Imaging - DETAIL
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What is detail?
Detail is degree of radiographic sharpness
How is resolution measured?
Line pairs per milimeter (lp/mm) or cycles per mm
How much lines per cycle can most humans usually see?
Their range can only usually see up to 5 lp/mm
What is spatial resolution?
It is digital imaging recorded detail
What determines spatial resolution?
- Spatial resolution is determined by:
- - matrix size
- - pixel size
- - gray scale bit depth
- - voxel
What are the ranges of spatial frequency? Which ones can be visualized?
There is either high frequency and low frequency.
- Shorter wavelengths have higher frequency and higher detail.
- Longer wavelengths have lower frequency and less detail.
How is spatial resolution measured?
- It is measured in 3 ways:
- - Point Spread Function ( PSF )
- - Line Spread Function ( LSF )
- - Modulation Transfer ( MTF )
What is nyquest criterion?
Its a process where it ensures that no data is missed by sampling the information twice.
What is aliasing?
When nyquest criterion is violated and messes up causing imaging problems such as the murray effect ( lines going across the image )
What is image noise?
Image noise is background information that the receptor receives. This is shown as quantum noise or quantum mottle ( Graininess of image because of insufficient photons )
What effect does resolution have on image?
Resolution demosntrates fine detail of structures close to the size limits of the naked eye.
How do you prevent motion in an exam?
- - With good communiocation.
- - FOr thsoe who cant stay still that well, reduce the length of exposure.
How do you reduce OID during an exam?
Get aptient right up to the IR when possible and use positions that reduce OID.
What does OID do to detail?
- Higher OID leaves room for more magnification which usually contintutes lost of detail
Why would a smaller focal spot size benefit detail?
A reduced focal spot size would mean a less divergent beam which in turn streams straighter photons resulting in better detail.
How does intesnifying screen phospor sizes help with detail?
Phosphor screens with smaller phosphors will result in better detail. ( Smaller crystals = better detail )
How does SID affect image detail?
Longer SID will result in better detail because of the divergence of the beam. With larger SID, you have a bigger divergence and a larger area for straighter photons to get through.
What's the neumonics for detail?
Stat Orders From Surgery Follow Cutting Mistakes
What does the neumonics stand for in SOFSFCM?
- S = SID
- O= OID
- F= Film Screen
- S= Screen Speed
- F= Focal Spot
- C= Contact
- M= Motion
How does SID affect detail?
Increased SID = Better detail
How does OID affect detail?
Less OID = better detail because of less magnification.
How does film screen affect detail?
Slow F/S = better detail because of smaller crystal sizes.
How does Focal Spot affect detail?
Smaller focal spot = better detail because its more of a straight beam than a wider one.
How does film screen contact affect detail?
More film screen cotnact = better detail
How does Motion affect detail?
Less motion = better detail
Whats the equation for reducing penumbra?
- FSS( Focal Spot Size ) x OID
- SID - Source to Image Distance
Smallest focal spot size, minum oid and longest SID.
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