80. ULTRASOUNDS: IMAGE ARTEFACTS Flashcards
- What are the 5 Image Artefacts?
- Mirror Image
- Acoustic Shadows
(Shadowing Artefacts) - Acoustic Enhancement
(Enhancement Artefacts) - Reverberation
- Refraction
(Edge artefacts)
- What are Artefacts?
- they are ultrasound images
- they do not represent anatomical structures
- How are Artefacts generated?
- they are generated by ultrasounds interacting with
structures within the body
- What are Shadowing Artefacts caused by?
THEY ARE CAUSED BY WHEN:
- an ultrasound encounters high-density structures
ALL OF THE ULTRASOUND CAN EITHER BE:
- absorbed by the surface of the structure
- or reflected from the surface of the structure
- How will the surface of the structure appear in Shadowing Artefacts?
- they will appear as Hyperechoic (white)
- What structures appear as Anechoic (black) in Shadowing Artefacts?
- bone
- anechoic
THIS IS BECAUSE:
- there is no ultrasound available deep to these
structures
- What is the black area of Shadow Artefacts known as?
- it is called the Shadow
- What do we use Shadowing artefacts for?
- we use them for identifying a structure
- Provide an example where we would need to use Shadowing Artefacts?
WE COULD USE IT WHEN ANALYSING:
- gallstones and gallbladder polyps
- they can appear as similar protrusions from the
gallbladder wall
- How do we tell apart gallstones and gallbladder polyps?
ONLY GALLSTONES:
- produce a shadow deep to their image
- this is because of their high density
- How are shadowing artefacts a disadvantage?
- they can obstruct the view of a deeper structure
- What kind of structures absorb the ultrasound?
- dense structures
- When do we have Enhancement Artefacts?
- when an Ultrasound passes through a low density
structure - this structure is filled with fluid
- it passes through this structure with very little
attenuation
EXAMPLE:
- gallbladder
- fluid filled cyst
- What happens when the Ultrasound reaches the fluid filled structures in an Enhancement Artefact?
- it will reach the deep tissues that surround the fluid
filled structure - it will reach them with more energy
THIS MAKES THE FLUID FILLED STRUCTURE LOOK MORE ENHANCED:
- this means that they it looks more white
- it is more echogenic than the surrounding tissues
- What do we use Enhancement artefacts for?
- we use them to distinguish between a fluid filled cyst
and a tumour
BOTH OF THESE LOOK LIKE:
- circular structures within a solid organ
- What will the Fluid Filled cyst produce?
- it will produce an enhancement artefact
- What will the tumour produce?
- it either won’t produce an enhancement artefact
- or it will produce much less of an enhancement
artefact
- What can an enhancement artefact introduce?
- it can introduce errors
- What parts of the gallbladder are enhanced when we take an Ultrasound image of it?
- the posterior wall is enhanced
- it appears thicker than it actually is
- When do we have a Mirror Image Artefact?
- when an ultrasound encounters a high reflective
curved surface - such as the diaphragm
PART OF THE REFLECTED ULTRASOUND TRAVELS:
- through the liver
- it then returns directly to the probe
HOWEVER:
- part of the ultrasound will follow a longer indirect
trajectory when it returns to the probe
- What does the Ultrasound system interpret this longer indirect trajectory as in a Mirror Artefact?
- it interprets it as a deeper structure
- this results in a mirror image of the liver
- this appears deeper than the diaphragm
- What stops the formation of a mirror image of the liver?
- the presence of a Pleural Effusion
- there will be no mirror image of the liver
- this liver is positioned near the anterior of the
diaphragm
- What is the disadvantage of the Mirror Artefact?
THE MIRROR IMAGE OF THE LIVER:
- can be misinterpreted as a more solid lung
- When do we have a Reverberation Artefact?
- when an ultrasound encounters two closely apposed
reflective surfaces - the ultrasound will reverberate between the two
surfaces
- What is an example of two closely apposed reflective surfaces?
- the Parietal and the Visceral Pleura
- Define “Reverberate”?
- this is when a sound wave is repeated several times as
an echo
- What do Reverberation Artefacts create?
- they create parallel linear artefacts
- these are at equidistance intervals on an image
- What do we call Reverberation Artefacts that occur while imaging the lung?
- they are called “A lines”
- What is the significance of a presence of “Alines” on an ultrasound image of the chest?
- they can be used in the assessment of a Patient with
dyspnoea
- When do we have a Refraction (edge) Artefact?
- when an ultrasound encounters the edge of a fluid
filled structure - this structure is curved
THE ULTRASOUND WAVES:
- are deflected from their path
- What do Refraction (edge) artefacts result in?
- they result in Anechoic artefacts
- these are black
- they project from the edge of the fluid filled structure
- they extend into the far-field
