Imaging System Characteristics

• Dual focus Tubes mm small and large:

  • small
  • 0.5mm
  • 0.6mm
  • 1.0 mm
  • 
    
  • large
  • 1.0mm
  • 1.2mm
  • 2.0mm
• • 0.3/1.0mm is typically used for : angiography and magnification procedures
  • 0.1/0.3mm is typically used for: mammography
• What is Microfocus Tubes

  FSS of 0.3mm or less
• Large focus

  • normal imaging
  • higher mA can be impressed for larger/dense body parts
• What is the main advantage of large FSS in relation to detail?

  Shorter exposure times to minimize motion
• Small focus

  • given amount of electrons cover smaller area on anode
  • cannot use high mA due to limited heat capacity
  • used for magnificatoin radiography where detail is required
  • for smaller and thinner body parts
• X-ray beam is polyenergetic and heterogeneous
• Filtration hardens the beam

  • makes beam more uniform by removing softer rays
• What are the two classifications of filtration?

  1. Inherent
  2. Added
• What is inherent filtration made of?

  glass or metal envelope (0.5mm Aluminum equivalent)
• What is added filtration?

  mirror in collimator box (1.0mm Aluminum equivalent)

  • another 1.0mm AI eq added between x-ray tube housing and collimator
• What is the total of inherent and added filtration?

  .5mm of Inherent Filtration+ 2.0mm of Added Filtration=

  2.5mm of Total Filtration AI equivalent
• Half-Value Layer (HVL)

  • improves quality of the beam
  • is the amount of material that reduce the intensity of the x-ray beam to half its original value
  • used for shielding and filtration
  • increase in HVL increases the quality of the beam
• Compensation Filter

  Different shapes of Aluminum mounted under the variable light aperture (collimator)
• Compensation filter balances intensity of x-ray beam for a more uniformed exposure to the image receptor
• What are the two different shapes of compensation filter?

  1. Wedge filter
  2. Trough Filter
• Wedge filter is good for:

  body parts thick on one end and thin on the other ex) foot, hips
• Trough Filter is good for:

  chest
• Anode Heel Effect

  • phenomenon which intensity of x-ray beam is greater towards the cathode side of the tube
  • the loss of intensity is a result of the electrons traveling farther to the anode heel portion of the target
• Where would you place the thicker part of the body?

  At the cathode end