Basics of X-ray and Mammographic Systems

• Focal spot size
• Source-image distance (SID)
• Object-image distance (OID)

Penumbra (partial shadow)

• Less penumbra = less unsharpness

Minimizing unsharpness

• Minimize focal spot size
  • Limits beam intensity
  • Lengthens exposure time
    • More potential for motion unsharpness
• Maximize SID
  • Limits beam intensity
  • Lengthens exposure time
    • More potential for motion unsharpness
• Minimize OID
  • Limited by
    • Thickness of table top
    • Space for grid & phototimer
    • Distance of body part of interest from where beam exits patient