Geometric Qualities: Detail & Distortion Flashcards
What are the geometric properties of radiographic quality?
Sharpness
- detail
- distortion
What is the term used for sharpness of recorded detail?
Resolution
Magnification is related to what type of distortion?
Size distortion
Name the 2 types of shape distortion.
Elongation
Foreshortening
The ability to image two separate objects and visually distinguish them from one another:
Resolution
What is resolution measured in?
Line pairs per mm
Sharp area or shadow under an object:
Umbra
Unsharp shadow surrounding the umbra; width of unsharpness; edge gradient:
Penumbra
First way to improve resolution:
Eliminate or minimize patient motion.
Second way to improve resolution:
Minimize OID.
Third way to improve resolution:
Increase SID.
Fourth way to improve resolution:
Reduce focal spot size.
Fifth way to improve resolution:
Use slower film/screen.
Patient motion is a controlling factor of:
Recorded detail.
SID=
OID + SOD
An increase in OID results in an increase or decrease in penumbra?
Increase.
Increasing penumbra increases or decreases recorded detail?
Decreases.
Increasing SID increases or decreases penumbra?
Decreases.
When a minimal OID cannot be achieved, what can be done to compensate?
Increase SID.
Does a small focal spot increase or decrease penumbra?
Decrease.
There is a decreased area over which X-rays are produced.
Small focal spot is used for sharp detail.
Decreased heat dissipation.
Quantum mottle refers to:
Image noise due to insufficient mAs.
Misrepresentation of the size or shape of the structure:
Distortion.
What are the two types of distortion?
Size
Shape
What is the only size distortion possible in general radiography?
Magnification, which is controlled by OID & SID.
Magnification degrades resolution.
As OID increases, does magnification increase or decrease?
Increase.
Does the X-ray beam diverge more with a shorter or longer SID?
Shorter SID.
Longer SID utilizes the central, more perpendicular portion of the beam.
Shape distortion is controlled by:
Beam/Part/IR alignment
Shape distortion can be reduced by:
Oblique positions
Central ray angulations
Factors that affect resolution:
Pt. motion SID OID focal spot size IR
Most important for a sharp image:
Reduce pt. motion.
Ways to reduce distortion:
Increase SID Reduce OID Align tube & IR Part parallel to IR Part perpendicular to CR CR through anatomy of interest
