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xray tubes
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- 2. CONTENTS • Introduction • Types •Construction of each tubes • Features of each tube • Line focus principle & anode heel effect • Tube rating • Tube failure • Care of tube • Conclusion
- 3. INTRODUCTION • A tubeis air evacuated device. • In which the x-rays are produced. • Characteristics-: i) produce electrons ii) attract electron iii) physical protective casing iv) radiation protection • Purpose: provide x-rays from near source.
- 4. INTRODUCTION Requirement: • Ability tocontrol quality and quantity. • X-ray emission from desired port • movement Basic principle: • High voltage across anode and cathode • electrons emitted • accelerated toward anode • Interact and produce x-ray.
- 5. TYPES • According tothe cathode Two types • Cold cathode tube(Crookes tube) • Hot cathode tubes (all other types) • According to the anode Three types • Stationary anode x-ray tube • Rotating anode x-ray tube ( conventional radiography tubes, mammography tube, grid control x-ray tube) • Rotating envelope x-ray tube
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- 7. Crookes Tube • Crookestube • Historically , x-rays were discovered radiating from experimental discharge tubes, called Crookes tube. • Invented by William Crookes and others. • Commonly known as cold tubes. • Used till 1920.
- 8. Crookes Tube Consists : •Tube Envelope • Anode • Cathode • Anti Cathode
- 9. Tube Envelope • Consistsof a partially evacuated glass bulb . • Material – sodium or cerium • Air pressure of 10-6 to 5x10-8 . Anode • Material- Platinum • (At no-78, mp-1768o c) Cathode • Material- Aluminium (At no -13, mp- 660o c) Anti cathode • Material - Copper plate CROOKES TUBE
- 10. Operation • Field emissionor cold emission. • DC voltage (100kv) across cathode and anode. • Gas atoms ionized , created positive ion. • Positive ion attracted to cathode and create more electron. • High speed electron strike anode. CROOKES TUBE
- 11. Disadvantage • Unreliable • Airabsorbed by wall, reduces pressure. • Overheating due to heavy use. • Intensity and energy of x-ray cannot be controlled independently. CROOKES TUBE
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- 13. COOLIDGE TUBE • Crookestubes improved by William Coolidge in 1913. • Called Coolidge tube or hot cathode tube. • Characteristic features- i) high vacuum ii) heated filament Iii) thermionic emission
- 14. COOLIDGE TUBE Construction • Tubeenvelope • Anode assembly • Cathode assembly
- 15. COOLIDGE TUBE Tube Envelope •Spherical tempered glass tube with two cylindrical arms- cathode and anode arm. • Made of borosilicate ( Pyrex) • Internal pressure 10-8 mmHg • Hold both electrodes
- 16. Anode assembly Consists Target • Material–tungsten embedded in copper. • Thickness- 2-3 mm, Size – 1.8 to 2.2 mm • Shape – Circular, square or rectangular • Anode angle – 6-20o • Typical angle – 16.5o • High atomic no. – W- 74 • High melting point – W- 3370o c • Evaporating point - 5600o c COOLIDGE TUBE
- 17. Cathode assembly • Focusingcup • Filament COOLIDGE TUBE
- 18. Focusing cup • Madeof molybdenum • Nickel coated (anticorrosive layer) • Streamline the thermionic cloud. Filament • Made of tungsten • High melting point-3370o c • High evaporation point- 5600o c • Highly ductile and malleable COOLIDGE TUBE
- 19. COOLIDGE TUBE Operation • Cathodefilament heated, emits electron. • Emitted electron accelerated towards positively charged anode. • X-ray produced- bremsstrahlung and characteristic .
- 20. COOLIDGE TUBE Advantages • Stability. •Intensity and energy of x-ray can be controlled independently.
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- 22. ROTATING ANODE X-RAYTUBE • The rotating anode tube is an improvement of the Coolidge tube. Characteristic feature- i) anode rotates ii) tungsten – rhenium alloy
- 23. ROTATING ANODE X-RAYTUBE Construction • Glass envelope • Anode assembly • Cathode assembly
- 24. ROTATING ANODE X-RAYTUBE Glass envelop • Borosilicate glass • Supports electrodes • Shape - cylindrical • Size - 30 – 50 cm length 20 cm broad • Thinner window – size 5x5 cm thickness 0.2mm • Highly evacuated • Internal pressure- 10-8 mmHg • Ceramic metal (adv prevent off focus radiation)
- 25. ROTATING ANODE X-RAYTUBE Anode assembly Target track • Material- 90% tungsten and 10% rhenium(high thermal capacity, less roughening) Anode disk Base – molybdenum ( advanced graphite alloy, light wt and heat dissipation) Anode angle- 7-17o ,typical angle – 12o Rpm- 9000 Shape – beveled
- 26. • Anode stem material– molybdenum thin and long restrict conduction of heat • Rotor material – copper and iron high thermal capacity and conductivity rotation of anode 9000 rpm Anode stem ROTATING ANODE X-RAY TUBE
- 27. • Bearing • Madeof metal balls • Lubrication – silver powder • ( adv – liquid gallium lubricated fluid dynamic bearing) • Stator induction Motor • Material – electromagnet • Supplied by AC power ROTATING ANODE X-RAY TUBE
