1. X-rays are produced when fast moving electrons are decelerated upon striking a metal target in an x-ray tube. 2. Modern x-ray tubes use a tungsten target and operate under vacuum to allow for control of the electron beam and prevent degradation of the tube. 3. X-ray output is determined by tube voltage (kVp), current (mAs), and filtration - with higher kVp and mAs producing higher quality and quantity respectively.

1. MODERATOR – DR. C.P. AHIRWAR
PRESENTOR – DR. NEELAM SONI

2. Discovery of x- rays !!!!

4.  1st x-ray photograph ???

7.  Form of electromagnetic radiation….
 Shorter Wavelength 0.01 to 10 nanometers
 Higher Frequency 30 petahertz to 30 exahertz
 High- Energy 120 eV to 120 keV
 Great penetrating power.
 Electrically neutral.
 Penetrate many materials opaque to light.
 Ionizing properties.
 Travel with the speed of light ,in a straight line and can not
be focused by lens.
 Photographic effect on silver halide crystal.

10. Kinetic
energy
 HEAT(99%) X-RAYS (<1%)
 X-rays are produced
by energy conversion
when a fast moving
electron is suddenly
decelerated by a
metal target

11.  Made of Pyrex glass that enclose a vacuum
containing two electrodes (This is a diode
tube).
 Earliest X-Ray tube were cold cathode gas
tube.

12. CROOKES TUBE
COOLIDGE TUBE

13.  KV & mAs are difficult to control
independently.
 Presence of gas produces blackening of tube
thus shortening its life.
 Variation in the no. & reduced speed of
electrons.
 Positive ion attracted by cathode cause spoiling
of cathode structure.

14.  Modern X-Ray Tube is based on Coolidge tube.
 Electrons produced at the cathode can be
accelerated by high potential difference toward
the anode.
 The purpose of vacuum in the modern X-Ray
tube is to allow the number and speed of the
electrons to be controlled independently.

15. X-ray Tube

16.  Electrons are produced by heated tungsten
filament
 Accelerated across the tube(by potential diff
between electrodes)→gain kinetic energy
 Hit the tungsten target
 X-rays are produced by energy conversion

17.  Electron source
 Target metal
 Potential difference
 Vacuum
 Coolant
 Glass/metal envelope

18.  Negative electrode
 Source of e
 3 components
 Filament
 Focusing cup
 Connecting wires

19.  A spiral of tungsten wire
 0.2mm thick→ coils 1 cm long , 2mm dia
Double filament
 Larger filament
-for larger exposures

20. Modern x-ray may be supplied with single
more commonly a double filament.
Mounted side by side or one above the other
with one being larger than the other.
Only one filament is used for any given
exposure

21.  When filament heated it become vaporize and
shorten the life of x-ray tube. so it should never
be heated for longer periods.
 Tungsten that is vaporized acquire a bronze
colored sunburn on inner surface of glass tube.
 Many modern x-ray circuits contain an
automatic filament boosting circuit.

22.  High melting point of 33700C
 Capable of stable electron emission at high
temperature.
 Higher mechanical strength and longer life.
 Easily drawn out in to a fine filament.
 Little tendency to vaporize.

24.  When filament is heated its atom absorb
thermal energy and some of electrons in the
metal acquire enough energy to allow them to
move a small distance from the surface of
metal. The process of their escape known as
thermionic emission.

25.  EDISON EFFECT :
The electron cloud surrounding the filament
produced by thermionic emission termed as Edison
effect.
 SPACE CHARGE :
Collection of negatively charged electrons in the
immediate vicinity of filament is called as the space
charge.
 SPACE CHARGE EFFECT :
The tendency of the space charge to limit the
emission of more electrons from the filament is called
the space charge effect.

26.  Made of nickel which surround the filament .
 Its electrical force cause the electron stream to
converge on to the target anode in the required
size and shape.
 Prevent spread out of electron stream and
bombardment of an unacceptably large area on
the anode.

28. Negative bias voltage is applied to focus the electron
distribution

30. REQUIREMENT FOR AN IDEAL ANODE -:
 High conversion efficiency.
 High melting point .
 High specific heat and thermal conductivity .
 Low vapor pressure even at high temperature.
 Suitable mechanical properties.
 Tungsten with an atomic no of 74 and melting
point of 3370 degree , meets most of these
requirements.

