X-ray tube, X-ray production and X-ray interaction with matters.pptx

Department of Radiodiagnosis.
This presentation describe about the core X-ray physics covering X-ray tube, X-ray production and X-ray interaction with matters.

1. X-ray tube X-ray production X-ray interaction with matter Presented by Dr. Pallavi Panjiyar Department of Radiodiagnosis

2. History Sir Wilhelm Conrad Roentgen , a German physicist, (1845-1923) Discovered x rays on November 8, 1895 when using a Crookes tube. He found that, sheet of barium platino-cyanide placed at distance was glowing even when tube was covered. He named this invisible rays, X-rays 9/21/2024 2

3. Atomic structure 9/21/2024 3

4. Properties of X ray Travel in straight line Electrically neutral Travel at speed of light Highly penetrating invisible rays Cannot be deflected by electric field or electromagnetic radiation Cannot be focused by lens Interact with matter producing photoelectric and Campton effect 9/21/2024 4

5. X-ray tube Protective housing Tube enclosure Cathode Anode 9/21/2024 5

6. Cathode 9/21/2024 6

7. 9/21/2024 7

8. Why is tungsten used in cathode ? Has very high melting point Low tendency to vaporize Good thermionic emitter Long life expectancy Flexible Cheap and readily available 9/21/2024 8

9. Space charge effect 9/21/2024 9

10. Anode Two types: Stationary Rotating 9/21/2024 10

11. Stationary anode:- Small plate of tungsten- 2.3 mm in thickness embedded on large mass of copper- better heat conductor Uses: Portable machines Dental 9/21/2024 11

12. Rotating anode:- Rotating anode disc Anode stem Induction motor - stator and rotor 9/21/2024 12

13. Anode discs Made of 90 % tungsten and 10% rhenium Why rhenium ?? Has higher thermal capacity More resistant to surface roughening Edge of target disc is beveled – 7 to 15 degree Anode disc: average speed of 3600 rpm 9/21/2024 13

14. Anode stem Molybdenum stem Small length as possible Reduce heat conduction from anode disc to rotor system 9/21/2024 14

15. Induction motor Works by electromagnetic induction 2 components : lubricated by metallic lubricant Stator coils –magnetic field produced by stator provides power to induce rotation Rotor coils Safety circuit- incorporated in x-ray circuit that prevents x-rays exposure from being made until rotor has reached it full speed 9/21/2024 15

16. Why is tungsten used in anode ? Has very high melting point Low tendency to vaporize Good conductor of heat and electricity 9/21/2024 16

17. Glass enclosure Vacuum - allow number and speed of accelerated electrons to be controlled independently. Metal - ceramic tube- Less off focus radiation Longer tube life with high tube current Higher tube loading – massive anode possible 9/21/2024 17

18. O ff-focus radiation  E mission of x-ray  photons  which originate outside of  anode focal spot N o use for diagnostic purposes Preventions – M etal housing M etal collimator 9/21/2024 18

19. Tube housing Coated with heavy metal like lead  s hields against leakage of x-rays Have window for x-rays to emerge Oil:- Cooling effect 9/21/2024 19

20. X-ray circuit Tube needs electrical energy for two purpose: To boil electron in filament- requires less voltage To accelerate electron from cathode to anode – needs high voltage in kilo volts. 9/21/2024 20

21. 9/21/2024 21

22. X-ray generator and rectifiers Main electrical supply to x-ray unit is standard AC current supply. But, x-ray production requires constant unidirectional high voltage supply Step up tr ansformer – convert low to high voltage Rectification – convert AC waveforms with positive and negatives to pulsed positive waveforms (unidirectional) Generators – provides constant high voltage 9/21/2024 22

23. Ripple – How much fluctuations present in current supply 9/21/2024 23

24. Contd.. Current passed through cathode ↓ cathode filament gets heated upto high temperature ↓ Violent atomic electric motion ↓ Emits electrons on surface by thermionic emission ↓ 9/21/2024 24

25. Contd.. Electrons accelerated towards target due to potential difference ↓ Gain kinetic energy ↓ On striking target looses kinetic energy ↓ Produces heat (99%) and x-rays (1%) 9/21/2024 25

26. Line focus principle To have better heat dissipation with better spatial resolution 9/21/2024 26

27. Line focus principle 9/21/2024 27

28. Anode heel effect 9/21/2024 28

29. Uses of Anode heel effect Abdomen and pelvis scan Foot x-ray Mammography Thoracic spine 9/21/2024 29

30. Factors affecting anode heel effect Anode angle - Large anode angle  decrease in distance of x-rays that need to traverse through target before emission- increase in intensity of x-rays beam on anode side  decrease in variation  lowers effect 9/21/2024 30