- 28. • Cathode AssemblyCathodeAssembly • Focusing cupFocusing cup • Same as in Coolidge's tube.Same as in Coolidge's tube. • Effectiveness of focusingEffectiveness of focusing cup depends uponcup depends upon • Shape , size , applied chargeShape , size , applied charge and length of filamentand length of filament ROTATING ANODE X-RAY TUBE
- 29. • FilamentFilament • DualfilamentDual filament • The size varies from 2.2mm toThe size varies from 2.2mm to 7mm in length in small filament7mm in length in small filament • The size varies from 7mm toThe size varies from 7mm to 15mm in length in large15mm in length in large filamentfilament • 99 % tungsten and 1% thorium99 % tungsten and 1% thorium • (prevent breakage, prevent(prevent breakage, prevent evaporation)evaporation) ROTATING ANODE X-RAY TUBE
- 30. ROTATING ANODE XRAYTUBE ADVANTAGES • Provide greater area for bombardment • Better heat dissipation than stationary anode tube
- 31. MAMOGRAPHY X-RAY TUBE •X-ray tube dedicated for mammography. • Characteristic features I) Low kv Ii) Characteristic radiation Iii) High spatial resolution
- 32. MAMOGRAPHY X-RAY TUBE •CONSTRUCTION • GLASS ENVELOPE • ANODE ASSEMBLY • CATHODE ASSEMBLY
- 33. Glass envelope • Borosilicateglass/ ceramic metal • Window- berrylium (z=4, mp=1287o c) Anode • Material- molybdenum – (z=42, mp=2623o c) rhodium - (z=45) • Anode angle (0 or 16)/ tube tilt(24 or 06) MAMOGRAPHY X-RAY TUBE
- 34. MAMOGRAPHY X-RAY TUBE •Cathode assembly consists Focusing Cup - Mo Filament • W for MO track • Rh for Rh track (Added filter – Mo)
- 35. GRID CONTROLLED XRAY TUBES •Used in fluoroscopy units • Purpose- reduced pt dose • Interval between exposure. • Focusing cup functions as a switch. • Focusing cup act as a third electrode. • Highly negatively charged -1.5 kV
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- 37. ROTATING ENVELOPE TUBE •Most advanced technology till date. • Idea of rotating envelope – 1917 Characteristic features • Electron beam is shaped and controlled by magnetic field. • Cooling surface of anode in direct contact with cooling fluid • And a rotating envelope
- 38. ROTATING ENVELOPE TUBE Itconsists of four system • Tube envelope system • Electron emission system • Magnetic deflection system • Cooling system
- 39. ROTATING ENVELOPE TUBE •Tube envelope system i. Material – non magnetic stainless steel ii. Directly Attached to anode disk iii. Annular/Circular Window (Thickness – 0.2 mm) iv. Max rotational speed – 150Hz
- 40. ROTATING ENVELOPE TUBE •Anode assembly • Consists Target track- 90% tungsten & 10% Rhenium Anode Disk – Tungsten , Zirconium, molybdenum body(TZM Alloy) BP- 4612, MP- 2600
- 41. ROTATING ENVELOPE TUBE •Electron emission system Cathode Assembly Consists Focusing cup Flat Emitter Shape of emitter – circular Material – tungsten Thickness -100µm Diameter - 5µm Meander like path – for filament heating .
- 42. RET • Magnetic deflectionsystem Three coils R- coils - Deflect the beam radial direction onto focal spot. (flying focal spot in z- direction,) Q-coils – focus the beam to determine the size Phi- coils – deflection of flying focal spot in tangential direction
- 44. ROTATING ENVELOPE TUBE •Microcontroller controls individual coil currents (real time ) Electronically adjusted focal spot Best image quality.
- 45. ROTATING ENVELOPE TUBE •Cooling system (convective) Anode disk comes in direct contact with cooling oil. Oil rotation is turbine flow Flow of oil - during exposure is 25ltr/min - during pump running 8 ltr/min Oil – Mineral oil
- 46. • Advantages • Betterheat dissipation. • Various size multiple focal spot • Longer tube life. • can be used in high kV and High mA technique for prolonged duration ( ie. High mAs) ROTATING ENVELOPE TUBE
- 47. Line focus principle •Introduced in 1918 • Relation between anode angle and focal spot • Three principles i) Incr anode angle – incr effective focal spot size ( decr intensity of x-ray beam, poor image quality) ii) decr anode angle – decr effective focal spot size (incr intensity of x-ray beam, better image quality) iii)without change in anode angle increasing the bombarding area incr actual focal spot ,effective and provide better heat dissipation.
- 48. Anode heel effect •Varying intensity of x-ray at anode side is lesser than cathode side. • Beveled anode absorbs some x-ray photon
- 49. TUBE RATING CHART •Capacity of focal spot supplied by manufacture. • Shows maximum power delivered for a given exposure time without over loading.
- 50. Tube failure • Anodepitting. • Rapid heat increase at anode. • Filament vaporization.
- 51. CARE OF X-RAYTUBE • Warm up the anode following manufactures recommendation • Minimize filament boost (prep) time. • Use lower tube current (mA). • Follow rating chart. • Do not exceed anode thermal capacity or heat dissipation rate of the target. • Do not make high mA exposure on cold target. • Do not rotate the tube housing rapidly from one position to another
- 52. Conclusion Mastery is notabout perfection, but a process ,a journey. • So lets be sure there is going to be more advanced technology and there will be x-ray tubes with better heat dissipation and lesser patient dose.