A ventilation/perfusion lung scan, also called a V/Q lung scan, or ventilation/perfusion scintigraphy, is a type of medical imaging using

scintigraphy Scintigraphy (from Latin ''scintilla'', "spark"), also known as a gamma scan, is a diagnostic test in nuclear medicine, where radioisotopes attached to drugs that travel to a specific organ or tissue (radiopharmaceuticals) are taken internally and ...

and

medical isotopes A medical isotope is an isotope used in medicine. The first uses of isotopes in medicine were in radiopharmaceuticals, and this is still the most common use. However more recently, separated stable isotopes have also come into use. Examples of ...

to evaluate the circulation of air and blood within a patient's

lungs The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of ...

, in order to determine the

ventilation/perfusion ratio In respiratory physiology, the ventilation/perfusion ratio (V/Q ratio) is a ratio used to assess the efficiency and adequacy of the matching of two variables: * V – ventilation – the air that reaches the alveoli * Q – perfusion – the blood ...

. The ventilation part of the test looks at the ability of air to reach all parts of the lungs, while the

perfusion Perfusion is the passage of fluid through the circulatory system or lymphatic system to an organ or a tissue, usually referring to the delivery of blood to a capillary bed in tissue. Perfusion is measured as the rate at which blood is deliv ...

part evaluates how well blood circulates within the lungs. As Q in physiology is the letter used to describe bloodflow the term V/Q scan emerged.

Uses

This test is most commonly done in order to check for the presence of a

blood clot A thrombus (plural thrombi), colloquially called a blood clot, is the final product of the blood coagulation step in hemostasis. There are two components to a thrombus: aggregated platelets and red blood cells that form a plug, and a mesh of cr ...

or abnormal blood flow inside the lungs (such as a

pulmonary embolism Pulmonary embolism (PE) is a blockage of an artery in the lungs by a substance that has moved from elsewhere in the body through the bloodstream (embolism). Symptoms of a PE may include shortness of breath, chest pain particularly upon breathing ...

(PE) although

computed tomography A computed tomography scan (CT scan; formerly called computed axial tomography scan or CAT scan) is a medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers ...

with

radiocontrast Radiocontrast agents are substances used to enhance the visibility of internal structures in X-ray-based imaging techniques such as computed tomography (contrast CT), projectional radiography, and fluoroscopy. Radiocontrast agents are typically i ...

is now more commonly used for this purpose. The V/Q scan may be used in some circumstances where radiocontrast would be inappropriate, as in Allergy to contrast agent or

kidney failure Kidney failure, also known as end-stage kidney disease, is a medical condition in which the kidneys can no longer adequately filter waste products from the blood, functioning at less than 15% of normal levels. Kidney failure is classified as eit ...

. A V/Q lung scan may be performed in the case of serious lung disorders such as

chronic obstructive pulmonary disease Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease characterized by long-term respiratory symptoms and airflow limitation. The main symptoms include shortness of breath and a cough, which may or may not produce ...

(COPD) or

pneumonia Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing. The severi ...

as well as a lung performance quantification tool pre- and post-lung

lobectomy Lobectomy means ''surgical excision of a lobe''. This may refer to a lobe of the lung (also simply called a lobectomy), a lobe of the thyroid ( hemithyroidectomy), a lobe of the brain (as in anterior temporal lobectomy), or a lobe of the live ...

surgery.

Significance of results

Decreased uptake of the inhaled radioisotope may indicate an impaired ability to breathe, airway obstruction, or possible pneumonia. Decreased circulation of the injected MAA indicates a problem with blood flow into or within the lungs. A localized area of decreased uptake, usually in a wedge shaped (or pie shaped) configuration with normal ventilation images (mismatched defect) suggests a

pulmonary embolus Pulmonary embolism (PE) is a blockage of an artery in the lungs by a substance that has moved from elsewhere in the body through the bloodstream (embolism). Symptoms of a PE may include shortness of breath, chest pain particularly upon breathing ...

or blood clot in the lungs, which leads to reduced perfusion beyond the obstruction.

Risks

Although this test uses radioactive materials, the total amount of radiation exposure is low. Typical effective doses for a V/Q scan range from 1-5 mSv. In order to decrease the radiation exposure in pregnant patients, the total radioactivity administered may be decreased or the ventilation phase omitted. A CT pulmonary angiogram (CTPA) with

can alternatively be performed, although this can result in a greater radiation dose to the patient.

Procedure

The ventilation and perfusion phases of a V/Q lung scan are performed together and may include a

chest X-ray A chest radiograph, called a chest X-ray (CXR), or chest film, is a projection radiograph of the chest used to diagnose conditions affecting the chest, its contents, and nearby structures. Chest radiographs are the most common film taken in me ...

for comparison or to look for other causes of lung disease. A defect in the perfusion images requires a mismatched ventilation defect to indicate pulmonary embolism. In the ventilation phase of the test, a gaseous radionuclides such as xenon-133,

krypton-81m There are 34 known isotopes of krypton (36Kr) with atomic mass numbers from 69 through 102. Naturally occurring krypton is made of five stable isotopes and one () which is slightly radioactive with an extremely long half-life, plus traces of radi ...

, or

technetium-99m Technetium-99m (99mTc) is a metastable nuclear isomer of technetium-99 (itself an isotope of technetium), symbolized as 99mTc, that is used in tens of millions of medical diagnostic procedures annually, making it the most commonly used medical r ...

DTPA Pentetic acid or diethylenetriaminepentaacetic acid (DTPA) is an aminopolycarboxylic acid consisting of a diethylenetriamine backbone with five carboxymethyl groups. The molecule can be viewed as an expanded version of EDTA and is used similarl ...

in an aerosol form is inhaled by the patient through a mouthpiece or mask that covers the nose and mouth. Ventilation imaging can also be performed using a Technegas machine which produces an aerosol of radioactive nanoparticles, specifically carbon nanoparticles containing

. The perfusion phase of the test involves the intravenous injection of radioactive technetium macro aggregated albumin (Tc99m-MAA). A

gamma camera A gamma camera (γ-camera), also called a scintillation camera or Anger camera, is a device used to image gamma radiation emitting radioisotopes, a technique known as scintigraphy. The applications of scintigraphy include early drug development ...

acquires the images for both phases of the study. A SPECT image can also be taken following an injection of Technetium labelled MAA. SPECT is often skipped if the patient has pulmonary hypertension. It is also possible to perform the scan with

positron emission tomography Positron emission tomography (PET) is a functional imaging technique that uses radioactive substances known as radiotracers to visualize and measure changes in metabolic processes, and in other physiological activities including blood flow, ...

(PET) rather than conventional gamma camera scintigraphy. This has been performed with Gallium-68 labelled carbon nanoparticles (Galligas) using a conventional Technegas machine for ventilation images, and with Gallium-68 labelled MAA (Ga68-MAA) for perfusion images. PET has multiple potential advantages including superior resolution, speed and quantification.

References

{{DEFAULTSORT:Ventilation perfusion scan Respiratory system imaging Scintigraphy

Uses

Significance of results

Risks

Procedure

See also

References