Physics Mod 8 Flashcards
Types of artifacts
1) reverberation
2) refraction
3) mirroring
4) shadowing and enhancement
5) speed error
Define reverberation
Fake structures that reverberates/rings between two surfaces
Gives multiple structures that are identical and appear deeper
Causes of reverberation
1) large acoustic impedance mismatch
2) specular reflector
3) highly angular
4) perpendicular to specular reflecting interface
Comet tail artifact
Reverberation from a small metal object
Refraction artifact
Fake image with lateral displacement
the one that is not in line with incident is real
Speed error artifact
When propagation speed different than 1540 m/sec then structures drawn at incorrect depths
Bayonet sign or broken needle sign
Speed error artifact giving the appearance that the needle is bent
Range ambiguity artifact
Reflected data from previous acoustic transmit (from deeper reflection) adding to reflection of current acoustic line
Mirroring artifact
Artificial structure symmetric to actual structure across the mirroring surface
Shadowing artifact
Excessive reflection, absorption or refraction producing ring down artifact
Enhancement artifact
Opposite of shadowing
Lack of reflection, absorption or refraction
Causes of aliasing
1) centre of vessel
2) bend in vessel
3) branch of vessel
4) narrowing of vessel
5) angle close to 0 or 180
6) scales are low
7) transmit frequency is high
Spectral mirroring causes
1) excessive transmit
2) excessive receive gain
3) superficial doppler with high frequency transducer
4) insonification angle close to 90
5) poor electronic design (poor separation between I and Q channel)
Causes of spectral broadening artifact
1) Insonification angle too high > 60
2) large array transducers (linear array)
3) superficial gate location
4) excessive gain
Blossoming artifact
Overgained signal resulting in higher than true peak velocity and potential loss of spectral window
