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Ultrasound Artifacts
Ultrasound Artifacts (Chapter 21)
77
Physics
Not Applicable
06/16/2016

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Term
Name the 6 artifact catagories.
Definition
  1. Not real
  2. Missing
  3. Improperly located
  4. Improper brightness
  5. Improper shape
  6. Improper size
Term

What are the 6 assumptions of artifacts?

 

(In any order)

Definition
  1. Sound travels in a straight line.
  2. Sound travels directly to the reflector and back.
  3. The amplitude of the returning echoes is directly related to the reflecting properties of the medium.
  4. Sound travels at exactly 1540 m/s in the body.
  5. The imaging plane is very thin.
  6. Reflections arise only from structures along the beams main axis.
Term
What is an artifact?
Definition

An error in imaging.

A misrepresentation of data on the display.

Term
List 5 causes of artifacts.
Definition
  1. Violation of assumptions.
  2. Equipment malfunction or poor design.
  3. The physics of ultrasound.
  4. Operator error.
  5. Patient movement.
Term
Slice thickness artifact is also called:
Definition
  • Beam width artifact
  • Elevational resolution artifact
  • Section thickness artifact
  • Partial volume artifact
Term
What causes elevational resolution artifact?
Definition

The beam is too tall.

 

(Echoes are received that originate, not only from the center of the beam (axial & lateral resolution), but also from the 3rd dimension - the height of the beam.)

Term
What does a beam width artifact look like?
Definition

Echoes in anechoic structures.  Improper placement of structures in elevational plane.

 

(The true reflector lies either above or below the assumed imaging plane, but is displayed within the image.)

 

 

Term
Where would you see a partial volume artifact?
Definition
In fluid filled structures.
Term
How can you reduce or eliminate slice thickness artifacts?
Definition
  • Reduce overall gain.
  • Move the TGC's to the left.
  • Subdicing.
Term
What assumption does a section thickness artifact violate?
Definition
The imaging plane is very thin.
Term
What causes an Acoustic Speckle artifact?
Definition
Constructive & destructive interference of small sound wavelets.
Term
What does acoustic speckle look like?
Definition
Bright & dark grainy spots on the display.
Term
Where would you see acoustic speckle?
Definition
In soft tissue like the liver.
Term
How can you reduce or eliminate acoustic speckle?
Definition
You really can't, but the book suggests spatial compounding.
Term
What assumption does acoustic speckle violate?
Definition
The strength of a reflection is related to the characteristics of the tissue creating the reflection.
Term
What causes noise artifact?
Definition
Electrical interference, pulsing vessels, internal movement.
Term
What does noise artifact look like?
Definition
Ghosting (color bleed) or small bands of strong echoes.
Term
Where would you see noise artifact?
Definition
On the Doppler spectrum (clutter) and/or on the Color spectrum (ghosting).
Term
How can you reduce or eliminate noise artifact?
Definition
Increase the wall filter to reduce clutter.  Harmonics are preprogrammed in the system to improve quality at deeper locations.
Term
What assumption does noise artifact violate?
Definition
None
Term
What causes a Crosstalk artifact?
Definition
A poor Doppler angle (like 80o) and overdriven gain.
Term
How can you correct a crosstalk artifact?
Definition
Shift your transducer angle and avoid 90o angles.
Term
What causes a spectral mirror artifact?
Definition
Over driven gain.
Term
How can you fix spectral mirror artifact?
Definition
Turn down the PW Doppler gain.
Term
What causes an aliasing artifact?
Definition
The PRF is set too low.
Term
What does an aliasing artifact look like?
Definition
The Doppler signal wraps around the baseline scale..
Term
How can you eliminate an aliasing artifact?
Definition
Increase the PRF.
Term
What causes a Reverberation Artifact?
Definition

2 strong reflectors that are very close together and parallel to the beam.

 

Small gas bubbles can cause Ringdown reverberation.

 

Foreign objects in the body (metal, IUD) can cause Comet Tail reverberation.

Term
What does reverberation artifact look like?
Definition

Equally spaced, parallel line.  Ladder like.

 

Comet Tail reverberation fans out more at the bottom.

 

Ringdown reverberation is more solid.

Term
Where would you see reverberation?
Definition
From gas bubbles or foreign objects like metal in the body.
Term
How can you reduce or eliminate reverberation?
Definition
Change your view or angle of the transducer.
Term
What assumption does reverberation violate?
Definition
Sound travels directly to the reflector and back.
Term
What causes a Mirror-Image artifact?
Definition
A strong reflector that redirects the sound beam.
Term
What does a mirror-image artifact look like?
Definition

2 reflections are seen on the display, but only 1 is real.

 

The artifact is always DEEPER.

