Artifacts Flashcards
Multiple equally spaced echoes caused by the bouncing of the sound wave between two strong reflectors positioned parallel to us beam
Reverberation
Reverberation resembles a
Ladder
Solid hyperechoic line directed downward. Created when closely spaced reverberations merge.
Comet tail
Appears when a sound wave bounces back and forth between two verily closely spaced objects
Comet tail
Hypoechoic or anechoic region appears when attenuation is higher
Shadow
Shadowing is unrelated to ___ in a medium
Speed of sound
Hypoechoic region extending down from the edge of a curved reflector caused by a decrease in intensity
Edge shadowing / shadowing by refraction
Hyperechoic beneath tissues with low attenuation
Enhancement
Special form of enhancement, in which a side to side region of an image appears brighter than tissues, that other depths
Focal enhancement / focal banding
Focal enhancement results from ____ at the focus
Increased intensity
This artifact is located deeper than the real structure. Sound reflects off a strong reflector and is redirected toward a second structure.
Mirror image
6 assumptions of imaging systems
1) sound travels in a straight line
2) sound travels directly to reflector
3) sounds travels at 1540 m/s
4) imaging plane is very thin
5) reflections arise only from structures positioned in the beams main axis
6)the strength of the reflection is related to characteristics of the tissue creating the reflection
Useful artifacts
shadowing and enhancement
Mirror image artifact that appears on a spectral doppler display
crosstalk
Appears as a step off and created when a sound wave propogates through a medium at a speed other than 1.54 mm/us
Speed error
There a correct number of reflectors but has an improper debth
speed error
When sound energy is transmitted in a direction other than along the beams main axis
lobe artifact
lobe artifact degrades
temporal resolution
Lobes created by a single crystal transducer such as a mechanical probe
side lobes
lobes created by array transducers are
grating lobes
Reducing lobe artifacts in 2 ways
subdicing and apodization
dividing each pzt element into small pieces
subdicing
Process of differential excitation.
exiting the subdiced elements with a different voltage
apodization
Created when a sound pulse changes direction during transmission and occurs when a sound wave strikes a boundary obliquely
Refraction
Refraction degrades
lateral resolution
side by side or same depth of the true reflector
Refraction
Slice thickness is also called
section thickness artifact / partial volume artifact
Related to the dimension of the beam that is perpendicular to the imaging plane
Slice thickness artifact
Determined by the thickness of the imaging plane
Elevation resolution
Anatomic reflectors absent on an image
shadowing, lateral resolution, axial resolution
Artifact positioned deeper than true anatomy
comet tail, ring down, reverberation, mirror image
Artifacts displayed to the side of true anatomy
refraction, side lobe, grating lobe
Anatomic structures appear at incorrect depth
Speed errors, range ambiguity artifact
Which artifact is unrelated to the dimensions of an us pulse
refraction
It is common to visualize artifacts when the dimension of the sound beam is ____ than the reflectors dimension
Larger
Which artifact produced an image with an incorrect number or reflectors
Side lobes
What determines spatial resolution of a digital display
pixel density
What determines spatial resolution of a display
Number of lines on the display
Lateral resolution can be approved by
focusing because it narrows the beam width
Low line density degrades
spatial resolution
What alters low velocity flows while leaving high velocity flow unchanged
Wall filter
Alter low velocity flows while leaving high velocity flow unchanged
Wall filter
What determines the spatial resolution in a digital display
Pixel density
This artifact produces an image with an incorrect number of reflectors
Side lobes
What happens to the position of all echoes produced from reflectors shallower than the mass
They are placed at the correct depth
What happens to the position of echoes from reflectors deeper than the mass
They are placed in too deep a location on the image
What type of artifact causes a reflection to be placed at an incorrect depth
Range ambiguity
Acoustic energy radiating in a direction other than the beams main axis causes
Side lobe artifact
Grating loves are most common with what transducers
Linear array
Technique to eliminate grating lobe artifact
Subdicing
How does slice thickness express itself
Fill in cystic structures
With depth resolution there are ___ reflectors on the image
Too few
What is a comet tail artifacts fundamental mechanism of formation
Reflection
What haze the higher value / axial or lateral
Lateral
When do artifacts appear
When the dimensions of a sound beam area is larger than the dimensions of the reflectors in the body
