xraytub3.pdf

Introduction
History
Types
Common faults
Advancements
Applications
Conclusion
2
Outline

INTRODUCTION :
.
 X-RAY TUBE:-a device which is meant for the
production of x-rays.
 An X-ray tube is a vacuum tube.
 Contains a pair of electrodes i.e. a Cathode and an Anode.
 Cathode is a filament that releases electrons when high voltage is applied.
 Anode is made up of tungsten, which attracts the electrons.
 When the electrons released from the cathode come in contact with the tungsten
, they release energy in the form of photons.
 These highly energized photons are channeled through a lead cylinder and
series of filters creating X-rays.

 X-rays were discovered by W.C. Roentgen
on Friday 8th November 1895 in Germany.
 At the time of discovery he was
experimenting about cathode rays when he
passed current through crooks type tube
covered with card board shield to stop any
light arising from the fluorescence of glass
walls in a dark room, he was surprised to
note small glow coming from near placed
sheet of paper painted with barium
platinocynaide. He confirmed these
emanation of rays coming from the tube and
named them x –rays.
4
History

 X-ray tube is a device based on the principle of energy
conversion.
 When the fast moving electron comes in the vicinity of the heavy
nucleus, it gets attracted towards the positively charged nucleus
due to columbic force and gets deviated from its original path ,In
this process kinetic energy of fast moving electron is lost and
converted into heat(99%) and X-ray energy (1%).
5
Principle

 In 1895: X-rays were discovered from experimental discharge
tube called as Crooks tube or Cold cathode tube.
 In 1913 : Crooks tube was improved by William Coolidge c/as
Coolidge tube or Hot cathode tube.
 In 1915: Hooded anode tube.
 In 1920: Oil cooled tube.
 In 1929: Rotating anode tube.
 In 1932: Grid controlled stationary anode tube.
 In 1937: Grid controlled rotating anode tube.
 In 1959: High speed tube.
8
History Of The Developments Of The
X-ray Tubes

 In 1962: Rhenium alloyed tungsten composite anode tube.
 In 1967: Mammography unit with Mb anode.
 In 1971 : Glass metal tube with Mb anode.
 In 1973: Three layer anode (W-Re)+ Mb ,or (W-Re)+W+(W-Zr-
………… Mb).
 In 1979: Metal ceramic tube.
 In 1981 : Three focus tube.
 In 1989: Direct anode cooling with noiseless rotor.
 In 1989: Introduction of helical CT tube ( by Siemens).
 In 1990: MRC tubes ( Maximus rotalix ceramic) by Philips.
Cont..
9

 In 1998: Development of grid control rotating
…….... anode for angiography by Toshiba.
 In 1999: Double focus stationary anode x-ray
……….. .tube for mobile c-arm.
 In 2000: Food inspection x-ray tube.....................................
 In 2002:High speed rotation bearing rotating
………. .anode tube for angiography.....
 In 2006: there is introduction of STATRON
x-ray tube by Siemens.
 In 2003: Micro-focus X-ray tube
…………… with .power supply used for
…………………………………………….inspection technology .
cont..

GAS TUBE (ION TUBE) OR CROOKES
TUBE
 Historically, X-rays were discovered from experimental discharge
tubes called Crookes tube.
 Invented by British Physicist Sir William Crookes.
 Also called as Cold cathode tube or Discharge tube.
 Early X-ray tube called as Gas tube because;
 its action depends upon the presence of small residual amount of
gas present in it and the radiographer kept a selection of tubes of
various mAs values on a rack, usually in the darkroom.
 When the change of mAs was required the radiographer
disconnected the tube and replaced it with a different one.

Crookes X-ray tube consists
of:
 Cathode is on the right the anode is in
the center with attached ‘heat sink’ at
left.
 The device at top is a Softener used to
regulate the gas pressure.
 Glass bulb with around 10-6 to (5 x
10-8) atm.pressure
 An Al. cathode plate having
curve shape to created the beam
of electrons.
 A platinum anode target –
(generate X-rays).

 During operation, the residual gas in the tube would be adsorbed
by the glass and the metal electrodes leading to a reduction in the
x-ray output. The side tube contained a few mica sheets which
would release small amount of gas when heated by an electric
heater wire.
 A high voltage was made between the electrodes; this induces an
ionization of the residual air, and thus an electron flow or
"discharge" from the cathode to the anode. When these electrons
hit the target, they are slowed down, producing the X-rays
(Bremsstrahlung).
13
How X-rays Produced In Crookes Tube

 Relatively low intensity of x-ray (not more than 5mA)
 was unreliable and unstable as x-ray production depended upon
the gas content which was a very variable factor.
 This tube can not produce X-rays continuously.
 We can not operate the kvp and the mAs independently as there is
presence of gases.
14
Limitations:

 The Coolidge tube was improved by William Coolidge in 1913.
The Coolidge tube, also called hot cathode tube, is the widely
used. It works with a very good quality vacuum (about 10-4 Pa, or
10-6 Torr).
 In the coolidge tube electrons are produced by Thermionic effect
i,e (on heating metal element emit electrons).
15
The Coolidge Tube (Hot Cathode X-Ray Tube)

 The filament is the cathode of the tube , which is negatively
charge.
 When high voltage potential is applied between the cathode and
the anode, the electrons are thus accelerated towards positively
charge anode in completely evacuated glass tube.
 Resulted into production of X-rays after striking the target.
 Coolidge tube is the prototype for modern X-ray tubes
being used today.
16
Cont..

