Physics 2 Test Ch 21 Flashcards
Causes of artifacts
Violation of assumptions Equipment malfunction/poor design Physics of ultrasound Operator error pg. 355
Types of artifacts
Not real Not seen on image Incorrect shape or size Incorrect position Incorrect brightness pg. 355
Characteristics of artifacts
Hyperechoic Hypoechoic Anechoic Isoechoic Homogenous Heterogenous
Assumptions of artifacts
- Sound travels in a straight line
- Sound travels directly to a reflector and back
- Sound travels in soft tissue at exactly 1540 m/s
- Reflections arise only from structures positioned in the beam’s main axis
- The imaging plane is very thin
- 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
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
What artifact appears as a hyperechoic region beneath tissues with abnormally low attenuation?
Enhancement
pg. 361
What are the characteristics of enhancement?
Hyperechoic
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
Improper depth
Appears as a step-off
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
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
