Image Quality Flashcards
What are the 3 constituent part of image quality/
Contrast
Resolution
Noise
What things affect the contrast of an x-ray image?
Physical characteristics
- thickness
- density
- composition/ atomic number
Technique Factors
- beam quality
- beam quantity
What are ‘characteristic curves’ in radiology?
The response of a given receptor/ detecter to different levels of exposure.
What is Quantum mottle?
The random fluctuations in the number of photons that hit any specific area
What technique factors decrease noise?
increasing mAs
increasing kVp
Increasing absorption efficiency
image/ frame averaging in flouroscopy
What is the ‘focal spot size’ in radiology?
the size of the anode area that releases x-rays for the image
What effect does a larger focal spot size have on image quality?
increases blurring
What is the name for increase blurring from an increased focal spot size?
penumbra
OR
Edge gradient
How does a larger focal spot size cause blurring?
x-rays from different edges of the focal spot will/ will not hit the edge of objects from different angles and will/ will not make it through to the receptor at certain angles
Sources of Blur in X-ray generation?
finite focal spot
patient motion
shape of absorber (e.g. penumbra/ absorption blur)
in CR: scattering of laser light
in DR: aperture of detector element
geometric blurr
What is SID in radiology?
source to image distance
What are the positives/ negatives of changing Source to Image Distance?
Increasing SID with meant that items that are further will be less distorted but more radiation/ mAs is required
What is OID in radiology?
Object to image distance
What is ‘Source to Image Distance’?
The distance between the x-ray source and the image receptor
What is ‘Object to Image Distance’?
the distance between an object and the image receptor
What are the positives/ negatives of changing object to Image Distance?
Decreasing OID decreases distortion/ blurring (the bit closer to the source isn’t as magnified, and there’s less of a penumbra).
What should you do with SID and OID to reduce blurring
maximise SID
minimise OID
What are the ways to measure blur/ spatial resolution (mathematical concepts)
point spread function
line spread function
edge spread function
Modulation Transfer function
PSF acronym in radiology
Point Spread Function
LSF acronym in radiology
Line Spread Function
ESF acronym in radiology
Edge spread function
MTF acronym in radiology
Modulation Transfer Function
What is Point Spread function
describes the lateral spread of information coming out of a single point. How blurred a point is
What is Line Spread function
describes the lateral spread of information coming out of a single line. How blurred a line is
What is Edge Spread function
How blurred a clearly define line appears on x-ray
What is Modulation Transfer Function
Fourier transformation of the line spread function.