Coolidge Tube Modified Coolidge Tube
With radiator
ANODE ASSEMBLY RADIATOR
CATHODE ASSEMBLY
CATHODE ASSEMBLY
X-RAY EXIT
PORT
18

 A source of electrons; Cathode
assembly i.e.(filament and
focusing cup.)
 A means to high voltage across
anode and cathode.
 A means to slow down the
electrons Anode assembly with
target (Tungsten).
 Glass envelope (Borosilicate) to
enclose two electrodes with
vacuum level – 10-7 to 10-8 mm of
Hg.
19
Basic Features Of An X-ray Tube
Cathode assembly anode target
Cathode& anode insulator
Rotor, stator coil
Focusing cup
and filament
Mo stem
With few technical modification modern x-ray tubes are similar to
coolidge tube

X-Ray Tube Components
 Housing
 Visible part of tube
 Glass Enclosure
(insert)
 Vacuum
 Electrodes
• Cathode
 Filament
• Anode
 Target
*

 Shields against leakage radiation
It is lead lined.
leakage limit:-100 mR / hour when tube operated at maximum
continuous current for its maximum rated kilovoltage.
 Shields against high voltage
• electrically grounded.
• high voltage cable receptacles (wells)
 Housing filled with oil
• Cools,
• electrical insulation,
• bellows on the end of tube allows
oil to expand when hot.
22
TUBE HOUSING
…

23
Component of a Tube Unit: The Housing

 The electrons of the X-ray tube must be sealed into an Glass
enclosure. Since, it is necessary for them to operate in vacuum.
 It serves to support the electrons and maintain the vacuum.
 Special alloys having same coefficient of linear expansion as that
of Pyrex glass are used.
 It has following features;
 It can withstand heat and mechanical stress.
 It is an electrical insulator capable to withstand high voltage.
 It should be capable of being sealed to the electrodes with a
vacuum-tight, heat proof seal.
24
Glass Enclosure And Its Contents

 It is the negative electrode of the X-ray tube.
 It consist of a metal structure to support the filament.
 It consists of
a) Filament –source of electron.
b) Connecting wires which supply the voltage (about 10 V) and
current(3 to 5 A)
c) Metallic focusing cup..
25
Cathode

 FILAMENT: Cathode
filament made of thin tungsten
wire which is a source of
electrons .
 It works on the phenomenon of
Thermionic emission i.e..
 Tungsten spiral wire [dia :
0.2mm].
 Length :1.0 cm
 Diameters of spiral : 0.2 cm
26
Filament

Tungsten is used as filament
material because of following
Reasons:
 It has high melting point
(33700C).
 Less tendency to vaporize
 High tensile strength means it
can be drawn into wires.
 High thermal conductivity and
specific heat.
 Appropriate Threshold or Work-
function.
.
27

 Used to supply voltage and current to the filament which are
attached with the filament heating circuit and also H.T.
Transformer.
 Cathode filament is mounted on two supporting or connecting
wire.
 One wire is connected to low voltage for filament current and
another is connected to high voltage current to produce high
voltage b/w anode and cathode.
 Current 3-5 amperes and 10-12 volts are used in filament supply
by filament heating transformer .
29
Connecting Wires

 It is the device surrounding the cathode filament in an X-ray tube.
 This is actually a third electrode in the tube, called a Wehnelt
electrode.
 Because of the forces of the mutual repulsion of large no. of
electrons this electrons stream would tend to spread itself out and
result in bombardment of large area on the anode of the X-ray
tube.
 This is prevented by a focusing cup which surround the filament.
 If this electrode is not present, the electrons would hit the anode
over a very large area.
30
Focusing Cup

 The focusing is achieved by keeping the focusing cup at the same,
or slightly higher, negative potential as that of the cathode
filament.
 It is usually made up of Ni because of:
a) Light wt.
b) Poor thermal conductivity
c) High melting point.
cont
31
…

 It is inability to operate the current and voltage of the x-ray tube
independently .
 When filament is heated emission of electrons takes place.
 In the absence of high voltage these electrons remain around the
filament . This cloud repels new electrons from the filament this
tendency is known as Space charge effect.
 Since, Space charge is negatively charged so its presence around
filament prevent further emission of electrons.
 When high voltage is applied electrons moved towards anode therefore,
space charge effect is diminished.
32
Space Charge
+ -
-
-
*

Most tubes have 2 filaments & thus 2 focal spots, only one used at
a time
 Small focus
– improved resolution
 Large focus
– improved heat ratings
– Electron beam strikes larger portion of target thus spreading
heat produced to a large area
33
Focal Spots

 Filament current is not tube current. It is the rate of electron flow
from filament to target.Electrons / second
 Measured in milliamperes (mA)
 Limited by
• filament emission (temperature / filament current)
• space charge.
34
Tube Current (mA)

