Tc-99m MAA

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


  • 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 mcg 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 reticuloendothelial system (RES)
  • excretion: renal, RES

Uses, doses and timings

  • V/Q perfusion
    • adult dose: 2-5 mCi IV (1 mCi if before ventilation)
    • timing: immediate
    • reduced injection of 100,000-200,000 particles advised in:
      • pulmonary hypertension, R-L shunt, single lung transplantation
      • pregnant patients
      • paediatric patients: weight-related dosing advised
    • 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
    • brain uptake is diagnostic of R-L shunt
Physics and imaging technology: nuclear medicine
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Article information

rID: 15562
System: Chest
Synonyms or Alternate Spellings:
  • Tc-99m MAA (microaggregated albulin)
  • Tc-99m microaggregated albulin (MAA)
  • Tc-99m microaggregated albulin

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