Diagnostic X-ray Imaging: Physics and Technology

1. Diagnostic X-ray Imaging: Physics and Technology Dr. Nabil Maalej

2. Outline • X-ray Production • X-ray Interaction with Matter • X-ray Damage to Tissue • X-ray Image Detectors • Major Advances in X-ray Imaging

3. Discovery of X-rays In December 1895, German physicist Wilhelm Roentgen discovered these mysterious rays X-rays, with X standing for unknown. In recognition of his discovery, Roentgen in 1901 became the first Nobel laureate in physics.

4. What are X-rays? • They are an electromagnetic radiation emitted by charged particles interactions • Photons which can penetrate through matter • They have no mass or charge • They travel at the speed of light • Energy = h = hc/

5. EM Spectrum

6. X-ray Production

7. Electron Striking High Z material 99 % or more of electron Energy goes into heat Electron 1 % or less of electron Energy goes into X-rays High Z Material X-ray Photon

8. Bremsstrahlung X-rays

9. Bremsstrahlung Spectrum

10. Characteristic X-rays Ejected Electron Electron Rebounding Electron Characteristic X-ray

11. X-ray Spectrum

12. X- ray spectrum

13. Outline • X-ray Production • X-ray Interaction with Matter • Photoelectric • Compton Scattering • Pair Production • Rayleigh scattering • X-ray Damage to Tissue • X-ray Image Detectors • Major Advances in X-ray Imaging

14. Photoelectric Interaction T h hν = T + BEelectron

15. Compton Scattering T h h’ hν = T + BEelectron + hν’

16. Pair Production h1 T+ h2 h T- hν = 2m0c2 + T++T

17. Rayleigh (Coherent) Scattering h h

18. X- ray Interactions

19. Importance of Different Interactions

20. Total Interaction Cross Section • Three relevant interaction processes with individual atomic cross-sections : Photoelectric absorption (a) Compton scattering (a) Pair production (a) • Total atomic cross section: aT = a + a + a

21. Linear Attenuation Coefficient • The linear attenuation coefficient  [/cm] is the probability of interaction per unit length •  = mass density [g/cm 3 ] • NA = 6.02....1023 [1/mol] (Avogadro’s number) • A = Atomic Weight [g/mol] • aT = Total atomic cross section [cm2]

22. Attenuation of X-ray Intensity (Narrow Beam Geometry) • I is the radiation intensity after traversing a thickness x • Io is the original radiation intensity • µ is the linear attenuation coefficient (cm-1) • x is the thickness of attenuating material (cm) I = Io e (- µ x) Io x

23. Attenuation Coefficients

24. Outline • X-ray Production • X-ray Interaction with Matter • X-ray Damage to Tissue • X-ray Image Detectors • Major Advances in X-ray Imaging

25. Damage to DNA

26. Damage to DNA • Direct damage to DNA molecule • Indirect damage to DNA by Ionisation of water and the release of free radicals: H20  H20+ + e- H20+ H+ + OH (free radical) OH + OH  H2O2 (Hydrogen peroxide) Release of H2O2 DNA damage

27. Biological Effects

28. Estimated Risk of Cancer

29. Outline • X-ray Production • X-ray Interaction with Matter • X-ray Damage to Tissue • X-ray Image Detectors • Film • Film-Screen Combination • Image Intensifier • Flat Panel Detectors • Major Advances in X-ray Imaging

30. X-ray Film (1-5 m)

31. Film Characteristic

32. Screen-Film Combination

33. Image Intensifier

34. Flat Panel Image Receptor Active Matrix Array sizes of up to 40 cm x 40 cm containing up to 9 million pixels

35. Direct Image Receptors

36. Film Vs. Flat panel Image

37. Film Vs. Flat Panel Detector Linearity for the flat panel detector and x-ray film. The X-ray film has a non-linear response and is limited in dynamic range.

38. Outline • X-ray Production • X-ray Interaction with Matter • X-ray Damage to Tissue • X-ray Image Detectors • Major Advances in X-ray Imaging

39. X-ray Radiography Machine

40. X-ray Images Chest X-ray Head X-ray

41. Fluoroscopy Enables radiologists to visualize X-ray images in real time on a television monitor. In most instances the procedure would involve the administration of some form of 'contrast' agent to outline the region of interest

42. Fluoroscopy Images Barium Used to Visualize Intestines

43. Mammography A mammography machine is an X-ray machine dedicated to breast images. Compared with conventional X-ray techniques, mammograms are obtained with much lower energy X-rays of around 20,000 volts.

44. Digital Angiography It is a diagnostic procedure that produces X-ray pictures of blood vessels. A catheter is inserted in the vessel to inject contrast fluid into the lumen of the blood vessel, which then becomes visible on X-ray images.

45. Digital Angiography Images First Angiogram(1896, Hankel): Mercury was injected in a post mortem hand Digital Subtraction Angiography (Mistretta, 1980s)

46. Digital Angiography Images 3-D Angiogram of The Brain Arteries Angiogram of The Coronary Arteries

47. Computerized Tomography (CT) The technique of CT scanning was developed in 1973 by Hounsfield. A thin fan beam of X-rays generated by a conventional X-ray tube passes through a single 'slice' of a patient through to a bank of X-ray detectors.

48. Principle of Image Reconstruction I0 Δy Δx I1 =I0e-(β1+β2)Δx β1 β2 I0 I2 =I0e-(β3+β4)Δx β3 β4 I4 =I0e-(β2+β4)Δy I3 =I0e-(β1+β3)Δy 4 equations solved for 4 unknown β

49. CT Image Reconstruction

50. CT Machine CT Machine CT Machine Rotating Parts