The X-Ray TubeThe X-Ray Tube
 X-ray tube is a component of x-rayX-ray tube is a component of x-ray
imaging system, it is contained in aimaging system,...
The eternal structure ofThe eternal structure of
xray tube consists of 3xray tube consists of 3
parts.parts.
 The support...
 The xray tube and housing assemblyThe xray tube and housing assembly
are quite heavy therefore they requireare quite hea...
Three main methods ofThree main methods of
xray tube suppotxray tube suppot
 Ceiling support systemCeiling support system...
X-RAY TUBEX-RAY TUBE
 MADE OF THIN PYREX GLASS ORMADE OF THIN PYREX GLASS OR
METAL ENCLOSURE TOMETAL ENCLOSURE TO
WITHSTA...
THE X-RAYTHE X-RAY TUBETUBE
 The X-Ray tubeThe X-Ray tube
is theis the singlesingle
mostmost importantimportant
component...
Protective housingProtective housing
Made of lead & steelMade of lead & steel
 When x-rays are produced, they areWhen x-r...
 Protective housing reduces theProtective housing reduces the
intensity of leakage radiation to lessintensity of leakage ...
Protective housingProtective housing
 X-rays that escape through theX-rays that escape through the
protective housing are...
Protective housingProtective housing
 Some tubes contain oil that serves asSome tubes contain oil that serves as
an insul...
Internal componentsInternal components
CathodeCathode
 The negative side of the tube and hasThe negative side of the tube...
CathodeCathode
 FilamentFilament
– Dual-filamentDual-filament
 Focusing cupFocusing cup
– Negatively chargedNegatively c...
TungstenTungsten
 Filaments are usually made ofFilaments are usually made of
tungstentungsten
 Tungsten providesTungsten...
FilamentFilament
 When current (mA) is applied to theWhen current (mA) is applied to the
coil of wire electron are ejecte...
Focusing cupFocusing cup
 The filament is embedded in a metalThe filament is embedded in a metal
cup that has a negative ...
Filament CurrentFilament Current
 When the x-ray imaging system is firstWhen the x-ray imaging system is first
turned on,...
Space-charge effectSpace-charge effect
 The cloud of e- = space chargeThe cloud of e- = space charge
 As the space charg...
Dual-focus tubesDual-focus tubes
 Most diagnostic tubes have two focalMost diagnostic tubes have two focal
spots; large &...
Dual-focus tubesDual-focus tubes
AnodeAnode
 Anode is the positive side of the x-rayAnode is the positive side of the x-ray
tubetube
 The anode conducts ...
Stationary AnodeStationary Anode
 Used for dental x-rays, some portableUsed for dental x-rays, some portable
imagingimagi...
Anode FunctionAnode Function
 An electrical conductorAn electrical conductor – the anode– the anode
receives electrons em...
Anode FunctionAnode Function
 Mechanical support for the targetMechanical support for the target
 Dissipates heatDissipa...
A layered anodeA layered anode
increases heat capacityincreases heat capacity
TargetTarget
 Is the area of the anode struck by theIs the area of the anode struck by the
e-from the cathodee-from the c...
Rotating AnodeRotating Anode
 Is powered by an induction motorIs powered by an induction motor
 The stator is on the out...
ElectromagneticElectromagnetic
inductioninduction
 As current is applied to the statorAs current is applied to the stator...
Focal spotFocal spot
 The area of the anode’s target whereThe area of the anode’s target where
x-rays are emittedx-rays a...
Focal spotFocal spot
 Unfortunately, as the size of the focalUnfortunately, as the size of the focal
spot decreases, the ...
Line-focus principleLine-focus principle
 By angling the target, the effectiveBy angling the target, the effective
area o...
Line-focus principleLine-focus principle
 EffectiveEffective
FocalFocal
SpotSpot
Target angleTarget angle
 The smaller the target angle theThe smaller the target angle the
smaller the effective focal sp...
Biangular targetsBiangular targets
The second factor of effectiveThe second factor of effective
focal spot is the incoming sizefocal spot is the incoming siz...
Focal spot size of the cathodeFocal spot size of the cathode
Anode Heel EffectAnode Heel Effect
 Because of the use of line-focusBecause of the use of line-focus
principle the conseq...
Heel EffectHeel Effect
 Because the e- on the anode sideBecause the e- on the anode side
must travel further than the e- ...
