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

1. V/Q scan
Dr Muhammad Qasim Khan

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

3. Indications
 diagnosis of suspected pulmonary embolism
 monitor pulmonary function following lung
transplant
 provide preoperative estimates of lung function
in lung cancer patients, where pneumonectomy is
planned

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

5.  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. The patient is then imaged in
the upright position in three phases: initial
breath, equilibrium and washout.

6.  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.

7. Interpretation
 Interpretive criteria developed from
the PIOPED, PIOPED 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).

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

9. Causes of ventilation/perfusion mismatch include:
 acute pulmonary embolism
 chronic pulmonary embolism
 obstruction of an artery by a tumor
 radiation therapy
The presence of a right-to-left shunt can be
assessed by searching for evidence of renal or brain
activity.

10. Thank You…