1. X-ray tube

2. THE TUBE CONSISTS OF CATHODE AND ANODE ENCLOSED WITHIN THE GLASS ENVELOPE (PYREX GLASS) OR METAL ENVELOPE ENCASED IN A PROTECTIVE HOUSING (LEAD+ METAL SHIELDING)

6. TUBE OPERATION

7. THE CATHODE IS A COMPLEX DEVICE AND CAN BE REFFERED TO AS THE CATHODE ASSEMBLY. THIS ASSEMBLY CONSISTS OF THE FILAMENTS, FOCUSING CUP, AND ASSOCIATED WIRING.

8. THE FILAMENT IS A SMALL COIL OF THIN THORIATED TUNGSTEN WIRE
THE FILAMENT IS A SMALL COIL OF THIN THORIATED TUNGSTEN WIRE. 1%-2% OF THORIUM INCREASES EFFICIENCY OF THERMIONIC EMISSION. THE WIRE IS ABOUT mm THICK AND 7-15 mm LONG. TUNGSTEN IS A MATERIAL OF CHOICE BECAUSE OF ITS HIGH MELTING POINT-3410 C . RHENIUM ( 3170C) AND MOLYBDENUM (2,620 C) CAN ALSO BE USED.

9. MELTING POINT- 3,410 DEG. CELSIUS
TUNGSTEN
Z # 74
MELTING POINT- 3,410 DEG. CELSIUS

10. THORIUM
Z # 90

11. DUAL FILAMENT

12. FILAMENT

13. SCHEMATIC OF DUAL FILAMENT

14. SELECTION OF COLD FILAMENT TUBES

15. MOST DIAGNOSTIC TUBES HAVE DUAL FILAMENT

16. A TUNGSTEN FILAMENT WILL NOT EXHIBIT SIGNIFICANT THERMIONIC EMISSION BELOW 2,200 C

18. NOT ALL OF THE ELECTRONS THERMIONICALLY EMITTED FROM THE FILAMENT ARE ATTRACTED TO ANODE. SMALL % WILL EVAPORATE AND CAUSE THE TUBE ARCING. AS A RESULT OF THIS, THE TUBE BREAKS DOWN.

19. ANOTHER MAJOR CAUSE OF TUBE FAILURE IS THE BRAKING OF THE FILAMENT ITSELF. FILAMENTS BECOME INCREASINGLY THIN AS VAPORIZATION TAKES PLACE. WHEN ABOUT 10% OF THE DIAMETER HAS VAPORIZED, FILAMENT BECOMES SUBJECT TO BREAKING.

20. AN AVERAGE DIAGNOSTIC X-RAY TUBE LIFE IS ONLY ABOUT 6-9 HOURS (10,000-20,000 EXPOSURE) AT NORMAL FILAMENT HEATING LEVEL. ROUTINELY DELAYED EXPOSURES WHILE THE FILAMENT IS ENDURING MAX. CURRENT SHORTEN TUBE LIFE BY 50-60% ( DOWN TO 5,000-6,000 EXPOSURES)

21. THE FOCUSING CUP IS THE SHALLOW DEPRESSION IN THE CATHODE ASSEMBLY DESIGNED TO HOUSE THE FILAMENT

22. MOST X-RAY TUBES HAVE THE FOCUSING CUP AT THE SAME NEGATIVE POTENTIAL AS THE FILAMENT

23. IT IS ALSO POSSIBLE TO USE HIGHER NEGATIVE POTENTIAL ON THE CUP TO EVEN FURTHER DECREASE THE SIZE OF ELECTRON BEAM. THIS TYPE OF FOCUSING CUP IS CALLED BIASED

24. AS MORE AND MORE ELECTRONS BUILD UP IN THE AREA OF THE FILAMENT, THEIR NEGATIVE CHARGES BEGIN TO OPPOSE THE EMISSION OF ADDITIONAL ELECTRONS. THIS PHENOMENON IS CALLED THE SPACE CHARGE EFFECT AND LIMITS X-RAY TUBES TO MAXIMUM mA ranges of 1,000-1,200 mA

25. FOCUSING CUP

26. THE ANODE IS THE +++++ SIDE OF THE X-RAY TUBE

27. FUNCTIONS OF ANODE: TARGET FOR PROJECTILE ELECTRONS
CONDUCTOR OF HIGH VOLTAGE FROM THE CATHODE BACK TO X-RAY GENERATOR.
PRIMARY THERMAL CONDUCTOR