31.  Positive electrode
 Target for e
 2mm thick tungsten embedded in a large mass
of cu
 Why tungsten.,?
 High melting point 3370
 High atomic number 74
 Reasonable conductor of heat
 Why cu.,?
 Good conductor of Heat
 A single exposure may raise the temp to 1000 c

33.  Anodes are of two types-:
1) Stationary anode.
2) Rotating anode.

34.  Target is small plate of tungsten ,2 or 3 mm thick
embedded in a larger mass of copper which has very
high heat storage capacity and conductivity for
efficient dissipation of heat.
 Actual size of target is larger then the area
bombarded by the electron stream.
 This is necessary because of relatively low melting
point of copper (10700C.).
 If target is smaller ,the heat produced would melt the
copper.

35.  The purpose of rotating anode is to spread heat
over a larger area of anode.

36.  Ability of the x-ray tube to achieve high x-ray
output is limited by the heat generated at the
anode.
 The rotating principle is used to produce x-ray
tube capable of withstanding the heat
generated by large exposure.
 Anode consist of large disc of tungsten which
rotate at a speed of about 3600 revolution per
min when an exposure is made.
 The electron will bombard a constantly
changing area of target and this will lead to
spread of heat over a larger area of anode.

38.  Anode stem is made of molybdenum has a high
melting point [26000C] and is poor heat conductor.
 Mb stem provide a partial heat barrier between
tungsten disc and bearing of anode assembly.
 Length of mb stem is as short as possible to
decrease the inertia of tungsten disc.
 Inertia of anode is reduced by decrease the weight
of anode itself.

39.  Ready before shoot??
Anode disc rotates
Filament gets heated

40.  Introduced by Philips medical system.
 Has a metal casing .
 Ceramic is used as insulator.
 Al oxide commonly used ceramic insulator.
 Metal part of tube is earth .
 Because of this grounding & ceramic insulator there
is reduction in the effect of radiation.

41.  Advantage of using metal as enclosure:-
 Less off focus radiation.
 Longer tube life with high tube current.
 Higher tube loading.

42.  Produced when high speed electron interact
with metal surface other than the focal track of
anode.
 Main source is electron backscatter from the
anode .
 Metal enclosure decrease off focus radiation by
attracting off focus electron to the grounded
metal wall

43.  small fraction of e scatter from the target and
are accelerated back to the anode, outside focal
spot
create a low-intensity x-ray
 Increases patient exposure, blurring, and
background fog.
 Reduced by:
 Lead collimator placed near
the x-ray tube output port
 Grounded anode
(Metal enclosure at the same
electrical potential as anode)

44.  Cause of tube failure
Extremely high voltage.
Burnout filament.
Anode melting .
Scarring of glass tube.
Tube become gassy.
Insulation failure.

45.  Appropriate radiographic factor (ma,kvp and
exposure time)
 Rating derived from tube rating chart should
never be exceeded.
 Anode should never be run unnecessarily.
 Preparation time should be kept as short as
possible.
 Adequate cooling of the tube housing must be
provided.

46. Thermionic emission
Space charge production
Application of potential difference
Cathode focusing cup
Interaction of electron beam
with x-ray tube target
>99% Heat
< 1% x-rays
Schema :

47.  kVp
 Kilo Volt peak
 ( max) Potential difference btw electrodes
 Determines kinetic
energy of e
 keV
 Kilo electron Volt
 Kinetic energy of e when acc by 1 Volt
(With kVp 100 the MAX energy expected will b 100 keV)
 mAs
 milli Ampere second (Tube current)
 Current carried by flow of e in tube
 Depends on no. of e/ filament current

48.  Up to saturation voltage an increase in kvp
produce a significant increase in x-ray current.
 Above this further increase in kvp produce
very little change tube current.
 Below saturation voltage current flowing is
limited by space charge effect.
 Above this it has no influence on tube current.

50.  What is focal spot.,?
 That part of anode impacted by
electrons
 Image resolution
 small focal spot
 Heat dissipation
 large focal spot

51.  Larger the area over which heat is
developed, less danger of destroying the tube.
 To have sharper anatomical picture ,the
apparent focal spot size should be of smaller
dimension.

