X ray physics


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X ray physics

  1. 1. X-ray physics By Dr. Tarek Mansour
  2. 2. Content      Introduction, history and basic physics. How radiograph produce. Interaction of x-ray with patient. Formation of the image. Processing the film.
  3. 3. Introduction, history and basic physics.
  4. 4. Discovery of x-rays   Discovered in 1895 by German physicist named Wilhelm Roentgen. He found shadow of his bone on fluorescent screen.
  5. 5.  X-rays are a form of electromagnetic radiation similar to visible light but with short wave length.
  6. 6. Radiation physics
  7. 7. Electromagnetic spectrum   Electromagnetic radiation consists of energy in small packets called photons. They are grouped according to there wave length and frequency.
  8. 8. Properties of x-rays  Are electromagnetic radiations composed of small packets of energy called photons.       Travel at speed of light. Travel in straight lines. Highly penetrating. Invisible. Blacken radiographic films. Produce scatter.
  9. 9. Atoms structures   Positively charged protons in nucleus. Neutrons of no charge also in the nucleus.  Negatively charged electrons in various orbits around the nucleus.
  10. 10. Atomic number    Lighter elements have fewer number of protons such as oxygen. Heavier elements have more such as lead. The number of protons is called the atomic number.
  11. 11. Density of matter.   Low density matter is loosely packed with large spaces between each atom like air. High density matter is tightly packed with atoms sitting close to each other like lead.
  12. 12. How radiographs are produced
  13. 13. Production of radiograph    X-ray are produced in the machine. X-ray interact with the patient. Image is recorded in the x-ray plate.
  14. 14. Production of the x-ray radiations on the machine.
  15. 15. The x-ray tube.  The tube head consists of a pair of electrodes. - A negatively charged cathode with include a heater filaments. - A positively charged a node with a tungsten target.
  16. 16. Steps in x-ray production.    Filament is heated and gives off cloud of electrons. A large electrical charge is placed in the cathode/anode space causing the electrons to race toward the anode. When they crush into the anode it causes x-ray to be given off.
  17. 17. X-ray machine components.    The tube head where the x-rays are generated. The control panel which regulate the strength and amount of the x-rays produced and trigger the exposure. The power supply which provide the energy to creates the x-rays.
  18. 18. X-ray tube head Stationary anode.  Found in smaller machines.  The target is fixed in block of copper.  Only capable of low output.  mA to 30 Rotating anode.  Found in large machines.  The target is rotate in tungsten disc.  Higher output producing.  mA up to 300
  19. 19. The control panel.  - The three factors that can be varied during producing radiograph are The kilovoltage (KV) difference applied between the anode and cathode during exposure. The milliamperage (mA) applied to the filament. The duration of exposure.
  20. 20. Control panel    Higher kv attract the electrons toward the anode by greater force. They smash the anode harder and produce x-ray with higher energy and greater tissue penetrating power. Increasing mA increase the number of electrons cloud around the filament. Result in higher number of x-ray produced per second.
  21. 21. How x-ray interact with patients.
  22. 22. Three things occured    Some x-rays absorbed. Some pass straight through the patient. Some scattered.
  23. 23. Depend on three things    X-ray energy. In high kv most of x-rays pass to the film through the patient. Atomic number of the absorber. Thickness and density of the object.
  24. 24. How image is formed
  25. 25.   As an x-ray beam leave the tube head, it fans out and become weaker. As the distance double, the strength is reduced.
  26. 26. Formation of the image    The distance from the anode target to the film is called the film focal distance. Changing the distance affect the quantity of the x-ray reaching the film. Increasing the distance means that less x-rays reaches the film.
  27. 27. Formation of image  Low density or low atomic number tissues allow more x-rays through causing more blackening of film.  High density or high atomic number tissues allow less x-ray through causing less blackening of the film.
  28. 28. Effect of kilovoltage.    Increasing kV, increases the penetrating ability of the x-rays photons. More x-ray photons get through to darken film. High kv produces darker images but poor contrast.
  29. 29. Effect of milliamperage and time.    Increasing the mA and mAs, increases the number of x-rays production. It does not affect the penetrating power of the photons. Increase mA will increase overall blackness of the film.
  30. 30. X-ray film composition.   Polyester base that provide support has bluish tint. Film emulsion is a thin layer of chemicals coating the base composed of. - Light sensitive silver halide (mainly Bromide AgBr) crystals. - gelatins that keep the silver bromide grains evenly dispersed.
  31. 31. Recording image  When x-ray hits the atoms in the film emulsion it causes it to change leaving a latent (hidden), image.
  32. 32. The cassette film     Light proof container for film. Lead backed to absorb transmitted radiations and prevent scatter. Intensifiers to use lower exposure. Calcium tungstate.
  33. 33. Grids     Composed of hundreds of alternating thin lead strips with aluminum or fiber interspaces. X-ray can pass through the interspaces without interaction. Lead strips absorb weak energy scatter x-ray that hit them. Strips is encased in protective cover.
  34. 34. Processing films
  35. 35. Processing the film There are five steps  Developing.  Rinsing,  Fixing.  Washing.  Drying.
  36. 36. Development    Chemical convert the exposed AgBr in to metallic silver. The bromine goes into solution. Unexposed AgBr is less affected.
  37. 37. Rinsing   Essential to rinse of the developer solution so that the fixer solution is not contaminated. Contamination leads to faster exhaustion of the fixer.
  38. 38. Fixing    Stops development. Washes away unexposed and undeveloped silver halide crystals. Hardens the emulsion.
  39. 39. Washing  To wash all traces of fixer from emulsion.
  40. 40. Draying   Hang up in dust free area to dry. Automatic processors by it by using hot air.