Factors controlling the X-ray beam intensity Flashcards
: Total amount of energy contained in the x-ray beam
Intensity
:Number of photons in the beam. Primarily related to tube current and exposure time and less so by tube voltage (kVp) Expressed as: tube current (mA) X time (sec) →mAs
Quantity
In relation to quantity and quality, what is the formula for Intensity?
Intensity: Quantity x Quality
:Average energy the x-ray beam.▪Controlled primarily by the tube voltage (kVp) X-ray of beam is heterogeneous.
Quality
As tube voltage increases, how is number of photons affected?
Number of photons generated increases (increased quantity)
As tube voltage increases, how is mean energy of photons affected ?
oMean energy of photons increases (increased quality)
As tube voltage increases, how is max energy of photons affected ?
oMaximum energy of photons increases
As exposure time increases, how is number of photons affected?
Number of photons generated increases (increased quantity)
As exposure time increases, how is mean energy of photons affected?
oMean energy of photons is unchanged
As exposure time increases, how is max energy of photons affected?
Maximum energy of photons is unchanged
As mA increases, how is number of photons affected?
Number of photons generated increases (increased quantity)
As mA increases, how is mean energy of photons affected?
oMean energy of photons is unchanged
As mA increases, how is max energy of photons affected?
Maximum energy of photons is unchanged
Selectively removes long wavelength (low energy) x-rays.
Filtration
_____ x-rays increase the dose of radiation without producing images
Low energy x-rays
As filtration increases, how is number of photons affected?
Number of photons decreases (reduced quantity)
As filtration increases, how is mean energy of photons affected?
oMean energy of photons increases (increased quality)
As filtration increases, how is number of max energy of photons affected?
Maximum energy of photons is unchanged
\_\_\_\_ filtration: o Glass envelope o Immersion oil o Metal housing o Tube window
Inherent filtration
_____ filtration:
o Aluminum disks
Added filtration
Restricts the size and shape of the beam.
Collimation
How does collimation affect number of photons?
oNumber of photons decreases
How does collimation affect mean energy of photons?
oMean energy of photons is unchanged
How does collimation affect max energy of photons
oMaximum energy of photons is unchanged
Intensity of the beam varies inversely to the square of the source-to-receptor distance.
Inverse square law
As distance increases, how is number of photons affected?
oNumber of photons decreases (decreased quantity)
As distance increases, how is mean energy of photons affected?
oMean energy of photons is unchanged (unchanged quality)
As distance increases, how is number of max energy of photons affected?
oMaximum energy of photons is unchanged
_____ –altered by factors affecting Quantity of the beam
DENSITY
–altered by factors affecting Quality of the beam
CONTRAST
oAmount of blackness of an image →Related to how many x-rays reach the receptor
-How dark it is
Density
Density is controlled by mAs or kVp?
mAs
If the image is darker and has high density, are there more or less x-rays reaching sensor?
More x-rays
How are mA and exposure time related?
Inversely proportional
o The difference in densities between light and dark regions of a radiograph
o Primarily controlled by the voltage
Contrast
Which contrast shows more gray scales?
Low contrast
____ contrast:
▪Low kVp(long wavelengths, less penetrating)
▪Density differences between adjacent areas are greater; fewer shades of gray.
High Contrast (Short Gray Scale)
_____ contrast:
▪High kVp(short wavelengths, more penetrating)
▪Density differences between adjacent areas are more subtle; more shades of gray.
Low Contrast (Long Gray Scale)
High contrast requires ____ kVp
Low kVP
Low contrast requires ____ kVp
High kVp
If I want to see bone in an x-ray, do you use high or low contrast?
Low contrast
If i want to see caries, do you want to use high or low contrast?
High contrast
