a simple seminar for MD radiology students for radio-physics.

1. BASICS OF RADIATION AND
PRODUCTION OF X-RAYS
Presented byDr. Dinanath Chavan
First year PGT, Department of
Radiodiagnosis
SMCH.
ModeratorDr. Mrinal Dey
Professor, Department of
Radiodiagnosis
SMCH.

2. Radiation
• Radiation is energy that travels through space or matter.
• Two types of radiation used in diagnostic imaging are
1. electromagnetic (EM) and
2. particulate.
Electromagnetic Radiation
• EM radiation includes:
(a) gamma rays,
(b) x-rays,
(c) visible light,
(d) radiofrequency

3. EM RADIATION
• In this type, the energy is "packaged" in small units
known as photons or quanta.
• Visible light, radio waves, and x-rays are different
types of EM radiation.
• EM radiation has no mass, is unaffected by either
electrical or magnetic fields, and has a constant
speed in a given medium.
• EM radiation travels in straight lines; however, its
trajectory can be altered by interaction with matter.
• EM radiation is characterized by wavelength (λ),
frequency (v), and energy per photon (E)

4. Particulate Radiation
• The other general type of radiation consists of small
particles of matter moving through space at a very high
velocity.
• Particle radiation differs from electromagnetic radiation
in that the particles consist of matter and have mass.
• Particle radiation is generally not used as an imaging
radiation because of its low tissue penetration.
• ex. Electron, alfa particles.

6. Electromagnetic spectrum
X-rays are electromagnetic radiation of exactly the same nature
as light but of very much shorter wavelength
Unit of measurement in x-ray region is Å and nm.
1 Å = 10-10 m, 1 nm = 10 Å = 10-9 m
X-ray wavelengths are in the range 0.5 – 2.5 Å.
Wavelength of visible light ~ 3900 - 7500 Å.

7. Electromagnetic radiation is the transport of energy
through space as a combination of electric and magnetic
fields.
Electromagnetic ( EM ) radiation is produced by a
charge ( charged particle ) being accelerated .
{ electrons are consider as standing waves around the
nucleus and therefore do not represent acclerating
charges. }
Any accelerating charge not bound to atom will emit
EM radiation .

8. Properties of electromagnetic
radiation
• Electromagnetic radiation → wavelike
fluctuation of electric and magnetic fields set up in
space by oscillating electrons

9. Electromagnetic radiation
According to the classical
theory Electromagnetic
radiation can be
considered as wave
motion .
According to the quantum
theory electromagnetic
radiation can also be
considered as a particles
called photons

10. Wave concept of electromagnetic radiation
•All EM radiations travel with the speed of light
186000miles/sec, 3×10ˆ8 m/sec but they differ in wavelength
•Wavelength (λ) – distance between 2 successive crests / trough
•Frequency (ν) – number of crests /cycle per second (Hz)
•
(λ) wavelength ↓ (ν) frequency ↑
•EM travel with the speed of light c , c=λν
•Wave concept of EMR explains why radiation may be reflected ,
refracted, diffracted and polarized .
If each wave has length λ and ν waves pass a given point in
unit time
velocity of wave is
v = λ× ν

11. Particle concept of electromagnetic radiation
•Short EM waves like XRAYS react with matter as if they are
particles rather than waves.
•These particles are discrete bundles of energy and each bundle is
called quantum /photon.
•Photon travel at the speed of light.
•Amount of energy carried by each photon depends on frequency
of radiation.
•If frequency doubled energy doubled .
•Particle concept can explain the interaction with matter like
photoelectric and Compton effect .
Energy calculated E=hν
h= Planck's constant (4.13×10 ˆ-18 Kev sec )

12. Relationship between wavelength and
energy
Relationship between wavelength and frequency
ν= c/λ
c – velocity of light (~3×108 m/s)
also E= hν
Instead of ν
E =hc/λ ( h×c = 12.4)
E= 12.4/λ
•Energy of photon =ev
•X-ray measured in kilo ev , 1Kev = 1000 ev

13. X-ray Production

14. Wilhelm Conrad Roentgen (18451923)
X-rays were first discovered in 1895 by the
German physicist William Roentgen, when using a
Crookes tube
He called them ‘x’ rays, ‘x’ for ‘unknown’.

15. Site of discovery
Roentgen's lab where, on 8
November 1895, he noticed an
extraordinary glow while
investigating the behavior of
light outside a shrouded
cathode tube. To his
astonishment, he saw the
shadows of the bones of his
hand when held between the
tube and a fluorescent screen.
Within two months he had
published a carefully reasoned
description of his work and the
famous radiograph of his wife's
hand.

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

17. X-ray tube
Basic elements of an X Ray source assembly

18. Glass enclosure
•Vacuum: to control the
number and speed of the
accelerated electrons
independently.
• Pyrex glass is used.

