Ch 13 2D B-Mode Artifacts

Question 1

What is an artifact?

Answer 1

Incorrect representations of anatomy or function

(either not real, missing, misplaced or of incorrect brightness/shape/size)

Question 2

List propagation (wave movement) artifacts?

Answer 2

-Comet tail
-Grating lob
-Mirror image
-Range ambiguity
-Refraction
-Ring down
-Reverberation
-Slice thickness
-Speckle
-Speed error

Question 3

List attenuation artifacts?

Answer 3

-Enhancement
-Focal enhancement
-Shadowing
-Refraction/Edge shadowing

Question 4

List some causes of artifacts?

Answer 4

-Interactions with the sound + tissues
-Incorrect use of gains, TGCs or the PRF/scale
-Equipment degradation (such as damaged crystals or displays)

Question 5

List 5 assumptions of the u/s system?

Answer 5

-That sound travels in a straight line
-That echoes return to the probe after a single reflection
-That echoes originate only from objects located on the beam axis
-That the amplitude of the returning echoes is directly related to the reflecting or scattering properties of those reflectors/scatters
-That the distance to the reflecting or scattering objects is directly proportional to the round trip travel time

Question 6

What is slice thickness artifact?

Answer 6

-Echoes that occur in the 3rd dimension of the u/s beam
-Anechoic structures (such as cysts) appear “hazy” or partially filled in

(aka sectional thickness OR partial volume artifact)

Question 7

How can we resolve slice thickness artifacts?

Answer 7

By using harmonic imaging

Question 8

What are slice thickness artifacts caused by?

Answer 8

By poor elevational (3D slice thickness) resolution

(greater beam thickness causes artifactual echoes to be placed in front + behind the intended plane of imaging)

Question 9

What is speckle noise artifact?

Answer 9

-Granular appearance of images that is due to interference of echoes from the distribution of scatterers in tissue
-Echoes can combine constructively or destructively
-May obstruct detection of low contrast objects

Question 10

What types of resolution does speckle degrade?

Answer 10

Spatial + contrast resolution

(although it gives tissues their characteristic image texture)

Question 11

How can we decrease speckle?

Answer 11

With speckle reduction imaging, such as compound imaging (this smooths tissues)

Question 12

What will dead/damaged elements look like on our images?

Answer 12

-Dropout (black lines throughout image)
-Can occur anywhere along the array

(are weak or dead elements)

Question 13

What is reverberation?

Answer 13

-Sound bouncing b/w a structure + the probe OR within a structure
-Equally spaced reflections of diminishing amplitude with increased imaging depth

(looks like horizontal lines going across image + blocking out the structure of interest)

Question 14

What is a comet tail artifact?

Answer 14

-Closely spaced reverberations
-Has a banding appearance
-Progressively decreased amplitude + width with increasing depths

Question 15

Comet tail is m/s seen with what 3 things?

Answer 15

-Metallic objects
-Calcifications
-Surgical clips

Question 16

What is ring down artifact?

Answer 16

-Type of reverberation
-Arises from resonant vibrations within trapped air bubbles
-Aka dirty shadowing

Question 17

Ring down is also known as what?

Answer 17

Dirty shadowing

Question 18

Ring down can be useful in identifying what?

Answer 18

Abnormal foci of air

Question 19

What is a mirror image artifact?

Answer 19

-Type of reverberation
-Duplication of a structure on the opposite side of a strong specular reflector

Question 20

Mirror image artifacts are m/c where?

Answer 20

Around the pleura, pericardium + diaphragm

Question 21

Mirror image artifacts break which assumption that the u/s machine has?

Answer 21

That sound travels in a straight line

Question 22

What is refraction artifact?

Answer 22

-Change in direction of the sound beam from 1 medium to the next
-Displaces structures laterally from their correct locations
-Aka ghosting

(slide image shows bending of u/s beam causing the AoV to be almost duplicated laterally from true AoV)

Question 23

What 2 things cause refraction artifact?

Answer 23

-Oblique angles
-Change in propagation speed b/w 2 boundaries

Question 24

Refraction is also known as what?

Answer 24

Ghosting artifact

Question 25

Refraction artifacts break which assumption that the u/s machine has?

Answer 25

That sound travels in a straight line + that sound travels at a consistent speed

Question 26

List common inducers of refraction?

