Test #3 (Unit 4)

What is an artifact?

Misleading appearances that do not accurately represent anatomical structures of physiologic events

What are some basic terms for ultrasound artifacts?

1. Not real

2. Missing

3. Misplaced

4. Incorrect

   1. Brightness

   2. Shape

   3. Size

What does the ultrasound machine automatically assume?

1. US travels in straight line

2. Echoes originate from central axis of beam

3. Attenuation rate is uniform and predictable

4. Rate of image acquisition exceeds rate of physiologic events and transducer movement

5. Arriving echo was generated by last emitted ultrasound pulse

6. Two comparable tissue reflectors in a similar location will generate a comparable echo amplitude

7. Speed of sound is constant

8. Operator is using system appropriately

9. Beam dimensions are small in height (axial), width (lateral) and thickness (slice thickness)

10. Each reflector only generates one echo

11. All system controls are adjusted correctly

12. Transducer elements and electronic system components are functioning normally and without interference from surrounding equipment

What speed does the ultrasound machine automatically assume?

1540 m/s

What are the four causes of artifacts?

1. System

2. Operator

3. Acoustics

4. Patient

What do artifacts represent?

1. Real echoes

2. Real absence of echoes

What do artifacts NOT represent?

Real structures

While ultrasound artifacts do not accurately reflect reality…

The ultrasound system artifacts appear perfectly “real”

What do sonographers need to know about artifacts?

1. Types

2. How each artifact arises

3. How to accentuate and use helpful artifacts

4. How to eliminate unhelpful artifacts

5. Causative agent(s)

6. Assumptions violated

7. Range artifact appearances

8. Diagnostic uses

Which artifacts are classified as propagation artifacts?

1. Comet tail

2. Grating lobe

3. Mirror image

4. Range ambiguity

5. Refraction

6. Reverberation

7. Ring-down

8. Slice (section) thickness

9. Speckle

10. Speed error

Which artifacts are classified as attenuation artifacts?

1. Enhancement

2. Focal enhancement

3. Refraction (edge) shadowing

4. Shadowing

What is electrical interference?

When a strong electrical interference from other nearby electrical devices can create interference patterns

What is a faulty element?

1. Damaged Piezoelectric crystal

2. Break in wiring of transducer

What does a faulty element look like on an ultrasound image?

Anechoic vertical lines

How do you confirm a faulty element?

1. Use more gel

2. Change approach

3. Use on various patients

4. Confirmed if artifact still appears in exact location

What is focal banding?

When there is a horizontal brightness at level of focus that results in an increased echo amplitude

Why does focal banding occur?

Increased intensity in focal zone

What are side lobes?

When echoes from a strong reflector are seen outside of central beam path

Which transducers can create side lobes?

Single element transducers

What are grating lobes?

When echoes from weaker beams are seen outside of central beam path

Which transducers can create grating lobes?

Array (multiple) element transducers

What do grating lobe artifacts look like on an ultrasound image?

Laterally duplicated structures

What is a slice thickness artifact?

When beam is too thick in an elevation plane and it results in debris in an echo-free structure

What is another name for slice-thickness artifact?

Partial volume filling

What is speckle?

The granular appearance of images caused by echoes interference from the distribution of scatterers in tissue

What is key to remember from the marble analogy for speckle?

Location of highest wave does not necessarily represent the location where the marble the impacted water

What is reverberation?

When sound waves bounce back and forth between two strong reflectors

How does reverberation appear on an ultrasound image?

Equally spaced extra reflectors

What are the two types of reverberation?

1. Comet tail

2. Ring-down

What is comet tail?

When small focal reflectors cause a narrow reverberation artifact

When can comet tail be useful in diagnostic imaging?

1. Adenomyomatosis/cholesterolosis of GB

2. Colloid thyroid nodules

What is ring-down?

When gas causes high amplitude streaks on an image

Where is ring-down commonly seen?

Bowel

When can ring-down be useful in diagnostic imaging?

1. Pneumobilia

2. Emphysetamous cholecystitis

3. Abscesses containing air

What is pneumobilia?

Air in bile ducts

What is emphysetamous cholecystitis?

Gas in GB wall

What is a mirror image artifact?

When US beam encounters a large specular reflector

What structure commonly causes mirror-imaging?

Diaphragm

How does a mirror image artifact appear on an image?

Duplication of objects opposite of a highly reflective structure

What are the two nicknames for refraction?

1. Duplication

2. Ghost artifact

What is refraction?

When a change in beam direction occurs due to the beam encountering a boundary between two materials with different propagation speeds

What does refraction appear as on an image?

1. Object projected laterally

2. Widening

What kind of artifact is edge shadowing?

Refraction

What is edge shadowing?

When there is a combination of reflection and refraction at the margin of a well-defined object

How does edge shadowing appear on an image?

Shadow originating from structure edge

What is a multipath artifact?

When a beam reflects off a structure at an angle

How does a multipath artifact appear on an image?

Structures displayed deeper than they are

What is propagation speed error?

When a structure has a propagation speed other than 1540 m/s

How does propagation speed error appear on an image?

1. Vertical displacement behind area

2. Shape distortion

How can propagation speed error be reduced?

Trick question: CANNOT BE ELIMINATED

How will a structure with a fast propagation speed be displayed on an image due to propagation speed error?

c > 1540 = shallower

How will a structure with a slow propagation speed be displayed on an image due to propagation speed error?

c < 1540 = deeper

What is range ambiguity?

When echoes from a previous pulse arrive after another pulse has been emitted

What are the causes of range ambiguity?

1. Shallow depth causes low attenuating structures to be out of FOV

2. Multiple focal zones

What is shadowing?

When a highly attenuating structure causes a complete absence of echo information behind it

What are the types of shadowing?

1. Scattering

2. Combination

3. Absorption

4. Reflection

5. Refraction

What is dirty shadowing?

When a highly attenuating structure produces some echoes but is highly attenuated in the process

How does dirty shadowing appear on an ultrasound?

Hypoechoic shadow behind structure

What is dirty shadowing commonly found in?

Bowel

What is enhancement?

When a lowly attenuating structure causes a band of increased echogenicity behind it

What can enhancement be used for in diagnostic imaging?

Distinguishing fluid-filled objects (cysts)

Which artifact(s) can be reduced by harmonics?

1. Side lobes

2. Grating lobes

3. Reverberation

Which artifact(s) can be reduced by changing probes?

Side lobe

Which artifact(s) can be reduced by changing your approach?

Mirror-image

Which artifact(s) can be reduced by spatial compounding?

1. Speckle

2. Edge shadowing

3. Enhancement

4. Dirty shadowing

Which artifact(s) can be reduced by persistence?

Speckle

Which artifact(s) can be reduced by sliding the transducer laterally?

Refraction

Which artifact(s) can be reduced by adjusting TGCs?

1. Focal banding

2. Enhancement

Which artifact(s) can be reduced by using one focal zone?

Range ambiguity

Which artifact(s) can be reduced by adjusting the power input or gain?

1. Range ambiguity

2. Enhancement