Kilovoltage & Space Charge
Raising kvp gradually overcomes space charge
• Higher fraction of electrons make it to
anode as kvp increases
• Below 40 kvp the current flowing is
limited by space charge effect
• Above 40 kvp the space charge has no
influence on current flowing in the x
ray tube
 With time, as the tube is used tungsten
from hot filament vaporizes on glass insert
• thins the filament
• filters the x-ray beam
• increases possibility
of arcing
• electrons attracted to
glass instead of target.
Saturation
Voltage
kVp

 Positive electrode .
 It consist of target (focal spot) and
cylindrical cu block or tungsten
Rhenium disk.
 Functions:
• Electrical conductor
• Mechanical support for the Target.
• Good thermal radiator.
 Target: The area of the anode struck
by the electrons from the cathode.
36
Anode

 Made up of a small plate of tungsten 2 or 3mm thick that is
embedded in a large mass of cu.
 Square or rectangular in shape with each dimension usually
greater than 1cm.Anode angle is usually 15-20 deg.
 We use TUNGSTEN as a target material because of following
reasons:
• High atomic no.(74)
• High melting point (3370 °C)
• High thermal conductivity.
• It doesn’t vaporize easily.
37
Cont..

Target material is based on three characteristics:
 Atomic number:- must be high so that it results in high efficiency
in x-ray production.
 Thermal conductivity:- must be able to conduct heat away from
the target.
• High melting point:- must be able to withstand high temperatures.
38
Target Material

 It is the area actually bombarded by the electron stream on the
target.
 It can be larger or smaller in size.
 A small focal spot is required for producing good radiographic
detail but it may also lead to overheating of target.
 Whereas large focal spot allows greater heat loading but doesn't
produce sharp image.
 This problem was solved in 1918 by the development of line focus
principle .
39
Focal Spot

 It states that as the anode angle is
made small, the apparent focal
spot also becomes small but with
increased heat loading.
 Focal spot steeply slanted.
 7-15 degrees typical.
Adv:
 This slope allows x-rays produced
at focal spot to leave the tube
sideways In such a way that the x-
ray beam emerges at right angle to
the long axis of the x-ray tube.
40
Line Focus Principle

 It permits large area for electron
bombardment and a small x-ray source.
more heat loading with good radiographic
detail.
 Sin 6⁰= 0.104
 Sin 21⁰=0.358
Target Angle
 Angle between target & perpendicular to
tube axis
 Typically 7 – 15 degrees
41
Cont..
+
Target
Angle,Q
Apparent FS = Actual FS X sin ѳ

 Large
• better heat ratings
• better field coverage
• Large fs
• Reduced image quality
 Small
• optimizes heat ratings
• limits field coverage
• Small fs
• Better resolution
42
Target Angle (cont.)
+
Large Target Angle
(large Actual Focal
Spot)
+
Small Target Angle
(small Actual Focal Spot)

43
Types Of X-ray Tubes
X-ray Tubes
Stationary Anode
x-ray tubes
Rotating Anode
x-ray tubes.

 Advantages
 Compact Unit
 Less cost
 Limitations
 Since area covered by electrons beam on the target i.e. x-ray
source and the area over which heat is spread are the same so
we cannot use higher electrical loads or high mAs
 Applications
 Dental x-ray sets, small portable and mobile x-ray units with
limited output
Stationary Anode X-ray Tube
44

1. A source of electrons: Cathode assembly i.e.(filament and
focusing cup.)
2. A means to accelerate the electrons to high velocity voltage
across anode and cathode.
3. A means to slow down the electrons Anode assembly with target
(Tungsten).
4. Glass envelope (Borosilicate) to enclose two electrodes with
vacuum level – with pressure of 10-7 to 10-8 mm of Hg.
45
Components Of A Stationary Anode X-ray
Tubes

46
Dental x-ray tube that showing stationary
anode
Fig : A fixed anode X-ray tube

Tungsten Target Plate
Copper Block
A Stationary Anode
The above photo shows the tungsten (W)
target plate mounted on its copper block.

 Area of electrons bombardment should be larger enough to
accommodate large amount of heat.
 Area of x-ray production should be as small as possible to get
sharp images and good radiographic detail.
Cylindrical cu-block
• The small tungsten target is bounded to larger cu-block to
facilitate heat dissipation. The cu prevent excessive rise in temp,
because of high thermal conductivity.
48
Two important consideration which govern target design are:

 Tube Housing :It is the lead lined aluminum alloy casing in
which x-ray insert in contained.
 The metal case provides protection against
1. Radiation risk
2. Electric risk
3. Serves as a mechanical support to x-ray tube.
Cont:
49

Construction of H.T. cable is:
1. Electrical conductor :- Inner most are electrical conductors
which supply current to X-ray tube.
2. Insulating layer :- It is made up of special rubber which is put
around the Cu core in a thick layer.
3. Metallic Sheet:- Around the rubber there is a flexible metallic
sheath braided together. This metal sheath is connected to the
earth and constitutes and the earthed metal screen.
4. Plastic Sheath :- Metal sheath is further covered with plastic
sheath. It is designed to protect the flexible metal braiding from
damage..
50
High Tension Cables