52.  Surface of target anode is inclined so that it forms an
angle with the plane perpendicular to the incident
beam.
 Anode angle may vary from 6 -20degree.
 Size of apparent focal spot is smaller then that of
actual focal spot and is directly related to the sine of
the angle of anode.
 Smaller the angle ,the apparent focal spot also
become smaller.

54.  “a reduction in the x-ray beam intensity
toward the anode side of the x-ray field.”

55.  Intensity of x-ray beam that leave the x- ray
tube is not uniform throughout all portion.
 Depends on the angle at which x-ray emitted
from the focal spot.This variation is known as
heel effect
 Intensity of beam toward anode is less than
toward cathode.

58.  the steeper the anode, the more
noticeable the heel effect becomes.
 less prominent with
 Smaller films
 Longer source-image
distance (subtends a
smaller angle)
 Application??

59.  The thicker portion of the anatomical part is
placed beneath the cathode end of the x-ray
tube.
S. Guilbaud, Education Director

60.  The following anatomical parts may be imaged
using the anode heel effect:
 Thoracic vertebrae
 Humerus
 Femur
 Tibia & fibula
 Forearm
S. Guilbaud, Education Director

61. S. Guilbaud, Education Director

64. BREMSSTRAHLUNG
RADIATION
CHARACTERISTIC X-
RAYS
 Incident electron
interacts with the
nucleus of target
atom
 Incident electron
interacts with an
orbital electron of
target atom
Involves two processes

65.  e comes within the proximity of a nucleus
→ Columbic forces attract and decelerate the e,
→ Loss of kinetic energy and change in
electron's trajectory.
 An x-ray photon with energy equal to the
kinetic energy lost by the electron is produced
 Distance between the bombarding electron and
the nucleus determines the energy lost ,
 closer it gets to nucleus greater the energy loss.

67.  Incident e with energy > binding energy
eject e from inner orbits
 e from outer shell (L) loses energy and
replaces
 The energy lost by this electron is
emitted as x-ray photon
 Energy of x-ray photon depends on
element and shell not on energy of
incident e (CHARECTERISTIC)
 In tungsten (K-72 L-11) k characteristic
radiation is ~59 keV

68. Characteristic radiation
 Results when the electrons bombarding the target eject
electrons from the inner orbits of the target atoms
 The wavelength of the x-rays produced are characteristic
of the atom that has been ionized and is not changed by
the kVp used (Of course, the applied kilovoltage must
be high enough to excite the characteristic radiation)
 The quantity of x rays generated is proportional to the
atomic number of the target material (Z), the square of
the kilovoltage [(kVp)2], and the milliamperes of x-ray
tube current (mA)
 The quality (energy) of the x-rays generated depends
almost entirely on the x-ray tube potential (kVp)

69.  Photon energy Vs.
Intensity
 QUALITY,
 The position of the spectrum
,on the x-axis the further to
the right it is the higher the
quality.
 QUANTITY ,
 The area under the spectrum
, the greater the area the
greater the quantity.
Quality:
Max photon energy
Max kinetic energy of e
Max potential diff betw electrodes
(kVp)
Quantity:
Number of e that flow (mAs)

71. Bremsstrahlung

72. Characteristic Radiation

73. Bremsstrahlung energy distribution

74.  Max energy - max kinetic energy
i.e.., kVp across electrodes
 Min energy - filters
 Typically peaking -at about 1/3 of the
projectile electron energy

76.  Effect of added filtration
What is the function of filters.?
…..Removes the low energy
photons and
improves quality.

77.  Tube current (mA):
 increases the amplitude of the spectrum (area under the
spectrum)
 Tube voltage (kV):
 increases the kinetic energy , amplitude of the spectrum
and shifts it to the right.
 Added filtration:
 will decrease the amplitude, more so on the left side than
the right.
 Target material:
 changing to a better target material will increase
amplitude AND shift discrete spike to the right.

78. Bremsstrahlung
radiation
“Breaking radiation”
the continuous x-ray
spectrum
at all kV settings
Characteristic x-rays
at least 70 kV. (k-shell
binding energy of
tungsten is 69.5 keV).
precisely
fixed, discrete, energies.