US Physics Chapter 21 Flashcards
Describe what reverberation artifact is and what causes it
Two strong evenly spaced reflectors with multiple lines like a ladder or Venetian blinds
Comet tail or ring down artifact what causes it
Closely spaced reverberations merge usually reflecting surfaces with very high propagation speed (such as mechanical heart valve) or can arise by resonance form small structures such as gas bubbles after bombarded by sound pulse
What causes shadow artifact?
Hypoechoic or anechoic region extending from highly attenuating structure
What causes edge shadow
Special form of shadowing that you see with hypo echoic region extending from edge of curved reflector.
What causes “enhancement artifact”
Opposite of shadowing - results from tool little attenuation. Locate beneath structure w/ abnormally low attenuation like gallbladder or cystic structure
What is another name for focal enhancement
Focal banding
What is cause of focal enhancement
Its a band that results form increased intensity at the focus
What causes mirror image artifact? Where does reflection appear?
A mirror object deeper than the true object due to reflection off a mirror plane
What does propagation speed error look like and what causes it?
When sound is transmitted at a speed other than that of the speed of sound in soft tissue 1540 m/s a step off can appear.
Which direction does displacement occur if speed of sound is slower in object (such as breast implant) with propagation speed error
Step off shows tissue deeper on display than it actually is.
Another name for propogation speed error artifact
range error artifact
What is another name for section thickness artifact
partial volume artifact
Whats another name for lateral resolution artifact
Point spread artifact
What causes lateral resolution artifact
If two objects are less than the width of the sound beam they may appear to merge into one
What causes axial resolution artifact
when two structures are closer than 1/2 the spatial pulse length.
Where along beam is lateral resolution artifact least likely to occur
at focus
What types of pulses are least likely to cause axial resolution artifact
Transducers that create short pulses (higher frequency and less ringing)
What causes multipath artifact
Sound pulses glance off a second structure away from primary structure and take longer to get back to receiver.
What is seen with curved or oblique reflector artifact?
Some reflected sound may be directed away from the transducer by a curved reflector. You get varying intensity of similar echogenic structure just from sound hitting boundary at different angles.
What is noise?
Small amplitude echoes resulting form multiple things including electrical interference signal processing and spurious reflections. More likely to affect low level hypo echoic areas than bright echogenic regions
What is speckle?
Results form constructive (in phase) and destructive (out of phase) interference of wavelets. Causes face detail like grainy tissue like appearance.
What reduces speckle artifact?
spatial compounding
