Part I

1. Part I

2. Physicists do it in Hospital Tong Xu Dept. of Physics Carleton University

3. Why there are physicists in the hospital?

4. Medical Physicists • Where in the hospital can you find them? • Diagnosis imaging departments: • Radiology and Nuclear Medicine (CT, MRI, PET…) • Cancer centre • Medical Physics department (Radiotherapy) • What is their job? • Make sure the equipments are working according to their physics specifications • Perform radiotherapy treatment planning

5. Why we need physicists to perform these tasks? Let’s to go back to the history of some of the medical technologies.

6. Related Medical Technologies Three examples … X-ray CT Magnetic Resonance Imaging Radiation Therapy

7. Discovery of X-ray • First discovered by German Physicist Wilhelm C. Röntgen in 1895 On a New Kind of RaysNature 53, 274-276 (23 January 1896)

8. Discovery of X-ray • Independently discovered by Nikola Tesla in 1896

9. Discovery of x-ray 1. Crookes Tube • Invented by Sir William Crookes, chemist and physicist, around 1860s. • A demonstration of the cathode ray – accelerated electron beam.

10. Discovery of x-ray2. Cathode ray

11. Cathode ray is a beam of electrons

12. Discovery of x-ray3. Rontgen’s experiment

13. A mystery radiation was coming out from the tube Röntgen called it X-ray In fact, x-ray is just a ray of light photons with much higher energy than ordinary light

14. Typical x-ray spectrum

15. Medical Application of x-ray

16. Röntgen received the First Physics Nobel price in 1901

17. X-ray radiograph It’s a shadow image of human

18. What do we need to see through a human? X-ray

19. X-ray Computer tomography

20. X-ray projections of heart

21. CT Image reconstruction Projections at different angle 3D structure http://rpop.iaea.org/

22. Inventers • Theory proposed by a physicist Allan MacLeod Cormack in1956 • two papers in the Journal of Applied Physics in 1963 and 1964 • First Prototype by electrical engineer Godfrey Hounsfield in 1969

23. The first CT prototype First Prototype by Godfrey Hounsfield in 1969

24. Cormack andHounsfield shared the Medical Nobel prize in 1979

25. Magnet Resonance Imaging1. Stern molecule beam (1922) Individual gas molecules fly through a pair of magnets developed by German Physicist Otto Stern and Walther Gerlach in 1922

26. N S N S Magnet Resonance Imaging2. Some nucleus are like tiny magnets Detector

27. N S N S N S N S Magnet Resonance Imaging2. Some nucleus are like tiny magnets Detector

28. Otto Stern received Physics Nobel prize in 1943

29. B Magnet Resonance Imaging3. Precession of magnetic dipoles • Some nuclear has magnetic momentum • They are like magnetic dipoles • They precess around the external magnetic field • Just like a Gyroscope • Check out this animation http://www.simplyphysics.com/MRI_shockwave.html

30. B Magnet Resonance Imaging3. Precession of magnetic dipoles • The precession frequency • ω is in the radio frequency range • is the Gyromagnetic ratio

31. B S N Magnet Resonance Imaging3. Precession of Magnetic dipoles Aligned against the external Magnetic field B Higher energy state Aligned with the external Magnetic field B Lower energy state The nucleus feel more comfortable to stay in lower energy state

32. Magnet Resonance Imaging4. Nuclear Magnetic Resonance What if I send nucleurs a Radio wave that has the same frequency as the precession? American physicist Isador I. Rabi had an great idea!

33. N S N Radio frequency signal ~ S Magnet Resonance Imaging4. Nuclear Magnetic Resonance Detector

34. Magnet Resonance Imaging4. Nuclear Magnetic Resonance • The nucleus will resonance with the RF wave • They absorb RF energy • And flip to higher energy state • Can measure the nuclear magnetic montemtum precisely

35. Isador I. Rabi received Physics Nobel prize in 1944

36. Magnet Resonance Imaging5. NMR with solids and liquids • In 1946, two other Americans, Edward M. Purcell and the Swiss-born Felix Bloch, separately apply this nuclear magnetic resonance (NMR) method to solids and liquids.

37. Purcell and Bloch received Physics Nobel prize in 1952

38. Principle of NMR Resonance frequency Since the gyromagnetic ratio γis unique for nucleus of each elements Nuclear Magnetic Resonance is a powerful tool for chemical analysis

39. Until 1970s….

40. Magnet Resonance Imaging5. Apply NMR to imaging • Paul Lauterbur & Peter Mansfield applied NMR to image body in 1970s • Introduced gradients to the magnetic field • Thus, frequency the radio wave emitted by the nucleus tell us where they are.

41. Magnetic Resonance Imaging

42. MRI scanner Source: sfu.ca

43. MRI A technique for imaging soft tissues source: lecture slides from Prof. I. Cameron

44. Lauterbur and Mansfield received Medical Nobel prize in 2003

45. Cancer diagnosis Chest X-ray Nuclear Medicine x-ray CT http://www.dcmsonline.org/

46. Physics in Cancer treatment

47. Radiation Therapy • Uses ionizing radiation • Kills tumour by damaging tumour cells

48. Radiation therapy

49. External beam radiation therapy • Use x-ray generated from linear accelerator. • Max energy: 4~20 (MeV, 106 eV) Mega-Electron-Volt • Compare to visible light: 2-3 eV • Compare to UV light: 3-5 eV • 1000,000 times higher than UV light

50. Linear accelerator (Linac) Accelerated high energy electron beam hit a Tungsten target Produce high energy x-ray beam Source: www.cerebromente.org.br