What Is a Lung Ventilation/Perfusion Scan?
A lung ventilation/perfusion scan, or VQ scan, is a
test that measures air and blood flow in your lungs.
This test most often is used to help diagnose or
rule out a
pulmonary
embolism (PULL-mun-ary EM-bo-lizm), or PE. A PE is a blood clot that
travels to the lungs and blocks blood flow. This results in low blood oxygen
levels, damage to the lungs, or even death.
The scan also can detect poor blood flow in the
lungs’ blood vessels and provide pictures that help doctors prepare for
some types of lung surgery.
Overview
A VQ scan involves two types of scans: ventilation
and perfusion. The ventilation scan shows where air flows in your lungs. The
perfusion scan shows where blood flows in your lungs.
Both scans use radioisotopes (a low-risk radioactive
substance). For the ventilation scan, you inhale a small amount of radioisotope
gas. For the perfusion scan, the radioisotopes are injected into a vein in your
arm.
Radioisotopes release energy inside your body.
Special scanners outside of your body use the energy to create images of air
and blood flow patterns in your lungs.
Outlook
VQ scans involve little pain or risk for most
people. During the perfusion scan, you may feel some discomfort when the
radioisotopes are injected. You also may have a bruise at the injection site
after the test.
The amount of radiation in the radioisotopes used
for both tests is very small. The amount of radiation in the gas and injection
together are about the same as the amount a person is naturally exposed to in 1
year.
Very rarely the radioisotopes used in VQ scans can
cause an allergic reaction. Hives or a rash may result. Medicines can relieve
this reaction.
Other Names for Lung Ventilation/Perfusion Scans
Lung ventilation/perfusion scans also are called
pulmonary ventilation/perfusion scans and nuclear medicine tests.
Who Needs a Lung Ventilation/Perfusion Scan?
People who have signs or symptoms of a
pulmonary
embolism (PE) may need lung ventilation/perfusion (VQ) scans.
A PE occurs when a blood clot travels to the lungs
and blocks blood flow. Signs and symptoms of PE include chest pain, trouble
breathing, rapid breathing, coughing, coughing up blood, and a rapid heart
rate. Some clots travel to the lungs from
veins
deep in the legs. This can cause pain and swelling in the affected limb(s).
Doctors use VQ scans to help find out whether a PE
is causing these signs and symptoms. A VQ scan alone, however, won’t
confirm whether you have PE. Your doctor also will consider other factors when
making a diagnosis.
Doctors also use VQ scans to detect poor blood flow
in the lungs’ blood vessels and to examine the lungs before some types of
surgery.
What To Expect Before a Lung Ventilation/Perfusion
Scan
Most people don’t need to prepare for a lung
ventilation/perfusion (VQ) scan. Your doctor may ask you to wear clothing that
has no metal hooks or snaps. These materials can block the scanner’s
view. Or, you may be asked to wear a hospital gown for the test.
Tell your doctor whether you’re pregnant or
may be pregnant. If possible, you should avoid unnecessary radiation exposure
during pregnancy. This is because of the concern that radiation may harm the
fetus.
You and your doctor will decide whether the benefits
of a VQ scan outweigh the small risk to the fetus, or whether another test
might be better.
If you’re breast-feeding, ask your doctor how
long you should wait after the test before you breast-feed. The radioisotopes
used for VQ scans can be passed to your baby through your breast milk.
You may want to prepare for the scan by pumping and
saving milk for 24 to 48 hours in advance. You can bottle-feed your baby in the
hours after the VQ scan.
What To Expect During a Lung Ventilation/Perfusion
Scan
A lung ventilation/perfusion (VQ) scan is done at a
radiology clinic.
You will lie on a table for about 1 hour and have
two types of scans: ventilation and perfusion. The ventilation scan shows where
air flows in your lungs. The perfusion scan shows where blood flows in your
lungs.
You must lie very still for the tests, or the
pictures may blur. If you’re having trouble staying still, your doctor
may give you medicine to help you relax.
Both scans use radioisotopes (a low-risk radioactive
substance). This substance releases energy inside your body. Special scanners
outside of your body use the energy to create images of air and blood flow to
your lungs.
The radioisotopes used in VQ scans can cause an
allergic reaction, including itching and hives. If this happens, your doctor
will give you medicine to relieve the symptoms.
Ventilation
For this scan, you lie on an open table that moves
under the arm of the scanner. You wear a breathing mask over your nose and
mouth and inhale a small amount of radioisotope gas mixed with oxygen.
As you breathe, the scanner takes pictures that show
air going into your lungs. You’ll need to hold your breath for a few
seconds at the start of each picture.
The scan is painless, and each picture takes only a
few minutes. However, wearing the mask can make some people feel anxious. If
this happens, your doctor may give you medicine to help you relax.
Perfusion
For this scan, a member of the health care team will
inject a small amount of radioisotope into a vein in your arm. The scanner then
takes pictures of blood flow through your lungs.
The scan itself doesn’t hurt, but you may feel
some discomfort when the radioisotopes are injected.
What To Expect After a Lung Ventilation/Perfusion
Scan
Most people can return to their normal routines
right after a lung ventilation/perfusion (VQ) scan.
