Physics Test Ch 21 Flashcards by Jessica Novak

Causes of artifacts

Violation of assumptions
Equipment malfunction/poor design
Physics of ultrasound
Operator error pg. 355

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Types of artifacts

Not real 
Not seen on image 
Incorrect shape or size 
Incorrect position 
Incorrect brightness pg. 355

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Characteristics of artifacts

Hyperechoic 
Hypoechoic 
Anechoic 
Isoechoic 
Homogenous 
Heterogenous

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Assumptions of artifacts

Sound travels in a straight line
Sound travels directly to a reflector and back
Sound travels in soft tissue at exactly 1540 m/s
Reflections arise only from structures positioned in the beam’s main axis
The imaging plane is very thin
The strength of a reflection is related to the characteristics of the tissue creating the reflection pg. 356

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Characteristics of reverberation

Appear in multiples
Appear equally spaced
Located parallel to sound beam’s main axis
Located at ever-increasing depths pg. 357

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What artifact appears as multiple, equally spaced echoes caused by the bouncing of the sound wave between 2 strong reflectors positioned parallel to the ultrasound beam?

Reverberation pg. 357

*only the first and second reflections, closest to the transducer are real, but the remaining echoes do not correspond to true anatomic structures

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What artifact appears as a solid hyperechoic line directed downward?

Comet tail aka Ring down artifact pg. 358

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What are the characteristics of comet tail?

Single long hyperechoic echo

Located parallel to sound beam’s main axis pg. 358

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What artifact appears as a hypoechoic or anechoic region extending downward from a highly attenuating structure?

Shadow pg. 359

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What are the characteristics of shadowing?

Hypo- or anechoic background
Result of too much attenuation
Located beneath the structure with abnormally high attenuation
Prevents visualization of true anatomy on the scan pg. 359

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What artifact is a special form of shadowing that appears as a hypoechoic region extending down from the edge of a curved reflector?

Edge shadow pg. 360

AKA shadowing by refraction

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What artifact appears as a hyperechoic region beneath tissues with abnormally low attenuation?

Enhancement pg. 361

*opposite of shadowing

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What are the characteristics of enhancement?

Hyperechoic
Result of too little attenuation
Located beneath a structure with abnormally low attenuation pg. 361

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What artifact is a special form of enhancement in which a side-to-side region of an image appears brighter than tissues at other depths?

Focal enhancement aka Focal banding pg. 362

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What artifact is created when sound reflects off a strong reflector and is redirected toward a second structure?

Mirror image pg. 363

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What are the characteristics of mirror image?

A second copy of a true reflector
Located deeper than true reflector
The mirror lies on a straight line between the artifact and transducer
True reflector and artifact are equal distances from mirror pg. 363

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What is crosstalk?

Mirror image on a spectral Doppler display pg. 363

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What artifact is created when a sound wave propagates through a medium at a speed other than soft tissue?

Speed error pg. 364

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What are the characteristics of speed error?

Correct number of reflections
Improper depth
Appears as a step-off (“split” or “cut”) pg. 365

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What artifact appears when sound energy is transmitted in a direction other than along the beam’s main axis?

Lobes pg. 366

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What resolution is degraded with lobe artifact?

Lateral resolution pg. 366

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What are the characteristics of lobe artifact?

Second copy of the true reflector

The artifact and true reflector are located side-by-side at the same depth pg. 366

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Which transducer creates side lobes?

Mechanical probe pg. 367

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What transducer creates grating lobes?

Array transducers pg. 367

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What artifact is created when a sound pulse changes direction during transmission?

Refraction pg. 368 *Remember- refraction is transmission with a bend

What are the characteristics of refraction?

Second copy of the reflector | The copy is side-by-side and the same depth of the true reflector pg. 368

What is an artifact?

It is an error in imaging

Reverberations resembles..

a ladder or Venetian blind

"Reverberation with the spaces squeezed out"

Comet tail

_________ appears when a sound wave bounces back and forth between two very closed spaced objects.

Comet tail

What might help provide valuable diagnostic information that helps to characterize tissue?

