3. X-ray Imaging System
PRINCIPAL PARTS
Operating Console
High-voltage generator
X-ray tube
PRIMARY FUNCTION
The system is designed to provide a large
number of e- at cathode with high kinetic
energy focused to a small target at anode.
5. How “X-rays” are created
Power is sent to x-ray tube via
cables
mA (milliamperage) is sent to
filament on cathode side.
Filament heats up – electrons are
produced
Negative charge
6. How “X-rays” are created
Positive voltage (kVp) is applied to anode
Negative electrons are attracted across
the tube to the positive anode.
Electrons slow down and finally come to
rest
Electron beam is focused from the cathode
to the anode target by the focusing cup
7. The distance between filament and the x-
ray tube target is 1 cm.
Velocity of electron is raised from
zero............half the speed of light
8. E- traveling from cathode to anode
Projectile electron interacts with the
orbital electron of the target atom.
This interaction results in the
conversion of electron kinetic energy
into thermal energy (heat) and
electromagnetic energy in the form
of infrared radiation (also heat) and
x-rays.
10. Heat
Most kinetic energy of projectile e- is
converted into heat – 99%
Projectile e- interact with the outer-shell
e- of the target atoms but do not transfer
enough energy to the outer-shell e- to
ionize
Outer shell electrons are simply raised to
an excited/ higher energy level.
11. Heat production
Outer shell electrons immediately drop
back to their normal energy level with the
emission of infrared radiation.
The constant excitation and return of
outer shell electrons are responsible for
most of the heat generation
12. Heat is an excitation
rather than an ionization
13. Heat production
Production of heat in the anode increases
directly with increasing x-ray tube current
Doubling the x-ray tube current doubles
the heat produced
Increasing kVp will also increase heat
production
14. Efficiency of x-ray production is
independent of the tube current
Efficiency of x-ray production increases
with increasing kVp.
At 60 kvp.........0.5%
At 100 kVp.......1%
At 20 MV..........70%
15. Characteristic Radiation
Projectile electron interact with inner shell
electron
Projectile e- with energy high enough to
totally remove an inner-shell electron of
the target atom e.g. tungsten
Characteristic x-rays are produced when
outer-shell e- fills an inner-shell
19. Bremsstrahlung Radiation
A projectile e- that completely avoids the
orbital e- as it passes through a target
atom may come close enough to the
nucleus of the atom to come under the
influence of its electric field
projectile e- kinetic energy to EM energy
electrostatic force
20. Bremsstrahlung Radiations
As the projectile electro passes by the
nucleus, it is slowed down and changes its
course, leaving with reduced kinetic
energy in a different direction .
This loss of kinetic energy reappears as an
x-ray.
22. X-ray energy
Characteristic x-rays have very specific
energies. K-characteristic x-rays require a
tube potential of a least 70 kVp
Bremsstrahlung x-rays that are produced
can have any energy level up to the set
kVp value. Brems can be produced at any
projectile e- value
24. Characteristic X-ray Spectrum
Characteristic has discrete energies based
on the e- binding energies of tungsten
Characteristic x-ray photons can have 1 of
15 different energies and no others
28. Factors Affecting
the x-ray emission spectrum
Tube current,
Tube voltage,
Added filtration,
Target material,
Voltage waveform
The general shape of an emission
spectrum is always the same, but the
position along the energy axis can change
33. kVp
A change in voltage peak affects both the
amplitude and the position of the x-ray
emission spectrum
34. Filtration
Adding filtration is called hardening the x-
ray beam because of the increase in
average energy
Filtration more effectively absorb low-
energy x-rays than high energy x-rays
Characteristic spectrum is not affected &
the maximum energy of x-ray emission is
not affected
35. Filtration
Adding filtration to the useful beam
reduces the x-ray beam intensity while
increasing the average energy (higher
quality)
Lowering the amplitude and shifting to the
right
37. Target Material
The atomic number of the target affects
both the quantity and quality of x-rays
Increasing the target atomic number
increases the efficiency of x-ray
production and the energy of
characteristic and bremsstrhlung x-rays
39. Voltage Waveform
5 voltage waveforms: half-wave
rectification, full-wave rectification, 3-
phase/6-pulse, 3-phase/12-pulse, and
high-frequency.
Maintaining high voltage potential
41. Factors affecting X-Ray beam quality
and quantity
An increase in Results in
Current(mAs) An increase in quantity; no change in
quality
Voltage (kVp) An increase in quantity and quality
Added filtration A decease in quantity and an increase in
quality
Target atomic number(Z) An increase in quantity and quality
Voltage ripple A decrease in quantity and quality