Artifacts Flashcards
Causes of Artifacts
- Violation of assumptions
- Equipment malfunction
- Natural physics of ultrasound
- Operator error
Hyperechoic
Parts of an image appear brighter than normal or surrounding tissue
Hypoechoic
Parts of an image that appear darker than normal or surrounding tissue
Anechoic
Without echoes, a severe form of hypoechoic
Isoechoic
Structures w/ equal echo brightness
Homogeneous
Parts of an image that have similar characteristics throughout
Heterogenous
Parts of an image that have differing characteristics throughout
Reverberation
Multiple, equally spaced echoes
→ Invalidates assumptions that echoes travel directly to a reflector and back
Characteristics od Reverberations
- Multiple, equally spaced
- Parallel to sound beam’s main axis
- Located at increasing depths
Comet Tail
aka ring down
Solid, hyperechoic line; occur when closely spaced reverberations merge
→ Invalidates assumptions that echoes travel directly to a reflector and back
Characteristics of Comet Tail
- Appear in areas w/ high prop. speed
2. Located parallel to the beam’s main axis
Shadow
Hypoechoic/anechoic region that extends below a highly attenuating structure
→ Invalidates assumption that the intensity of the reflector is related to the tissue causing the reflection
Edge Shadow
Special form of shadowing that appears at the edge of a curved reflector; caused by refraction from curve reducing intensity
→ Invalidates assumption that intensity of the reflector is related to the characteristics of the tissue causing the reflection
Enhancement
Hyperechoic region below tissues with very low attenuation
→ Invalidates assumption that intensity of the reflector is related to the characteristics of the tissue causing the reflection
Focal Enhancement
aka focal banding
Side-to-side region of image that is hyperechoic; strongly focused beam = brighter echoes
→ Invalidates assumption that intensity of the reflector is related to the characteristics of the tissue causing the reflection
Mirror Image
Replica of true reflector
→ Invalidates assumptions that sound travels in a straight line, and directly to a reflector and back
Characteristics of Mirror Image
- Replica of true reflector (appears DEEPER than true reflector)
- Mirror (bright reflector) appears in between artifact & transducer
- True reflector & artifact are equal distances from mirror
Crosstalk
Mirror image artifact for ONLY spectral Doppler; identical spectrum above and below the baseline
Occurs when gain is too high or incident angle is near 90 degrees
Speed Error
aka range error artifact
Step-off; occurs when wave propagates at speed other than 1.54 km/s
→ Invalidates assumption that sound always travels at 1.54 km/s
Slower Speed Error
Sound travels too slow and appears deeper; reported distance is too large
Faster Speed Error
Sound travels too fast and appears closer; reported distance is too small
Lobes
Appear when sound energy is transmitted in a direction other than the beam’s main axis
→ Invalidates assumption that reflections arise from structures located on beam’s main axis
Characteristics of Lobes
- Located side by side to true reflector
2. True anatomy can be determined by using multiple views
Side Lobes
Lobes created by a single crystal transducer
Grating Lobes
Lobes created by multiple element (array) transducers; can be reduced w/ subdicing & apodization
Refraction
Created when a sound pulse changes direction during transmission; side by side to reflector
→ Invalidates assumption that sound travels in a straight line
Slice Thickness
Reflections from structures above/below imaging plane from dimension of beam perpendicular to imaging plane
→ Invalidates assumption that imaging plane is thin and uniform
Characteristics of Slice Thickness
- Reduced w/ thinner imaging planes
2. Fills in hollow structures such as cysts
Axial
Appearance of only 1 structure out of 2 that are laid in front of the other; appears if structures are closer than 1/2 SPL
Lateral
Appearance of only 1 structure out of 2 that are side by side; occurs when reflectors are closer than the width of sound beam
Least likely to occur at focus
Point Spread
Component of lateral resolution artifact; small reflector is displayed as a wide line rather than a narrow dot
Multipath
Occurs when sound pulses bounce off a second structure on the way to or from the primary reflector
Curved/Oblique
Reflection of sound away from transducer; results in reflectors being absent, weak, or appear different from surrounding structures
Temporal
Poor frame rate results in inaccurate positioning of moving reflectors
Spatial
Low line density results in less detail/poor resolution
Range Ambiguity
Reflector is located deeper/shallower on image; eliminated by increasing PRP
Noise
Small amplitude echoes resulting from electrical interference, signal processing, and fake reflectors
Speckle
Noise resulting from constructive & destructive interference
Clutter
Noise from false echoes located outside the main sound beam (i.e. side/grating lobes, section thickness)
In Doppler: contamination of accurate Doppler signals by vessel walls or heart muscles & their high amplitude reflections
