Ch. 21 Artifacts Flashcards
5 types of artifacts
-not real
-seen on the image
-incorrect shape or size
-incorrect position
-incorrect brightness
Causes of Artifacts
-violation of assumptions
-equipment malfunction or poor design
-the physics of ultrasound
-operator error
Image Characteristics
-hyperechoic
-hypoechoic
-anechoic
-isoechoic
-homogeneous
-heterogeneous
Hyperechoic
portions of an image that are brighter then surrounding tissues
Hypoechoic
portions of an image that are not as bright as surrounding tissues, tissues that are less bright than normal
Anechoic
entirely without echo or sonolucent
Isoechoic
structures with equal echo brightness
Homogeneous
portion of tissue or an image that has similar echo characteristics throughtout
Heterogeneous
portion of tissue or an image that has differing echo characteristics throughtout
Six assumptions of imaging systems
- sound travels in a straight line
- sound travels directly to a reflector and back
- sound travels in soft tissue at exactly 1,540 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
Artifacts appear when
these six assumptions are not true
When corrective measures are taken, artifacts often
vanish
Reverberation
appears as multiple, equally spaced echoes caused by the bouncing of the sound wave between two strong reflectors positioned parallel to the ultrasound beam
Which assumptions does reverberation break?
Assumption #2, sound travels directly to a reflector and back
Characteristics of reverberation
-appear in multiples
-appear equally spaced
-are located parallel to the sound beam’s main axis
-are located at ever-increasing depths
Reverberation artifacts places too many
reflections on the image
Reverberations resemble what?
a ladder or Venetian blind
With reverberations the first two reflections are real the rest are artifacts.
Reverberation is diagnostic.
Comet Tail also know as
ring down artifact
Comet tail
is reverberation with the spaces squeezed out appears as a solid hyper echoic line directed downward
Comet tail artifact is created when
Closely spaced reverberations merge
When are comet tail’s most likely to appear?
When the reflecting surfaces are located in a medium with a very high propagation speed, such as a mechanical heart valve.
-(when a sound wave bounces back and forth between two very closely spaced objects)
Comet tail breaks which assumption?
Assumption #2, sound travels directly to a reflector and back
Characteristics of comet tail
-appears as a single long hyperechoic echo
-is located parallel to the sound beam’s main axis
Shadow
appears as a hypoechoic or anechoic region extending downward from a highly attenuating structure.
shadows are the same color as
the images background
When does shadowing occur?
shadows appear when the attenuation is higher in the tissue above the shadow than in the surrounding tissue
shadowing prevents
the display of true anatomic structures
Shadow breaks which assumption?
Assumption 6, the strength of a reflection is related to the characteristics of tissue creating the reflection.
