Pulmonary ventilation/perfusion scan
Alternate Names : V/Q scan; Ventilation/perfusion scan; Lung ventilation/perfusion scan
Definition
A pulmonary ventilation/perfusion scan is a pair of nuclear scan tests that use inhaled and injected radioactive material (radioisotopes) to measure breathing (ventilation) and circulation (perfusion) in all areas of the lungs.
How the test is performed
Two tests that may be performed separately or together.
The perfusion scan is performed by injecting radioactive albumin (99m Tc macroaggregated albumin) into a vein. The patient is immediately placed on a movable table that is positioned under the arm of the scanner. The patient's lungs are scanned to detect the location of the radioactive particles as blood flows through the lungs.
The ventilation scan is performed by scanning the lungs while having the person inhale radioactive gas (air mixed with 133 xenon or 99m Tc DTPA aerosol). A mask is placed over the nose and mouth, and you are asked to breathe the gas while sitting or lying on the table beneath the arm of the scanner.
How to prepare for the test
No diets, medications, or fasting are necessary before the test.
A chest X-ray is usually performed prior to or following a ventilation and perfusion scan.
The patient usually signs a consent form and is asked to wear a hospital gown or comfortable clothing without metal fasteners.
Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
infant test or procedure preparation (birth to 1 year)
toddler test or procedure preparation (1 to 3 years)
preschooler test or procedure preparation (3 to 6 years)
schoolage test or procedure preparation (6 to 12 years)
adolescent test or procedure preparation (12 to 18 years)
How the test will feel
The table may be hard or cold. There may be a sharp prick during injection of material into the vein for the perfusion portion of the scan. The mask used during the ventilation scan may give some persons a claustrophobic feeling. The patient must lie still during scanning.
The radioisotope injection usually does not cause a specific feeling.
What the risks are
Risks are essentially the same as for X-rays (radiation) and needle pricks.
There is a small exposure to radiation from the radioisotope. The radioisotopes used during scans are short lived, with almost all radiation gone in a few days. However, as with any radiation exposure, caution is advised during pregnancy or if a woman is breastfeeding. No radiation is emitted from the scanner; it detects radiation and converts it to a visible image.
Any time a needle is placed in the body there is a slight risk for infection or bleeding. The risk with perfusion scan is no different than for placement of an intravenous needle for any other purpose.
It is extremely rare, but a person may develop an allergy to the radioisotope, which may include a serious anaphylactic reaction.
Why the test is performed
The ventilation scan is used to evaluate the ability to aerate all portions of the lungs. The perfusion scan measures the supply of blood through the lungs.
A ventilation and perfusion scan is most often performed to detect pulmonary embolus. It is also used to evaluate lung function in people with advanced pulmonary disease such as COPD. It is also used to detect the presence of shunts (abnormal circulation) in the pulmonary blood vessels.
Who is a candidate for the test?
The healthcare provider may order a pulmonary perfusion scan in the following circumstances: � the person has chest pain or shortness of breath � results of the person's pulmonary function tests are abnormal � a woman is on oral contraceptives and shows signs of a pulmonary embolus, or a blood clot to the lungs � to rule out deep venous thrombosis in a person with leg pain � an individual has breathing problems after surgery
How is the test performed?
For the scan, a person is often asked to sit upright. If a person is unable to sit, he or she can lie flat on a table. A radioactive substance known as Tc-99m macroaggregated albumin will be injected into a vein in the arm. The substance gives off gamma rays from within the body. These rays are detected by a "gamma camera" that is positioned over the chest.
A computer then generates pictures that can be interpreted by a radiologist. The lungs will be scanned in multiple positions (usually six). The exam takes approximately 45 minutes. Usually, a second test called a pulmonary ventilation scan will follow the perfusion scan.
What is involved in preparation for the test?
The individual will undress from the waist up and put on an exam gown. All jewelry and metal objects will be removed.
What do the test results mean?
A normal test shows that the blood flow to the lung is normal. An abnormal test result often indicates a problem with blood flow to the lungs caused by a pulmonary embolus.
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