Physics 2 - Module 6 ARTIFACTS* Flashcards
What are the 4 things that artifacts are a result of?
- Malfunctioning equipment
- Defective recording device
- Improper operation of equipment
- Acoustic properties of tissues and propagation of sound waves
What are the 4 assumptions about how sound propagates made by the machine?
- All tissue has the same acoustic velocity
- The sound beam always travels straight
- Echo strength indicates organ echogenicity only
- The distance to each reflector equals the round trip time
What are the 4 categories of artifacts?
- Not real
- Missing
- Improper location
- Improper brightness, shape, size, etc
What are the 2 main groups of artifacts?
- Propagation group
2. Attenuation group
Objects <1/2 SPL apart in the axis of the beam appear as a single echo
Axial resolution artifact
Also called point spreading. Reflector appears smeared across the screen
Lateral resolution artifact
Also known as volume averaging, can account for the filling in of anechoic structures with false debris.
Slice thickness artifact
How to assist with acoustic speckle?
Persistence
Constructive and destructive interference that creates heterogenous areas of brightness due to scatter
Acoustic speckle artifact
Reflection of sound between the transducer and a strong interface
Reverberation
How to correct reverberation?
Harmonics
The type of reverberation seen with metal, calcium, cholesterol, etc
Comet tail
What type of reverberation is seen in gas?
Ring down. Appears as dirty shadowing
Duplication of an object due to odd angle and strong reflector.
Mirror image
This artifact is the result of the assumption that the beam travels in a straight line and is corrected by getting more perpendicular to the structure of interest
Multipath artifacts
Shadows at the edges of strong, curved reflectors
Edge shadow
Why does edge shadowing occur?
Refraction. The beam changes direction when angle of incidence is not perpendicular
Appears as lateral duplication of an echo due to refraction of the beam by a strong interface
Refractive duplication
The echo is falsely allocated laterally from its true position due to bending of the beam
Refractive malposition
Linear echogenic bands due to radial mode vibration
Side/grating lobe artifacts
How to correct side lobes?
Insulator ring
How to correct for grating lobes?
Apodization and sub-dicing
Misallocation of a reflector more prox or distal to its actual location.
Propagation speed error
Rare in 2D, common in doppler. Echoes appear closer to the transducer than they actually are.
Range ambiguity.
What causes range ambiguity artifact?
PRF too high. Sending a second pulse before the first one returns
Name 7 propagation artifacts
- Axial resolution artifact
- lateral resolution artifact
- section thickness artifact
- acoustic speckle
- reverberation
- mirror image
- multipath
- refraction
- grating/side lobes
- speed error
- range ambiguity
What are the 4 attenuation artifacts?
- shadowing
- enhancement
- focal enhancement
- edge shadowing
A lack of echoes beneath a highly attenuating structure
Shadowing
Posterior brightness to structures that are less attenuating
Enhancement
False brightening to a particular area of the image at the level of the focal zone. Corrected with TGCs
Focal enhancement
Name 5 doppler artifacts
- Aliasing
- Slice thickness
- Reverberation
- Mirror image
- Flash or clutter
- Noise
- Refraction
Multiple flows seen within one flow envelope due to beam width
Doppler slice thickness
Reverberation on a stone that produces a mosaic of colour
Twinkle artifact (a doppler reverberation artifact)
Appears as a false vessel or spectral doppler flow on both sides of the baseline
Doppler mirror image
How to correct for doppler mirror image?
Decrease gains, decrease angle of insonation (it’s too close to 90)
Low level echoes of colour seen in the tissue as a result of movement
Doppler flash or clutter
What is used to eliminate doppler flash/clutter
Filter presets on the machine
Doppler gains set too high causing the colour to blossom outside of the vessel
Doppler noise
What are the artifacts associated with malfunction of equipment?
- Electronic interference
- Faulty software
- Faulty scan converter
- Faulty equipment
- malfunctioning crystal
- cracked damping material
- defective recording device
- improper transducer shielding
False location of a structure lateral to its actual position
Refractive malposition
How would one correct for artifacts related to lateral resolution?
Scan in the near zone
