Definition
A frequently used imaging method for the representation of the lungs is computed tomography (CT). This is a special X-ray examination in which several body cross-sections are recorded and combined into a three-dimensional image with very high resolution. The imaging is performed with the help of X-rays, which are absorbed to varying degrees by the various tissues of the body.
A so-called CT thorax is prepared to show the lungs. This is an image of the thorax (lungs and heart). It often serves as a supplement to conventional x-ray images. For some lung diseases, a particularly high-resolution computer tomography (HRCT) procedure is used.
Indications for a CT of the lungs
Computer tomography of the lungs is used in the diagnosis of many diseases. Compared to conventional x-rays, it is characterized by a significantly higher resolution and three-dimensional imaging, which allows even very fine structures in the lung tissue to be displayed. The CT thorax is used particularly frequently for the identification, progression and follow-up of tumors and metastases in the lung area.
In addition, numerous inflammatory diseases of the lung can be well visualized in the CT thorax. In addition to classic pneumonia, chronic obstructive pulmonary disease (COPD) can also be diagnosed. In addition, the CT thorax is suitable for imaging vascular changes in the area of the large pulmonary arteries.
Vascular occlusions (e.g. in pulmonary embolism) as well as vascular changes (e.g. due to atherosclerosis or aneurysms) can be clearly identified with the help of computer tomography. Last but not least, the CT thorax is also used for planning major operations in the thorax region, as structures relevant to the operation are displayed very finely.
Depending on the issue at hand, it may be necessary to administer a contrast medium containing iodine in order to better distinguish the individual tissue structures from each other in terms of colour. Pulmonary embolism is a vascular occlusion of one or more pulmonary arteries. This is often caused by a thrombus that has been infiltrated into the lungs, mainly from the deep veins of the legs.
As a result, the lung tissue is less supplied with blood and the right heart is put under greater strain. A CT-guided imaging of the vessels (CT angiography) is suitable for imaging pulmonary embolism. For this purpose, the patient is administered an iodine-containing contrast medium intravenously.
In the CT images, the thrombus can thus be clearly distinguished from the otherwise well perfused vessel. In addition, blood is often taken to confirm the diagnosis and the D-dimer concentration in the blood is determined. Pneumonia can manifest itself in different ways in the lung area.
Both the air-filled alveolar space (alveolar pneumonia) and the connective tissue of the lung located in between (interstitial pneumonia) can be affected. Depending on age and cause of infection, a wide range of pathogens (bacteria and viruses) can be responsible for the development of pneumonia. The main criterion in the diagnosis of pneumonia is a newly occurring infiltrate detected in the X-ray image.
This infiltrate appears as a white shadow in the area of the air-filled (black) alveolar space. If the X-ray findings are unclear, a CT thorax can be made to confirm the diagnosis. Furthermore, computed tomography is also regularly used in the identification as well as the follow-up and monitoring of lung tumours and metastases.
Fuzzily defined round foci of the lung appear as white shadows. Depending on the type of tumour, these may be located at different sites in the lung. Basically, any unclear round foci in patients over 40 years of age are evaluated as lung cancer until proven otherwise.
For better differentiation and to assess the blood supply to the tumour, a contrast medium is often administered in the course of CT diagnostics. To confirm the diagnosis, the tumor is also punctured (lung biopsy) by CT to analyze the tumor tissue. In chronic obstructive pulmonary disease (COPD), the small airways become inflamed (chronic obstructive bronchitis), causing them to become increasingly congested and the lungs to over-inflate (emphysema).
As a result, breathing is significantly restricted. There are several possibilities for diagnosing COPD. In addition to a routinely performed test of lung function, a conventional X-ray thorax is used to visualize the over-inflation of the lungs.
For a better assessment of the localization and distribution of emphysema, a CT thorax can be performed additionally. Lung fibrosis is the final stage of many different lung diseases. This results in a significant increase in connective tissue within the lung, which makes breathing more difficult for the patient.
Often chronic inflammation in the lung area is the cause. The diagnosis of pulmonary fibrosis is also based on a test of lung function as well as on imaging using X-rays. A conventional X-ray thorax is often supplemented by a CT thorax.
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