Ch. 6 Artifacts in scanning

Question 1

Improper Doppler-shift information from a pulsed wave Doppler or color Doppler instrument when the true Doppler shift exceeds one half the pulse repetition frequency

Answer 1

Aliasing

Question 2

Echo-free

Answer 2

Anechoic

Question 3

Movement of the zero Doppler-shift frequency or zero flow speed line up or down on a spectral display

Answer 3

Baseline shift

Question 4

Series of closely spaced reverberation echoes

Answer 4

Comet tail

Question 5

Leakage of strong signals in one direction channel of a Doppler receiver in the other channel; can produce the Doppler mirror-image artifact

Answer 5

Cross-talk

Question 6

Increase in echo amplitude from reflectors that lie behind a weakly attenuating structure

Answer 6

Enhancement

Question 7

Having relatively weak echoes

Answer 7

Hypoechoic

Question 8

Artifactual gray-scale, color flow, of Doppler signal appearing on the opposite side (from the real structure or flow) of a strong reflector

Answer 8

Mirror image

Question 9

Several reflections produced by a pulse encountering a pair of reflectors; reverberation

Answer 9

Multiple reflection

Question 10

Doppler-shift frequency above which aliasing occurs; one half the pulse repetition frequency

Answer 10

Nyquist limit

Question 11

Artifact produced when echoes are placed too close to the transducer because a second pulse was emitted before they were received

Answer 11

Range ambiguity

Question 12

Condition where a driven mechanical vibration is of a frequency similar to a natural vibration frequency of the structure

Answer 12

Resonance

Question 13

Multiple reflections

Answer 13

Reverberation

Question 14

Artifact resulting from a continuous stream of sound emanating from an anatomic site

Answer 14

Ring-down

Question 15

Thickness of the canned tissue volume perpendicular to the scan plane; also called slice thickness

Answer 15

Section thickness

Question 16

Reduction in echo amplitude from reflectors that lie behind a strongly reflecting or attenuating structure

Answer 16

Shadowing

Question 17

Granular appearance of images and spectral displays that is caused by the interference of echoes from the distribution of scatterers in tissue

Answer 17

Speckle

Question 18

Propagation speed that is different from the assumed value (1.54 mm/ms)

Answer 18

Speed error

Question 19

Axial resolution

Answer 19

Caused by: Pulse length

Question 20

Comet tail

Answer 20

Caused by: Reverberation

Question 21

Grating lobe

Answer 21

Caused by: Grating lobe

Question 22

Lateral resolution

Answer 22

Caused by: Pulse width

Question 23

Mirror image

Answer 23

Caused by: Multiple reflection

Question 24

Refraction

Answer 24

Caused by: Refraction

Question 25

Reverberation

Answer 25

Caused by: Multiple reflection

Question 26

Ring down

Answer 26

Caused by: Resonance

Question 27

Section thickness

Answer 27

Caused by: Pulse width

Question 28

Speckle

Answer 28

Caused by: Interference

Question 29

Speed error

Answer 29

Caused by: Speed error

Question 30

Range ambiguity

Answer 30

Caused by: High-pulse repetition frequency

Question 31

Shadowing

Answer 31

Caused by: High attenuation

Question 32

Edge shadowing

Answer 32

Caused by: Refraction or interference

Question 33

Enhancement

Answer 33

Caused by: Low attenuation

Question 34

Focal enhancement

Answer 34

Caused by: Focusing

Question 35

Aliasing

Answer 35

Caused by: Low-pulse repetition frequency

Question 36

Spectrum mirror

Answer 36

Caused by: High Doppler gain

Question 37

Artifacts in sonography occur as apparent structure that are one of the following

Answer 37

1. Not real 2. Missing 3. Misplaced 4. Of improper brightness, shape, or size

Question 38

Propagation Artifact do what?

Answer 38

Affects the beam as it travel through the body

Question 39

Name some Propagating Artifacts

Answer 39

``` Section thickness Speckle Reverberation Mirror image Refraction Grating lobes Speed error Range ambiguity ```

Question 40

Attenuation Artifacts do what?

Answer 40

Affects the beam as it reduces in amplitude

Question 41

Name some Attenuation Artifacts

Answer 41

Shadowing | Enhancement

Question 42

Spectral Doppler Artifacts are used to______________

Answer 42

Detect Doppler shifts

Question 43

Name some Spectral Doppler Artifacts

Answer 43

``` Aliasing Nyquist limit Range ambiguity Mirror image Noise ```

Question 44

Color Doppler Artifacts are used to _________________________

Answer 44

Detect flow direction

Question 45

Name some Color Doppler Artifacts

Answer 45

``` Aliasing Mirror image Shadowing Clutter Noise ```

Question 46

Focal banding can also be caused by:

Answer 46

Incorrect gain and TGC settings

Question 47

Methods of reducing or eliminating aliasing

Answer 47

``` Shift the baseline* Increase the pulse repetition frequency* Increase the Doppler angle Use a lower operating frequency Use a continuous wave device ``` *These are the most convenient and commonly used methods. Both are required in extreme cases

Question 48

Aliasing is the most _________ artifact encountered in Doppler ultrasound

Answer 48

Common

Question 49

Focal enhancement or focal banding

Answer 49

Brightening of echoes also can be caused by the increased intensity in the focal region of a beam because the beam is narrow there