V/Q scan

V/Q (ventilation/perfusion) scan is a scintigraphic examination of the lung that evaluates pulmonary vasculature perfusion and segmental bronchoalveolar tree ventilation.

A chest x-ray should be performed within 12 to 24 hours and reviewed prior to lung scintigraphy 2 as there are other causes of perfusion defects such as atelectasis

The ventilation scan performed using radio-isotope labeled aerosols like technetium-99m DTPA delivered to the patient through a non-rebreathing mask, with the patient supine. The micro-aerosol particles are small enough to reach the distal tracheobronchial tree and reflect regional ventilation 1. The patient is then imaged in the upright position in three phases: initial breath, equilibrium and washout.

The perfusion lung scan involves injecting Tc-99m MAA intravenously in the supine position. The MAA particles are just small enough to get lodged in the pre-capillary arterioles. A high resolution, large field of view gamma camera is used to image the lungs.

Interpretive criteria developed from the PIOPEDPIOPED II, or PISAPED trials can be used to determine the probability of a pulmonary embolism on a V/Q scan. For the diagnosis of PE, a V/Q scan has a reported sensitivity of 77.4% and specificity of 97.7% when compared to CT pulmonary angiography (CTPA) or digital subtraction angiography (DSA) 3.

A normal ventilation scan (even distribution of radionuclide throughout the lung fields) with multiple, bilateral perfusion defects are the classical findings of pulmonary embolism 1.

Causes of ventilation/perfusion mismatch include:

The presence of a right-to-left shunt can be assessed by searching for evidence of renal or brain activity.

Article information

rID: 46829
System: Chest
Section: Radiography
Synonyms or Alternate Spellings:
  • VQ scans
  • VQ scan
  • Lung scintigraphy
  • Ventilation/perfusion scan

ADVERTISEMENT: Supporters see fewer/no ads

Cases and figures

  • Case 1: normal V/Q scan
    Drag here to reorder.
  • Case 2: pulmonary embolism
    Drag here to reorder.
  • Updating… Please wait.

     Unable to process the form. Check for errors and try again.

     Thank you for updating your details.