basic principle of x-ray by prahlad maurya

1. Prahlad Maurya
teacher Assistant
kgmu

2. Contents-
Introduction
History
Basic Physics of Radiation
 Continuous Spectrum
 X-ray tube

3. Wilhelm Conrad Roentgen
(1845-1923)
German scientist Wilhelm Roentgen who discovered
these on November 8, 1895, who usually is credited as its
discoverer, and who named it X-radiation to signify an
unknown type of radiation.

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

5. Basic x-ray physics :-
 X-rays: a form of electromagnetic
energy
 Travel at the speed of light
 Electromagnetic spectrum
 Gamma Rays
 X-rays
 Ultraviolet
 Visible light
 Infrared light
 Microwaves
 Radio waves
 Radar

7. Continuous Spectrum
 X-rays are produced whenever matter is irradiated
with a beam of high-energy charged particles or
photons
 In an x-ray tube, the interactions are between the
electrons and the target. Since energy must be
conserved, the energy loss from the interaction
results in the release of x-ray photons
 The energy (wavelength) will be equal to the energy
loss (Equation 4).
 This process generates a broad band of continuous
radiation (a.k.a. bremsstrahlung or white radiation)

8. Continuous Spectrum
 The minimum wavelength (
in angstroms) is dependent
on the accelerating potential
( in KV) of the electrons, by
the equation above.
 The continuum reaches a
maximum intensity at a
wavelength of about 1.5 to 2
times the min as indicated
by the shape of the curve
VV
hc 398.12
min 

9. Generating Characteristic Radiation
 The photoelectric effect is
responsible for generation of
characteristic x-rays. Qualitatively
here’s what is happening:
 An incoming high-energy
photoelectron disloges a k-shell
electron in the target, leaving a
vacancy in the shell
 An outer shell electron then
“jumps” to fill the vacancy
 A characteristic x-ray (equivalent
to the energy change in the
“jump”) is generated
L-shell to K-shell jump produces
a K x-ray
M-shell to K-shell jump produces
a K x-ray

11. Continuous and Characteristic Spectrum

13. -: X-RAY TUBE :-
 Made of thin Pyrex glass or
metal enclosure to withstand
high heat load and minimize
x-ray absorption
 Is gas evacuated
 So electrons won’t collide
with the air molecules in the
tube
 The X-Ray tube is the single
most important component of
the radiographic system. It is
the part that produces the X-
rays

15. X-ray tube construction :-

16. X-ray tube construction
 May have two filaments for a large
and small focal spot
 When heated, boils off electrons
 Made of Thoriated Tungsten
 High thermionic emission
 High melting point (3410OC for
those fact lovers)
 Not likely to burn out like a light
bulb
 Thorium enhances thermionic
emission and prolongs tube life
Electron Sources
(Cathode)
X-Ray filament

17. Protective housing :-
Made of lead & steel
 When x-rays are
produced, they are
emitted isotropically,
Equal intensity in all
directions
 We only use x-rays
emitted through the
window or port Called
the useful or primary
beam

19. Protective housing :-
 X-rays that escape through the protective housing
are leakage radiation
 Provides mechanical support for the tube and
protects from rough handling
 Some tubes contain oil that serves as an insulator
against electric shock and as a thermal cushion
Dissipate heat
 Some protective housing has cooling fan to air-
cool the tube and oil

20. Internal components Cathode
 Discovery of cathode rays by Sir Willium Crooke
 The negative side of the tube and has two primary parts
a filament and focusing cup
 Filament = a coil of wire about 2mm in diameter and 1 or
2 cm long.

21. Cathode :-
 Filament
 Dual-filament
 Focusing cup
 Negatively charged

22. Tungsten :-
 Filaments are usually
made of tungsten
 Tungsten provides higher
thermionic emission than
other metals
 Tungsten has a very high
melting point
 Suitable mechanical
properties for construction
purpose
 Allso known as Diamond
of x-ray

23. Filament :-
 When current (mA) is
applied to the coil of wire
electron are ejected the
outer-shell electrons of
the filament atom are
“boiled off”. This is
known as Thermionic
Emission or Edison
Effect.