Anode Heel AffectAnode Heel Affect
 The smallerThe smaller
the anodethe anode
angle, theangle, the
larger thelarger the
h...
Extrafocal RadiationExtrafocal Radiation
 X-ray tubes are designed so that theX-ray tubes are designed so that the
projec...
Extrafocal RadiationExtrafocal Radiation
 These rays can also be called off-These rays can also be called off-
focus radi...
Off-focus radiationOff-focus radiation
Fixed diaphragm in theFixed diaphragm in the
tube housingtube housing
 Another solution is the metalAnother solution is the metal
enclosure x ray tube so that reflectedenclosure x ray tube so...
ThanksThanks
The x ray tube
The x ray tube
The x ray tube
The x ray tube
The x ray tube
The x ray tube
The x ray tube
The x ray tube
The x ray tube
The x ray tube
The x ray tube
The x ray tube
The x ray tube
Upcoming SlideShare
Loading in …5
×

The x ray tube

8,871 views

Published on

The x ray tube

  1. 1. The X-Ray TubeThe X-Ray Tube
  2. 2.  X-ray tube is a component of x-rayX-ray tube is a component of x-ray imaging system, it is contained in aimaging system, it is contained in a protective housing and therefore isprotective housing and therefore is inaccessibleinaccessible..
  3. 3. The eternal structure ofThe eternal structure of xray tube consists of 3xray tube consists of 3 parts.parts.  The support structureThe support structure  The protective housingThe protective housing  Glass or metal enclosureGlass or metal enclosure
  4. 4.  The xray tube and housing assemblyThe xray tube and housing assembly are quite heavy therefore they requireare quite heavy therefore they require a support mechanism so thea support mechanism so the radiologist technologist can positionradiologist technologist can position them.them.
  5. 5. Three main methods ofThree main methods of xray tube suppotxray tube suppot  Ceiling support systemCeiling support system  Floor to ceiling support systemFloor to ceiling support system  C-arm support systemC-arm support system
  6. 6. X-RAY TUBEX-RAY TUBE  MADE OF THIN PYREX GLASS ORMADE OF THIN PYREX GLASS OR METAL ENCLOSURE TOMETAL ENCLOSURE TO WITHSTAND HIGH HEAT LOAD ANDWITHSTAND HIGH HEAT LOAD AND MINIMIZE X-RAY ABSORPTONMINIMIZE X-RAY ABSORPTON  IS GAS EVAUCUATEDIS GAS EVAUCUATED  so electrons won’t collide with the airso electrons won’t collide with the air molecules in the tubemolecules in the tube
  7. 7. THE X-RAYTHE X-RAY TUBETUBE  The X-Ray tubeThe X-Ray tube is theis the singlesingle mostmost importantimportant component ofcomponent of the radiographicthe radiographic system. It is thesystem. It is the part thatpart that produces the X-produces the X- raysrays
  8. 8. Protective housingProtective housing Made of lead & steelMade of lead & steel  When x-rays are produced, they areWhen x-rays are produced, they are emittedemitted isotropicallyisotropically – Equal intensity in all directions  We only use x-rays emitted through the window or port – Called the useful or primary beam
  9. 9.  Protective housing reduces theProtective housing reduces the intensity of leakage radiation to lessintensity of leakage radiation to less than 100mR/hr at 1m.than 100mR/hr at 1m.
  10. 10. Protective housingProtective housing  X-rays that escape through theX-rays that escape through the protective housing areprotective housing are leakageleakage radiationradiation  Provides mechanical support for theProvides mechanical support for the tube and protects from rough handlingtube and protects from rough handling
  11. 11. Protective housingProtective housing  Some tubes contain oil that serves asSome tubes contain oil that serves as an insulator against electric shock andan insulator against electric shock and as a thermal cushionas a thermal cushion – Dissipate heatDissipate heat  Some protective housing has coolingSome protective housing has cooling fan to air-cool the tube and oilfan to air-cool the tube and oil
  12. 12. Internal componentsInternal components CathodeCathode  The negative side of the tube and hasThe negative side of the tube and has two primary partstwo primary parts – A filament and focusing cupA filament and focusing cup  Filament = a coil of wire about 2mm inFilament = a coil of wire about 2mm in diameter and 1 or 2 cm long.diameter and 1 or 2 cm long.
