Components of Dental X-Ray Machine and Production Of X-Rays

2. Under the Guidance of :
Dr. Rajendra G Patil
Dr. Simmi Thankkapan
Dr. Atha Durgvanshi
Presented by :
Dr. Praveen Kumar
PG 1st Year
PRODUCTION OF X-RAYS

3. X-ray Machine
Tube HeadControl Panel Extension Arm
On/Off switch
Exposure button
Control devices
Autotransformer
(Time, Kv & mA selector)
Suspends X-Ray
tube head
Houses electrical
wires extending
form control panel to
tube head
Allows movement &
positioning of tube
head
Metal housing
X-Ray tube
Transformers
Insulating oil
Tube head seal

4. Metal housing :
• Metal body of tube head that surrounds X-Ray tube,
transformers & is filled with oil
• Protects X-Ray tube
• Grounds high voltage
Insulating Oil :
• Surrounds X-Ray tube and transformer inside the tube head
• Prevents overheating by absorbing heat produced from
production of X-Rays
• Maintains insulation properties of glass envelope
• Also insulates tube from metal shield
Components of Tube Head

5. Tube head seal :
• Aluminium or leaded glass of the tube head that
permits exit of X-Rays from the tube head
• Seals the oil in the tube head
• Acts as Filter to the X-Ray beam
X-Ray tube :
• Main X-Ray generating system

6. Filtration :
Inherent
Added
existing in something as a permanent
• Occurs between glass of X-Ray
tube, insulating oil and tube head
seal
• Equivalent to 0.5 – 1.0 mm of Al
thickness
• Refers to the placement of Al disc
placed perpendicular to the path of the
x-ray beam in between collimator and
tube head seal
• Al may be added in 0.5 mm increment
Filtering out non-penetrating longer wavelength x-rays resulting
into higher energy more penetrating useful beam which is less
harmful to the patient

7. Total Filtration
Inherent Added
Regulated by State & Federal Law in USA
Dental machine operating :
• At or below 70 kVp require a min. total filtration of 1.5 mm of Al thickness
• Above 70 kVp require a min. total filtration of 2.5 mm of Al thickness

8. Lead Collimator :
• Lead plate with central hole that fits directly over opening
of the metal housing from where X-Ray exits
• Restricts size and shape of X-Ray beam thus reducing
exposure to the patient
i. Fixed ii. Adjustable
Round
Rectangular
• Produces a cone shaped beam of
2.75 inch in diameter
• Larger than size of the two IOPA films
• Leading to ↑ dose to the patient
• Restricts the size of the X-Ray beam to an
area slightly > a single size 2 IOPAF film
• Significantly reducing the exposure
Size of the beam can be
controlled according to the
requirement of area of exposure
Collimator

9. Position indicating device : PID
• An open ended lead cylinder extending from
opening of metal housing of tube head
• Also called Cone
• Appears as an extension of the tube head
• Aims and shapes X-Ray beam
Types of PID :
1. Conical
A closed pointed plastic cone extending from opening of metal housing of tube head
X-Ray exiting from conical PID’s produce scattered radiation
2. Rectangular
Most effective in reducing patient exposure
3. Round
• Now a days only round and rectangular PID’s are preferred
• As they do not produce scattered radiation
• Available in two lengths short 8” and long 12”
• Long PID are preferred as cause less divergence of X-Ray beam

10. Primary components of X-Ray Machine :
1. X-Ray Tube : Composed of Cathode and Anode situated in an
evacuated glass tube
2. Power Supply :
To heat the cathode filament
To create a high Potential Difference between cathode & anode

11. Cathode : composed of a filament and a focussing cup
Filament
A coil of Tungsten wire
About 2mm in diameter
1-2 mm wide, 0.1-0.2 mm thick & 7-15 mm in length
Contains 1% Thorium ( ↑es release of
electrons from heated wire)
Mounted between two stiff support wires
carrying current to heat the filament
(W – wolfram; At No. 74, Melting point 3380C)
.

