Lung CT scan is a radiation diagnostic technique based on obtaining an image of lung tissue in the form of layered sections with a thickness of 0.1-1 cm. It is used to determine tumor processes and their prevalence, damage to intra-thoracic lymph nodes, pathological changes in the lung tissue and pleural cavity, the condition of the pulmonary artery, thoracic aorta, superior vena cava, trachea and bronchi of various caliber. Depending on the objectives of the study, a “pulmonary” mode or a mediastinal examination mode can be used for CT; contrast enhancement is possible to improve the image quality.
Lung CT scan is indicated when pathological changes or formations are detected on a review radiography to clarify their nature, localization and prevalence. The study can also be recommended if, with existing complaints and objective signs of lung damage, conventional radiographs do not reveal structural changes. CT has high diagnostic capabilities in detecting volumetric formations (tumors, abscesses, cysts), disseminated pathology (tuberculosis, sarcoidosis, metastases, etc.), diffuse parenchymal diseases (pneumonia, pneumoconiosis, dermatomyositis, Wegener’s granulomatosis, pneumosclerosis, etc.), COPD (emphysema, chronic bronchitis), anomalies of the bronchopulmonary and vascular system (lobar emphysema, hypoplasia of the lung, sequestration, Cartagener syndrome, arteriovenous aneurysms, agenesis or hypoplasia of the pulmonary artery, etc.).
Lung CT scan is indicated when receiving chest injuries to determine the violation of the integrity of the chest and post-traumatic changes in lung tissue. Tomography may be required before lung biopsy, planning the volume of surgery and in the postoperative period to monitor the stability of the result. In addition to changes in lung tissue and blood vessels, CT scans reveal changes in the pleura, diaphragm, mediastinum, and intra-thoracic lymph nodes.
CT is not indicated for extremely severe patients, pregnant women, patients whose body weight exceeds the maximum load on the device. It is better to refuse from conducting computer diagnostics with contrast in patients with renal insufficiency, severe diabetes mellitus, allergy to contrast agent.
Methodology of conducting
Native lung CT scan is performed without special preparation, contrast tomography is performed on an empty stomach. When performing the scan, the patient remains in clothes, it is required to remove all metal objects (jewelry, hairpins, glasses, dentures, hearing aid, etc.). The tomograph is a large device with a movable research table that moves in and out through a special tunnel. During the CT scan, an X-ray emitter and electronic detectors rotate around the motionless patient, transmitting the image to a computer that processes the results of a layer-by-layer scan. Thanks to computer processing, artifacts associated with a respiratory excursion of the chest, vascular pulsation are excluded.
The use of the “pulmonary mode” in lung CT scan allows to examine the interstitial slits, intersegmental septa, main, lobular and segmental bronchi, pulmonary vessels of various calibers. In the “mediastinal” mode, the trachea, heart, ascending and descending aorta, superior vena cava, pulmonary trunk and its branches, intra-thoracic lymph nodes are studied. During the diagnosis, several short-term breath delays (on exhalation or inhalation) are required at the doctor’s command. Intravenous contrast is performed when it is necessary to study the pathology of the pulmonary and main vessels (PE, aortic aneurysms, etc.), sometimes – neoplasms of the mediastinum and lungs. The procedure lasts no more than 15-20 minutes, while the scan itself lasts 30 seconds.
Interpretation of results
When interpreting the scan, the radiologist examines the location and size of the lungs, the presence of anomalies in them; the condition of the pulmonary parenchyma for the presence of infiltrates, cavities, formations, bullae; the airiness of lung tissue; the condition of the tracheobronchial tree, vessels, lymph nodes, mediastinum, fiber, pleural cavities, ribs, soft tissues of the chest. Normally, infiltrative and focal changes in the lung tissue are not detected with lung CT scan. The intra-thoracic lymph nodes are not enlarged. The anatomical structures of the mediastinum are differentiated without changes, the heart has the correct configuration. There is no free fluid in the cavities of the pleura and pericardium. The lumen of the bronchi and trachea is not changed.
Complications of lung CT scan may be associated with intravenous contrast and manifest as urticaria or anaphylactic reactions. The toxicity of contrast can cause the development of renal failure in patients with initial renal dysfunction, dehydration, diabetes mellitus. Breastfeeding women can resume breastfeeding a day after CT using contrast. The dose of active radiation during tomography is higher than during radiography or fluorography, and is about 10 mSvt. In general, the diagnostic potential of lung CT scan exceeds the risks associated with radiation and the use of contrast.
With the help of computed tomography of the lungs, structures that are indistinguishable during fluorography and radiography of the lungs are visualized. Projection layering of tissues through which X-rays penetrate is also excluded, which significantly increases the informative value of tomography. CT sensitivity in detecting lung pathology is about 94%, while chest radiography is about 80%. The detection of X-ray morphological signs of pathology in CT is achieved in the early stages of the disease, which led to the widespread use of the method. Nevertheless, according to the existing rules, a CT scan of the lungs should always be preceded by an overview X-ray.