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Tc-99m MAA

Tc-99m MAA (microaggregated albulin) is one of the technetium radiopharmaceuticals used in lung perfusion imaging.

Characteristics

  • photon energy: 140 KeV
  • physical half life: 6 hours
  • biological half life: 2-3 hours
  • normal distribution: lungs, liver, spleen, kidneys
  • pharmacokinetics:
    • >90% particles trapped in lung capillaries during first pass
    • particles < 10 um phagocytosed by liver and spleen
    • ~100,000 of 280 billion capillaries occluded during normal lung perfusion scan
    • particles eventually enter systemic circulation and phagocytosed by RES
  • excretion: renal, RES
  • miscellaneous facts:
    • reduced injection in pulmonary HTN, pediatric patients, pregnant patients, R-L shunt
    • brain uptake is diagnostic of R-L shunt
    • blood should not be drawn back into the syringe to ensure needle is in vein before injection (in contrast, to other studies). Blood causes MAA aggregation which results in hot pulmonary microemboli

Uses, doses and timings

  • V/Q perfusion
    • adult dose: 2-5 mCi IV (1 mCi if before ventilation)
    • timeing: immediate

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