Lung ventilation (aerosol or radioactive gas) imaging is used in conjunction with lung perfusion imaging in the diagnosis of pulmonary embolism.  The combination of these studies assists in differentiating COPD (and other lung disorders) from pulmonary emboli.  Since lung perfusion imaging demonstrates the blood flow to the lung fields, it can also be used in follow-up to assess response to therapy of a known pulmonary emboli.

Principle:

Ventilation imaging of the lungs is accomplished by inhalation of an aerosolized radiopharmaceutical (99mTc-DTPA).  Small (< 2 microns) uniform particles travel to the distal alveoli where they are deposited by sedimentation and gravitational impaction.  Pulmonary embolism generally does not affect this process, therefore, in the absence of other lung disorders, the ventilation images will appear uniform.

Perfusion imaging of the lungs is accomplished by injection of small (20-40 microns) macroaggregated albumin particles radiolabeled with 99mTc (99mTc-MAA).  More than 90% of these particles become trapped in the capillaries and arterioles of the lung fields based on the blood flow.  Normal perfusion shows uniform distribution throughout the lungs.

A positive V/Q scan for pulmonary emboli presents as segmental zones of reduced or absent perfusion associated with normal ventilation.  Since other conditions such as pulmonary edema, interstitial lung disease and lymphatic obstruction may affect lung perfusion without affecting lung ventilation, a current chest x-ray (within 24 hours) is helpful in assessing other causes for a positive lung V/Q.

Required scheduling information:

• Patient name, DOB, current weight and home phone.

• Reason for study.  

• Is this to evaluate prior to lung surgery?  If yes, a quantitative lung V/Q should be scheduled.

• Recent chest x-ray?  If yes, please send them to Nuclear Medicine for review at time of V/Q imaging

• Is this a call report before patient is allowed to leave?

Nuclear Medicine
Sacred Heart Medical Center
1255 Hilyard St., Eugene
(541) 686-7010

Please call 686-7010 to schedule your patient's exam.

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