Module 16 Artifacts Flashcards
What are four primary assumptions of artifacts?
- The beam travels in a straight line
- The retuning pulse is received before the next pulse is sent
- The round trip time of the pulse is proportional to the distance travelled
- Objects viewed are located in the central portion of the sound beam
Are the four primary assumptions of artifacts always true?
No
What are artifacts that clarify? 4
- Attenuation
- Enhancement
- Shadow
- Comet tail
What are artifacts that confuse? 5
- Refraction
- Reflection
- Reverberation
- Side lobes
- Ring down
What can be noted in terms of reflections and sound travel?
Sound does not always travel in a straight line
In terms of reflection what affects the pathway of sound?
It depends on the change in velocity of sound travelling from one medium to another
What happens with sound Beams with reflections?
The sound beam bounces off the interface without entering the second medium which displaces information
What kind of reflector does reflection usually occur with?
Specular reflector
What happens in terms of reflection in this image?
Incorrect information placed at the edge of the fetal head
What does refraction do to the acoustic beam as it travels?
Changes the direction
Where does the information in the acoustic beam go in terms of refraction?
Information is placed in a different location
What are examples of refraction artifacts?
Edge shadowing and duplication
When does curved edge refraction shadows happen?
When the beam hits a curve Specular reflector (edge of cysts and bones or canal of cervix)
How many types of curved edge refraction shadows are there? And what are they?
2 types
- 1st type: Low velocity medium to high velocity medium see a wide shadow
- 2nd type: From high velocity medium to low velocity medium see a narrow shadow
In terms of this image what is happening with this image? And what is the process of it happening?
Curved edge refraction shadow
- Beam hits a curved Specular reflector
- Low velocity maternal soft (tissue) to high velocity (bone)
- Thick shadow is produced
What artifact is this an example of?
Refraction
What is this an example of?
Curved edge refraction from a fibroid
What is happening in this image?
There is a shadow on the left of the cranium. We need to adjust the angle to see the full image of the skull
What happens with a critical angle?
The sound beam is completely reflected when the angle of transmission and angle of incidence equals 90 degrees
What does a critical angle cause?
Produces a wide shadow deep to tissue that should not shadow
How does a split image artifact happen?
When the beam travels through fat, then muscle, it is no longer in a straight line. The machine does not compensate for this
What causes split image artifacts?
Refraction
What might we see in terms of split image artifacts?
We may see partial or complete duplication of structures
What are examples in the body we may see split image artifacts?
- Linea alba
- Pseudo twin gestational sacs
What is this an example of?
Split image artifacts
What is a heterotropic pregnancy?
Multiple pregnancies
What is reverberation?
Multiple reflections of sound between a structure and the transducer face
What kind of structures does reverberation occur in?
In structures with a high degree of mismatch
What are examples of structures reverberation occur with?
Bone and soft tissue
What can reverberation be described as looking like?
- Equidistant
- Parallel
- Decreasing amplitude
What is this artifact?
Reverb
How does pseudo mass reverberation occur?
A beam striking a curved Specular reflector, and then hitting other curved interfaces causes an indirect path back to the probe
How is pseudomass reverberation interpreted
The signal is interpreted as part of another beam path
What is an example of pseudomass reverberation?
Multi path/ mirror image artifacts
What is one situation where we see pseudomass artifacts?
With extremely full bladders
What is comet tail reverberation?
Internal reverberation that occurs in dense, highly reflective objects
What does comet tail reverberation artifacts look like?
Multiple echoes, equal distance apart
What are things that result in comet tail artifacts?
- IUCD
- Surgical clips
- Shotgun pellets
What is this an image of?
IUCD with reverberation artifact
In terms of ring down reverberation, resonance artifacts are created by what?
Gas bubbles
Bubbles in resonance artifacts form what?
Fluid bugles
When the fluid bugles of resonance artifacts oscillate what happens?
It causes the liquid to vibrate and sends a continuous signal of decreasing amplitude back to the transducer.
The fluid bugle of resonance artifacts, what determines the frequency used? What does this mean?
The fluid bugle resonates at a frequency determined by its size, therefore independent of original transducer frequency
What is a ring down frequency similar in appearance to?
Comet tail
What is another way of thinking of attenuation?
Shadowing
Sound does what as it travels through a medium?
It attenuates
What kind of attenuating structure is bone?
Bone is extremely dense and attenuate a lot of sound
Having a shadow behind an echogenic focus means what?
It is calcified
What is enhancement?
Opposite of shadow
How does enhancement happen?
Increased amplitude is seen behind fluid filled structures
How does fluid attenuate?
Fluid attenuates very little sound
Why is enhancement useful?
To determine whether a mass contains fluid
An anechoic mass without posterior enhancement is what?
Not a cyst
What are side lobe artifacts?
Multiple side beams of lower intensity that emanate from the transducer, surrounding the main beam.
Side lobes happen because of what?
Multiple side beams scattering after hitting a Specular reflector
What are side lobes depending on?
Beam angle and intensity
What is this an example of?
Side lobe artifact
How does a slice thickest artifact happen?
When a cystic structure is off axis of the beam, and an averaging effect occurs between the cyst and the surrounding tissue, cause the cyst to fill in with echoes
How doe we reduce artifacts? 4
- Appropriate gain settings
- Proper transducer settings
- Proper focal zones in correct area
- Change probe position/ scan plane