28. THE ENTIRE ANODE IS COMPLEX DEVICE AND IS REFFERED TO AS ANODE ASSEMBLY. IT CONSISTS OF: 1. ANODE 2. STATOR 3. ROTOR

29. ANODE ASSEMBLY

30. TWO TYPES OF ANODES
STATIONARY
ROTATING

31. ANODES:

32. ANODES:

33. ANODE +++++
TUNGSTEN
TARGET

35. ANODE ANGLES: 5 – 15°

36. ANODE ANGLES:

37. LINE FOCUS PRINCIPLE

38. TUNGSTEN IS THE MATERIAL OF CHOICE FOR THE TARGET OF GENERAL USE X-RAY TUBES. REASONS ARE:
HIGH ATOMIC NUMBER ( Z#) 74. HIGH Z# INCREASED EFFICIENCY OF X-RAY PRODUCTION.
HIGH MELTING POINT 3410 C
HIGH THERMAL CONDUCTIVITY

39. SPECIALTY X-RAY TUBES FOR MAMMO
SPECIALTY X-RAY TUBES FOR MAMMO. HAVE MOLYBDENUM & RHODIUM TARGETS BECAUSE OF THEIR LOW K-SHELL CHARACTERISTIC X-RAY ENERGY

40. DURING NORMAL USE FOCAL TRACK REACHES TEMP. BETWEEN 1,000-2000 C

41. BECAUSE OF TUNGSTEN HIGH MELTING POINT, IT CAN WITHSTAND NORMAL OPERATING TEMPS.RHENIUM PROVIDES MECHANICAL STRENGTH & THERMAL ELASTICITY IN ROTATING ANODES

42. INDUCTION MOTOR ROTATES THE ANODE

43. INDUCTION MOTOR
ROTOR
STATOR

45. ROTATION SPEED OF ANODES
REGULAR TUBES 3,000-4,000 RPM
HIGH PERFORMANCE 10,000-12,000 RPM

46. EFFECT OF THE FAILURE OF THE INDUCTION MOTOR

47. WHEN FIRST ACTIVATING AN X-RAY UNIT USE AN ANODE WARM UP PROCEDURE.

48. FAILURE TO FOLLOW THE WARM-UP PROCEDURE CAN CAUSE THE WHOLE ANODE TO CRACK.

49. MANY NEWER ANODES ARE STRESS RELIEVED
THEY DISSIPATE HEAT MORE EFFICIENTLY
THEY DO NOT REQUIRE ELABORATE WARM-UP PROCEDURE

50. PITTING OF THE ANODE FROM EXTENDED USE

51. X-RAY PRODUCTION PROCESS IS VERY INEFFICIENT IN THE DIAGNOSTIC RANGE
X-RAY PRODUCTION PROCESS IS VERY INEFFICIENT IN THE DIAGNOSTIC RANGE. >99% OF ELECTRONS KINETIC ENERGY IS CONVERTED TO HEAT & ONLY <1% RESULTS IN X-RAYS IN MEDIUM RANGE KVP.

52. ELECTRONS TRAVEL FROM CATHODE TO ANODE WITH APPROX
ELECTRONS TRAVEL FROM CATHODE TO ANODE WITH APPROX. ½ SPEED OF LIGHT IN MEDIUM RANGE KVP ( 70-80KVP)

53. X-RAY BEAM FILTRATION

54. X-RAY BEAM IS FILTERED TO INCREASE ITS QUALITY AND DECREASE THE PATIENT DOSE

55. FILTRATION TYPES
INHERENT
ADDED

56. INHERENT FILTERS ARE: TUBE WINDOW, OIL, HOUSING PORT. APPROX
INHERENT FILTERS ARE: TUBE WINDOW, OIL, HOUSING PORT. APPROX. 0.5 mm OF Al equiv.

57. ADDED FILTERS ARE: Al PLATE, COLLIMATOR MIRROR, PLASTIC COVER. APPROX
ADDED FILTERS ARE: Al PLATE, COLLIMATOR MIRROR, PLASTIC COVER. APPROX. 1-2 mm Al equiv.

58. INHERENT

59. ADDED

60. TOTAL FILTRATION= INHERENT + ADDED AT LEAST 2. 5 mm AL equiv
TOTAL FILTRATION= INHERENT + ADDED AT LEAST 2.5 mm AL equiv. FOR TUBES OPERATING ABOVE 70 kVp

61. RADIATION COMING THROUGH THE HOUSING. NO MORE THAN 100mR/ Hr AT 1m
LEAKAGE RADIATION
RADIATION COMING THROUGH THE HOUSING. NO MORE THAN 100mR/ Hr AT 1m

62. X-RAY TUBE AND COLLIMATOR

63. COLLIMATION
PBL
CONES
CYLINDERS
DIAPHRAGMS

64. CONE

65. CYLINDER

66. DIAPHRAGM