1. Medical Imaging Radiation I

2. Naked to the Bone: Medical Imaging in the Twentieth Century (Paperback)by Bettyann Kevles Bettyann Kevles E=mc2: A Biography of the World’s Most Famous Equation by David Bodanis More suggested reading:

3. Energy that travels through space and matter We are interested in electromagnetic radiation: X-ray waves Visible waves Radio waves Gamma-rays (...) Radiation is:

4. Monochromatic radiation, electric and magnetic field can be represented as: This is the solution of the one dimensional wave equation Electromagnetic wave

5. The electromagnetic wave: ADD steve EM wave

6. f = 1 / T Period Wavelength The electromagnetic wave:

7. red=300nm blue=900nm The electromagnetic wave:

8. Wavelength [m] Frequency [Hz] Energy [ev] EM radiation

9. Electron volt [eV]: is the kinetic energy gained when a single electron is accelerated between two plates that differ in potential by 1V. Before leaving the negatively charged plate, the electron has potential energy of 1eV. Energy eV + - ------ ++++++ 1eV=1.6x10 -19 J 1Joule [J]=1kg m 2 s -2

10. Wavelength [m] Frequency [Hz] Energy [eV] EM radiation Speed of light in vacuum

11. Wavelength [m] Frequency [Hz] Energy [ev] EM radiation

12. Why is knowing the wavelength important?

13. EM spectrum Wavelength [m]

14. Wavelength and size of an object! Is object large or small compared to the wavelength?

15. Frequency,Energy, Wavelength are related E

16. Frequency,Energy, Wavelength are related E f

17. The photon The smallest amount of EM radiation possible, fundamental particle Has no rest mass Move at speed of light c, (c/n in media) Travel in straight line (bends at interfaces)

18. The atom 2e - 8e - 18e - KLMNOP 32e - 50e - 72e - Bohr model Electron Nucleus Orbitals 98e -

19. Binding Energy (BE) Energy binding electron to atom A photon will need an energy > than binding energy to remove an electron from a atom Nomenclature - binding energies are negative (eV) Ionization Energy = - BE, energy necessary to remove 1 electron from the atom.

20. Binding Energy Stronger bound (KeV) Less strong bound Weak bound (eV) Valence electrons, # of electrons in outer orbital, determines chemical properties of atom

21. The atom 2e - 8e - 18e - KLM Z-Atomic Number, # of protons N-Neutron number, # of neutrons Mass Number, A m = Z + N Na 22 11 Atomic Mass, actual mass of the atom Protons Neutrons Oxygen-16 Atomic Mass -> 15.9949 amu Mass Number ->16

22. Excitation Absorption E = E 3 -E 2 Photon Electrons want to be as close as possible to the nucleus

23. BREAK !!

24. Relaxation Emission E = E 2 -E 1 Photon Vacancy -Visible -IR -X-Ray DEPENDS ON ATOMIC NUMBER I.E BE emission shorter or longer ??

25. Radiation II Ch. 3 of, The essential physics of medical imaging, Bushberg et al. We focus on X-rays and Gamma-rays production and interaction with matter

26. X-Rays (  -Rays) interactions

27. Scattering and Absorption Absorption - All energy of incident photon is absorbed by a material, the photon is destroyed Scattering - Photon path is altered by a “scattering event”, loss of energy can occur (inelastic scattering) or not (elastic scattering) Transmission - No interaction

28. Absorption Photon detector

29. Scattering Photon detector

30. Transmission Photon detector

31. X-rays,  -rays interactions Rayleigh scattering (coherent) Compton Scattering Photoelectric effect Pair production

32. Rayleigh scattering Photon excites the ALL ATOM Low energy X-rays (15-30 keV) Photon energy makes all electrons oscillate in phase A photon is emitted in a different direction NON IONIZING It’s noise in X-ray imaging 12% of photons <30 keV 5% of photons >70 keV

33. Rayleigh scattering Incident photon Scattered photon What is important to note here

34. Rayleigh scattering Polarized radiation Isotropic radiation

35. Compton scattering Inelastic scattering Dominates X-Rays scattering from 26keV to 30MeV in soft tissue Photon interact with valence electrons Electron is ejected from shell generating an ion Compton scattering is noise in X-Rays imaging Safety hazard!

36. Compton scattering Incident photon

37. Compton scattering Incident photon  Compton electron  Scattered photon        sc E sc =E o -E e- E sc E e- EoEo

38. Compton scattering Higher E o generate more forward scattering photons (smaller  )  =m e c 2 =511keV

39. Compton scattering Forward scattering Back scattering

40. Photoelectric effect All incident photon energy is absorbed Often interaction between photon and electrons in K shell An electron in the K shell is ejected E e- =E o -E b Lower binding energy electron fills the empty orbital - electron cascade Emitted energy can be Auger or X-Rays

41. Photoelectric effect Incident photon

42. Photoelectric effect Incident photon

43. Photoelectric effect Incident photon 

44. Photoelectric effect Incident photon      X-rays

45. Photoelectric effect Incident photon  Auger Electron

46. Photoelectric effect Incident photon  Auger Electron

47. Photoelectric effect Incident photon  Auger Electron X-rays

48. Photoelectric absorption Photoelectric cross section likelihood of p.e. absorption to occur Atomic Number Photon energy

49. Photoelectric effect Photoelectric absorption process is most likely for E o  I K, L, M,... (resonance) Photoelectric absorption cross section decreases strongly with photon energy (  E p -3 ) as photon energy increases relative to I K, L, M,... Photoelectric absorption cross section increases strongly with Z (~ Z 3 ) because I  Z Photoelectric absorption in K shell usually dominates

50. Photoelectric effect Absorption edge 33.3keV is 6 times most likely to have photoelectric interaction than 33.1keV in iodine atom 406080x10 3 K edge

51. Pair production & photodisintegration Require high energy photons >1MeV Interaction with nuclei Pair production photon is absorbed by nucleus the energy is converted into an electron and positron Electron (511keV) positron (511keV) Pair production threshold 1.02MeV Photodisintegration, photon absorbed by nucleus, nucleons are ejected by nucleus

52.  /  [cm 2 /g] Z = 6 Z = 53 Z = 82 Legend:  : Photoelectric absorption  : Compton scatter  : Pair production  r : Raleigh scatter

53. X-Rays generation

54. White radiation, Bremsstrahlung X-Ray Coulombic interaction -Inelastic interaction with nuclei -Loss of kinetic energy -Xray (E) = lost kinetic E -High kinetic energy -Forward radiation -Emission  Z 2 (Atomic number) # of protons (Brake) electron

55. White radiation, Bremsstrahlung X-Ray a -Smaller a produce larger X-ray -Broad range of wavelengths