Answer 26

-Costal cartilage -Fascial structures -Adipose tissue -Pleural + pericardial surfaces

Question 27

How to fix refraction artifacts?

Answer 27

Alter probe angle + position

Question 28

What are grating lobe artifacts?

Answer 28

-Additional weaker beams emitted from the probe that propagate in different directions than the main beam -It duplicates structures laterally to the true ones

Question 29

When do grating lobe artifacts occur?

Answer 29

When the grating lobes reflects off a strong reflector (such as bone or gas)

Question 30

List 5 ways we can reduce grating/side lobe artifacts?

Answer 30

-Apodization (m/c) -Harmonic imaging -Reducing overall gain -Changing scan plane -Repositioning pt

Question 31

What are speed error artifacts?

Answer 31

-Occurs when the speed of sound in soft tissue is faster/slower than the assumed 1540 m/s -Displaces structures axially Slower = places echoes deeper Faster = places echoes closer

Question 32

Speed error artifacts break which assumption that the u/s machine has?

Answer 32

That the propagation speed of sound is constant

Question 33

What is the bayonet sign?

Answer 33

-Classic example of a speed error artifact -This is when the needle appears broken (confirms that the needle is placed within the cyst/mass)

Question 34

What is range ambiguity artifact?

Answer 34

-Occurs when all echoes are NOT received before the next pulse is sent out/emitted -Places structures much closer to the surface than they should be

Question 35

Range ambiguity artifacts break which assumption that the u/s machine has?

Answer 35

That for each pulse all echoes are received before the next pulse is emitted

Question 36

List 3 ways to reduce range ambiguity artifacts?

Answer 36

-Reduce PRF -Reduce # of focal zones -Increase imaging depth

Question 37

As sound travels through tissue, _____ decreases with increasing distance?

Answer 37

Amplitude

Question 38

What is attenuation mostly due to?

Answer 38

Absorption (but is also contributed by reflection, scattering + divergence of sound beam)

Question 39

Attenuation artifacts break which assumption that the u/s machine has?

Answer 39

That the amplitude of the returning echoes is directly related to the reflecting or scattering properties of those reflectors/scatters

Question 40

What is posterior shadowing artifact?

Answer 40

-Weakening of echoes distal to a strongly attenuating or reflecting structure (or else from the edges of a refracting structure) -Decreases brightness behind a strongly attenuating structure

Question 41

List 4 examples where we would see posterior shadowing?

Answer 41

-Bone -Calcified plaque -Stones -Stiff breast lesions

Question 42

List 3 things posterior shadowing can help us identify?

Answer 42

-Common bile duct + kidney stones -Calcific plaque -Differentiation b/w mobile shadowing gallstones + non-mobile gallbladder polyps

Question 43

List 3 ways we can alter the appearance of posterior shadowing?

Answer 43

-By changing the focus (this will minimize slice thickness artifacts + maximize shadowing) -By using spatial compounding (this will decrease + change shape of shadowing) -By using higher operating frequencies + harmonic imaging (this will increase shadowing)

Question 44

What is refractive/edge shadowing artifact?

Answer 44

-Refractive artifact that occurs at the EDGE of a large curved boundary, with a different speed of sound than the other surrounding tissues -Appears as hypoechoic parallel lines, distal to the edges of the structure

Question 45

Give 2 clinical examples of edge shadowing?

Answer 45

-Fetal skull -Round cysts (looks like 2 hypoechoic lines on either side of the structure)

Question 46

List 2 main factors that cause edge shadowing?

Answer 46

-Oblique angles -Change in propagation speed b/w 2 boundaries (exact same factors as refraction artifacts)

Question 47

What is posterior enhancement artifact?

Answer 47

-Occurs through fluid filled regions -It is the strengthening of echoes distal to a weakly attenuating structure -Increases brightness behind a weakly attenuating structure (ex. a cyst will have this artifact)

Question 48

List 3 common examples where we would see posterior enhancement?

Answer 48

-Cystic structures -Bladder -Blood pool

Question 49

What is posterior enhancement helpful in distinguishing?

Answer 49

Cystic from solid structures

Question 50

What is focal enhancement?

Answer 50

-Aka focal banding -It is brightening of echoes caused by increased intensity in the focal region (at + before the focus)

Question 51

What 2 things can alter the appearance of posterior enhancement?

Answer 51

-Spatial compounding (alters brightness + shape of enhancement) -Harmonic imaging (will increase enhancement)