Term
Where would you see a mirror-image artifact?
Definition
Common around the lung/diaphragm/liver interface.
Term
How can you eliminate a mirror-image artifact?
Definition
Change the angle of your scan.
Term
What assumption does a mirror-image artifact violate?
Definition
Sound travels in a straight line.
Sound travels directly to a reflector & back.
Term
What causes a Multipath artifact?
Definition
When the reflection glances off of another strong reflector on its way back to the transducer and its path changes.
Term
What does a multipath artifact look like?
Definition
Cannot be identified.
Term
Where would you see a multipath artifact?
Definition
The structure will show DEEPER on the display than it really is.
Term
How can you correct a multipath artifact?
Definition
Unable to correct.
Term
What assumption does a multipath artifact violate?
Definition
A pulse travels directly to the reflector and back.
Term
What causes Refraction artifact?
Definition
Oblique incidence and different propagation speeds cause the beam to change directions during transmission.
Term
What does a refraction artifact look like?
Definition
A 2nd copy of the reflector that is side-by-side or at the same depth as the true reflector.
Term
Where would you see a refraction artifact?
Definition
At any interface with 2 different propagation speeds.  Like a mass.
Term
How can you remove or eliminate a refraction artifact?
Definition
Change the scanning angle.  Multiple views.
Term
What assumption does a refraction artifact violate?
Definition
Sound travels in a straight line.
Term

What causes Side/Grating Lobes?

(Lateral artifact)

Definition
When sound energy is transmitted in a direction other than along the beam's main axis from a strong reflector.
Term
What do side/grating lobes look like?
Definition

Side lobes: Reflections produced & received from "off axis positions" will be placed at proper distances, but wrong locations. They produce low-level echoes. 

Grating lobes: If they encounter a strong reflector, the echoes will usually appear lateral (side-by-side) to the real ones. 

*Echoes produced by lobes are weaker than the main beam and do not normally make echoes that are imaged.

Term
Where would you see side/grating lobe artifacts?
Definition
Usually close to the surface & with fluid filled structures.
Term
How can you reduce or eliminate side/grating lobe artifacts?
Definition
Apodization or use a gel pad.
Term
What assumption does side/grating lobe artifact violate?
Definition
Reflections arise from structures located along the beam's main axis.
Term
What causes Propagation speed/Range error artifacts?
Definition
When a sound wave propagates through a medium at a speed other than that of soft tissue.
Term
What does propagation speed/range error artifact look like?
Definition

If "C" is greater than 1540m/s, the echoes will arrive sooner and the display will put the reflector too close to the transducer.

 If "C" is less than 1540m/s, then the reflector will be displayed too far from the transducer because the echoes arrive later. 

(Correct # of reflectors, wrong depths, appears as a step-off)

Term
Where would you see a propagation speed/range error artifact?
Definition
Tissues with different propagation speeds.
Term
How can you reduce or eliminate a propagation speed/range error artifact?
Definition
May not want to because it can be useful for diagnosing.
Term
What assumption does propagation speed/range error artifact violate?
Definition
Sound travels at a speed of exactly 1540m/s.
Term
What causes a Range Ambiguity artifact?
Definition
When the reflection from the 1st pulse is not received by the transducer before the 2nd pulse is sent.  Caused by deep structures.
Term
What does a range ambiguity artifact look like?
Definition
The reflector is placed at a SHALLOW location on the image.
Term
Where would you see a range ambiguity artifact?
Definition
Anywhere.
Term
How can you remove or eliminate a range ambiguity artifact?
Definition
By increasing the PRP.  The PRP/PRF is linked to the Depth button on the machine.
Term
What assumption does a range ambiguity artifact violate?
Definition
None.
Term
What causes a Shadowing artifact?
Definition
Strong attenuators
Term
What does a shadowing artifact look like?
Definition
A dark path beneath/behind a high attenuating structure.
Term
Where would you see a shadowing artifact?
Definition
Gallstones, fecal impactions, bones (ribs), etc.
Term
How can you remove or eliminate a shadowing artifact?
Definition
You shouldn't.  It can provide valuable diagnostic information.
Term
What assumption does a shadowing artifact violate?
Definition
The intensity of a reflection is related to the tissue  creating the reflection.
Term
What causes an Enhancement artifact?
Definition
Weak attenuators.  It is the opposite of shadowing.
Term
What does an enhancement artifact look like?
Definition
Hyperechoic below the structure.
Term
Where would you see an enhancement artifact?
Definition
With any weak attenuators or fluid filled structures.
Term
How can you reduce or eliminate an enhancement artifact?
Definition
You don't want to.  It can be clinically useful.
Term
What assumption does an enhancement artifact violate?
Definition
The intensity of a reflection is related to the characteristics of the tissue.
Term
What causes a Focal Banding/Enhancement artifact?
Definition
Increased intensity at the focus.  Using multiple foci.
Term
What does a Focal Banding/Enhancement artifact look like?
Definition
A bright band of echoes from one side of the image to the other.
Term
Where would you see a Focal Banding/Enhancement artifact?
Definition
At the focus (or foci).
Term
How can you reduce or eliminate a Focal Banding/Enhancement artifact?
Definition
Reduce your focus or remove some of the focal zones.
Term
What assumption does a Focal Banding/Enhancement artifact violate?
Definition
The intensity of a reflection is related to th characteristics of the tissue.
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