19. Cathode -------•Negative terminal of
the x-ray tube is called
cathode or filament.
•Along with filament 2
other elements :
connecting wires and
focusing cup
Filament made of tungsten wire 0.2 mm diameter coiled to
form a vertical spiral 0.2 cm diameter and 1 cm length

20. CATHODE --------
MADE OF TUNGSTEN + 1%-3% THORIUM ( better emission of electrons. )

21. Filament and focusing cup
( Nickel )
•
Modern tubes have two
filaments
1. Long One : higher
current/lower
resolution, larger
exposure
2. Short One : lower
current/higher
resolution.
Focusing cup maintained
At one point only one at same negative potential
is used
as the filament .

22. Focusing Cup
Cathode assembly of a dual-focus x-ray
tube. The small filament provides a
smaller focal spot and a radiograph with
greater detail, provided that the patient
does not move. The larger filament is
used for high-intensity exposures of short
duration.
1: long tungsten filament
2 : short tungsten filament
3 : real size cathode

23. Focusing cup
Current across
tube one direction
only
Mutual repulsion
↑Number of
electrons
Prevented by focusing cup – forces the
electron stream to converge on the anode
in required shape and size
Electron stream
spread out
Bombarding
Large area of
anode

24. Thermionic emission
When Current flows – wire heated
Absorbs thermal energy – electrons move a small
distance from the surface of metal
This escape is referred to as thermionic
emission

25. Thermionic emission
Emission of electrons resulting from the absorption of
thermal energy – thermionic emission
(Tungeston heated >22000C)
Electron cloud surrounding the filament produced by
thermionic emission is termed “Edison effect”

26. Space charge
•Collection of negatively charged electrons in the vicinity
of filament when no voltage applied btw cathode and
anode – space charge
•Number of electrons in space charge remain constant
•Tendency of space charge to limit the emission of more
electrons from the filament is called space charge effect
Filament current →filament temperature →rate of
thermionic emission

27. Space charge cloud
Temperature limited
Space charge cloud shield the electric field for tube voltages of 40kvp
and less ( space charge limited ) , above 40kvp space charge cloud is
overcome by voltage applied

28. Tungsten
1.
2.
3.
4.
5.
Thin wire
Strong
High melting point
Less tendency to vaporize
Long life expectancy
Z # 74
MELTING POINT- 3,370 DEG. CELSIUS

29. Filament vaporization
•Filament vaporization – shorten the life
•Not heated for too long- filament boosting circuit
•Vaporized filament usually deposited on the inner
surface of glass wall
•Color deepens as the tube ages- bronze colored
“sunburn”
•Tends to increase filtration and changes the
quality of beam

30. Anode +++++
Stationary anode
Tungsten target in copper anode

31. Rotating anode+++
Spread the heat produced during an exposure over a large area of
anode – capable of withstanding high temperature of large exposures

32. Anode +++ parts
1. Anode disk –tungsten
•3600rpm
•Beveled edge – line focus
•Target area increased but
effective focal size remains the
same.
2. Stator
3. Rotor
4. Bearings - metallic
lubricants (silver )
5. Stem - molybdenum
90%tungsten W and 10 % rhenium Re- ↑resistance to surface
roughening - ↑thermal capacity

33. Anode +++
Modification of tube to improve speed of rotation and in
turn increased ability to withstand heat .
1.Stem length
2.Bearings
3.weight
• As short as possible
• Decrease inertia
• 2 sets as far as possible
• Decrease weight ( molybdenum + W Re alloy )
• Reduced inertia

34. Focal spot
•True focal spot :Area of the tungsten target (anode)
that is bombarded by electrons from the cathode.
•The size and shape of focal spot is determined by the
size and shape of the electron stream which hits the
target.
•Heat uniformly distributed on focal spot

35. Line focus principle
•Anode angle : defined as
the angle of the target
surface with respect to the
central ray in the x-ray field.
•Anode angle range :6°- 20°
•Line focus principle Effective focal spot size is
the length and width of the
focal spot projected down
the central ray in the x-ray
field .

36. Line focus principle
Foreshortening of the focal spot length

37. Line focus principle
effective focal length = focal length • sin
Effective focal spot<actual focal spot

38. Anode angle
Large focal spot = greater heat loading.
Small focal spot = good radiographic detail.

39. Heel effect
The heel effect: The heel
effect is due to a portion
of the x-ray beam being
absorbed by the anode.
This results in an x-ray
beam that is less
intense on the anode
side and more intense
on the cathode side. The
heel effect is more
pronounced with
steeper anode angles.

40. Heel effect
Intensity of exposure on
anode side < cathode side
of tube
Heel effect less noticeable
with large focus-film
distance
Heel effect is less with
smaller films
Cathode
←Intensity→
Anode

41. • The intensity of the x-rays emitted through the heel of
the target is reduced because they have a longer path to
travel in the target. The diff in intensity is as much as
45%
Factors affecting the heel effect:
1. Anode angle: the steeper the target → ↑↑ heel effect.
2. FFD: ↑↑ FFD → ↓↓ heel effect "with fixed film size".
3. Film size: ↓↓ film size → ↓↓ heel effect "with fixed FFD".
4. Roughening of the target surface → ↓↓ X-rays output & ↑↑
the heel effect.
• In radiographs of body parts of different thicknesses →
the thicker parts should be placed toward the cathode
(filament) side of the x-ray tube.
• e.g. AP film of the thoracic spine → anode end over the
upper thoracic spine where the body is less thick & the
cathode end of the tube is over the lower thoracic spine
where thicker body structures will receive the increased
exposure.

