Artefacts Flashcards
What 4 things are artefacts due to?
1) violation of assumptions
2) Operator error
3) physical principles
4) equipment malfunction or error
Describe reverberation artefact.
Occurs when reflected soundwave encounters strong reflector on its way back to the probe and causes back and forth reflection between transducer and reflecting surface
What does reverberation artefact look like?
Series of bright bands
Parallel to sound beams main axis
Decreasing in intensity
How do we solve reverberation artefact?
Decrease the gain or use alternative image plane
Describe acoustic shadowing.
Soundbeam encounters a highly attenuation structure. Little sound is transmitted beyond the structure and shadowing occurs.
Describe acoustic enhancement.
Soundbeam encounters a structure with less attenuation, energy transmitted through is increased and posterior structure will produce brighter echoes in comparison to surrounding tissue
Describe mirror image artefact.
Structure is located in front of strong reflector, it is interrogated twice. First echo is real structure and second will be mirror image of the first.
Describe refraction artefact.
After refraction the display assumes beam travels in straight line and misplaces returning refracted echoes next to the objects true location
Describe side lobe artefacts.
Secondary low-energy beam that diverge away from main beam, detectable in front of strong reflector.
Describe slice thickness artefacts
Originate from outside the main beam and are reduced amplitude. Appear as hallow structures that are filled in.
Describe beam-width artefacts.
Two side by side reflectors are seen as one
List some imaging assumptions
1) transmitted US beam is a narrow straight line
2) US travels along this straight line and does not deviate
3) US pulse always travels directly from transducer to a given reflector and the echo from that object travels directly back to the transducer
4) Propagation speed of US is 1540m/s
5) Attenuation is the same in all tissues
6) All echoes detected by transducer are caused by the most recent transmit pulse
Describe edge shadowing artefact.
US beam strikes the edge of a curved structure (reflection and refraction occurs)
Describe propagation speed artefact.
US travels through tissue with different propagation speed than 1540m/s, echoes displayed at incorrect depth
Describe ring-down artefact.
Type of reverberation when reflectors are small gas bubbles.
