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Name the three spatial categories of resolution
Axial
Lateral
Elevational
What does spatial resolution give us the ability to see?
Detail on an image
What is spatial resolution related to?
Directly related to # of scan lines
Related to # of pixels in a monitor
What size resolution is always better?
Smaller
Less distance between reflectors to be displayed as separate objects
What is axial resolution?
The minimum reflector separation necessary to resolve reflectors parallel to sound beam
What is axial resolution determined by?
SPL
What does LARD stand for? (Has to do with AR)
Longitudinal, Axial, Range, Depth
To improve AR, SPL must be _____
Reduced
As SPL decreases, AR ____
Decreases
As frequency increases, AR _____
Decreases
Does axial resolution change with depth? Why?
No
AR is constant along beam path
What is lateral resolution?
Minimum reflector separation necessary to resolve reflectors perpendicular to beam
What is lateral resolution determined by?
Beam width
Does lateral resolution vary with depth? Why?
Yes
Because of sound beam shape
What does LATA stand for? (Has to do with LR)
Lateral, Angular, Transverse, Azimuthal
Where is LR the best?
At the focus
What is elevational resolution?
Minimum reflector separation necessary to resolve reflectors in thickness of beam
Slice thickness or section thickness
What is elevational resolution determined by?
Beam thickness
Where is the best ER at?
At the focus
ER varies with ____ because of the shape of the sound beam
Depth
ER is improved by…
Focusing
Harmonics
How is ER improved by focusing?
Only in near field (increase diameter or frequency)
Mechanically (lens or curved elements)
Electronically with 2D arrays (phasing)
When does a slice thickness artifact occur? How do they appear?
When adjacent structures are displayed overlapping structures in scanning plane
Appears as echoes within a fluid-filled structure
What is contrast resolution?
The ability of gray-scale display to distinguish subtle differences in echogenicity, or brightness, of adjacent tissues
What is contrast resolution determined by?
Number of pixels in an image
Number of shades of gray displayed in each pixel
What is contrast resolution controlled by?
System’s memory
Dynamic range settings
What is temporal resolution?
Ability to follow moving structures in temporal detail
What is frame rate?
Number of images displayed per second
Faster FR = _____ temporal resolution
Improved
Frame Rate is dependent on… (5 things)
Line density
Lines per frame
Depth & PRF
Sector Width
Number of foci
To avoid ______, the machine waits the time needed for all echoes to return from the selected depth before the next pulse
Range Ambiguity
What is line density?
# of scan lines per degree of sector
# of scan lines per centimeter
What is lines per frame?
# of lines in each frame
More lines = ____ spatial resolution
Improved
How are line density and lines per frame related to FR?
Inversely
Low LD or LPF = ___ time
Less
High LD or LPF = ____ time
More
Sector Width is _____ related to FR
Inversely
High sector width = ____ FR
Low
Low sector width = ____ FR
High
____ sector width improves image quaility
Low
Why does a low sector width improve image quaility?
Less tissue interrogated
Less artifacts
Improved signal to noise ratio
What does the ultrasound machine automatically do to avoid range ambiguity?
Adjusts PRF based on depth selected
Depth and PRF are ____ related
Inversely
Depth is ____ related to FR
Inversely
PRF is ____ related to FR
Directly
Each pulse can have ____ focus
One
Multiple foci improves _____
Lateral Resolution
Multiple foci requires ____ per scan line
More than 1 pulse
Multiple Foci are _____ related to FR
Inversely
What saves time?
Decrease depth
Decrease sector width
Decrease # of scan lines
Decrease Line Density
Use one focus