Flashcards in Physics Test Ch 21 Deck (73)
Causes of artifacts
Violation of assumptions
Equipment malfunction/poor design
Physics of ultrasound
Operator error pg. 355
Types of artifacts
Not seen on image
Incorrect shape or size
Incorrect brightness pg. 355
Characteristics of artifacts
Assumptions of artifacts
1. Sound travels in a straight line
2. Sound travels directly to a reflector and back
3. Sound travels in soft tissue at exactly 1540 m/s
4. Reflections arise only from structures positioned in the beam's main axis
5. The imaging plane is very thin
6. The strength of a reflection is related to the characteristics of the tissue creating the reflection pg. 356
Characteristics of reverberation
Appear in multiples
Appear equally spaced
Located parallel to sound beam's main axis
Located at ever-increasing depths pg. 357
What artifact appears as multiple, equally spaced echoes caused by the bouncing of the sound wave between 2 strong reflectors positioned parallel to the ultrasound beam?
Reverberation pg. 357
*only the first and second reflections, closest to the transducer are real, but the remaining echoes do not correspond to true anatomic structures
What artifact appears as a solid hyperechoic line directed downward?
Comet tail aka Ring down artifact pg. 358
What are the characteristics of comet tail?
Single long hyperechoic echo
Located parallel to sound beam's main axis pg. 358
What artifact appears as a hypoechoic or anechoic region extending downward from a highly attenuating structure?
Shadow pg. 359
What are the characteristics of shadowing?
Hypo- or anechoic background
Result of too much attenuation
Located beneath the structure with abnormally high attenuation
Prevents visualization of true anatomy on the scan pg. 359
What artifact is a special form of shadowing that appears as a hypoechoic region extending down from the edge of a curved reflector?
Edge shadow pg. 360
AKA shadowing by refraction
What artifact appears as a hyperechoic region beneath tissues with abnormally low attenuation?
Enhancement pg. 361
*opposite of shadowing
What are the characteristics of enhancement?
Result of too little attenuation
Located beneath a structure with abnormally low attenuation pg. 361
What artifact is a special form of enhancement in which a side-to-side region of an image appears brighter than tissues at other depths?
Focal enhancement aka Focal banding pg. 362
What artifact is created when sound reflects off a strong reflector and is redirected toward a second structure?
Mirror image pg. 363
What are the characteristics of mirror image?
A second copy of a true reflector
Located deeper than true reflector
The mirror lies on a straight line between the artifact and transducer
True reflector and artifact are equal distances from mirror pg. 363
What is crosstalk?
Mirror image on a spectral Doppler display pg. 363
What artifact is created when a sound wave propagates through a medium at a speed other than soft tissue?
Speed error pg. 364
What are the characteristics of speed error?
Correct number of reflections
Appears as a step-off ("split" or "cut") pg. 365
What artifact appears when sound energy is transmitted in a direction other than along the beam's main axis?
Lobes pg. 366
What resolution is degraded with lobe artifact?
Lateral resolution pg. 366
What are the characteristics of lobe artifact?
Second copy of the true reflector
The artifact and true reflector are located side-by-side at the same depth pg. 366
Which transducer creates side lobes?
Mechanical probe pg. 367
What transducer creates grating lobes?
Array transducers pg. 367
What artifact is created when a sound pulse changes direction during transmission?
Refraction pg. 368
*Remember- refraction is transmission with a bend
What are the characteristics of refraction?
Second copy of the reflector
The copy is side-by-side and the same depth of the true reflector pg. 368
What is an artifact?
It is an error in imaging
a ladder or Venetian blind
"Reverberation with the spaces squeezed out"