Image formation and exposure Flashcards
Describe exponential attenuation
The beam intensity diminishes according to the thickness of the material
The fall in intensity is exponential
Describe penetration thickness
Absorption characteristics of anatomy are determined by composition
What is the importance of photoelectric absorption
Provides blackening of image
As bone is more dense, creates contrast
Describe quality in reference to the x-ray beam
Penetrating power
Not the same as quantity or radiation
Beam is heterogenous
Describe quantity in reference to the x-ray beam
Intensity
Measure of quantity of radiation energy
Affected by tube current
What 3 elements does the radiograph require? and what colour do they appear?
Penetrated photon (black)
Absorption (white shades)
Scatter (grey shades)
Describe penetrated photons
Number of photons that reach the detector
Determine the area of black on the image
Describe contrast
We don’t want all the photons to hit the detector as we wouldn’t have any contrast
Describe scatter
Level of scatter determines how many shades of grey are present
kVp influences contrast - it produces scatter
Describe the relationship between scatter and photoelectric
As kVp increases, compton and photoelectric interaction decreases
PE interactions decrease quicker than C
At very high kVp majority of interactions are Compton
Describe tube charge mAs
Number or quantity of x-ray photons created
Describe kVp
Level of energy that we give to x-ray photons
Alters photon behaviour and interaction
Describe the 15% rule
15% increase or decrease in kVp is equivalent to doubling or halving mAs
What is the effect of focal spot size?
As focal spot size increases, image will become less sharp, spatial resolution decreases
As focal spot size decreases, image becomes more sharp, spatial resolution increases
What is SID?
Source to image receptor distance
