Motion and Flow with Principle 2 and Artifacts Flashcards
What are the components of principle 2 and what is changed from principle 1?
- Beam former
- Signal processor
- Display
- Image processor (principle 1) is now the image FORMER (principle 2)
In principle 2, what is the image former responsible for?
Scanning, focusing, and apodization
What are the functions of the signal processor? (3)
- Bandpass filtering
- Detection/demodulation
- Compression
In principle 2, the entire image is in focus due to what?
VIRTUAL beam forming - sorts out the combined echo information to determine the precise echo from each pixel location
T or F? Virtual beams are THINNER than physical beams?
TRUE
Name the 5 ultrasound assumptions.
- Sound travels in a straight line
- Echoes return to the transducer after a single reflection
- Echoes originate only from objects on the beam axis
- The amplitude of the returning echoes are directly related to the reflecting properties of those reflectors
- The distance to the reflecting object is proportional to the round trip travel time
What artifact is seen where anechoic structures appear partially filled in or ‘hazy’?
Slice thickness artifact - improved by THI
What is slice thickness artifact caused by?
Poor elevational resolution - beam thickness is larger than the structure
What artifact is caused by the interference of echoes from the distribution of scatterers in the tissue? (hint: granular appearance)
Speckle - degrades spatial and contrast resolution
How can speckle be reduced?
Spatial compounding (x beam)
What type of artifact is produced by echoes bouncing between structures?
Reverberation
Name the types of reverberation (3)
- comet-tail due to metallic objects and calcifications
- Ring-down due to gas or air bubbles AKA dirty shadowing
- Mirror-image due to strong reflector - breaks the assumption that sound travels in a straight line
What artifact can help detect abnormal foci of air?
Ringdown
What factors does refraction rely on?
- Oblique angles
- Change in propagation speed from one medium to the next
What artifact displaces structures LATERALLY?
Refraction
Refraction artifact is also known as?
Ghosting
What artifact duplicates structures laterally?
Side-lobes
What artifact is known as: additional weaker beams emitted from the transducer that propagate in a different direction other than the main beam?
Side-lobes - reflecting off a strong reflector
What can eliminate grating lobes? (2)
- THI
- Apodization
Speed error artifact displaces structures _________ ?
Axially
In speed error artifact, when speed is slower, where will echoes be placed?
Slower - places echoes DEEPER
What artifact is created when not all echoes are received before the next pulse is emitted?
Range ambiguity - puts the structure closer to the surface than it should be
How do we reduce range ambiguity?
- decrease PRF
- decrease number of focuses
- Increase image depth
Attenuation is mostly caused by?
Absorption
What artifacts violates this assumption: the amplitude of the returning echoes are directly related to the reflecting properties of those reflectors
Attenuation - decreased amplitude with increased depth
What artifact is the weakening of echoes distal to a strongly attenuating structure?
Posterior shadowing
What artifact appears as hypoechoic parallel lines distal to the edges of a structure?
Edge shadowing
What artifact is a strengthening of echoes behind a weakly attenuating structure?
Posterior enhancement
