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UNIT 2 X-ray Tube Review & Dedicated X-ray machines

UNIT 2 X-ray Tube Review & Dedicated X-ray machines. BUSHONG- Ch. 6 & 7 Merrills’s V. 3 Ch. 32 RT 244 Week 10. Major Topics. Review the components of the x-ray tube Saturation current Line focus principal/Anode heel affect Anode cooling/HU Off focus radiation

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UNIT 2 X-ray Tube Review & Dedicated X-ray machines

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  1. UNIT 2 X-ray Tube Review & Dedicated X-ray machines BUSHONG- Ch. 6 & 7 Merrills’s V. 3 Ch. 32 RT 244 Week 10

  2. Major Topics • Review the components of the x-ray tube • Saturation current • Line focus principal/Anode heel affect • Anode cooling/HU • Off focus radiation • Dedicated x-ray machines

  3. A B D F C G E X-ray Tube Construction WHAT TYPE OF MOTOR IS ROTOR? The energy of electrons comprising the tube current is measured in ______________ ?

  4. What makes the Anode spin? • Electromagnetic Induction Motor • How fast does it turn? • ______________ rpm

  5. A motor is a device that converts • electrical energy into mechanical energy

  6. Cathode - Filaments • Negative Electrode • Tungsten with thorium • Filament circuit heats (>2200°C)with 3-5 amps • Thermionic Emission • Vaporization • Space charge • Saturation current • Focusing cup

  7. Molybdenum or Graphite base Anodes - Target • Rotating Anodes • 2” to 5” disk (focal track) • Induction motor • Speed 3000 to 10000 rpm Cu W • Other target materials • Tungsten-rhenium • Molybdenum • Rhodium

  8. Angle (5°-15°) e- effective actual Line-Focus Principle • Effective FS < actual FS • Beveled anode • Improves heat capacity • Small angle =  FS • Small FS =  resolution • AHE  • Field coverage  • Heat loading on smaller anode surface area

  9. Anode Angles and Heat • Small the angle = more heat load • Larger angle – less heat load • Different anode angles are used for different types of equipment: • Diagnostic vs special procedures

  10. ANODE HEEL EFFECT • MORE PRONOUNCED WITH SMALLER ANODE ANGLE • (sm anode angle = larger heel effect) • 120% ~75% difference of intensity across beam • How does this affect positioning? FAT – CAT HIGHER AT CATHODE See pg 139 Bushong

  11. Leakage Radiation <100 mR/hr @ 1 m Extra-focal Radiation rebounding e- Off Focus Radiation Protective Housing Miscellaneous Terms

  12. OFF FOCUSRADIATION

  13. SHADOW OF SOMEONE’S HEAD = OFF FOCUS FROM TUBE

  14. LEAKAGE RADIATIONmay not EXCEED • TUBE HOUSING 100mR / HR @ 1 meter

  15. Tube Failures & Prevention • Failure Causes • Anode pitting/cracking after single excessive exposure • Bearing damage from numerous long exposures • Vaporization of the filament • Filament break • Coating of glass envelope with tungsten • Prevention • Warm up tube before use • Avoid “boost & hold” exposures if possible • Use acceptable levels of exposure (e.g. tube rating charts)

  16. Tube Rating Charts (mA)

  17. Tube Rating Charts (kVp)

  18. Heat Units • HU – measure of thermal energy applied to the x-ray tube from an exposure • Formula based on generator HU1Ø = kVp x mAs x 1 HU3Ø6p = kVp x mAs x 1.35 HU3Ø12p = kVp x mAs x 1.41 • Multiply if consecutive exposures are made, HUT = HU x # exposures

  19. Anode Cooling Chart

  20. TYPES OF EQUIPMENT • FIXED • MOBILE • DEDICATED • Bone densitometry, Chest, Head, Mammography, Panorex & Tomography

  21. Bone density scan or DEXA

  22. Chest Mammography

  23. HeadPanorex CT Scanner

  24. TOMOGRAPHY

  25. Tomography

  26. Tube is “Prepped”

  27. Exposure Time

  28. TomographyLONGER AMP = THINNER SLICE

  29. thinner slice = longer arc thicker slice = shorter arc

  30. 1 second exposure time Need to adjust mA How do you adjust the fulcrum?

  31. Conventional Tomography

  32. Which image is more anterior?

  33. Tomographic motion terms

  34. Which terms do not apply ? • Linear • Curvilinear • Hypocycloidal • Trisprial • Oscillating • Circular • Figure 8 • Reciprocating • Elipictal

  35. Conventional tomo vs. CT images Questions?

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