Mammography

Describe the differences in image acquisition in magnification mode during mammography compared to conventional mammography. Indicate with reasons how you expect these will affect the MGD.  

• Magnification Mammography
  • Uses a smaller 0.1mm focal spot to reduce geometric blurring
    • Reduces the maximum tube current limit to 25mA for Mo target so a 100mAs will require 4 second exposure time
    • Reciprocity law failure for screen film needs causes increased MGD to achieve the required OD
  • Breast placed in breast support platform (magnification stand) so the breast is closer to X-ray focal spot (above shooting down )
    • Increases the dose to 2-3x~ due to inverse square law
    • Air gap to reduce scatter – improves contrast but reduces x-rays at the detector, AEC compensates by increasing mAs which increases MGD
  • Collimate the x-ray beam only to the volume of interest
    • Reduces scatter and MGD
  • No anti-scatter grid (due to magnification stand)
    • Reduces MGD by a factor of 2-3
  • Uses compression paddle
    • Reduces MGD (less tissue for the x-rays to traverse)