Shadows and enhancement

What two artifacts are unrelated to the speed of sound in a medium?

Shadowing and enhancement

Characteristics of edge shadow

Hypo- or anechoic (background color) Results when the beam spreads after striking a curved reflector Extends downward from the curved reflector's edge, parallel to the beam Prevents visualization of true anatomy on the scan

Characteristics of focal enhancement

A hyperechoic side-to-side region (appears the same as the foreground color) Results from increased intensity at the focus

What is also called range error artifact?

Propagation speed errors

Methods to eliminate lobes

1. subdicing- dividing each PZT element into small pieces | 2. apodization- exciting the subdiced elements with different voltage

What resolution is degrades with refraction artifact?

Lateral resolution

Reverb violates which assumption?

#2 (sound travels directly to the reflector and back)

Comet tail violates which assumption?

#2 (sound travels directly to the reflector and back)

Shadowing violates which assumption?

#6 (reflection strength is related to the tissue creating the reflections)

Edge shadowing violates which assumption?

#6 (reflection strength is related to the tissue creating the reflections)

Enhancement violates which assumption?

#6 (reflection strength is related to the tissue creating the reflections)

Focal enhancement violates which assumption?

#6 (reflection strength is related to the tissue creating the reflections)

Mirror image violates which assumption?

#1 (sound travels in a straight line) and #2 (sound travels directly to the reflector and back)

When the medium's speed is __ than soft tissue, the reflector appears deeper than it really is.

slower

When the medium's speed is __ than soft tissue, the reflector appears shallower than it really is.

faster

Speed error violates which assumption?

#3 (sound travels at 1540 m/s in soft tissue)

Lobe artifact violates which assumption?

#4 (reflections only arise from structures positioned in the beam's main axis)

Refraction violates which assumption?

#1 (sound travels in a straight line)

Slice thickness is also known as...

section thickness or partial volume.

This is related to the dimension of the beam that is perpendicular to the imaging plane.

slice thickness

This is determined by the thickness of the imaging plane

elevational resolution

Slice thickness is reduced with...

1.5 D array transducers

Slice thickness artifact violates which assumption?

#5 (the imaging plane is very thin)

This occurs when a pair of side-by-side reflectors are closer than the width of the sound beam.

lateral resolution artifact aka point spread

T/F? Lateral resolution artifact is least likely to occur at the focus.

true

This is created when a long pulse strikes two closely spaced structures, where one is in front of the other.

axial resolution artifact

Transducers that create __ minimize axial resolution artifact.

short pulses (high frequency, less ringing)

This is created when sound pulses glance off a second structure on the way to or from the primary reflector.

multipath artifact

This is a subtle artifact that often cannot be explicitly identified on the image.

multipath

Multipath violates which assumption?

#2 (sound travels directly to the reflector and back)

What kind of reflectors direct reflected sound away from the transducer?

curved or oblique reflectors

Spatial resolution is affected by the number of...

horizontal scan lines per frame.

This occurs when a reflecting structure is located deeper than the imaging depth of the image.

range ambiguity artifact

Range ambiguity artifact is eliminated by increasing the...

PRP *longer PRP means deeper imaging and decreased PRF

This appears as small amplitude echoes and results from many sources, including electrical interference, signal processing and spurious reflections.

noise

This is noise resulting from the constructive and destructive interference of small sound wavelets.

speckle

This is an effective tool to reduce speckle.

spatial compounding

This is the presence of false echo signals arising from locations outside of the main sound beam.

clutter

Name three examples of clutter.

side lobes grating lobes section thickness

This reduces an image's noise content.

harmonic imaging

Crosstalk results from..

Doppler gain is set too high (electronic crosstalk) | The incident angle is near 90 degrees between the sound beam and the flow direction, when flow is at the beam's focus

Color flash can be referred to as

Ghosting