 Process by which heat is dissipated
1. Conduction
2. Convection.&
3. Radiation
52
Methods Of Heat Dissipation In Modern X-ray
Tube

 The first step is heat removed from the target area, passing most
of the heat, by conduction into cu block of anode.
 The cu block conducts heat along its length and thus to out side
of the tube. The target also conveys a small part of its heat by
radiation across the x-ray tube to glass envelope.
 Through the anode and glass envelop the heat thus reaches the
oil and heat is conveyed to metal casing by convection process.
 It is then conducted through the casing to its outer surface,
which is dissipated in the room by radiation process.
Cont..
53

 Fenestration: In this anode is connected to a large metal of
considerable heat capacity . It is capable of absorbing many
calories & becomes hot itself & radiate heat to the surroundings.
USE: in fluoroscopy tube which is cooled by outside air.
 Water cooling:Used in therapy tubes where anode is cooled by oil
which is cooled by water.
 Oil cooling: Used in both therapy and diagnostic tubes.
54
Methods of Heat Dissipation
 Fan cooling: used for heat dissipation from anode by means of
fans used in low & medium therapy tubes.

 Limitations of stationary anode
tube were overcome by rotating
anode tube which were introduced
in 1936.
 Based on the principle of removal
of target from the selection beam
before it reaches too, high a
temperature by replacing it by
another cooler target I.e. the target
from the face of the rotating disc
or the end of rotating cylinder.
55
Rotating Anode X-rayTubes

 The anode disc is between 55mm and 100mm in diameter and 7
mm thick machined to high tolerance to prevent in balance and
wobble.
 Anode disc is made of Tungsten has its periphery beveled
at an angle 10⁰-20°.
 The disc has a tungsten rhenium target area as tungsten has a high
melting point 3370 ⁰C and atomic number of 74. The addition of a
small quantity (5-10%) of rhenium prevents crazing of the anode
surface, the tungsten is faced onto a molybdenum disc as
molybdenum whilst not having as high a melting point as tungsten
has twice the heat capacity
56
Main Features of Rotating Anode

 The target disc is mounted on a molybdenum stem attached to the
copper rotor.
 Rotor rotates with speed of 3000 RPM on ball bearings (made of
steel) with dry lubricant( silver or lead coating).
 The target is cooled by radiation to the glass then oil.
57
Cont..

Rotating anode x-ray tube: The lead shield cut open
58

 The anode disc needs to be rotate at high speed and this is
achieved by attaching the stem to a large copper rotor, which
forms the armature of a motor.
 The target disc, with rotor, is mounted on a shaft extending from a
rotor body, which can spin on internal bearings on the rotor shaft.
 This rotor shaft extends through the end of the insert to the outside
of the insert vacuum for connection to the anode wire, and also is
the mounting point for the insert inside the housing.
 The rotor bearing are special as they need to operate in a vacuum,
conduct a high voltage and reach high temperatures (500oC).
Using steel bearings lubricated by silver powder solves the
problem.
59
The Rotor and Bearing System

60
Component of the insert: the rotor

 The anode stator motor must
accelerate the anode to working
speed rapidly, to ready it for an
x-ray exposure and then must
bring it back to stop equally
rapidly to prevent wear and
wobble on slowing down.
 The “motor” consists of
electromagnet coils round the
glass to provide a rotating
magnetic field to be induced by
the currents and produce the
forces needed to rotate the
copper rotor
61
The Anode Stator Motor
Stator
coil
Xray Exit
port
Electric
supply

 Advantages
 It permits selection of higher electrical load (exposure
factor without risk of overheating)
 Applications
 Almost universal use in radiography
 Advances
 Reduced target angle
 New anode materials
 Increased speed of anode rotation
 Grid Controlled x-ray tube
 Metal / ceramic x-ray tube
62
cont..

 The information in details of the electrical loads which may be applied
to the X- Ray Tube without damaging it & the safe duration of such
loads.
 It is usually provided by the manufacturer
The amount of heat that can safely be used in any given tube is of course
determined by the physical characteristics of the tube itself.
These characteristic would include:
 Focal area
 Anode diameter
 Material of which anode is made
 Speed of anode rotation
 Target angle.
 Heat dissipations i.e volume of oil within the casing.
63
HEAT RATING:
indicates load limits that a tube can safely accept

 Ability of X-Ray tube to withstand a single exposure.
 Ability of X-Ray tube to function despite rapid exposure.
 Ability of X-ray tube to withstand multiple exposure during
several hours of heavy use.
Three types of x-ray tube rating charts are particularly important:
1.Radiographic rating charts
2.Thermal rating i.e. Anode cooling chart.
3.Angiogrphic rating chart
64
In considering the tube rating three characteristics are
encountered:

 Radiographic rating chart is most important because it states
which radiographic technical factor are safe & which are unsafe
for tube operation.
 Each chart contain a family of curves representing the various tube
voltage in KVp. The x axis & Y axis show scale of two
radiographic parameter- time & mA .For a given KVp any
combination of mA & time that lies below KVp curve is safe. Any
combination of mA & time that lies above the curve is unsafe.
 If unsafe exposure was made the tube might fail abruptly.
65
1. Radiographic rating chart

