Chapter 21 Flashcards
Artifact = Error in Imaging and includes reflections that are:
Not Real
Not seen on the image
Not of correct size or shape
Not of correct brightness
Causes of artifact
Violation of assumptions
Equipment malfunction or poor design
The physics of ultrasound
Operator error
Hyperechoic:
tissues that appear brighter than normal
Hypoechoic:
tissues that appear less bright than normal
Anechoic:
an extreme form of hypoechoic meaning without echoes or echo free
Isoechoic:
structures with equal echo brightness
Homogenous:
tissue that has similar echo characteristics throughout
Heterogenous:
tissue that has differing echo characteristics throughout
6 imaging assumptions
-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
Reverberation
-appears on the display as multiple, equally spaced echoes
-caused by the bouncing of the sound wave between a strong reflector and the probe or two strong reflectors positioned parallel to the beam
Characteristics of Reverberation
Appears in multiples
Appears equally spaced
Located parallel to the sound beam
Located at ever increasing depths
Comet Tail
Closely spaced reverberations merge i.e. “the spaces are squeezed out”
Solid hyperechoic line directed downward
AKA ring down artifact
Shadow
Hypoechoic or anechoic region extending downward from a very strong attenuating medium
Edge Shadow
Special form of shadowing that appears as a hypoechoic region extending along the edge of a curved reflector
AKA shadowing by refraction
Enhancement
Appears as a hyperechoic region beneath tissues with abnormally low attenuation (cystic or fluid filled structures)
Focal Enhancement
Special form of enhancement in which a side-to-side or horizontal region of an image is hyperechoic or brighter
AKA focal banding
Mirror Image
Image shows mirror like reflector or line with real reflector on one side shallower and the false replica on other side deeper
Deeper vessel is artifact
Crosstalk
Same spectral Doppler display above and below baseline
Flow appears bidirectional when it is unidirectional
Speed Error
Occurs when sound travels thru a medium at a speed other than that of soft tissue
Reflector is placed at incorrect depth
Lobes
Unintentional side beams
reflector will appear twice, side by side, at the same depth
Refraction
Occurs when a sound pulse changes direction during transmission
Slice Thickness
is when structures in front of or behind the “assumed” thin imaging plane appear in the plane
Hollow structures like cysts appear partially filled in
Lateral Resolution Artifact
Occurs when a beam is wider than the distance between two reflectors that are located side by side or perpendicular to the beam
Two side by side objects appear as one on the display, or a narrow reflector appears wider
Axial resolution artifact
Occurs when a long pulse strikes two closely spaced structures, one in front of the other or parallel to the sound beam
Only one longer reflection appears on the display
Multipath Artifact
Sound beams hit a reflector, some beams return directly to probe, others take an extended path
Curved/Oblique Reflector Artifact
When a sound beam strikes a curved or oblique reflector, some of the reflected sound may be directed away from the probe
Temporal Resolution Artifact
When frame rates are too low, we are unable to precisely position a moving structure from instant to instant; can miss brief event on color flow
Spatial Resolution Artifact
Factors that contribute to poor spatial resolution
Fewer lines
Analog
Digital
Range Ambiguity Artifact
occurs when a reflection from a structure deeper than the maximum imaging depth is inadvertently received by the probe.
Contrast Resolution Artifact
Fewer shades of gray or few shades devoted to low level signals can provide for poor contrast resolution (lose the ability to discern between similar adjacent tissues)
Noise
appears as small amplitude or spurious reflections and results from many sources such as electrical interference and signal processing
Speckle
Is a form of noise, arises from small amplitude sound waves interfering with each other close to the transducer
Appears as grainy false tissue texture
Clutter
Noise around the baseline on the Doppler spectrum due to low Doppler shifts off tissue being displayed, best eliminated with wall filter
Translational artifact – motion artifact
Structure moves in and out of view
