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37 Cards in this Set
- Front
- Back
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the system always assumes the signal arrives from the ____ direction
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steered
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category & type of artifact?
the structure is artifactually drawn along the presumed straight path even though the structure is along a bent path |
location: refraction
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category & type of artifact?
occurs between two or more highly specular interfaces |
location: reverberation
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category & type of artifact?
typically happens in near field sound bouncing back and forth |
location: reverberation
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name ways in which reverberation artifacts can occur (3)
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between a strong specular reflector and transducer
between two strong specular reflectors scattering from a structure then between two strong specular reflectors (complex) |
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what ways can be used to determine that an structure is not a reverberation artifact (2)
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look for strong reflectors in the near field
change the image or steering angle |
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category & type of artifact?
usually from small air sacs tail like image below air sac below the bright reflectors are white "flashlights" |
location: reverberation, ring down
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category & type of artifact?
usually from calcified or metal structure striated tail of bright reflection below the structure |
location: reverberation, comet tail
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category & type of artifact?
incorrectly displays the depth of the structure result of insonating a specular reflector at an oblique angle |
location: multi-path
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category & type of artifact?
caused by the existence of lower pressure or weaker beams pointing off-axis weaker beams return echoes from undesired locations |
location: side lobe (single element)
grating lobe: (multi-element) memory aid: Side is a Single element. Grating is a Group of elements. |
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how is the image displaced with side lobe or grating lobe artifacts
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laterally
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how is the image displaced with multi-path
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deeper than it should be
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how is the image displaced with the reflection artifact
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laterally
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category & type of artifact?
image is displayed at different location because of encountering a significantly different propagation velocity |
location: speed error
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what type of structures typically cause speed errors
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air, bone or anything man made such as valves, discs, wires, clips
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the "bayonet sign" typically is seen in which type of artifact
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speed error
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category & type of artifact?
echoes from two locations are superimposed usually occurs at very shallow depths |
location: range ambiguity
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this artifact appears as a grayish haze and/or scintillations in the relatively near field and is sometimes referred to as "herbies"
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range ambiguity
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the artifact is inline with the sound beam - multi path / mirroring
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multi path
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the artifact is not inline with the sound beam - multi path / mirroring
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mirroring
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the artifact is simply deeper - multi path / mirroring
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multi path
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the artifact is deeper and to the side of the real image - multi path / mirroring
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mirroring
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most imaging artifacts result from interactions with _____ _____
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specular reflectors
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category & type of artifact?
happens when any form of attenuation is stronger than the attenuation from the surrounding area |
attenuation: shadowing
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shadowing can be caused by these things (3)
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strong reflection
strong attenuation beam refraction (critical angle at sides of circular structures as an example) |
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category & type of artifact?
reciprocal of shadowing |
attenuation: enhancement
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category & type of artifact?
beam goes thru a weakly attenuated area and signal is stronger beyond that area |
attenuation: enhancement
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category & type of artifact?
scattering from multiple reflectors that add constructively and destructively to create bright and dark spots |
attenuation: speckle
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higher/lower frequencies produce finer speckle
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higher
higher frequencies tend to go in and out of phase in a shorted distance |
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category & type of artifact?
violation of the Nyquist criteria |
Doppler: aliasing
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category & type of artifact?
more likely to occur using a shallow gate depth more likely to occur with fixed focus transducer |
Doppler: range ambiguity
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category & type of artifact?
with spectral Doppler this artifact happens when the signal amplitude is greater than the separation between two channels |
Doppler: spectral mirroring
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category & type of artifact?
artificially smears the spectrum, increasing the velocity the angle to flow from each element of an array is slightly different can become substantial with large linear arrays insonating at > 70 degrees |
Doppler: spectral spread (artificial spectral broadening)
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category & type of artifact?
signal that bleeds into neighboring regions of the spectrum could be caused by too much power or signal gain |
Doppler: blossoming
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category & type of artifact?
bright lines from top to bottom on spectrum caused when clutter signals are not adequately attenuated |
Doppler: wall filter saturation
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category & type of artifact?
happens when a vessel takes a deep dive Doppler signal completely disappears |
Doppler: refraction (critical angle is reached so Doppler signal disappears)
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the most effective way to identify an artifact caused by specular reflectors
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change the angle (specular reflectors are highly angle dependent)
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