X-ray Production

rad elect

To make x-rays requires 3 things…

electron source, a way to accelerate electrons, a dense target

2 Set of Interactions

in the x-ray tube between filament electrons and anode target atom

interactions in body with x-ray photons and tissue atoms

2 Types of Radiation Interactions in the x-ray tube between filament electrons and anode target atom…

bremsstrahlung radiation
characteristic radiation

Interactions in the body between x-ray photons and tissue atoms can be classified as 5 types…

– classical
– compton
– photoelectric
– pair production
– photodisintegration

Electron Target Interaction

Heat Production
Bremsstrahlung radiation
Characteristic radiation

Heat Production

projectile electrons

Electrons travel from cathode to anode (1-3 cm) at about half the speed of light

Many projectile electrons are

not of sufficient energy to ionize the target atoms

What % of kinetic energy of projectile electrons is converted to heat?

99%

When kV INCREASE,

efficiency INCREASES

Heat Units - Single Phase

kV x mA x sec x # of exposures

Heat Units - Three Phase, Six Pulse

kV x mA x sec x 1.35 x # of exposures

Heat Units - Three Phase, Twelve Pulse

kV x mA x sec x 1.41 x # of exposures

Heat Units - High Frequency

kV x mA x sec x 1.45 x # of exposures

Bremsstrahlung Radiation

Occurs with the deceleration of projectile e- near the nucleus of tungsten atom, no ionization, Does not involve e- in the orbital tungsten shells

Bremsstrahlung Radiation Constitutes…

80-90% of x-ray production at the target

As kV INCREASES, brems INCREASES (# & strength)

Average x-ray energy is 1/3 og

Characteristic Radiation

Occurs when the filament electron hits and dislodges an inner shell of the target
– Outer shell electron drops into hole to fill the vacancy
– As the electron move from one shell to another it releases photon energy

Characteristic Radiation Constitutes…

10-20% of x rays production

Photon is named for the…

“hole” filled (k-characteristic, L-characteristic, etc)

Energy of characteristic radiation is the difference in…

binding energies

As Z INCREASES…

character radiation INCREASES

Only k-characteristic is useful in diagnostic x-ray…

0% k- characteristic produced below 69 kV

X-ray Emission Spectrum

The NUMBER of x-rays emitted can be plotted as a function of the ENERGY of each individual X-ray

Changes in the mA, kVp, filtration & atomic #
of a target affect…

the optical density (OD) and contrast of an image.

– These factors therefore affect the x-ray emission spectrum

Factors Affect the Size and Position of X-ray Emission Spectrum

Tube Current (mA)
Tube voltage (kVp)
Added filtration
Target material

Tube Current (mA) effects…

Amplitude of spectrum

Tube voltage (kVp) effects…

Amplitude and position

Added filtration effects…

Amplitude and position (most effective at low energy)

Target material effects…

Amplitude of spectrum and position of spectrum