  13. 13. CathodeCathode  FilamentFilament – Dual-filamentDual-filament  Focusing cupFocusing cup – Negatively chargedNegatively charged
  14. 14. TungstenTungsten  Filaments are usually made ofFilaments are usually made of tungstentungsten  Tungsten providesTungsten provides higher thermionichigher thermionic emission than other metalsemission than other metals  Tungsten has a very high melting pointTungsten has a very high melting point
  15. 15. FilamentFilament  When current (mA) is applied to theWhen current (mA) is applied to the coil of wire electron are ejectedcoil of wire electron are ejected  The outer-shell electrons of theThe outer-shell electrons of the filament atom are “boiled off”.filament atom are “boiled off”. – This is known as thermionicThis is known as thermionic emissionemission
  16. 16. Focusing cupFocusing cup  The filament is embedded in a metalThe filament is embedded in a metal cup that has a negative chargecup that has a negative charge  Boiled off e- tend to spread out due toBoiled off e- tend to spread out due to electrostatic repulsion. The focusingelectrostatic repulsion. The focusing cup confines the e- cloud to a smallcup confines the e- cloud to a small areaarea
  17. 17. Filament CurrentFilament Current  When the x-ray imaging system is firstWhen the x-ray imaging system is first turned on, a low current passesturned on, a low current passes through the filament to warm it andthrough the filament to warm it and prepare it for the thermal joltprepare it for the thermal jolt necessary for x-ray productionnecessary for x-ray production  The current is not enough to energizeThe current is not enough to energize the tube, just warm the wire of thethe tube, just warm the wire of the filamentfilament
  18. 18. Space-charge effectSpace-charge effect  The cloud of e- = space chargeThe cloud of e- = space charge  As the space charge becomes moreAs the space charge becomes more negative by the boiling off of morenegative by the boiling off of more electrons it makes it difficult for moreelectrons it makes it difficult for more e- to be emittede- to be emitted – Electrostatic repulsionElectrostatic repulsion – Space-charge effectSpace-charge effect – Space-charge limiting at low kVp & high mASpace-charge limiting at low kVp & high mA
  19. 19. Dual-focus tubesDual-focus tubes  Most diagnostic tubes have two focalMost diagnostic tubes have two focal spots; large & smallspots; large & small  Large is used when large body partsLarge is used when large body parts are imagedare imaged  Small is used when better spatialSmall is used when better spatial resolution is desired – better detailresolution is desired – better detail  Filament sizeFilament size
  20. 20. Dual-focus tubesDual-focus tubes
  21. 21. AnodeAnode  Anode is the positive side of the x-rayAnode is the positive side of the x-ray tubetube  The anode conducts electricity,The anode conducts electricity, radiates heat and contains the targetradiates heat and contains the target  Two types of anodesTwo types of anodes – Stationary & RotatingStationary & Rotating
  22. 22. Stationary AnodeStationary Anode  Used for dental x-rays, some portableUsed for dental x-rays, some portable imagingimaging  Used when high tube current andUsed when high tube current and power are not required because theypower are not required because they are not capable of producing high-are not capable of producing high- intensity x-ray beams in a short timeintensity x-ray beams in a short time
  23. 23. Anode FunctionAnode Function  An electrical conductorAn electrical conductor – the anode– the anode receives electrons emitted by thereceives electrons emitted by the cathode and conducts them throughcathode and conducts them through the tube to the connecting cables andthe tube to the connecting cables and back to the high-voltage generator.back to the high-voltage generator.
