Factors Affecting Image Quality Flashcards
Factors affecting Image Quality:
- Noise
- Screen and Film Speed
- Magnification
- Shape Distribution
- Focal-spot Blur
- Subject Factors
Noise
- Random fluctuation in the density
- Grainy appearance on a radiograph
What are the different types of noise
- Film Graininess
- Structure Mottle
- Quantum Mottle
Film Graininess
irregular clumping of silver halide crystals
Structure mottle
physical imperfections of intensifying screens
Quantum Mottle
- IR has been exposed to an uneven “shower” pf light photons from the device, which is due to the fact that the x-ray beam itself is uneven
- Short exposure times and fast screens (decreases x-rays/detail)
Speed
- Increase in speed
- Increase in Noise
- Decrease in Radiographic Quality
Geometric Factors refers to the _____________ of the image and the accuracy with which the true edges of the anatomy may be seen
recorded detail
What are the different geometric factors?
- Magnification (size distortion)
- Shape distribution
- Blur
Magnification (Size Distortion)
Misrepresentation of true size of the object
Magnification is influenced by _______,_______, and _________
- SID: source to image distance
- SOD: source to object distance
- OID: object to image distance
_________ or _________ in distances will result in magnification
- Variation
- changes
Law of Magnification
Image size/Object size = SID/SOD
Magnification factor:
MF=SID/SOD
% of Magnification
(Image size-Object size/ Object size ) x 100
Shape distribution
Misrepresentation of true shape of the object
Object Position
- Tube, Object, IR not in alignment
- Elongation/Foreshortening
- Decrease in Radiographic Quality
Elongation
change in tube or IR angulation/alignment
Foreshortening
Inclination of an object results in a foreshortened image
Macroradiography (Magnification Radiography)
-SID is decreased to induce magnification
- Angiography: 0.3mm/1.0mm
- Mammography: 0.1/0.3mm
***Fractional Focus (microfocus) Tube
FSS of 0.3 mm or less
Small FSS
Decrease FSS, Decrease focal spot blur (penumbra), Increase radiographic quality (detail)
Large FSS
Increase FSS, Increase focal spot blur (penumbra), decrease radiography quality (detail)
FSS does _____ affect magnification
NOT
Focal Spot Size Evaluation involves:
- Nominal (quoted by manufacturer)
- Pinhole Camera (effective dimensions)
- Resolution Test Patterns (Line pairs/mmm)