 Thermal rating i.e. Anode
cooling chart provides
information on how rapidly and
how many times a single
exposure can be repeated
without putting too much heat
into the x-ray tube.
67
2. Thermal rating Chart

 Heat units HU. It is an arbitrary unit that is used to plot heating
and cooling curve charts.
 For a single phase unit,
 HU = kVp x mA x s
 For a 3 phase 6 pulse unit,
 HU = 1.35 x kVp x mA x s
 For a 3 phase 12 pulse unit,
 For a high frequency unit,
68
Calculating Heat Units

 It tells us of the total no. of exposures which can
be made at various exposure rates per sec.
Fluoroscopic rating chart.
 During fluoroscopy the heat produced is
relatively small and is maintained over a
relatively long period of time.
 It is defined as the no. of HU /sec that can be
applied indefinitely with continuous running
69
3.Angiogrphic rating chart

70
.
Application Heat storage capacity Target
angle
Focal spot size
1.Nueroradiography 0.3 MH.U. 70 0.3mm
2.Angiography 0.4 - 1.35 MHU 12o 0.3,0.6,1.2mm
3. Mammography 0.3 MHU 100 0.6mm
4. General radiography 0.3 - 0.6 MHU 120 0.3,0.6,1.2mm
5. CT 3.5 - 7.6 MHU 120 0.6mm

 The intensity of the x ray beam as it leaves the x ray tube is not
uniform throughout all portions of the beam.
 The intensity of the beam depends on the angle at which the x
rays are emitted from the focal spot .
 The intensity of the film exposure on the anode side of the x ray
tube is less than that on the cathode side of the tube.
71
Heel effect

 The decreased
intensity of the x
ray beam that is
emitted more
nearly parallel to
the surface of the
angled target is
caused by the
absorption of some
of the x ray photons
by the target itself.
72
Cont:

 Intensity of x- rays on anode side of x-ray tube is significantly
less than that on cathode side. This factor is useful in obtaining
balanced densities in radiographs of body parts of different
thickness.
 Heel effect is less noticeable when longer focus film distances
are used.
 For equal FFD heel effect will be less for smaller films.
73
Three Clinically Important Aspects Of Heel
Effect:

74
Common faults in x-ray tube
Any type of problem that deteriorate or block the output of x-rays from the x-
ray unit is termed as common faults of x-ray unit……..
Faults related with the TARGET
Faults related with the GLASS ENVELOPE
Faults related with ROTOR STATOR ASSEMBLY
Faults related with CATHODE
Faults related with HOUSING SYSTEM

 Fault: melted spots on anode/crazy paving of anode/ erosion of
target track
 Cause :-due to over use specially (heat capacity exceeded).Incase
of the stationary anode x-ray tube
 Effect :- increased heel effect ,heterogeneous x-ray output.
 Remedy :-use of rhenium that increase the target life by providing
mechanical stability due to pitting/operate the tube in safe rating
zone.
75
Common faults related with target

 Fault:-no exposure/thermal shock
 Cause: heavy radiography
exposure made on a cold target
can cause (high mA on cold
anode)
 Effect: anode disc splits radically./
can cause cracks in anode (tube
death)/noisy rotation
 Remedy: do warm up exposure.
Or use of the stress relieved anodes.
As described
76
Cont:

 Eliminates thermal shock
from high mA exposures on
cold anode.
 Warm-up needed whenever
tube cold.
 Once in the morning not
sufficient if tube not used
for several hours.
77
Preventions

Indication :
 No exposure
Reason
 Due to evaporation of filament
 Due to continuous exposure the filament become thinner and
thinner an finally breaks.
Remedy
 Replacement of tube insert
 Filament boosting time should be kept as short as possible.
78
Faults In Filament

 Fault:-Formation of mirror due to heat, vaporized tungsten is
deposited as a thin layer on inside of glass envelope, producing
mirror like reflecting surface./ arcing of the glass.
 Causes – can be caused by filament evaporation
 deposition of filament on glass envelope as result of
• high filament currents
• long filament boost time
 Effect :-results off focus radiation. /electrons move from filament
to tube housing instead of to anode
• Remedy :-reduce by not holding first trigger longer than
needed/use of metal ceramic tube.
79
Faults in glass envelope

 Fault:-cracking of glass tube
 Causes – mishandling of x-ray unit specially in the case of mobile
x-ray tube
 Effect : increased leakage radiation dose.
 Remedy :-Use of metal ceramic tube .
Cont..
80

 electrons move from filament to tube housing instead of to anode
 very short exposure with instantaneously very high mA
 Generator often drops off line
81
High Voltage Arcs
+
arcing

 prevents proper rotation of
anode
• anode can run too slow
• anode can stop
 results in thermal damage to
anode (melted spots)
 Filament break
 renders one focal spot
completely inoperative
82
Tube Insert Damage

 May be accompanied
by air bubble in
housing.
 Eventually causes high
voltage arcing.
 Requires immediate
service attention.
83
Oil Leaks

How To Maximize X-ray Tube Life:
 Minimize filament boost time.
 Use lower tube current (mA).
 Follow Tube rating chart.
 Do not exceed anode thermal capacity or dissipation rate of the
target.
 Do not make high mA exposure on a cold target.
 Anode should not be run unnecessarily.