If you got medicine to help you relax during the
scan, your doctor will tell you when you can return to your normal routine. The
medicine may make you tired, so you’ll need someone to drive you home.
You may have a bruise on your arm where the
radioisotopes were injected. You will need to drink plenty of fluids to flush
the radioisotopes out of your body. Your doctor can advise you about how much
fluid to drink.
If you’re breast-feeding, ask your doctor how
long you should wait after the test before you breast-feed. The radioisotopes
used for VQ scans can be passed to your baby through your breast milk.
You may want to prepare for the scan by pumping and
saving milk for 24 to 48 in advance. You can bottle-feed your baby in the hours
after the VQ scan.
What Does a Lung Ventilation/Perfusion Scan Show?
A lung ventilation/perfusion (VQ) scan shows how
well air and blood are flowing through your lungs. Normal results will show
full air and blood flow to all parts of your lungs.
If air flow is normal but blood flow isn’t,
you may have a
pulmonary
embolism (PE). PE occurs when a blood clot travels to the lungs and blocks
blood flow.
The results of the scan will show whether
you’re at high, medium, or low risk for PE. However, a VQ scan alone
won’t confirm whether you have PE. A scan showing low blood flow in spots
may reflect other lung problems, such as lung damage from
COPD
(chronic obstructive pulmonary disease).
Your doctor will use the VQ scan results along with
results from a physical exam,
chest
x ray, and other tests to make a diagnosis.
What Are the Risks of a Lung Ventilation/Perfusion
Scan?
Lung ventilation/perfusion (VQ) scans involve little
risk for most people. The radioisotopes used for both tests expose you to a
small amount of radiation. The amount of radiation in the gas and injection
together are about the same as the amount a person is naturally exposed to in 1
year.
Although rare, the radioisotopes may cause an
allergic reaction.
Radiation
The radiation from the radioisotopes used in VQ
scans leaves the body after a few days.
Exposure to radiation is associated with a risk of
cancer. However, it’s not known whether the amount of radiation from a VQ
scan puts you at higher risk than the amount of radiation you’re
naturally exposed to.
You and your doctor will decide whether the benefits
of a VQ scan outweigh any possible risks. Your doctor also will try to avoid
ordering repeated VQ scans over a short period.
If you’re pregnant or breast-feeding, talk to
your doctor about the risk of radiation related to this test. He or she will
consider whether another test can be used instead.
Allergic Reaction
Very rarely the radioisotopes used in VQ scans can
cause an allergic reaction. Hives or a rash may result. Medicines can relieve
this reaction.
Key Points
- A lung ventilation/perfusion scan, or VQ scan, is
a test that measures air and blood flow in your lungs.
- The test most often is used to help diagnose or
rule out a
pulmonary
embolism (PE). The scan also can detect poor blood flow in the lungs’
blood vessels and provide pictures that help doctors prepare for some types of
surgery.
- People who have signs or symptoms of a PE may
need VQ scans. These signs and symptoms may include chest pain, trouble
breathing, rapid breathing, coughing, coughing up blood, rapid heart rate, and
pain or swelling in a leg.
- Most people don’t need to prepare for VQ
scans. Your doctor may ask you to wear clothing that has no metal hooks or
snaps. These materials can block the scanner’s view. Or, you may be asked
to wear a hospital gown for the test.
- Tell your doctor whether you’re pregnant or
may be pregnant. If possible, you should avoid unnecessary radiation exposure
during pregnancy. This is because of the concern that radiation may harm the
fetus.
- During the VQ scan, you will lie still on a table
for about 1 hour and have two types of scans: ventilation and perfusion. A
ventilation scan shows where air flows in your lungs. A perfusion scan shows
where blood flows in your lungs. If you’re having trouble staying still,
your doctor may give you medicine to help you relax.
- Both scans use radioisotopes (a low-risk
radioactive substance). This substance releases energy inside your body. The
scanner uses this energy to create images of air and blood flow in your lungs.
- Most people can return to their normal routines
right after a VQ scan. If you got medicine to help you relax during the scan,
your doctor will tell you when you can return to your normal routine. The
medicine may make you tired, so you’ll need someone to drive you home.
- If you’re breast-feeding, ask your doctor
how long you should wait after the test before you breast-feed. The
radioisotopes used for VQ scans can be passed to your baby through your breast
milk. You may want to prepare for the scan by pumping and saving milk for 24 to
48 hours in advance. You can bottle-feed your baby in the hours after the scan.
- Normal results from a VQ scan will show full air
and blood flow to all parts of your lungs. If air flow is normal but blood flow
isn’t, you may have a PE. However, a VQ scan alone can’t diagnose a
PE. Your doctor will use the VQ scan results and the results from a physical
exam,
chest
x ray, and other tests to make a diagnosis.
- VQ scans involve little pain or risk for most
people. The radioisotopes used for both tests expose you to a small amount of
radiation. Very rarely the radioisotopes can cause an allergic reaction. Hives
or a rash may result. Medicines can relieve this reaction.
Links to Other Information About Lung
Ventilation/Perfusion Scans
NHLBI Resources
Non-NHLBI Resources
Clinical Trials
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