Mechanisms of Localization:

Capillary Blockade

• Pulmonary perfusion imaging is performed following an IV injection of a radio-labeled, precipitated, biodegradable macroaggregate of human serum albumin
   
• Radiopharmaceutical: Tc-99m MAA
   
• Diameter of average capillary: 7 mm; legal particle size range: 90% of all particles must be between 10-90 mm; 0% >150 mm
   
• Ideal number of particles to be injected:

adult 200K - 700K

adult w/ pulmonary HTN:   150 K

child (scaled up by body mass) 100K-350K

neonate (0-1 yr old) 50 K

• 1/100,000 capillaries blocked by typical injection
   
• t_biol = 5-12 hr depending upon manufacturer
   
• Imaging performed immediately after injection