1. Violation of assumptions 2. Equipment malfunction 3. Natural physics of ultrasound 4. Operator error

Artifacts Flashcards by Katherine Ha

Causes of Artifacts

Violation of assumptions
Equipment malfunction
Natural physics of ultrasound
Operator error

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Hyperechoic

Parts of an image appear brighter than normal or surrounding tissue

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Hypoechoic

Parts of an image that appear darker than normal or surrounding tissue

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Anechoic

Without echoes, a severe form of hypoechoic

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Isoechoic

Structures w/ equal echo brightness

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Homogeneous

Parts of an image that have similar characteristics throughout

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Heterogenous

Parts of an image that have differing characteristics throughout

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Reverberation

Multiple, equally spaced echoes

→ Invalidates assumptions that echoes travel directly to a reflector and back

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Characteristics od Reverberations

Multiple, equally spaced
Parallel to sound beam’s main axis
Located at increasing depths

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Comet Tail

aka ring down
Solid, hyperechoic line; occur when closely spaced reverberations merge
→ Invalidates assumptions that echoes travel directly to a reflector and back

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Characteristics of Comet Tail

Appear in areas w/ high prop. speed

2. Located parallel to the beam’s main axis

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Shadow

Hypoechoic/anechoic region that extends below a highly attenuating structure
→ Invalidates assumption that the intensity of the reflector is related to the tissue causing the reflection

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Edge Shadow

Special form of shadowing that appears at the edge of a curved reflector; caused by refraction from curve reducing intensity
→ Invalidates assumption that intensity of the reflector is related to the characteristics of the tissue causing the reflection

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Enhancement

Hyperechoic region below tissues with very low attenuation
→ Invalidates assumption that intensity of the reflector is related to the characteristics of the tissue causing the reflection

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Focal Enhancement

aka focal banding
Side-to-side region of image that is hyperechoic; strongly focused beam = brighter echoes
→ Invalidates assumption that intensity of the reflector is related to the characteristics of the tissue causing the reflection

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Mirror Image

Replica of true reflector

→ Invalidates assumptions that sound travels in a straight line, and directly to a reflector and back

Characteristics of Mirror Image

Replica of true reflector (appears DEEPER than true reflector)
Mirror (bright reflector) appears in between artifact & transducer
True reflector & artifact are equal distances from mirror

Crosstalk

Mirror image artifact for ONLY spectral Doppler; identical spectrum above and below the baseline
Occurs when gain is too high or incident angle is near 90 degrees

Speed Error

aka range error artifact
Step-off; occurs when wave propagates at speed other than 1.54 km/s
→ Invalidates assumption that sound always travels at 1.54 km/s

Slower Speed Error

Sound travels too slow and appears deeper; reported distance is too large

Faster Speed Error

Sound travels too fast and appears closer; reported distance is too small

Lobes

Appear when sound energy is transmitted in a direction other than the beam’s main axis
→ Invalidates assumption that reflections arise from structures located on beam’s main axis

Characteristics of Lobes

Located side by side to true reflector

2. True anatomy can be determined by using multiple views

Side Lobes

Lobes created by a single crystal transducer

Grating Lobes

Lobes created by multiple element (array) transducers; can be reduced w/ subdicing & apodization

Refraction

Created when a sound pulse changes direction during transmission; side by side to reflector → Invalidates assumption that sound travels in a straight line

Slice Thickness

Reflections from structures above/below imaging plane from dimension of beam perpendicular to imaging plane → Invalidates assumption that imaging plane is thin and uniform

Characteristics of Slice Thickness

1. Reduced w/ thinner imaging planes | 2. Fills in hollow structures such as cysts

Axial

Appearance of only 1 structure out of 2 that are laid in front of the other; appears if structures are closer than 1/2 SPL

Lateral

Appearance of only 1 structure out of 2 that are side by side; occurs when reflectors are closer than the width of sound beam Least likely to occur at focus

Point Spread

Component of lateral resolution artifact; small reflector is displayed as a wide line rather than a narrow dot

Multipath

Occurs when sound pulses bounce off a second structure on the way to or from the primary reflector

Curved/Oblique

Reflection of sound away from transducer; results in reflectors being absent, weak, or appear different from surrounding structures

Temporal

Poor frame rate results in inaccurate positioning of moving reflectors

Spatial

Low line density results in less detail/poor resolution

Range Ambiguity

Reflector is located deeper/shallower on image; eliminated by increasing PRP

Noise

Small amplitude echoes resulting from electrical interference, signal processing, and fake reflectors

Speckle

Noise resulting from constructive & destructive interference

Clutter

Noise from false echoes located outside the main sound beam (i.e. side/grating lobes, section thickness) In Doppler: contamination of accurate Doppler signals by vessel walls or heart muscles & their high amplitude reflections