Grid Efficiency (Functional Factors)

• What is Grid Efficiency?

  • Describes the ability of the grid to absorb scatter radiation.
  • There are 2 physical and 3 functional factors that affect grid efficiency
• What 2 physical and 3 functional factors affect grid efficiency?

  Physical Factors:

  1. Grid Ratio
  2. Grid Frequency

  Functional Factors:

  1. Selectivity
  2. Contrast Improvement factor (K)
  3. Bucky Factor (B)
• Selectivity refers to the grids ability to discriminate scatter radiation from the primary beam

  • the greater the selectivity, the greater the grids efficiency
  • ex) 16:1 grid ratio will have better selectivity than 8:1
• Contrast improvement factor (K) measures the ability of the grid to improve contrast

  • higher grid ratios will have higher (K)
  • ex) 16:1 grid ratio will have a higher contrast improvement factor compared to 8:1 grid ratio
• Bucky Factor (B) defines the requirement for increasing exposure factors to maintain the same density with the use of a grid
• • The higher the grid ratio, the higher the bucky factor
  • The bucky factor, is often used in clinical situations where mAs or kV is manipulated to compensate for different grid ratios
• Bucky Factor

  
• Example: A radiograph without a grid requires 110kV at 2.0mAs. If a 16:1 grid is used, what would be the new exposure factors?

  • 16:1 is 6X mAs
  • 2mAs x 6= 12 mAs