Radiographic Image Quality Flashcards
Radiographic Image Quality depends on:
Geometric factors
Image receptor factors
Subject factors
Geometric factors which affect image quality:
Magnification
Distortion
Unsharpness/Penumbra
What is meant by geometric unsharpness?
Also known as penumbra
Refers to the the fact the focal spot is not from a point source. This results in a loss of definition in image quality
The penumbra is _____ on the anode side
Smaller
Contrast_____ with higher kVp as ______ ________ _______ is energy dependent
Reduces
Linear Attenuation Coefficient
In mammography ____ kVp is used because….
Low
So we can maximise subject contrast
If we lower kVp to improve tissue contrast:
Reduce penetration of the x-ray beam
Increase patient dose due to more PE
What is contrast resolution?
The ability to distinguish between
adjacent areas in the image
What is spatial resolution?
The ability to detect fine detail
(spatial resolution increases with increasing subject
contrast)
Modern digital imaging receptors have ….
a large dynamic range!
Meaning a range of exposures that produce optical density within useful range
However a disadvantage associated with a large dynamic range is …
Dose creep
Advantages of a large dynamic range:
Very few images rejected (can window to get
adequate image)
Better contrast resolution
Can reduce patient dose!!!
kVp is a major controlling factor for
radiographic contrast
mAs is a major controlling factor for
Optical density
What is quantum mottle?
Number of photons which fluctuate randomly
