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66 Cards in this Set
- Front
- Back
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What is artifact?
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Any perturbation of a signal which distorts a display from ‘truth’
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How does artifact apply to diagnostic imaging?
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There are times when artifacts are extremely useful for making a correct diagnosis and there are times when artifacts obscure necessary information.
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What are the four categories of artifacts
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Imagine detail resolution
Location artifact Attenuation artifact Doppler artifact |
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What are detail resolution artifacts
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Artifacts associated with limited detail resolution include an inability to correctly visualize dimension or even the presence of structures laterally, axially, and/or elevationally.
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Axial resolution is determined by what?
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SPL
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Lateral resolution is determined by what?
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Beamwidth
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When there is lateral distortion at greater depths how do you solve it?
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Move focus and / or turn on harmonics
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When there is a problem with axial resolution how do you solve it
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Decreasing SPL by increasing MHz
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What does the elevation plane relate to?
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The non-visualized slice thickness
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What is an example of elevation resolution artifact?
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when the tissue from the side of a vessel wall or the gallbladder is seen in a sagital view
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How does one fix elevation resolution artifact?
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focus or harmonics
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what are some sources of locational artifact?
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refraction
reverberation (comet tail, ring down) multipath grating lobes (side lobes) speed error range ambiguity mirror image |
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Explain refraction artifacts
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when there is lateral displacement of a structure within an image due to angle and speed of insonation through tissue
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when law specifically has to do with refraction?
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snell's law
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should you use doppler to differentiate real versus refraction artifact?
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no because both the real and artifact structures will have identical signals
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how does reverberation occur?
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when sound reverberates or rings between two or more surfaces
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reverberation is highly.....
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angle dependent
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reverberation is more likely when there is
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a large acoustic impedance mismatch and relatively specular reflection
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reverberation is usually worst when the sound is_____ to the specular reflector interface
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perpendicular
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reverberation causes which structures to replicate?
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all structures and tissue between the reverberating structures as well as the reverberating structure itself
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Reverberation is very common/uncommon and is often/not often identified by the tech or reader
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common, not
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What is an example of reverb artifact and how is it resolved
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when the aspirating needle is more perpendicular to the transducer
take a steeper path |
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a mirror image
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replicates identically
if it is not identical it is reverb not mirror |
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when using spectral doppler in a reverb artifact vessel the signals will
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be less than the true vessel but the waveform will be the same
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when you suspect reverb artifact on an image, what do you do
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change insonation angle/path and see if it goes away
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what is an example of ring down reverb artifact
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gas/air shadowing
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what is an example of a comet tail reverb artifact?
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a prosthetic mitral valve
the valve leaflets are strong reflectors leaving shadows increasing in size with depth below them |
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what is twinkle artifact associated with
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comet tail reverb artifact
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what is twinkle artifact
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color artifact in the 'comet tail' of a stone or structure, it will not have spectral doppler signal
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what causes twinkle artifact
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our motion
respiratory motion contamination of the signal within the machine |
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what is multi-path artifact
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a structure appearing deeper than reality because of the elongated path length caused by sound waves bouncing off of a strong relector
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Grating lobes are associated with ____ element transducers
and Side lobes are associated with ___ element transducers |
multi
single |
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what is grating/side lobes artifact
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the lateral displacement of structures within an image cause by energy in regions other than the main beam which is cause for the reflections
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an example of grating lobes is
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in PSAX a spurious second aortic valve appears next to the real valve
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what is speed error artifact
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when the propagation speed is different from 1540 m/sec and structures are displayed at incorrect depths
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what is an example of a speed error artifact
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when the aspirating needle shows a 'broken needle' or 'bayonet' sign as in crosses into the cystic structure
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range ambiguity artifact is the result of
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reflected data from the previous acoustic transmit adding to the reflection of the current acoustic line
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mirroring results in
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an artificial structure symmetric to the actual structure across the "mirroring structure"
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and example of mirror artifact is
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a calcification in the liver is mirrored in the pleural space because of the diaphragm
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what are examples of attenuation artifacts
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shadowing artifact
refractive (edge) shadowing enhancement artifact |
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shadowing is caused by
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excessive reflection, absorption, or refraction
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what are some examples of shadow artifact
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calcified plaque
stones |
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what is an example of refractive edge shadowing
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fetal head imaging
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what is the critical incidence angle
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90 degrees
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what is enhancement
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the reciprocal of shadowing
usually deep to the a fluid filled structure |
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what is enhancement also known as
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through transmission
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what are the different types of doppler artifacts
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aliasing
range ambiguity spectral mirroring spectral broadening blossoming circuit saturation refraction |
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what does aliasing occur
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when the Nyquist criterion is violated
the frequency shift is higher than one half the PRF the doppler signal wraps around |
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how does one fix aliasing
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move the baseline and increase the PRF
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what is the difference between true and display aliasing
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true aliasing you cannot determine the true peak velocity
with display it can be adjusted to improve it and you can find the peak |
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how would you fix spectral aliasing
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use CW
shallow the sample depth (if not heart) HPRF |
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how do you know in cases of spectral mirroring which trace is the real one?
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use your ears
check insonation angle turn down gain turn down power |
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what causes a worsening in spectral mirroring
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excessive transmit gain
excessive receive gain superficial doppler with high MHz transducer insonificaiton at or close to 90 degrees poor separation between I and Q channels |
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an example of color mirroring is
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when insonation angle of a vessel is 90 degrees, half of vessel is blue and half is red
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what does spectral spread/broadening look like
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a diminished window, with a overestimated peak velocity
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what worsens spectral spread
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large array transducers (linear)
superficial gate location large insonation angles (bigger than 60) excessive gain |
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what is blossoming
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excessive gain to the point that the window decreases and the peak velocity is overestimated
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what is wall filter saturation
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when the dynamic range is not adequately reduced by the wall filters, circuit saturation occurs
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what is an example of a circuit saturation?
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high shift movement
valve clicks |
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in order for a lab to be accredited there must be
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one or more registered technologists
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how many cme's must a registered tech complete per triennium?
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30
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what is a medical director
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licensed medical practitioner with proficiency in ultrasound
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what does the medical director do
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he is responsible for the operations of the lab
quality of service services provided maintaining tech adherence to protocols and lab standards |
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who is the technical director
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a person credentialed in all areas of accreditation application
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what does the technical director do
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supervision of staff
daily operations of lab tech training compliance of staff to standards operation and maintenance of lab equipment coordinate with medical director to maintain quality of pt care |
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who is the medical staff
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qualified physicians who demonstrate competency in ultrasound interpretation
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