Unit 2 Quality Factors III: Details and Distortion Flashcards
Spatial Resolution
Degree of sharpness of structural lines in a radiographic image
Distortion
Misrepresentation of the size shape of the part being examined
Controlling factors for Recorded Details
-Geometric Factors: Focal Spot Size, Imaging Distances
-Image Receptor: Equipment Speed
-Motion: Patient movement, Equipment movement
Controlling factors for Distortion
Geometric factors: Imaging Distances, Part/IR/CR Alignment
Does a small or large Focal Spot size produce images with better detail?
Small
Spatial Resolution is improved at a ______ SID
Long
________ angle produces higher spatial resolution
Smaller
Penumbra
-Image blur, not detailed/sharp
How do you asses exposure?
With the S number
Penumbra Formula
GU = FS (OID)
————
SOD
An increased SID = ___________ spatial resolution
A decreases SID = ___________ spatial resolution
Increased;
Decreased
Source to Object Distance (SOD) equation
SID-OID = SOD
Screen Speed
Describes how sensitive the IR is to radiation
-Higher Speed = More Sensitive to radiation = Less radiation needed to produce quality images
What is the trade off for higher screen speed?
Reduced Spatial Resolution/Detail at higher speeds
Spatial Resolution is measured using
Line pair test tool
Line pair test tool
-Measures Focal Spot resolution
-More visible line pairs = better spatial resolution
Types of Motion
-Voluntary:
• Under direct control of patient
• Communication
-Involuntary:
• Not under conscious control of patient
• Reduced Exposure times & Immobilization
-Equipment:
• Ensure equipment is stable for exposure
How do you reduce exposure time for Involuntary Motion
-Increase mA, cut down time
-Increase kVp by 15%
RECORDED DETAIL VS. VISIBILITY OF DETAIL
Recorded detail:
• FS
• SID/OID
• Screen Speed
• Motion
Visibility of detail:
• Scatter
• Artifacts
If an image has good spatial resolution, what 2 factors might cause reduced visibility of detail
Scatter and Artifact
What is the ONLY possible size distortion in radiography?
Magnification
Size Distortion
• Misrepresentation of the size of an object
• Magnification
Is minimization possible for magnification/distortion?
No
Size distortion controlling factors
• SID
• OID
Magnification is reduced at a _______ SID
Long
Magnification is increased at a _______ SID
Short
Magnification Factor Equation
M = I
—
0
I = SID or Image Size
0 = SOD or Obiect Size
M = Magnification Factor
SHAPE DISTORTION
Elongation: Project objects so they appear longer than they are
-Tube and IR not aligned
Foreshortening: Project objects so they appear shorter than they are
-Part and IR not aligned
