X-Rays in Medicine

1. X-Rays in Medicine Tyler Bradshaw- Fall 2008

2. Discovery of X-Rays -Wilhelm Conrad Roentgen-1895 -Electrical discharges in a vacuum tube -Caused a phosphored screen to fluoresce -Formed an image of bone -First x-ray photograph of wife’s hand/ring

4. X-rays in Medicine • One year later British doctors were already using x-ray imaging. • Prolonged exposure to x-rays caused tissue burns. • Wounds were abnormal- took time before appearing.

5. Electro-Magnetic Spectrum • X-rays are electro-magnetic radiation. • Same as radio waves, sunlight, or microwaves. • The difference is in the wavelength/frequency Radio Waves: ~3 km 10000 Hz Microwave: ~ 1 cm 1010 Hz Visible Light: ~0.000005 mm 1015 Hz X-Rays: ~ 10-10 m 1018 Hz *Not to scale. Not even close.

6. ENERGY

7. PHOTONS -The energy of a light-wave is carried by packets called photons -The energy of a photon depends on the light’s wavelength -Smaller wavelengths have larger energies

8. ENERGY Photon energies are usually given in units of electron volts (eV) 1 eV = 1.602x10-19 Joules Need 56,000,000,000, 000,000,000,000 eV to cook an egg.

9. How do you create x-rays? • Bremsstrahlung • Fluorescence

10. Creating X-rays: Bremsstrahlung • Charged particles emit photons when decelerating. • To form x-rays it must be very abrupt. • An electron arcs around the nucleus, emits an x-ray photon

11. Creating X-rays: Bremsstrahlung Heavy Atom High speed electron Energy released depends on the electron’s speed and proximity to the nucleus.

12. Creating X-rays: Fluorescence Characteristic X-rays • Electron-electron collision • Both leave atom, leaving a vacancy in the inner orbital • Vacancy filled by an outer electron • Transition releases high energy photon High speed electron Heavy Atom

13. BremsstrahlungvsX-ray Fluorescence Both methods occur in an x-ray machine Bremsstrahlung: • Photon energies vary: 10,000-90,000 eV. • Lower energy x-rays are more common. Fluorescence: • Specific energies per atom. • Higher energy. • More useful.

14. X-Ray Machines *Electron beam collides with a spinning tungsten disk *Electrons interact with the tungsten atoms *Both Bremsstrahlung and flourescence occur *Filter absorbs low energy x-rays X-Ray Machine Video

15. Uses of X-rays 1) Imaging 2) Killing diseased/cancerous tissue X-rays are used because of their unique interaction with tissue and bone. There are four types of interactions…

16. 1st: Elastic Scattering • Absorbs x-ray, bounces up and down • Re-emits x-ray • No effect on the atom • Bends the x-ray’s path (fuzziness)

17. 2nd: Photoelectric Effect • X-ray photon is absorbed • Electron shoots away from the atom. • Larger atoms are more likely to absorb an x-ray than smaller atoms.

18. Bone (Ca) absorbs x-rays • Tissue (C, H, O, N) transmit x-rays

19. Photoelectric effect: useful in imaging • When treating cancer, however, you must avoid harmingsurrounding tissue • To target the tumor, another type of interaction is used… 3rd: Compton Scattering

20. Compton Scattering -1,000,000+ eV photons used -Photon collides with an electron -Both bounce off like billiard balls

21. Compton scattering affects only a fraction of the tissue. To target the tumor it must be treated from many different angles.

22. When a 1,000,000 eV photon collides with an atom, another type of interaction occurs… 4th: Electron-positron Pair Production

23. E=mc2 Einstein postulated that energy can become mass, and mass can turn into energy. A small amount of mass can create a lot of energy.

24. Electron-Positron Pair Production e- Electron e+ Positron

25. Antimatter: Symmetry in the universe. Almost all particles have an antimatter… Proton Antiproton Neutron Antineutron ElectronPositron

26. Matter-antimatter collisions turn mass into energy, and create an explosion. e+ e- “Annihilation”

27. *These electron-positron pairs are formed in radiation treatment. *The newly formed positron quickly “annihilates” another electron. *Helps kill tumors.