12. vaporize
gaseous form
solidify on the walls of glass tube
Sun burning or Sun tanning of tube
• Tungsten filament particles
↓ed output of the X-Ray tube
Destruction of vacuum & integrity of the tube
Resulting in Arcing & ultimate tube failure
(It is an electrical breakdown of a gas
that produces an ongoing electrical
discharge)
over a period of time

13. • The thorium atoms migrate to the surface of
the filament and form the emissive layer.
• Thoriated filaments can have very long
lifetimes and are resistant to the ion
bombardment that occurs at high voltages,
because fresh thorium continually diffuses to
the surface, renewing the layer.
To make the Tube last longer
Thorium is included as a
component of cathode filament

14. Focussing Cup :
( Filament lies in focussing cup )
• -ve ly Charged concave reflector made of Molybdenum
• Electrostatically focuses the electrons emitted by the
incandescent filament into a narrow beam thereby
restricting the size of the electron cloud
• Electrons are directed at a small rectangular area in
anode – i.e. Focal Spot (An area on the target metal
where electron beam strikes)

15. Vacuum in the X-Ray Tube :
i. Prevents collision of fast moving electrons with gas molecules
↓es the speed of electrons resulting
into Low KE and thus lesser x-ray
production
ii. Prevents oxidation or burn out of the filament
To facilitate the movement of electron cloud the
X-Ray tube is evacuated as completely as
possible

16. Anode :
Consist of wafer thin Tungsten plate embedded in solid Cu Stem
Purpose is to convert KE of electrons
generated from the filament into X-Ray
photons
Position of the anode is indicated
externally as a depression, usually a red
dot on the tube head by the manufacturer
Various properties supporting
Tungsten to be an ideal target
metal
High At. No (Z)
High Melting Point
High Specific Heat
Low Vapour Pressure

17. • Indicates more no. of protons i.e. high charge on the nucleus
• High binding energy of orbital electrons
• Accelerated electrons from cathode collide with electrons in
the outer shell producing high energy X-Ray photons
High At. No (Z):
High melting point :
High specific heat : Amount of heat per unit mass required to
raise the temperature by 1 C i.e, conduction of heat
3380 , even if the Temperature rises the target will not meltC
.
Low vapour pressure :
• At higher temperature it does not evaporate
• Hence, Vacuum of X-Ray tube is maintained
.
but Tungsten itself is a poor conductor of heat
• Hence Tungsten target is embedded in solid Cu stem which is a very good conductor of heat
• Thus facilitate the dissipation of heat more quickly
• Reduces the risk of target melting

18. Power supply :
Provided by
Step Down Transformer
(Filament Transformer)
For low voltage current
Step Up Transformer
For high voltage current
To heat Cathode filament
To generate high potential difference
between cathode & anode
To accelerate electrons
towards metal target
• Reduces voltage to about 3-5 volt
in filament circuit
• Adjusts resistance & current flow
through filament
i.e.
regulates
Filament Temperature
No.s of electron emitted
Auto Transformer
serves as voltage
compensator that corrects
the minor fluctuations
in the current

19. Transformers –
Three transformers are used in the production of X-Rays
1. Step down transformer –
Used to decrease the incoming line voltage of 110-220 V to 3-5 V
as required for the filament circuit
It has more coils in primary coil than the secondary coil
2. Step up transformer –
Used to increase the incoming 110-220 V to 60-120 kV as required
by high voltage circuit
3. Auto transformer –
Serves as voltage compensator that corrects the minor fluctuations
in the current

20. Focal Spot :
• An area on the target metal to which focussing cup directs the electron
beam & from where X-Rays are produced
• The radiographic image quality is dependent on the geometry of the target
• The sharpness of radiographic image increases as the size of radiographic
source (i.e. focal spot) decreases
• But as the focal spot becomes smaller heat generated per unit target area
becomes greater
• In order to derive benefits of a small focal spot to produce a radiographic
image of good quality the target metal is placed an angle to electron beam
to provide a greater surface area for effective dissipation of heat
• The target is inclined at an angle of 20 degree to the central ray of
electrons, this causes the effective focal spot to be 1mm x 1mm in contrast
to 1mm x 3mm of the actual focal spot size
• Results in a smaller source of X-Rays and sharper image with a larger
actual focal spot for effective heat dissipation and is known as “ Line Focus
Principle”
• The twenty degree angle to which target metal is inclined is called Angle of
Truncation
Focal spot on
tungsten target

21. Inclining Target Metal at abt 20`
A larger surface area over
which electron beam falls
Actual Focal Spot
When seen perpendicular to
target from the direction of central
X-Ray beam area seems smaller
Effective Focal Spot
More dissipation of Heat
↑ed Sharpness
Line Focus Principle :
Smaller source of X-Rays & sharper image with larger actual focal
spot for effective heat dissipation
Angle of Truncation

