Ventilation/ventilation scans , also called V/Q lung scan , is a type of medical imaging using skintigraphy and medical isotopes to evaluate the circulation of air and blood in the patient's lungs, to determine ratio of ventilation/perfusion. The ventilation part of this test looks at the ability of the air to reach all parts of the lungs, while the perfusion part evaluates how well the blood circulates inside the lungs. As Q in physiology is a letter used to describe blood flow the term V/Q scan appears.
Video Ventilation/perfusion scan
Usage
This test is most often performed to check for the presence of blood clots or abnormal blood flow in the lungs (such as pulmonary embolism (PE) although computed tomography with radiocontrast is now more commonly used for this purpose.Q scan may be used in some circumstances where radiocontrast is not accordingly, as in renal failure.
V/Q lung scans can be performed in cases of serious lung disorders such as chronic obstructive pulmonary disease (COPD) or pneumonia as well as pulmonary lung function quantification before and postoperative pulmonary lobectomy.
Results significance
Decreased absorption of inhaled radioisotopes may indicate impaired ability to breathe, airway obstruction, or possible pneumonia.
The decreased circulation of injected MAA indicates problems with blood flow to or within the lungs. Localized areas of declining retreat, usually in wedge-shaped (or pie-shaped) configuration with normal ventilation images (mismatched mismatch) indicate pulmonary embolus or blood clots in the lungs, leading to reduced perfusion beyond obstruction.
Maps Ventilation/perfusion scan
Risk
Although this test uses radioactive material, the total amount of radiation exposure is low. A typical effective dose for the V/Q scan range of 1-5 mSv. To reduce radiation exposure in pregnant patients, the total radioactivity given may be reduced or the ventilation phase is eliminated. A CT pulmonary angiogram (CTPA) with radiocontrast may be performed alternatively, although this may result in a larger radiation dose for the patient.
Procedures
The ventilation and perfusion phase of the V/Q lung scan is performed together and may include chest X-rays for comparison or to look for other causes of lung disease. Defects in image perfusion require improper ventilation defects to indicate pulmonary embolism.
In the test ventilation phase, gaseous radionuclides such as xenon-133, kripton-81m, or DTPA technetium-99m in the form of aerosols are sucked by the patient through a funnel or mask covering the nose and mouth. Ventilation imaging can also be performed using Technegas machines that produce radioactive aerosol nanoparticles, especially carbon nanoparticles containing technetium-99m. The perfusion phase of the test involves intravenous injection of radioactive technetium albumin aggregate (Tc99m-MAA). The gamma camera acquires images for both phases of research. The SPECT image can also be retrieved after the Technial injection labeled MAA. SPECT is often bypassed if the patient has pulmonary hypertension.
It is also possible to scan with positron emission tomography (PET) rather than conventional gamma camera scintigraphy. This has been done with Gallium-68 labeled carbon nanoparticles (Galligas) using a conventional Technegas engine for ventilation images, and with Gallium-68 labeled MAA (Ga68-MAA) for perfusion images. PET has several potential advantages including resolution, speed, and superior quantification.
See also
- Ventilation/perfusion ratio
References
Source of the article : Wikipedia
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