Test 1: lecture 4 Flashcards
___ The ability to distinguish between tissues with different x-ray attenuation properties
contrast resolution
what is subject contrast
the amount of xrays that get through a patient based on what the xrays have to go through
difference in xray intensity that is transmitted through a patient →the amount of attenuation
what are three things that contribute to intrinsic subject contract
thickness
density
atomic number (Z)
thinner tissue will have ___ attenuation then a thick tissue
less
how does density effect xrays
the denser = more attenuation= whiter= more opaque
less dense= low penetration= less attenuation= blacker= less opaque
radiolucency
more black- less attenuation- less density
photoelectric effect
atomic number 3/energy 3
PE= better contrast when low energy(low kVP) and high atomic number
PE= absorption
which one have more PE, which one have more kVP?
PE= absorption= increased contrast
if air has a Z of 7.6 why is it more lucent then water with a Z of 7.4
air is more black (more lucent) because its density is so low
Z= atomic number is not the only thing that determines opacity (whiteness)
how does contrast work to make better picture
increases atomic number
increases the photoelectric effect= more absorption= more contrast
factors that affect scatter
subject thickness
field size (collimation- bigger picture= not as focused= more scatter)
kVP (more energy = more scatter)
collimation ___ the field size
decreases
___ ability to be able to visualize 2 separate adjacent structures as being separate
spatial resolution
4 things that contribute to spatial resolution
blur (sharpness)
magnification
distortion
pixel size
how to decrease blur
decrease ODD (object to detector distance)
have object as close to detector as possible
blur is due to ___ factors
geometric
closer to the plate = clearer image
according to blue, objects look ___ when closer to detector
sharper
how to decrease magnification
decrease distance form the plate (ODD)
why is L more blury?
L is farther away from the plate, will increase blur and magnification
Variation in size/shape of an object (e.g. unequal magnification) on an image when compared to its true size/shape
distortion
higher pixel number will have ___
better quality
Images are made up of many pixels – entire arrangement is called a ___
matrix
increase in matrix size =
more pixels= better picture
Subject contrast is the difference in X-ray intensity transmitted through different parts of the subject. Subject contrast does NOT depend on:
Atomic number differences
Density differences
Radiation quality, film thickness and kVp
Photoelectric effect
Thickness differences
Radiation quality, film thickness and kVp
Higher kVp techniques will result in…
Higher subject contrast
No effect in the image quality
Lower radiation dose
Underexposure
Lower subject contrast
Lower subject contrast
increase kVp= more compton scatter= lower contrast
lower kVp= more PE = more contrast
Which one of the following statements regarding pixels is FALSE?
Pixel stands for picture element
A smaller matrix size (e.g. 512 x 512) has smaller pixels compared to a larger matrix (e.g. 1024 x 1024), assuming the digital detector size is equal
A higher number of pixels in an image increases spatial resolution
An arrangement of pixels is called a matrix
A smaller matrix size (e.g. 512 x 512) has smaller pixels compared to a larger matrix (e.g. 1024 x 1024), assuming the digital detector size is equal
(smaller matrix = larger pixels)
