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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
Note 
Flashcard (49)