Exam

How are artifacts misleading? (6)

• Not real

• Missing

• Misplaced

• Incorrect brightness

• Incorrect shape

• Incorrect size

Ultrasound travels in ____ during transmission & echoes follow?

straight line

What is the constant speed of sound in the body?

1540 m/s

Machine assumes attenuation rate is?

uniform and predictable

Machine assumes 2 comparable tissue reflectors in a similar location will generate a

comparable echo amplitude

Machine assumes The beam dimensions are?

small

Machine assumes Each reflector generates?

One echo

Machine assumes The arriving echo was generated by

The last emitted pulse

Machine assumes Echoes originate only from?

Central Axis of beam

Machine assumes the rate of image acquisition exceeds the?

The rate of physiologic events and rate of transducer movement

Machine assumes that the ___ is using the system ___?

Operator; appropriately

Machine assumes all system controls have been?

Adjusted correctly

Machine assumes that the transducer elements and electronic system components are?

Functioning normally and without interference from other equipment

4 causes of artifacts

• System

• Operator

• Acoustics

• Patient

What do we need to know? (8)

• Types of artifacts

• How artifacts arise

• Causative agents of artifacts

• System assumptions violated

• Range of appearance of artifacts

• Use and accentuate helpful artifacts

• Diagnostically use artifacts

• Eliminate unhelpful artifacts

Other nearby electrical devices create interference patterns?

Electrical Interference

Crystals are damaged; displayed as anechoic vertical lines?

Faulty Elements

How do you confirm faulty elements? (4)

• Use more gel

• Change Approach

• Use on multiple patients

• Confirmed if it appears in exact location

Horizontal brightness at level of the focus?

Focal Banding

Why does focal banding occur

Increased intensity at the focal zone

How do you fix Focal banding?

Adjust TGCs

Caused by echoes from strong reflector outside central beam; single element

Side Lobe

How to reduce side lobes?

Harmonics

Echoes from weaker beams outside the main beam; array transducer?

Grating Lobes

How does grating lobe appear?

Duplicated structures laterally

How to reduce grating lobes?

Harmonics

Other name for partial volume filling?

Slice thickness artifact

Beam is too thick in elevation plane

Slice Thickness Artifact

Appearance of slice thickness artifact

Debris in echo-free structure

Granular images; caused by interference of echoes from distribution of scatterers

Speckle

How to reduce speckle?

Spatial Compounding & Persistence

Beam encounters large specular reflector

Mirror Image

How to reduce Mirror Image

Change Approach

Where is mirror image common?

Diaphragm

Sound waves bounce back & forth between structures & strong reflectors?

Reverberation

How to reduce reverberation?

Harmonics

Small focal reflectors cause narrow reverberation artifact?

Comet Tail

What does comet tail help diagnose? (3)

• Adenomyomatosis

• Cholesterolosis of GB

• Colloid Thyroid Nodules

Other names for refraction

Duplication & Ghost Artifact

Change in beam direction when beam encounters a boundary between materials with different propagation speeds

Refraction

How does refraction appear?

Widening & Duplication

How do you reduce refraction?

Sliding transducer laterally

What type of artifact is edge shadowing?

Refraction

What is edge-shadowing caused by?

Combination of reflection & refraction at margin of well-define object

How to reduce edge shadowing

Spatial compounding

Beam reflects off structure at an angle

Multipath

How does multipath display objects and why?

Deeper because beam doesn’t travel in straight line

A structure of lower or higher prop speed than 1540 m/s

Propagation speed error

What does propagation speed error appear as?

Vertical displacement behind area & distortion of shape of object

How to fix prop speed error?

Cannot be eliminated

When echoes from preceding pulse arrive after another pulse was sent?

Range Ambiguity

Causes of range ambiguity?

Shallow depth with attenuating structure beyond FOV & Multiple focal zones

How to reduce range ambiguity?

Beyond FOV: decrease gain

Switch 1 focal zone

What is shadowing caused by?

Highly attenuating structure

What can cause attenuation behind a structure? (5)

• Reflection

• Scattering

• Absorption

• Refraction

• Combination

What is shadowing?

Complete absence of echo behind attenuating structure

Shadow with some echoes that are hypoechoic

Dirty Shadow

Where is dirty shadow usually seen?

Behind bowel

Another name for enhancement

Posterior Acoustic Enhancement

Band of increased echogenicity behind an area of low attenuation

Enhancement

How to reduce enhancement

Gain & TGCs

Spatial Compounding

How can enhancement be useful?

Distinguish fluid-filled from solid

If prop speed is faster than 1540?

Superficial

If prop speed is slower than 1540?

Deeper