22. Tube Current = Flow of electrons from Cathode to Anode
Tube voltage = High voltage / High Potential Difference across anode &
cathode to accelerate electrons i.e. to give sufficient energy to generate X-rays
Primary
Voltage
From
Input source
110 v
High voltage Transformer
Boosts Peak voltage upto
60,000 -120,000 volts
(60-120 Kv)
Boosts Peak energy of electrons to 60-120
Kilo electron volt (KeV)
Tube Voltage
kVp Dial
selects Peak operating voltage
i.e. Tube Voltage

23. Operating Peak Voltage
60-90 kVp
Intra Oral,
Panormic,
Cephalometric
machines
90-120 kVp
Cone Beam Computed
Tomography machines

24. Line Voltage (v) :
Primary voltage from input source
+110 v
-110 v
1/120 s 1/60 s
60 cycles/s
1 cycle
+ve polarity
-ve polarity
As polarity of Line current
alternates @ 60 cycles/sec
Polarity of X-Ray tubes
alternate at the same
frequency
Line Voltage
Varies continuously
between cathode & anode
So does
Voltage Potential

25. Anode Voltage :
+110 v
-110 v
1/120 s 1/60 s
60 cycles/s
1 cycle
1st half
2nd half
Points where polarity of anode is +ve
and maximum
around filament are
accelerated towards +ve
target
X-Rays are generated
Anode becomes –ve
Cathode becomes +ve
e-s
e-s doesn’t flow across the tube
Inverse voltage or Reverse Bias
No X-Rays are generated

26. X-Ray Tube
Powered with 60
cycles AC
60 pulses of X-Rays are
generated each having a
duration of 1/120 sec
X-Ray production is limited
to 1st half of the AC cycle
Self Rectified
Or
Half Wave Rectified
e.g. All conventional dental X-Ray
machines

27. Timer :
• Use to control X-Ray exposure time
• Built into primary high voltage circuit
• Controls the duration of exposure i.e. the time during which the tube
current flows and X-Rays are produced
• The timing circuit 1st sends a current through the filament to get it to
the proper operating temperature, once the filament is heated a time
delay switch applies power to the high voltage circuit
Electronic timer controls :
• The length of time that high voltage is applied to the tube
• And time during which electrons flows & X-Rays are produced

28. Production of X-Rays
Filament Cathode Target Anode
e-s
EK
of
e-s
Mostly in the form of heat i.e. abt 99 %
Only 1 % of convert their into X-Rays
by forming
e-s EK
Bremsstrahlung Radiation
Characteristic Radiation
Bremsstrahlung Radiation :
Sudden braking / stopping
or slowing of high speed e-s
By Tungsten nuclei
in the target
• Bremsstrahlung in German means “Braking Radiation”
Bremsstrahlung Radiation
Primary source of X-Ray
Type of X-Rays

29. e-s
W
Tungsten Atom
High Speed
Direct hit interaction
(Occasionally)
High speed electrons directly hit the nucleus
e- Loose all its KE
In a production of
single X-Ray Photon
Near or Wide miss interactions
(Mostly)
High speed electrons pass by
W nuclei with near or wide
misses
e-
High speed Attracted
towards +ve
nucleus
Loose some of its velocity i.e.
decleration & thus deflection of path
Loss of some of KE
Generation of many X-Ray Photons
Greater braking effect

30. Bremsstrahlung interaction :
• The electron that misses the nucleus continues to
penetrate many such tungsten atoms producing many
lower energy X-Ray photons before it imparts all its KE
• As a result general radiation consist of X-Rays of many
different energies and wavelength and this is called
continuous spectrum
• Energy of X-Ray photon is described by Peak
Operating Voltage (kVp)
e.g.
If 70 kVp
Voltage applied
across the tube
Produces continuous spectrum of
X-Ray Photons with energy
ranging to a maximum of 70 kVp

31. Characteristic Radiation :
• It is made when a high speed electron ejects an inner
electron from the tungsten target
• This state is highly unstable, as a result an electron
from the outer orbit is quickly attracted to the void in
deficient inner orbital
• When the inner orbital electron is replaced by an outer
orbital electron a photon is emitted with energy
equivalent to difference in binding energies of two
orbitals
• Characteristic radiation accounts for a very small
amount of x-rays produced
• The difference between the binding energy of the
electrons will vary from element to element and thus so
the energies of the photons emitted
• The energy level values and their difference are
characteristic of the element
• The radiation emitted constitutes the ‘Line Spectrum’ &
is called the characteristic radiation of that element