24. Focusing cup :-
 The filament is embedded in a metal cup that has a
negative charge
 Boiled off e- tend to spread out due to electrostatic
repulsion. The focusing cup confines the e- cloud to a
small area

26. Filament Current :-
 When the x-ray imaging
system is first turned on,
a low current passes
through the filament to
warm it and prepare it
for the thermal jolt
necessary for x-ray
production
 The current is not
enough to energize the
tube, just warm the wire
of the filament

27. Space-charge effect :-
 The cloud of e- = space charge
 As the space charge becomes
more negative by the boiling off
of more electrons it makes it
difficult for more e- to be emitted
 Electrostatic repulsion
 Space-charge effect
 Space-charge limiting at low
kVp & high mA

29. Dual-focus tubes :-
 Most diagnostic tubes
have two focal spots;
large & small
 Large is used when large
body parts are imaged
 Small is used when better
spatial resolution is
desired – better detail
Filament size

31. Anode :-
 Anode is the positive side
of the x-ray tube
 The anode conducts
electricity, radiates heat
and contains the target,
Diameter 7.5 - 12.5 cm
 Two types of anodes
Stationary & Rotating

32. Stationary Anode :-
 Used for dental x-rays,
some portable imaging
 Target is button of
tungsten set in block of
copper
 Used when high tube
current and power are not
required because they are
not capable of producing
high-intensity x-ray beams
in a short time

34. S
T
A
T
I
O
N
A
R
Y
ANODE

35. Rotating Anode :-
 Tungsten mixed with 5-6%
rhenium, molybdenum is
used as the base material
 Is powered by an induction
motor
 The stator is on the outside
of the glass, consist of a
series of electromagnets
 The rotor is a shaft made of
bars of copper and soft iron
built into one mass

38. Rotating Anode

39. Reason for choosing tungsten as
filament :-
 It is capable of stable
electron emission at high
temperature.
 It has high melting point.
 It has mechanical
strength, long life, and
can be easily drawn out
into a fine filament.
 The remnant gas atom
can be removed with
relative ease.

40. Electromagnetic Induction Motor :-
 Anode speed 3,000-9000
rpm (revolutions per minute)
 The anode is driven by an
electromagnetic induction
motor.
 The induction motor consists
of two principle art
1. Stator
2. Rotor
 Anode Cooling Chart
 Heat Units (HU)

42. Electromagnetic induction :-
 As current is applied to
the stator sequentially so
the magnetic field rotates
on the axis of the stator
 This magnetic field
interacts with the metal
(ferromagnetic rotor)
causing it to rotate in
unison with the magnetic
field of the stator

43. Dead-man switch :-
 Rotor/Prep – applies
current (mA) to the tube
 Allows rotor to accelerate
to its designed RPM.
Rotor stops about 1 min
after exposure
 Filament current is
increased to create e-
cloud
 Exposure – applies voltage
(kV) to make exposure

44. Focal spot :-
 The area of the anode’s target
where x-rays are emitted
 The smaller the focal spot the
better the resolution of the
resultant image
 Unfortunately, as the size of
the focal spot decreases, the
heat of the target is
concentrated into a smaller
area
 This is the limiting factor to
focal spot size

46. Line-focus principle :-
 By angling the target, the effective area of the target is
much smaller than the actual area of electron interaction
 Effective
 Focal
 Spot
 The anode angle q determines the effective focal spot
size:
 The angle q also determines the X-ray field size
coverage. For small angles the X-ray field extension is
limited due to absorption and attenuation effects of X-ray
photons parallel to the anode surface.
effective focal length = focal length • sinq

47. Biangular targets

48. Target angle :-
 The smaller the target angle the
smaller the effective focal spot
 The inclination of target face is
usually 17 degrees
 Angles from 5 degrees to
20degrees
 Biangular targets are available
that produce two focal spot sizes

