ventilation/perfusion scan is a series of two lung scans. The
scans are either performed together or one after the other, but are often referred
to as one procedure.
One of the scans is called a VQ scan, which
stands for ventilation quotient. This scan measures how well air is able to
flow through your lungs. The other scan is called a perfusion scan, which shows
where blood flows in your lungs.
Both scans involve the use of a low-risk
radioactive substance that can be traced by a special type of scanner. The
substance will show up in the scanned image and can tell your doctor
information about how well your lungs are working. The substance will gather at
areas of abnormal blood or airflow, which may indicate a blockage in the lung.
Why is the scan ordered?
A VQ scan is used most frequently to screen
for a pulmonary embolus, which is
also known as a blood clot in the lungs. Symptoms of pulmonary embolus may include:
- rapid heart rate
- trouble breathing
- decreased oxygen saturation
- chest pain
This scan may also be used to screen for
other lung conditions, or to test the lung function in people with lung
disease. The VQ scan may be used to screen for or test lung function related to
the following conditions:
- lung infections or inflammation, such as bronchitis, pneumonia, or
- chronic lung diseases, such as chronic obstructive pulmonary
disease (COPD) or emphysema
- pulmonary effusion, which occurs when fluid collects around the
- pulmonary artery narrowing
- atelectasis, which is a collapsed area in the lung
- airway obstruction, which can be
caused by a tumor
Preparing for the test
Your doctor will explain the procedure of the
VQ scan to you, as well as the risks associated with the test. You will be
asked to sign a consent form after the possible risks have been explained to
you and you’ve had a chance to ask any questions.
Before the test, you should tell your doctor
about any known allergies you have, particularly to contrast dyes or latex. This
will make sure your doctor and the rest of the medical staff are prepared for the
possibility of an allergic reaction during the test.
It’s also important that you tell your doctor
if you are pregnant or breastfeeding. The contrast dye used may be passed on to
the fetus or through breast milk.
You should inform your doctor if you have had
a test that included the use of radioactive materials — called a nuclear test —
in the past 48 hours. If you have, there may be radioactive dye remaining in
your body, which can affect the results of the test.
You should try to wear loose fitting clothing
without metal fasteners to the test, or you may be asked to change into a
patient gown. It’ll also necessary to remove any metal jewelry, including
piercings, so you may wish to also avoid wearing jewelry to the test. Generally,
there is no special dietary preparation, such as fasting, before the scan.
You may also be asked to have an X-ray of
your chest done 24 to 48 hours before your test.
What happens during the test
For the entire scan, which takes about 45
minutes, you’ll be asked to lie down on an examination table. For the perfusion
scan, a technician will set up an intravenous (IV) line. Radionuclide dye will
be introduced into your bloodstream through a needle, usually using a vein on
the inside of your elbow or on the back of your hand. This dye usually contains
small amounts of radioactive technetium. You may feel mild to moderate pain
from the IV or a pricking sensation.
When the dye has been injected, the
technician will remove the IV and you will then be moved under a special
scanner. This scanner will detect the dye and look at how it flows into your
lungs via your bloodstream.
You will need to lie still while the images
are being captured. However, the technician may ask you to move positions to get
pictures from different angles.
For the VQ scan, you will be given a
mouthpiece while you are still lying underneath the scanner. You will be asked
to breathe through the mouthpiece, which contains a gas with a radioactive
substance, usually radioactive xenon or technetium.
The scanner will take images of your lungs
while you are breathing in the gas. You should try not to swallow this gas. It
could interfere with the images that need to be taken of the lungs. You may be
asked to hold your breath to capture certain images.
When the technician has taken all the
necessary pictures, the mouthpiece will be removed, and you will be able to
leave the scanner. And your breathing will gradually remove the gas from your
What are the risks?
There is a low risk associated with a VQ
scan. The amount of radiation a person is exposed to in this process is roughly
equal to the amount they are naturally exposed to in a year, according to the National Heart, Lung, and Blood Institute.
However, problems can arise due to the
radioactive substances and the insertion of the IV. Possible risks include:
- excessive bleeding at the IV site
- infection at the IV site
- allergic reaction to the radioactive dye
After the test
You may be monitored for a short time after
the test to check for any allergic reactions. Someone will also check the IV
site for redness and swelling. You may feel slightly dizzy from lying down during
It is important that you drink plenty of
fluids after your test to help flush the radioactive substances from your body.
If you notice any redness, swelling, or pain at the IV site once you return
home, notify your doctor as this may be sign of an infection.
You can eat and drink as usual, unless your
doctor says otherwise. Also, avoid having any other nuclear procedures for the
next 24 to 48 hours.