Basics of X-ray and Mammographic Systems

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RSNA / AAPM

mA

• Stands for "milliamps"
• Rate of electron flow of electrons from filament (cathode) to target (anode) during exposure
• Exposure intensity proportional to mA
• Energy spectrum independent of mA

mAs

• Stands for "milliamp-seconds"
• Product of mA & exposure time
• A given mAs @ a particular kVp results in a constant exposure
  • doubling mA & halving time is like driving twice as fast for half as long

mA & Radiographic Images

• Doubling mA (no other change)
  • Doubles electrons striking target
  • Doubles photons produced
  • No effect on spectrum
• Doubling mA and cutting exposure time in half results in
  • Same number of electrons hitting the target
  • Same number of x-ray photons
  • Same x-ray beam energy spectrum
  • Same patient exposure
  • Reduced motion caused by shorter exposure time

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