A V/Q (ventilation/perfusion) scan is a diagnostic procedure used to assess lung perfusion and ventilation, particularly for suspected pulmonary embolism. It involves imaging techniques with radionuclide aerosols and intravenous injections to evaluate pulmonary function and potential obstructions. The scan is crucial in preoperative assessments for lung cancer and in monitoring post-lung transplant function.

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…