use bone filter
    • Larger WW
29
Q

Name it. How do we fix it?

A
  • Ring artifact: due to a broken detector element
  • Call someone
30
Q

Name the artifact.

What is the cause of the artifact? How can you fix it?

A
  • Memory
  • DR needs a brief latent period to allow photoconductors to return to ground state. If a second exposure is made before this happens, can have a faint, superimposed negative (indirect DR) or positive (direct DR) impression of the previous image
31
Q

Name the artifact

A
  • Dead pixel
32
Q

Name the artifact

A
  • Calibration mask
  • Errors in original calibration (e.g., dust on the calibration mask) will leave an imprint on the mask of variable attenuation
  • FIX: clean and recalibrate
33
Q
A

Upside-down cassette

34
Q

Name it

A
  • Grid cutoff
  • Incorrect position or orientation of the grid will lead to excessive reduction of incident x-rays
  • Generally appears as underexposed, white strips at the periphery of the radiograph
  • FIX: adjust grid placement
35
Q
A
  • Double exposure
  • CR – same plate used twice without being read-out in between
  • DR – electrical interruptions or data transfer error
  • FIX: with CR, plate readout immediately every time
36
Q
A
  • Quantum mottle
  • Insufficient number of incidents x-rays due to low mAs technique –> increased noise (grainy image)
  • FIX: increase exposure factors, blurring techniques.
37
Q

What two artifacts are shown in this image?

A
  • Saturation & planking
  • Both occur secondary to overexposure
  • FIX: re-take and decrease exposure
38
Q

What is this artifact and how do you fix it?

A

Paradoxical overexposure

FIX: decrease exposure factors

39
Q

What is this artifact and how do you avoid it?

A
  • Radiofrequency interference
  • FIX: keep detector away from RF sources
40
Q

What is this artifact?

A
  • Light leak (CR only)
  • Plate exposed to light after xray exposure but before readout
  • FIX: maintain functional cassettes
41
Q

What is the artifact in the image on the left (A)? How do you prevent it?

A
  • Fading
  • Readout of cassette performed long after exposure leads to loss of energy and grainy image
  • FIX: read out immediately
42
Q

What is this artifact?

A

Debris on the cassette

43
Q

What is this artifact and how do you fix it?

A
  • Dirty light guide
  • FIX: clean it
44
Q

What is this artifact and how do you fix it?

A
  • Moire artifact
  • Occurs when the grid frequency and readout frequency intersect
  • FIX: use an oscillating Bucky grid oriented perpendicular to the detector
45
Q

What is this artifact and how do you fix it?

A
  • Faulty transfer
  • Fluctuation in power or loose data cable
  • FIX: secure power source and stabilize connection
46
Q

What is this artifact and how do you fix it?

A
  • Border detection
  • Erroneous application of image border at the margins between highly attenuating objects or when imaging plate is rotated more than 3* relative to the collimated field
  • FIX:
    • Use semiautomatic detecion
    • Don’t use separate sections of the same plate for multiple rads
    • Reprocess with deactivation of border detection
47
Q

What is this artifact and how do you fix it?

A
  • Diagnostic specifier
  • Error in post-processing in the automatic or manual LUT
    • Incorrect selection of area of interest (thorax, abdomen, etc)
  • FIX: Reprocess; select correct area of interest
48
Q

What is this artifact and how do you fix it?

A
  • Clipping
  • Information in the area of interest is discarded
  • FIX: retake
49
Q
A
  • Density threshold
  • Very high attenuation objects result in widening of the grayscale, which makes the lower attenuation objects darker and less contrasting
  • FIX: adjust to make objects above the density threshold appear white
50
Q

What is this artifact and how do you fix it?

A
  • Uberschwinger
  • Caused by unsharp masking techniques for edge enhancement
  • FIX: reduce use of edge enhancement
51
Q

What two artifacts are shown?

A
  • Cracked NaI crystal and edge-packing
  • FIX:
    • Replace crystal (crack)
    • Edge-packing = highly intense ring of activity at edge around flood field – fix by masking the ring mechanically or electronically
52
Q

What is this artifact and how do you fix it?

A

Malfunction of PMT – hot or cold area in flood field

FIX: call service

53
Q

What is this artifact and how do you fix it?

A

Blown PMT

FIX: call service to replace the PMT

54
Q

What is this artifact and how do you fix it?

A
  • Septal penetration
  • Incident photons penetrate through lead collimator septa of a lower energy collimator
  • FIX: use correct collimator (medium energy) with higher energy nuclides
55
Q

What is this artifact?

A

Collimator septal damage

56
Q

What is this artifact and how do you fix it?

A
  • Pixel rollover
  • Image depth is too low
  • Acquire imades in “word mode” (16 bit)
57
Q

What is this artifact and how do you fix it?

A

Off peak floods

Left = 10% below peak

Right = 10% above peak

58
Q

What is this artifact and how do you fix it?

A

Self-contamination (urine)

59
Q

What is this artifact and how do you fix it?

A
  • Aliasing (wraparound)
  • Imaging FOV is smaller than the anatomy being imaged
  • FIX:
    • Align PEG with the shortest anatomical axis
      • Swap PE & FE directions
    • Increase FOV
    • Pre-saturation pulses to extraneous tissue
    • No phase wrap technique (extended matrix/oversampling)
60
Q

What is this artifact and how do you fix it?

A
  • Chemical shift misregistration
  • Fat-containing structures are misregistered in the FREQUENCY ENCODING direction
  • Can’t be totally avoided, but can be improved with:
    • Increased receiver bandwisth
    • Fat suppression techniques
    • Decrease FOV
    • Align FEG with long structures
61
Q

What is this artifact, why does it occur, and how do you fix it?

A
  • Magic angle
  • Normal tendons/ligaments have low SI due to their highly structured nature –> fast T2 relaxation time due to high dipole-dipole interactions between protons.
  • When angle is about 55, dipole interaction (trigonometry involving cosine) = 0 –> normally low SI is now increased
  • FIX:
    • Longer TE (>120 ms)
    • Change angle of structure
    • Decrease FA on GRE sequences
62
Q

What is this artifact and how do you fix it?

A
  • Bladder pseudolayering
  • Occurs with varying concentrations of Gd in the urine – with a high concentration of Gd (23-45 mmol/L), T2 shortening effects predominate and it’ll become hypointense again
  • No fix, but just be aware
63
Q

What is this artifact and how do you fix it?

A
  • Zipper artifact
  • Leakage of external RF signals into MR room either from a break in shielding or from electrical equipment in the room
  • Affects all sequences
  • OCCURS IN THE FREQUENCY ENCODING DIRECTION
  • FIX: remove electrical things, fix shielding
64
Q

What is this artifact?

A

Spike shielding artifact

Spike in noise due to a bad data point in k-space; usually due to bad electrical connection or build-up of static electricity

65
Q

What is this artifact and how do you fix it?

A
  • Ghosting
  • FIX:
    • Swap PEG/FEG
    • Saturation bands
    • Sequences with faster acquisition times
    • ECG/RR-gating
    • Motion correction algorithms
66
Q

What is this artifact and how do you fix it?

A
  • CSF flow artifact
  • Altered magnetization of CSF as it moves; more prominent in areas of turbulent flow
  • FIX:
    • Image in different planes
    • Try a GRE sequence

KL Boards (12 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions