MODERATOR – DR. C.P. AHIRWAR
PRESENTOR – DR. NEELAM SONI
Discovery of x- rays !!!!
 1st x-ray photograph ???
 Form of electromagnetic radiation….
 Shorter Wavelength 0.01 to 10 nanometers
 Higher Frequency 30 petahertz to 30 exa...
Kinetic
energy
 HEAT(99%) X-RAYS (<1%)
 X-rays are produced
by energy conversion
when a fast moving
electron is suddenl...
 Made of Pyrex glass that enclose a vacuum
containing two electrodes (This is a diode
tube).
 Earliest X-Ray tube were c...
CROOKES TUBE
COOLIDGE TUBE
 KV & mAs are difficult to control
independently.
 Presence of gas produces blackening of tube
thus shortening its life....
 Modern X-Ray Tube is based on Coolidge tube.
 Electrons produced at the cathode can be
accelerated by high potential di...
X-ray Tube
 Electrons are produced by heated tungsten
filament
 Accelerated across the tube(by potential diff
between electrodes)→g...
 Electron source
 Target metal
 Potential difference
 Vacuum
 Coolant
 Glass/metal envelope
 Negative electrode
 Source of e
 3 components
 Filament
 Focusing cup
 Connecting wires
 A spiral of tungsten wire
 0.2mm thick→ coils 1 cm long , 2mm dia
Double filament
 Larger filament
-for larger exposur...
Modern x-ray may be supplied with single
more commonly a double filament.
Mounted side by side or one above the other
wi...
 When filament heated it become vaporize and
shorten the life of x-ray tube. so it should never
be heated for longer peri...
 High melting point of 33700C
 Capable of stable electron emission at high
temperature.
 Higher mechanical strength and...
 When filament is heated its atom absorb
thermal energy and some of electrons in the
metal acquire enough energy to allow...
 EDISON EFFECT :
The electron cloud surrounding the filament
produced by thermionic emission termed as Edison
effect.
 S...
 Made of nickel which surround the filament .
 Its electrical force cause the electron stream to
converge on to the targ...
Negative bias voltage is applied to focus the electron
distribution
REQUIREMENT FOR AN IDEAL ANODE -:
 High conversion efficiency.
 High melting point .
 High specific heat and thermal co...
 Positive electrode
 Target for e
 2mm thick tungsten embedded in a large mass
of cu
 Why tungsten.,?
 High melting p...
 Anodes are of two types-:
1) Stationary anode.
2) Rotating anode.
 Target is small plate of tungsten ,2 or 3 mm thick
embedded in a larger mass of copper which has very
high heat storage ...
 The purpose of rotating anode is to spread heat
over a larger area of anode.
 Ability of the x-ray tube to achieve high x-ray
output is limited by the heat generated at the
anode.
 The rotating pri...
 Anode stem is made of molybdenum has a high
melting point [26000C] and is poor heat conductor.
 Mb stem provide a parti...
 Ready before shoot??
Anode disc rotates
Filament gets heated
 Introduced by Philips medical system.
 Has a metal casing .
 Ceramic is used as insulator.
 Al oxide commonly used ce...
 Advantage of using metal as enclosure:-
 Less off focus radiation.
 Longer tube life with high tube current.
 Higher ...
 Produced when high speed electron interact
with metal surface other than the focal track of
anode.
 Main source is elec...
 small fraction of e scatter from the target and
are accelerated back to the anode, outside focal
spot
create a low-inten...
 Cause of tube failure
Extremely high voltage.
Burnout filament.
Anode melting .
Scarring of glass tube.
Tube become gass...
 Appropriate radiographic factor (ma,kvp and
exposure time)
 Rating derived from tube rating chart should
never be excee...
Thermionic emission
Space charge production
Application of potential difference
Cathode focusing cup
Interaction of electr...
 kVp
 Kilo Volt peak
 ( max) Potential difference btw electrodes
 Determines kinetic
energy of e
 keV
 Kilo electron...
 Up to saturation voltage an increase in kvp
produce a significant increase in x-ray current.
 Above this further increa...
 What is focal spot.,?
 That part of anode impacted by
electrons
 Image resolution
 small focal spot
 Heat dissipatio...
 Larger the area over which heat is
developed, less danger of destroying the tube.
 To have sharper anatomical picture ,...
 Surface of target anode is inclined so that it forms an
angle with the plane perpendicular to the incident
beam.
 Anode...
 “a reduction in the x-ray beam intensity
toward the anode side of the x-ray field.”
 Intensity of x-ray beam that leave the x- ray
tube is not uniform throughout all portion.
 Depends on the angle at whic...
 the steeper the anode, the more
noticeable the heel effect becomes.
 less prominent with
 Smaller films
 Longer sourc...
 The thicker portion of the anatomical part is
placed beneath the cathode end of the x-ray
tube.
S. Guilbaud, Education D...
 The following anatomical parts may be imaged
using the anode heel effect:
 Thoracic vertebrae
 Humerus
 Femur
 Tibia...
S. Guilbaud, Education Director
BREMSSTRAHLUNG
RADIATION
CHARACTERISTIC X-
RAYS
 Incident electron
interacts with the
nucleus of target
atom
 Incident e...
 e comes within the proximity of a nucleus
→ Columbic forces attract and decelerate the e,
→ Loss of kinetic energy and c...
 Incident e with energy > binding energy
eject e from inner orbits
 e from outer shell (L) loses energy and
replaces
 T...
Characteristic radiation
 Results when the electrons bombarding the target eject
electrons from the inner orbits of the t...
 Photon energy Vs.
Intensity
 QUALITY,
 The position of the spectrum
,on the x-axis the further to
the right it is the ...
Bremsstrahlung
Characteristic Radiation
Bremsstrahlung energy distribution
 Max energy - max kinetic energy
i.e.., kVp across electrodes
 Min energy - filters
 Typically peaking -at about 1/3 of...
 Effect of added filtration
What is the function of filters.?
…..Removes the low energy
photons and
improves quality.
 Tube current (mA):
 increases the amplitude of the spectrum (area under the
spectrum)
 Tube voltage (kV):
 increases ...
Bremsstrahlung
radiation
“Breaking radiation”
the continuous x-ray
spectrum
at all kV settings
Characteristic x-rays
at le...
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  • Bound e hvnegenrg, binding enr is given to free them , pot dif acc them
  • Neelam

    1. 1. MODERATOR – DR. C.P. AHIRWAR PRESENTOR – DR. NEELAM SONI
    2. 2. Discovery of x- rays !!!!
    3. 3.  1st x-ray photograph ???
    4. 4.  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.
    5. 5. 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
    6. 6.  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.
    7. 7. CROOKES TUBE COOLIDGE TUBE
    8. 8.  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.
    9. 9.  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.
    10. 10. X-ray Tube
    11. 11.  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
    12. 12.  Electron source  Target metal  Potential difference  Vacuum  Coolant  Glass/metal envelope
    13. 13.  Negative electrode  Source of e  3 components  Filament  Focusing cup  Connecting wires
    14. 14.  A spiral of tungsten wire  0.2mm thick→ coils 1 cm long , 2mm dia Double filament  Larger filament -for larger exposures
    15. 15. 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
    16. 16.  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.
    17. 17.  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.
    18. 18.  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.
    19. 19.  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.
    20. 20.  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.
    21. 21. Negative bias voltage is applied to focus the electron distribution
    22. 22. 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.
    23. 23.  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
    24. 24.  Anodes are of two types-: 1) Stationary anode. 2) Rotating anode.
    25. 25.  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.
    26. 26.  The purpose of rotating anode is to spread heat over a larger area of anode.
    27. 27.  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.
    28. 28.  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.
    29. 29.  Ready before shoot?? Anode disc rotates Filament gets heated
    30. 30.  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.
    31. 31.  Advantage of using metal as enclosure:-  Less off focus radiation.  Longer tube life with high tube current.  Higher tube loading.
    32. 32.  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
    33. 33.  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)
    34. 34.  Cause of tube failure Extremely high voltage. Burnout filament. Anode melting . Scarring of glass tube. Tube become gassy. Insulation failure.
    35. 35.  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.
    36. 36. 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 :
    37. 37.  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
    38. 38.  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.
    39. 39.  What is focal spot.,?  That part of anode impacted by electrons  Image resolution  small focal spot  Heat dissipation  large focal spot
    40. 40.  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.
    41. 41.  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.
    42. 42.  “a reduction in the x-ray beam intensity toward the anode side of the x-ray field.”
    43. 43.  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.
    44. 44.  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??
    45. 45.  The thicker portion of the anatomical part is placed beneath the cathode end of the x-ray tube. S. Guilbaud, Education Director
    46. 46.  The following anatomical parts may be imaged using the anode heel effect:  Thoracic vertebrae  Humerus  Femur  Tibia & fibula  Forearm S. Guilbaud, Education Director
    47. 47. S. Guilbaud, Education Director
    48. 48. 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
    49. 49.  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.
    50. 50.  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
    51. 51. 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)
    52. 52.  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)
    53. 53. Bremsstrahlung
    54. 54. Characteristic Radiation
    55. 55. Bremsstrahlung energy distribution
    56. 56.  Max energy - max kinetic energy i.e.., kVp across electrodes  Min energy - filters  Typically peaking -at about 1/3 of the projectile electron energy
    57. 57.  Effect of added filtration What is the function of filters.? …..Removes the low energy photons and improves quality.
    58. 58.  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.
    59. 59. 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.

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