Tube Warm-up Procedures
 By warming the anode through a series of exposures and
increasing kvp settings, the anode will build up heat that is needed
to avoid fracture of the anode.
 This process takes a little over one minute put will add to the life
of the tube.
 Close shutters of collimator.

86
Advancement in rotating x-ray tube
Advancement in target angle
Advancement in target material
Advancement in target diameter
Advancement in speed of target

Advancement with target
Grid controlled x-ray tube
Metal ceramic x-ray tube
Stereoscopic x-ray tube
Other advancement

Main feature of rotating X-ray tube:
 The shape of the glass envelope has been modified to
accommodate the different types of the electrode and the rotating
assembly.
 Dry lubricants are used for rotation like silver , lead
 Rotation of anode is achieve by the process of electro-magnetic
induction in rotor and stator assembly.
 Cathode cup and filament are offset the target track near the
periphery of the beveled anode track( angled at 6*-20*)
 Disc is connected to anode stem made up of Mb.
87
Advancements in rotating x-ray tube

Reduction In target angle:-as
the cooling capacity is
increases so now a days we
can go on reduced target
angle to get sharp image with
small target by minimizes the
ordertoobtainsharpimageas
small focal spot decreases the
geometric unsharpness. Now
adayswehaveswitchingto6
degree from20degree..
88
Advancement in target of x-ray tube

89
Biangular Tubes
 The anode of a biangular
tube has two focal tracks
(Inner for fine focus) and
outer for broad focus with
cathode having two
filaments arranged one
above the other
 The surface of the anode
disc is beveled at two angles
 Thus fine focus used for
radiographic exam requiring
more details, where as large
for routine radiography.

Earlier it was tungsten alone .
 Rhenium 10% + tungsten 90% .(less roughening . Higher tube
life)
 (Rhenium + tungsten ) over molybdenum base . (less weight .
Inertia.)
 Rhenium + Tungsten (+titanium + Zirconium + molybdenum).
 (Rhenium + tungsten ) over molybdenum base . + graphite as
backing layer
 (Rhenium + tungsten) + CVD Graphite base.
Advantage
• Higher heat storage capacity permitting higher tube rating with
prolonged tube life
90
New Anode Materials

 Gallium liquid alloy used as liquid
within spiral grooves.
 Advantages
 Allow use of high mA and
shorter exposure time.
 Allow possible use of smaller
focal spot.
 Disadvantages
 Initial high cost of equipment
 Longer prepare time
 Greater wear and tear bearings
 Require breaking system
91
Spiral Grooves Bearing

 The method is applied to those anodes having slits and grooves.
Where the rear surface is blackened which results in reduction of
anode temp.
 A blackened anode disc increases the fluoroscopic output of a tube
due to the reduction of anode heating.
 At normal speed the anode rotates with the speed 3000 RPM
whereas at high speed 9000-10,000 RPM with 3- phase supply.
 At high speed quicker rate of heat dissipation will be there
allowing greater input load (higher rating capacity) but at short
exposure.
92
Blackening of anode disc
Increased Speed Of Anode Rotation

 A more recent development in X-ray tube construction is the metal-
ceramic tube, which is made from a steel (ferrochrome ) cylinder
brazed to alumina ceramic (aluminum oxide )insulators at each end.
These insulators carry the anode and cathode assemblies. The
metal-ceramic tubes are smaller and more robust than their glass
equivalents. They have another advantage, in that they enable more
flexibility in the electrical circuitry associated with the tube.
 Offers greater heat dissipation results less load to the x-ray tube.
 Metal envelope grounded offers no chance of arcing of x-ray tube.
 Anode rotates on a axle with bearing at each end providing greater
stability and reduced stress on shaft this permits use of massive
anode.
93
Metal-ceramic tubes are now being used in
X-ray equipment

 Offer greater heat dissipation results less load to the
x-ray tube .
• Metal envelope grounded offers no chance of arcing of x-ray
tube
94
Features of Metal ceramic X-ray tube

 Higher Tube Loading
 Allows higher tube currents to be used because of larger heat
storage capacity of anode
 Longer Tube Life
 Deposition of tungsten on the glass wall acts as electrode
causing arcing bet. Glass and filament shortening tube life.
When metal enclosure is grounded, this deposition will not
alter grounding thus increasing its life
 Reduced off Focus Radiation
 Electrons back scattered from the anode may strike anode
again producing x-rays from areas other than focal spot. The
metal enclosure decreases off focus radiation by attracting off
focus electrons to the grounded metal wall relatively Positive
as compared to electrons. Low atomic no. of metal may
produce few and low energy x-rays.
95
Advantages Of Metalceramic Tube

 A third electrode called grid is used.
 Focusing cup surrounding the filament cup is used as third
electrode to control the flow of electron.
 A negative bias voltage around 1500 V is applied to the cup
relative to the filament to punch off the flow of electron.
 Thus focusing cup acts as exposure switch to turn the current
ON or OFF when required.
 Application in capacitor discharged mobile radiographic
equipment , pulsed-fluoroscopy and cardio-angiography and
vascular angiography.
96
Grid Controlled X-ray Tube

