Presentation on X-Ray Production (Radio-Physics). #Radiophysics #Radiology #X-Rays

1. X-Ray
Productio
n
D R . S A C H I N S H A R M A
P G R E S I D E N T- 1
D E P T. O F R A D I O - D I A G N O S I S

2. X-Rays :-
• Discovered in 1895 by German physicist Sir Wilhelm Conrad Roentgen.
• Got First Nobel Prize in Physics in 1901

3. The first x-ray photograph:
Roentgen’s wife Bertha’s hand

4. ELECTRON TARGET INTERACTIONS
• The mechanism to produce x-rays is to accelerate electrons
from the cathode to the anode in the x-ray tube.
• The three principal parts of x-ray imaging system -
• Operating console,
• X-ray tube,
• High-voltage generator.
• Acceleration of electrons produces kinetic energy.
• Large number of electrons with high kinetic energy are
focused onto a small spot on the anode(focal spot).

5. •All electrons have the same mass; therefore, to increase
kinetic energy kVp has to be raised.
•If electron kinetic energy is increased, both the intensity
(quantity) and the energy (quality) of the x-ray beam are
increased.
•In an x-ray imaging system operating at 70 kVp, each
electron arrives at the target with a maximum kinetic
energy of 70 keV.
•As we know 1 eV is equal to 1.6x10-19J and 1 keV is equal
to 1.6x10-16J, So at 70 keV there is energy equivalent to
1.12x10-14J.

6. • Electron from the cathode interacts with the orbital
electrons or the nuclear field of target atoms.
• These interactions result in the conversion of electron
kinetic energy into thermal energy (heat) and electro-
magnetic energy in the form of infrared radiation and
x-rays.
• The electrons interact with the outer- shell electrons of
the target atoms.
• The outer-shell electrons are simply raised to an
excited, or higher, energy level.

7. • The 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
generated in the anodes of
x-ray tubes.

8. HEAT
• Approximately 99% energy is converted into heat and only
1% of electron kinetic energy is used for the production of x-
rays.
• Production of heat in the anode increases directly with
increasing x-ray tube current.
H=P x t and P=V x I
H= V x I x t (we know V=I x R)
So ,H= I x R x I x t
= I2Rt.
So ,from above equations we came to know that Heat(H)
produced is directly proportional to square of I(current).

9. • 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%

10. Characteristics 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.
• When an outer shell electron fills the vacancy in the K
shell, an x-ray is emitted.

11. • Characteristic x-rays are
produced after ionization
of a K-shell electron. When
an outer shell electron fills
the vacancy in the K shell,
an x-ray is emitted.

12. Only K-characteristic
x-rays of tungsten
are useful for
imaging

13. Bremsstrahlung Radiation
• Bremsstrahlung radiation is produced when projectile e- interacting
with the nucleus of a target atom loses its kinetic energy.
• This kinetic energy is converted into EM energy.
• The closer the projectile electron gets to the nucleus, the more it is
influenced by the electric field of the nucleus.
• As the projectile electron passes by the nucleus, it slows down and
changes its course, leaving with reduced kinetic energy in a different
direction.
• This loss of kinetic energy reappears as an x-ray.

14. •A low-energy bremsstrahlung x-ray results when
the electron is barely influenced by the nucleus.
•A maximum- energy x-ray occurs when the
electron loses all its kinetic energy and simply
drifts away from the nucleus.

15. Bremsstrahlung is a German word meaning
“slowed-down Radiation”

16. •K-characteristic x-rays require an x-ray tube
potential of at least 69 kVp.
•At 100 kVp, approximately 15% of the x-ray
beam is characteristic, and the remaining is
bremsstrahlung.

17. X-RAY EMISSION SPECTRUM
•It is a Discrete spectrum.
•The word discrete refers to individually
separate and distinct.
•The word spectrum refers to the range of
values of any quantity such as x-rays.

18. • Suppose there was a device
that could eject all types of
balls randomly. The most
straightforward way to
determine how often each
type of ball was ejected on
average would be to catch
each ball and then identify it
and drop it into a basket
• At the end of the observation
period, the total number of
each type of ball could be
counted.

19. • In this figure only five
distinct types of balls are
involved, so it is an example
of discrete spectrum.
• Connecting the bars with a
curve as shown would
indicate a large number of
different types of balls. Such a
curve is called a continuous
ejection spectrum.
• A continuous spectrum
contains all possible values.

