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41 Cards in this Set
- Front
- Back
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Recorded Detail
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The sharpness of the structural lines that make up the recorded image
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Recorded detail is controlled by?
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1) minimizing geometric unsharpness
2) minimizing receptor unsharpness 3) eliminating motion unsharpness |
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Determining factors of Geometric Unsharpness
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-Focal Spot Size
-Source Image Distance -Object Image Distance |
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FSS - size in general diagnostic tubes?
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0.5mm to 1.2mm
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FSS effects?
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Detail only
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As FSS increases:
unsharpness? recorded detail? |
increases
decreases |
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As FSS decreases?
unsharpness? recorded detail? |
decreases
increases |
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Stated FSS can vary how much?
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+or - 50%
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Testing for FSS?
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-pin hole camera measures actual FFS
-resolution test tool (star or line pair pattern) |
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The smaller the FSS the more limited you are on technique because of?
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Heat loading
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Selection of FSS determined by?
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amount of technique needed and amount of detail required
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SID increases:
unsharpness? detail? magnification? |
decreases
increases decreases |
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Accuracy of SID indicator must be within what percent?
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2
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OID has major effect on?
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detail (more than SID or FSS)
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As OID increases:
detail? unsharpness? magnification? |
decreases
increases increases |
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Geometric unsharpness formula
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FSS x OID
___________ SOD |
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How do you find SOD?
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SID minues OID
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As system speed increases detail?
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decreases
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As system speed decreases detail?
unsharpness? |
increases
decreases |
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Any gap between film and screens yields?
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loss of detail in that area (divergents)
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Test device for film/screen contact?
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laminated wire mesh
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Resolution
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the ability to distinguish two adjacent objects as being separate and distinct
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Resolution is determined by?
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Spacial resolution and contrast resolution
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Spacial Resolution
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The smallest detail that can be detected in an image
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Does conventional or digital radiography have higher spacial resolution
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conventional
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The more line pairs seen equals
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higher spacial resolution
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Contrast Resolution
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The ability to distinguish between small objects having similar subject contrast
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Does conventional or digital radiography have higher contrast resolution
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digital
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What is the most destructive factor of detail?
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Motion
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Causes of motion
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Tube Motion, part motion, IR motion
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How can you minimize patient motion?
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-mAs with higher mA and shorter exposure times
-clean concise instructions -use of immobilization devices (pig-o-stat; sand bags) |
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Distortion
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Misrepresentation of the size (magnification) or shape of the anatomic part
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as distortion increases, detail?
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decreases
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Size Distortion (Magnification)
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Increase in dimension along both axis's
Determined by: SID & OID |
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as SID increases, magnification?
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decreases (inverse)
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as OID increases, magnification?
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increases (direct)
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Calculating magnification factor
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MF = SID/SOD = Image size/object size
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Shape Distortion
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Increase in dimension along one axis
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Types of Shape Distortion
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Elongation: longer than actual object
Foreshortening: shorter than actual object |
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Shape Distortion minimized by alignment of
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-x-ray tube – angulation
-part - long axis parallel to IR -IR - perpendicular to central ray -entry or exit point of central ray - centered to object of interest |
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All of the geometric factors that effect conventional imaging effect digital imaging the same , except for?
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system speed has no effect on detail in digital systems
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