 Depending Upon Applications
 Mammography tube
 CT X-ray tube
 X-ray tube for angiography
 Radiotherapy X-ray tube
 Stereographic X-ray tube
 Field emission X-ray Tube
97
Different Type Of X-ray Tubes

 Formaximum visualization
of soft tissues of the breast
having similar ability to
absorb x-rays a beam of
soft radiation (longer
wavelength ) is required
 Longer wavelength can be
produced by selecting x-
ray tube which operate at
low KVp (20-40)
98
Mammography X-ray Tube

 Use of target made of molybdenum.
 Closer spacing of cathode and anode.
 Beryllium window : is used as it has low atomic no.(4)
& lower absorption of x-rays.
 Use of molybdenum filter in place of aluminum filter.
 Focal spot size-0.3-0.35mm.
 Heat storage capacity- 0.3-0.5 M.H.U .
99
Features of a Mammography Tube

 Introduction of the dual metal x ray tubes (having dual track of
molybdenum/vanadium & rhodium).rhodium track & filter
produces a slightly higher x ray spectrum for superior penetration
of the dense breast tissue in the younger women and in those who
have undergone radiation treatment or on hormone therapy.
 Mo /tungsten dual track with a high emission flat emitter cathode
with different k-edge filters mo & rhodium meant for normal and
dense breast.
 But with an increase in x-ray tube voltage from 25 to 30Kv
simultaneously replacing Mo with a rhodium filter the x-ray
spectrum for a tungsten anode is clearly shifted and higher energy
especially advantageous for the radiography of large subject/dense
breasts.
100
Latest developments in Mammography Units

 These are oil cooled stationary anode tube.
 Tube for deep therapy have kvp in the range of 200-300 kv and
usually work at 15-20 mA .
 Single focus tubes size( 6-8 mm) with hooded anode & target
angle of about 35 degree.
 Hood is made up of Copper + Tungsten.
 To allow emission of required primary x-ray beam a hole is cut in
the hood below the target.
101
Radiotherapy X-ray Tube

103
Stereographic X-ray Tube
 Similar to conventional
rotating anode x-ray except:-
 Rotating anode is bombarded
simultaneously by two beams
of electrons from two
independent cathode
assemblies.
 Used for stereographic and
stereofluoro scopic x-ray
examination.
Anode target disk Two Filaments
With focusing cup
Anode target disk

FIELD EMISSION X-RAY TUBE
• It is also known as cold cathode tubes.
• Electrons are extracted from the cathode to anode by an intense electric
field rather than by thermionic emission.
Features
• A conical anode surrounded by a cylindrical cathode containing facing
rows of needle (actually more than two).
• The x-ray beam passes through a window in the end of the tube with less
intensity in the center of the field.
• Needle tip diameter about 1μ
• Since electrons which can be emitted are less in no. these tubes can be used
only for neonatal radiography.
• If higher voltage (up to 350 KV) is applied these tubes can be used for high
KV chest radiography. But not useful for general radiography purpose.
104

Field emission x-ray tube
Emission of electron takes place due to high potential difference

Transmission type x ray tube
•In these tubes the x-rays are
generate when electrons from the
filament strike a thin sheet of target
material.
•The electrons produced at two
filaments are focused with the help
of deflecting and focusing coils on a
thin target which may or may not be
a cathode.
•This unit was used in prototype for
high beam x-ray therapy machines.

 Since CT require longer continuous exposure time at higher KV
and mA than needed for general radiography.
 These have been charged with heavy duty rotating anode tube
with higher thermal capacity and smaller focal spot (up to 0.6mm).
These tubes are air cooled with current value up to 600mA.
 It Should supply monochromatic X-ray beam for accurate
reconstruction.
 Earlier model used were oil cooled ,Fixed anode relatively large
(2x16mm)focal spot operated at 120 kVp & 30 mA & heavily
filtered as those use in radiotherapy.
107
CT X-Ray Tube

 One of the more interesting developments is the Siemens Straton
x-ray tube, which is currently available as an option on Sensation
16 scanners (Fig ).
 The tube itself is a radical new design, where the entire tube body
rotates, rather than just the anode, as is the case with conventional
designs. This change allows all the bearings to be located outside
the evacuated tube, and enables the anode to be cooled more
efficiently.
 The Straton has a low inherent heat capacity of 0.8 MHU, but an
extremely fast cooling rate of 5 MHU / min.
108
Developments in CT Tubes

 This compares with typical figures of 7-8 MHU and up to 1.4
MHU / min for existing tubes.
 The heat capacity and cooling rate combine to produce a tube
which Siemens claim is ‘0 MHU', implying that tube cooling
considerations are a thing of the past. Sensation 16 scanners fitted
with the Straton tube now have a fastest scan time of 0.37 seconds.
Cont..
109