  24. 24. Anode FunctionAnode Function  Mechanical support for the targetMechanical support for the target  Dissipates heatDissipates heat – 99% of the kinetic energy from the e- is99% of the kinetic energy from the e- is converted into heat; 1% is converted intoconverted into heat; 1% is converted into x-raysx-rays – Copper, molybdenum and graphite areCopper, molybdenum and graphite are common anode materialcommon anode material
  25. 25. A layered anodeA layered anode increases heat capacityincreases heat capacity
  26. 26. TargetTarget  Is the area of the anode struck by theIs the area of the anode struck by the e-from the cathodee-from the cathode  Tungsten is the material of choice forTungsten is the material of choice for the target in general radiographythe target in general radiography
  27. 27. Rotating AnodeRotating Anode  Is powered by an induction motorIs powered by an induction motor  The stator is on the outside of theThe stator is on the outside of the glass, consist of a series ofglass, consist of a series of electromagnetselectromagnets  The rotor is a shaft made of bars ofThe rotor is a shaft made of bars of copper and soft iron built into onecopper and soft iron built into one massmass
  28. 28. ElectromagneticElectromagnetic inductioninduction  As current is applied to the statorAs current is applied to the stator sequentially so the magnetic fieldsequentially so the magnetic field rotates on the axis of the statorrotates on the axis of the stator  This magnetic field interacts with theThis magnetic field interacts with the metal (ferromagnetic rotor) causing itmetal (ferromagnetic rotor) causing it to rotate in unison with the magneticto rotate in unison with the magnetic field of the statorfield of the stator
  29. 29. Focal spotFocal spot  The area of the anode’s target whereThe area of the anode’s target where x-rays are emittedx-rays are emitted  The smaller the focal spot the betterThe smaller the focal spot the better the resolution of the resultant imagethe resolution of the resultant image
  30. 30. Focal spotFocal spot  Unfortunately, as the size of the focalUnfortunately, as the size of the focal spot decreases, the heat of the targetspot decreases, the heat of the target is concentrated into a smaller areais concentrated into a smaller area  This is the limiting factor to focal spotThis is the limiting factor to focal spot sizesize
  31. 31. Line-focus principleLine-focus principle  By angling the target, the effectiveBy angling the target, the effective area of the target is much smaller thanarea of the target is much smaller than the actual area of electron interactionthe actual area of electron interaction
  32. 32. Line-focus principleLine-focus principle  EffectiveEffective FocalFocal SpotSpot
  33. 33. Target angleTarget angle  The smaller the target angle theThe smaller the target angle the smaller the effective focal spotsmaller the effective focal spot  Angles from 5 degrees to 15 degreesAngles from 5 degrees to 15 degrees  Biangular targets are available thatBiangular targets are available that produce two focal spot sizesproduce two focal spot sizes
  34. 34. Biangular targetsBiangular targets
  35. 35. The second factor of effectiveThe second factor of effective focal spot is the incoming sizefocal spot is the incoming size of e- streamof e- stream
  36. 36. Focal spot size of the cathodeFocal spot size of the cathode
  37. 37. Anode Heel EffectAnode Heel Effect  Because of the use of line-focusBecause of the use of line-focus principle the consequence is that theprinciple the consequence is that the radiation intensity on the cathode sideradiation intensity on the cathode side of the x-ray field is higher than that onof the x-ray field is higher than that on the anode sidethe anode side
  38. 38. Heel EffectHeel Effect  Because the e- on the anode sideBecause the e- on the anode side must travel further than the e- that aremust travel further than the e- that are close to the cathode side of the target,close to the cathode side of the target, the anode side x-rays have slightlythe anode side x-rays have slightly lower energy than the cathode side x-lower energy than the cathode side x- raysrays
  39. 39. Anode Heel AffectAnode Heel Affect  The smallerThe smaller the anodethe anode angle, theangle, the larger thelarger the heel affectheel affect
  40. 40. Extrafocal RadiationExtrafocal Radiation  X-ray tubes are designed so that theX-ray tubes are designed so that the projectile e- interacts with the target.projectile e- interacts with the target. However, some of the e- bounce offHowever, some of the e- bounce off the target and land on other areasthe target and land on other areas  This caused x-rays to be produced outThis caused x-rays to be produced out side the focal spotside the focal spot
  41. 41. Extrafocal RadiationExtrafocal Radiation  These rays can also be called off-These rays can also be called off- focus radiationfocus radiation  Extrafocal radiation is undesirableExtrafocal radiation is undesirable because it extends the size of thebecause it extends the size of the focal spot, increases patient skin dosefocal spot, increases patient skin dose & reduces image contrast& reduces image contrast
  42. 42. Off-focus radiationOff-focus radiation
  43. 43. Fixed diaphragm in theFixed diaphragm in the tube housingtube housing
  44. 44.  Another solution is the metalAnother solution is the metal enclosure x ray tube so that reflectedenclosure x ray tube so that reflected electrons are extracted and conductedelectrons are extracted and conducted awayaway
  45. 45. ThanksThanks

×