Equine Lung Perfusion


When particles in the size range of 20-50 micron are administered intravenously,  they are filtered out and entrapped in the lungs.  If injected in sufficient numbers,  they will be evenly mixed with blood and distributed to the lungs in proportion  to pulmonary blood flow.  Particles labeled with an appropriate radionuclide provide a means of imaging  areas of the lung where there is pulmonary arterial flow down to the capillary level.  Areas of obstructed flow, regions of shunting or areas where capillaries are absent will appear photon deficient. 


  • Evaluate pulmonary perfusion
  • Suspect pulmonary emboli
  • Chronic obstructive pulmonary disease
  • Evaluate regional pulmonary perfusion

Patient Preparation

  • Mild sedation as needed


  • Gamma camera:  Large field of view
  • Collimator: Low energy, High resolution, Parallel hole.
  • Energy window:  20% centered at 140keV


  • 40-50 mCi Tc99m macroaggregated albumin  administered intravenously.


  • Administer the radiopharmaceutical intravenously.   Do not draw blood into the syringe or flush with blood after the injection. Blood drawn back into the syringe forms small clots, the radionuclide will adhere to the clots and on injection will form "hot spots".  Scanning may start immediately.
  • Acquire each view in the motion correction mode for 45 seconds, or static acquisition mode for a minimum of 300k counts. 
  • Views: Depending on the size of the horse and/or the size of the detector, 3 or 4 lateral views are acquired as well as 2-3 dorsal views.



  • Areas of decreased pulmonary arterial perfusion appear as areas of decreased radioactivity. These can be caused by a large number of things. Comparison of the scan with a chest x-ray will often help clear up the differential diagnostic problem.
  • Emboli are mostly segmental because they block the blood supply.
  • Parenchymal disease is mostly non-segmental because it is not primarily vascular
  • Emboli or  parenchymal disease can cause sub segmental defects 
  • COPD causes patchy non segmental or sub segmental decreased perfusion o the lung. 
  • With atelectasis there is complete shunting of blood from that segment. The surrounding lung hyperinflates.
  • Acute or chronic inflammatory disease causes decreases in perfusion in areas of inflammation which are usually seen on chest x-rays.   



Copyright 2001 University of Pennsylvania School of Veterinary Medicine
Faculty Sponsor: Dr. Michael W. Ross
Technologist: Vivian S. Stacy CNMT
Comments and suggestions to vstacy@vet.upenn.edu