CHARACTE-
RISTIS
DIAGNO
STIC
TUBE
THERAPY TUBE MAMOGRA-
PHY TUBE
CT TUBE
1 Tube Glass tube Glass tube Glass tube Metal ceramic
tube
2Type of Anode Stationary
or
Rotating
type
Stationary type Rotating type Rotating type
3 Target Angle 6⁰-20° 25°- 35° 100 120
4 Focal spot
size
.3, 0.6,1.2
mm
6x6 mm 0.6 mm 0.6mm
5 Exposure time Shorter longer shorter longer
6 Heat Unit
capacity
0.3-0.6
MHU
0.1-0.3 MHU 0.3-0.6 MHU 1-2 MHU
7 Type of focal
spot
Dual
focus
Single focus Dual focus Dual focus
8 Pt. radiation
dose
less more less more
.
e

 Nano focus tubes
 X-ray diffraction tubes
 Miniature x-ray tubes
 ISOVOLT mobile
 Portable x-ray units
 Tire Inspection
 Thickness Gauzing
 Food Inspection
113
New Applications:

 In case of nanofocus tubes, the focal
spot is further minimized by means of
a special setup consisting of lenses
and diaphragms. The user may
choose from a range of operating
modes, each providing different tube
voltages and image resolutions. The
most potent operating mode offers
detail detectabilities down to 200
nm (0.2 µm).
 Inspection technology.
114
Nano Focus Tubes

 Radiography (X-ray) is a
Nondestructive Testing (NDT)
method that examines the volume
of a specimen. Radiography (X-
ray) uses X-rays and gamma-rays
to produce a radiograph of a
specimen, showing any changes in
thickness, defects (internal and
external), and assembly details to
ensure optimum quality in your
operation
115
Radiography (X-ray)

 MINIATURE X-RAY TUBES UTILIZING CARBON-
NANOTUBEBASED COLD CATHODES
 The electron field-emission properties of carbon nanotubes enable
the fabrication of cold cathodes for a variety of vacuum device
applications. The utilization of these cathodes is an attractive
alternative for the replacement of thermionic or hot cathodes for
generating X-rays. Miniature X-ray tubes uses triode-style carbon
nano tube based cathodes.
 Driving gate voltages below 1000 volts for easy pulsing has been
achieved, and the extended lifetime data suggests that a regulated
power supply would be ideal for a constant AC operation mode.
The 1mm focal spot size achieved so far is suitable for most
applications.
116
Miniature X-ray Tubes

 The ISOVOLT Mobil has been
designed for operations where
access to the inspection area is
difficult. It is ideal for use in the
energy, mineral and petro
chemical industries where
pipelines and container tanks
require X-ray inspection. The
ISOVOLT Mobil is equipped
with a small X-ray tube and
high voltage cable up to 20 m
(32 ft.) in length to allow
positioning in hard to reach
places not accessible by other
types of X-ray equipment.
117
ISOVOLT Mobile

 Today special X-ray
tubes are used to
inspect the tires of
trucks, cars, motor
bikes & heavy earth
movers.
 These tubes having
flat target angles from
0*-20* and conical
targets are available.
118
Tire Inspection

Thickness Gauzing: X-rays are used in rough industrial
online processes to measure the thickness of sheets & foils of
different sizes and materials. The transmission through
the material is precisely measured in the cold and hot milling
process.
 The X-ray tubes are designed for ultra stable emission output with
high reliability.
Food Inspection: various food articles( e.g. chocolate
jars with jams and baby food) are controlled with fan
beam x-ray tubes in digital inspection system.
 High x-ray output and small focal spots ensures that metal
parts ,o-rings or broken glass are sorted out before shipment.
119
Cont..

Portable x-ray unit:
Portable X-ray units are
designed to be reliable in
some of the world’s
toughest conditions.
Using modern compact
electronics to minimize
weight and provide a
high power output with
extremely low ripple,
and a sturdy metal
ceramic X-ray tube.

These are used for mobile inspection of heat-exchangers.
121
Special X-ray tubes

Analytical X-ray : Analytical X-ray is the industry
standard for X-ray diffraction techniques.
Standard systems are used for material
characterization in research & development
and for quality assurance in various industries.
A variety of machines are designed for special
applications.
X-ray Diffraction Tubes
 Waves interact with crystalline structures
whose repeat distance is about the same the
wavelength.
 X-rays scattered from a crystalline structure
constructively interferes and produces a
diffracted beam.
122

..
 These are special type of slim
X-ray tubes
 Used in Nuclear plants to
inspect weldings in narrow
pipe to pipe space.

 X-ray tube has experienced a rapid development from its
beginning till now. The basic principle of X-ray
production is same in all the x-ray tubes but some new
advancements like new anode material, high speed of
anode rotation, target angle, heat load and dissipation
capacity etc are the factors which improved the X-ray
tube .So we can say that
“An x-ray equipment without an x-ray tube is like a human
body without heart”
All these advancements have proven to obtain a quality
of image.
124

REFRENCES
 Physics for radiology by christensen.
 A practical approach to modern imaging equipment by
Thompson.
 X-ray equipment for student radiographer by Muriel o.
Chesney.
 http.//www. E radiography .com
 http.x ray tube wikipedia.com
 http. //www.mycopedia.com

126
THANKS
THANKS
THANKS
T H A N K S
T H A N K S
“Small experiments can leads you a big discovery”

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