One of the most important imaging tests for a lung exam is the Lung scintigraphy. It is the standard procedure, especially when diagnosing pulmonary embolism.
What is pulmonary scintigraphy?
Lung scintigraphy is one of the non-invasive procedures and is a nuclear medicine imaging examination method to assess the blood flow and ventilation of the lungs. Even the smallest circulatory disorders can be made visible via a gamma camera, which makes them indispensable for diagnosing pulmonary embolism.
Lung scintigraphy is used to diagnose pulmonary embolism in various lung diseases and malformations. It also has the advantage that this method can also be used to calculate the blood flow between the lungs in order to assess surgical risks and to be able to make prognoses after the removal of lung tissue in the case of lung cancer.
Function, effect & goals
A lung scintigraphy consists of various techniques that can be combined with one another:
- Ventilation scintigraphy
- Inhalation scintigraphy
- Perfusion scintigraphy
During ventilation scintigraphy, a radioactive noble gas, usually 133Xenon, must be inhaled and exhaled by the patient. The body does not absorb noble gases. During inhalation and exhalation, the gamma camera records 3 images (three-phase scintigraphy): image 1 is recorded when inhaling, image 2 during the distribution of the gas in the lungs and image 3 when the gas is exhaled. The gas distribution shows the ventilation in the respective area. The aim of this technique is to determine whether the air flow is obstructed or the lungs are not able to expand. But it is technically complex and the patient has to inhale and exhale at the right moment.
In inhalation scintigraphy, the smallest, radioactively marked particles of a carrier substance are finely vaporized or nebulized and fed into the patient's breath. It is usually used before a perfusion scintigraphy, because it allows the ventilation and blood flow in the lungs to be compared. The doctor can also recognize the original complaints and use this knowledge to initiate the right therapy.
In perfusion scintigraphy, the patient is injected intravenously with radioactively marked protein building blocks, which migrate through the veins into the lungs. Less radioactive particles are visible where blood flow is impaired. When distributing the radioactive particles, the patient's posture during the injection is important. In healthy people, deeper lung areas are depicted more strongly due to gravity, while with pulmonary high pressure (increased blood pressure in the lungs, all areas are depicted equally.
If a life-threatening embolism due to a blood clot is suspected, perfusion scintigraphy is usually the first choice and is combined with a chest X-ray.
It can also detect right-left shunts in the pulmonary circulation, in which blood is pumped from the lungs into the body via a connection between the pulmonary and body circulation without the supply of oxygen. Normally, the radioactive particles remain in the lungs and are also broken down again via the lungs. In the case of a shunt, on the other hand, they migrate into the body's circulation and are excreted with the urine via the kidneys. The computer can use the volume of blood flowing through the kidneys per minute to calculate the volume and extent of the shunt.
In lung cancer, the inhalation scintigraphy is combined with the perfusion scintigraphy before and after the operation in order to be able to assess the function of the lungs or the remaining lung portion before and after the operation and to be able to give a prognosis after the operation.
Lung scintigraphy with gallium citrate enables the assessment of diseases of the cartilage framework and inflammatory processes in the lungs and is particularly used in the examination of pneumonia or tuberculosis. Pneumonia and pulmonary infarction can also be detected more quickly with a lung scintigraphy than with other examination methods.
Risks, side effects & dangers
Side effects are rather rare with a lung scintigraphy, at best there is a risk of low radiation exposure from the radioactive drugs used, which is considerably below the normal radiation exposure in one year. There are no known interactions with other drugs. With intravenous injection, slight allergic reactions to the protein components can sometimes occur. If you have a protein allergy, you should consider whether lung scintigraphy is useful in this case. Patients who have to take blood thinners (e.g. Marcumar) should expect a little bleeding at the injection site.
Nuclear medical examinations such as a lung scintigraphy can with restrictions also be carried out during pregnancy, but the most important thing here is the healthy development of the child. Possible side effects and risks should be carefully weighed and discussed with the pregnant woman. Possibly. the dose can be reduced. Breastfeeding women should not breastfeed for 48 hours after nuclear medicine exams.
No special preparation is required for lung scintigraphy and patients do not have to appear sober. Patients with asthma should take bronchodilator medication prior to the exam. The costs are covered by the statutory health insurance.
Since a lung scintigraphy is associated with few risks and side effects, it is a highly recommended method for examining the blood flow and ventilation of the lungs and the best examination method for diagnosing pulmonary embolism. At most, there are minor limitations in the informative value of chronic obstructive pulmonary diseases (COPD).
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