49. Anode Heel Effect :-
 Because of the use of line-focus principle the
consequence is that the radiation intensity on the
cathode side of the x-ray field is higher than that on
the anode side
 Because the e- on the anode side must travel
further than the e- that are close to the cathode side
of the target, the anode side x-rays have slightly
lower energy than the cathode side x-rays

50.  The smaller the anode
angle, the larger the
heel affect
 Better use anode heal
effect for AP view of
thoracic spine x-ray
Anode Heel Effect :-

51. Extra focal Radiation :-
 X-ray tubes are designed so that
the projectile e- interacts with the
target. However, some of the e-
bounce off the target and land on
other areas
 This caused x-rays to be
produced out side the focal spot
 These rays can also be called
off-focus radiation
 Extra focal radiation is
undesirable because it extends
the size of the focal spot,
increases patient skin dose &
reduces image contrast

53. Fixed diaphragm in the tube
housing :-
 Using a grid
does not reduce
extra focal
radiation

55. The Control Console :-
 The control console
is device that allows
the technologist to
set technical factors
(mAs & kVp) and to
make an exposure.
 Only a legally
licensed individual is
authorized to
energize the console.

56. kVp = Energy mAs = Amount

57. Kilovoltage Peak :-
 kVp
 kVp= controls contrast (differences from black to white)
 One kilovolt is = to 1000 volts
 The amount of voltage selected for the x-ray tube
 Range 45 to 120 kVp (diagnostic range)
 kVp controls contrast
 Determine the energy of electron
 Higher kVp then higher energy of x-ray
 kVp is direct proportional of velocity of electron
 220Volts incoming – up to 120,000 volts (120kVp) to anode
side of x-ray tube

58. Milliampere :-
 mAs
 One milliampere is equal to one thousandth of an
ampere.
 The amount of current supplied to the x-ray tube
 Range 10 to 1200 mA
Time :-
 In seconds
 How long x-rays will be produced
 0.001 to 6 seconds

59. Milliampere seconds :-
 mAs
 mAs – density (Amount of black on the film)
 Greater mAs, more then electron produce
 mAs is direct proportional of current
 Voltage current is reduced to milliamps to the filament
(cathode) side of the tube.
mA X s = mAs

60. How do x-rays passing through the body
create an image?
 X-rays that pass through the body render the image dark
(black)
 X-rays that are totally blocked render the image light
(white)
 Air = low atomic # = x-rays get through = image is dark
(black)
 Metal = high atomic # = x-rays blocked = image is light
(white)

61. 5 Basic Radiographic Densities
 Air
 Fat
 Soft tissue/fluid
 Mineral
 Metal

62. Radiographic Analysis
 Any structure, normal or pathologic, should be
analyzed for:
1. Size
2. Shape and contour
3. Position
4. Density (You must know the 5 basic densities)

63. Operating Console

64. Operating Console
 All consoles have the same basic controls:
 On/Off Switch
 Kilovoltage control
 Milliampere control
 Length of exposure/timer
 Focal Spot Size
 Automatic Exposure Control
 Selection of appropriate chamber
 Density Controls
These are examples of manual
exposure controls. Anything not
performed with AEC is considered
a manual exposure. Your distal
extremities are manual exposure!

65. Manual Control

66. Automatic Exposure Control (AEC)
 Automatic Exposure Control is an automatic time that
detects the amount of radiation passing through the patient
and terminates the exposure after a appropriate amount of
time
 Minimum reaction (response) time is determined by the
length of time necessary to for the AEC to respond to the
radiation and for the generator to terminate the exposure.
 Backup time is set at 150% (1.5 times) that of the anticipated
manual exposure.
 If exposure is expected to be 75 kV at 100 mAs, it will terminate
at 150 mAs.
 Most common and popular AEC device is the three
chambers:

67. ***Remember the selection
of an incorrect chamber
can cause an over or
underexposed image!!!

68. THANK YOU
 The goal of the education is the
advancement of knowledge and
the dissemination of truth.