42. Properties of xrays
1.
2.
3.
4.
X-rays travel in straight lines.
X-rays are electrically neutral
X-rays are Polyenergetic and heterogeneous
X-rays travel at the speed of light electromagnetic radiation
5. X-rays are highly penetrating , invisible rays.

43. Properties of x-rays
6. X-rays cannot be deflected by electric field or
magnetic field.
7. X-rays cannot be focused by lens.
8. Photographic film is blackened by X-rays.
9. Fluorescent materials glow when X-rays are directed
at them.
10. Produce chemical and biologic changes by ionization
and excitation.
11. Liberate minute amounts of energies while passing
through matter.
12. X-rays interact with matter produce photoelectric
and Compton effect.

44. Processes of x-ray generation
When high speed electrons lose energy in the target
of the x-ray tube
2 processes of xray generation
General
Characteristic
General radiation ( Bremsstrahlung)
• High speed electrons with nucleus of the tungsten atom
Characteristic radiation
• High sped electrons with the electrons in the shell of tungsten
atoms

45. Degree of deceleration
0.5%time electron
comes in proximity
with nucleus
Coloumbic forces attract
and decelerate the
electron
Loss of kinetic energy and
change in trajectory
e‾
+
e‾
+

46. Bremsstrahlung ( braking radiation )

47. Enrgy of photon = enrgy of
initial ectron – enrgy of
braked electron
Energy of photon E = 12.4 /λ
Energy is related to the potential difference across tube or
λmin = 12.4 / kVp

48. Continuous spectrum
Highest energy determined by the kVp
Minimum wavelength determined by the kVp
Maximum wavelength determined by the filters used

49. Brems radiation- Polyenergetic

50. Characteristic radiation
Characteristic radiation results when the Electrons bombarding the
target eject electrons from the inner orbits of target atoms

51. Characteristic X-Ray Production
M Shell
Outgoing projectile electron
(lower energy)
Target atom
L Shell
K shell
Incoming projectile electron
(high energy)
W
K X-ray
L X-ray
Characteristic X-ray emission
Ejected electron
ionizes atom

52. Characteristic radiation
BINDING ENERGIES
OF DIFFERENT SHELL ELECTRONS
K-70 KEV
L-11 KEV
M-2 KEV

53. Characteristic radiation
L
K
M
K
(β)70-2 = 68 keV
L
11-2 = 9 keV
M
(α)70-11= 59 keV
Between 80 and 150 kVp , k shell characteristic contributes to
about 10 %(80kVp) to 28%(150kVp) of useful beam.

54. Characteristic radiation
THERE ARE MANY
CHARACTERISTIC RADIATION
PRODUCED IN ONE ATOM
THEREFORE CHARACTERISTIC
RADIATION
IS ALSO POLYENERGETIC !

55. Characteristic radiation
Less Polyenergetic

56. Typical x-ray pattern

57. Factors affecting x- ray spectrum:1) Effect of tube current (mA) (while others
remain constant):
 More mA more e- s flow from cathode to anode
 Change in mA is directly proportional to the change
in the amplitude of the x-ray spectrum
 Shape of the curve remain unchanged
The effect on the
tube spectrum when
the mA has been
halved.

58. 2)Effect of kV ( other factors remaining constant)
-> As kV is raised area under the curve increased
-> The position of the curve has been shifted to
the right to the high energy side
-> The increase is relatively greater for high
energy x-ray than for low energy x-ray
-> Characteristic curve doesn't change position
The effect on the tube
spectrum when the kV
has been reduced from
80 kV to 70 kV.

59. 3)Effect of added filtration: ( other factors remaining
constant)
-> Added filtration absorbs low energy x-rays and allow
high energy x-rays to pass through.
-> The curve is shifted. The bremsstrahlung emission
spectrum is reduced more on left than on right.
->effect of added filtration is the increase in the effective
energy of the x-ray beam (high quality)
-> Characteristic curve doesn't change position
The effect on the
tube spectrum
when filtration has
been added to the
exit beam.

60. Super Rolatix ceramic x-ray tube
Metal casing instead of glass envelope.
Three ceramic insulators – two insulators for the two high voltage
cables, and one supports the anode stem.
• Allows more compact tube design.
• Most common - Aluminium oxide.
Anode rotates on an axle which has bearings at each end – provides
greater stability and reduce the stress on shaft.
• Allows use of massive anode up to 2KG.
• larger heat storage capacity. Allows higher mAs settings.

61. Advantages of Metal -• less off focus Radiation .
• higher tube loading.
• longer tube life with high tube currents.
Cooling –
better cooling due to more efficient transfer of heat to the oil
through the metal enclosure, as compare to the glass
enclosure. ( metal is better conductor of heat )

62. Super Rolatix ceramic x-ray tube

64. Thank you