31. Contd.. Focus film distance - increase distance less variations lowers effect 9/21/2024 31

32. Contd.. Field size - x-ray beam collimated to smaller region  decrease in variation  lowers effect 9/21/2024 32

33. X-ray tube cooling A node heat is dissipated by infrared radiation to tube enclosure and thus to oil in housing unit Heat passes through oil by convection and is then conducted through the shield. H eat is then removed from shield by surrounding air by convection . 9/21/2024 33

34. Xray tube rating R adiographic rating charts X-ray tube rating is exposure settings that tube can withstand without causing damage For given anode disc rotation speed, exposure time, and kVp , milliamperage (mA) values falling under curve can be selected 9/21/2024 34

35. A node cooling charts Informs about time intervals to be observed between two exposures to allow adequate heat dissipation A mount of heat generated by any exposure is called heat unit (HU) M odern x-ray units have inbuilt devices that directly measure temperature of anode disc and oil in housing 9/21/2024 35

36. X-rays production 9/21/2024 36

37. Bremsstrahlung radiation U nder influence of electric field of target nucleus ↓ S trong electrostatic forces develop between projectile electron and target nucleus ↓ L oss of kinetic energy in form of x-rays H as continuous radiation spectrum 9/21/2024 37

38. Characteristics radiation E lectron fall from outer shell ↓ T o inner shell ↓ L oss of kinetic energy in form of x-rays H as single line spectrum with energy dependent on target material. 9/21/2024 38

39. 9/21/2024 39

40. X-ray spectrum 9/21/2024 40

41. Factors effecting x-ray spectrum L arger AUC, larger number of x-rays  increased quantity of x-rays. C urve moves to right, more x-ray energy  increased quality of x-rays X-ray intensity  number of photons × photon energy per unit area Intensity  combined measure of both quantity and quality of x-ray beam 9/21/2024 41

42. Factors effecting x-ray spectrum M illiamperage (mA) is unit for tube current  number of electrons flowing from cathode to anode per unit of time. Increase in mA  increase in contrast Kilovoltage peak ( kVp ) is peak potential applied to  x-ray tub e , which accelerates electrons from cathode to anode. Increase in kvp  increase in penetration 9/21/2024 42

43. 1. Effect of kvp on x-ray spectrum 9/21/2024 43

44. 2. Effect of mA on emission spectrum Increase in mA  increases x-ray beam amplitude I ncrease in mAs increases contrast on image. 9/21/2024 44

45. Contd.. 9/21/2024 45

46. 3.Effect of target material on emission spectrum Increasing atomic number of target material increases x-ray beam intensity M ammography tubes - molybdenum target 9/21/2024 46

47. 4. Effect of filtration on emission spectrum Inherent filtration- absorbs low- energy x-ray photons A dded filtration  aluminium discs 9/21/2024 47

48. 5. Effect of voltage rectification on emission spectrum 9/21/2024 48

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50. X-ray interaction with matter I ncrease in energy ↓ Decreases in i nteraction 9/21/2024 50

51. Contd.. Coherent/classical scattering Compton scattering Photoelectric effect Pair production photodisintegration 9/21/2024 51

52. Compton scattering 9/21/2024 52

53. Contd.. 9/21/2024 53

54. Contd.. Interaction of moderate energy x-rays With outer shell electron With loosely bound electron Increase in x-ray energy Increased penetration through tissue without interaction Reduced Compton scattering Increase in atomic number No effect in Compton scattering Increase in mass density Proportional increase in Compton scattering 9/21/2024 54

55. Photoelectric effect 9/21/2024 55

56. Contd.. 9/21/2024 56

57. Contd.. D irectly proportional to third power of atomic number Inversely proportional to third power of energy of x-rays 9/21/2024 57

58. Contd.. 9/21/2024 58

59. Contd.. Interaction of incident x-rays With inner shell electron With tightly bound electrons When x-ray energy is just higher than electron binding energy Increase in x-ray energy Increased penetration through tissue without interaction Less photoelectric effect Increase in atomic number of absorber D irectly proportional to third power of atomic number Increase in mass density of absorber Proportional increase in photoelectric absorption 9/21/2024 59

60. 9/21/2024 60

61. References Textbook of Radiology and Imaging, David Sutton, Edition 8 Textbook of Radiology sciences for technologist, Stewart Carlyle Bushong , Edition 11 th https://radiopaedia.org/articles/x-ray-tube-1 9/21/2024 61