20. Characteristic X-ray Spectrum
•Characteristic radiation 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

21. Characteristic X-ray Spectrum
• This plot is called the
characteristic x-ray emission
spectrum.
• Five vertical lines
representing K x-rays and four
vertical lines representing L x-
rays are included.
• The lower energy lines
represent characteristic
emissions from the outer
electron shells.

22. Bremsstrahlung X-ray
Spectrum
•These energies range from
the peak electron energy all
the way down to zero.
•In other words, when an x-
ray tube is operated at 90
kVp, bremsstrahlung x-rays
with energies up to 90 keV
are emitted.

23. • The farther to the right a spectrum is, the higher the
effective energy or quality of the x-ray beam.
• The larger the area under the curve, the higher is the
x-ray intensity or quantity.

24. •Graphically, the total
number of x-rays
emitted is equivalent
to the area under the
curve of the x-ray
emission spectrum.

25. FACTORS AFFECING THE X-RAY EMISSION SPECTRUM
• Tube current(mAs),
• Tube voltage(kVp),
• Added filtration,
• Target material,
• Voltage waveform.

26. Effect of Tube Current(mAs)
• A change in mA results
in the amplitude change
of the x-ray emission
spectrum at all energies.
• The shape of the curve
will remain the same.

27. Effect of kVp
• A change in voltage peak
affects both the amplitude
and the position of the x-ray
emission spectrum.
• In the diagnostic range a 15%
increase in kVp is equivalent
to doubling the mAs.

28. Effect of Added Filtration
• Adding filtration is called hardening the x-ray beam because
of the increase in average energy.
• Filtration more effectively absorbs low energy x-rays than
high energy x-rays.
• Characteristic spectrum & the maximum energy of x-ray
emission are not affected.
• The result of added filtration is an increase in the average
energy of the x-ray beam with an accompanying reduction in
x-ray quantity.

29. In this figure ,x-ray tube
is operated at 95 kVp
with 2-mm aluminum
(Al) added filtration
compared with the
same operation with 4-
mm Al added filtration.

30. Types of Filtration
1.Inherent filtration
• 0.5 mm Al equivalent
X-ray tube design.
• Glass or metal
envelope.
• Dielectric oil bath.
• Glass window of
housing.

31. 2.Added Filtration
• 1.0 mm Al equivalent.
• Any filtration outside x-ray tube and housing.
• Silver on collimator mirror.
• Thin layers of aluminium or copper permanently added
between the collimator and protective housing.

32. 3.Compound filtration
K-edge filters
• Each layer absorbs characteristic photons created in
previous layer.
4.Compensation Filtration
• Evens radiographic density with parts that have uneven
tissue thickness or densities
• E.g. : wedge for foot or T-spine trough for CXR.

33. Compensation Filtration Applications

34. Effect of 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
bremsstrahlung x-rays

35. Effect of Voltage Waveform
•5 voltage waveforms:
• half-wave rectification,
• full-wave rectification,
• 3- phase/6-pulse, 3-
phase/12-pulse, and
• high-frequency.

36. Factors Affecting Size and Relative Position of X-ray Emission
Spectra(Summary)

37. Factors affecting X-Ray beam quality and quantity

38. SUMMARY
• When electrons are accelerated from the cathode to the target
anode, three effects take place:
• Production of heat,
• Formation of characteristic x-rays, and
• Formation of bremsstrahlung x-rays.
• Characteristic x-rays are produced when an electron ionizes an inner-
shell electron of a target atom and inner-shell void is filled.
• Bremsstrahlung x-rays are produced by the slowing down of an
electron by the target atom’s nuclear field. Most x-rays in the
diagnostic range are bremsstrahlung x-rays.

39. • X-ray emission spectra can be graphed as the number of x-
rays for each increment of energy in keV
• Characteristic x-rays of tungsten have a discrete energy of 69
keV
• Bremsstrahlung x-rays have a range of energies up to X keV,
where X is the kVp.
• Four factors influence the x-ray emission spectrum:
• low-energy electrons interact to produce low-energy x-rays,
• successive interactions of electrons result in the production of x-rays with
lower energy,
• low-energy x-rays are most likely to be absorbed by the target material,
and
• added filtration preferentially removes low-energy x-rays from the useful
beam.