Computed tomography of the chest

As a rule, computed tomography of the chest cavity is performed in the transverse direction (axial slices) with a slice thickness and scanning step of 8 - 10 mm. For example, when performing slices 10 mm thick, with an overlap of 1 mm, the table is advanced with a step of 8 mm. The diagram accompanying the corresponding CT images will help you better navigate the localization of anatomical structures on the slices. In order not to miss pathological changes in the lungs, it is necessary to print slices on a printer both in the soft tissue and in the pulmonary window or save the video information of the study on a CD. In this case, each slice can be viewed in either of the two windows. On the other hand, a large number of images inevitably entails the need for a clear system for their evaluation, so as not to waste time viewing slices unsystematically.

Sequence of CT image analysis

Beginner doctors often ignore the examination of the soft tissues of the chest wall, because they automatically consider the examination of the lungs and mediastinal organs to be more important. But, first of all, it is necessary to evaluate the tissues of the chest wall. Pathological changes are usually localized in the mammary gland and axillary fat. Then, using the installed soft tissue window, they move on to searching for pathological formations of the mediastinum. The aortic arch, which even an inexperienced researcher will find, will help you navigate the structures located here. Above the aortic arch is the upper mediastinum, where pathological formations should be distinguished from the large vessels located nearby: the brachiocephalic trunk, the left common carotid artery and the subclavian artery. Also located nearby are the brachiocephalic vein, the superior vena cava and the trachea, and a little behind - the esophagus. Typical locations of enlarged lymph nodes below the aortic arch include the aortopulmonary window, just below the tracheal bifurcation, in the area of the pulmonary roots, and next to the descending aorta behind the crura of the diaphragm (retrocrural). Normally, several lymph nodes up to 1.5 cm in diameter may be detected in the aortopulmonary window. Normal-sized lymph nodes located anterior to the aortic arch are rarely visible on CT. A soft tissue window examination is considered complete when the heart (presence of coronary sclerosis, dilated cavities) and pulmonary roots (vessels are clearly visible and there is no dilation or deformation) have been examined. Only after all this has been done does the radiologist move on to the pulmonary or pleural window.

Due to the significant width of the pleural window, in addition to the lung tissue, the bone marrow in the vertebral bodies is well visualized. Along with the pulmonary vessels, the bone structure can also be assessed. When examining the pulmonary vessels, attention should be paid to their width, which normally gradually decreases from the roots to the periphery. The depletion of the vascular pattern is normally determined only along the borders of the lobes and on the periphery.

To distinguish volumetric formations from cross-sections of vessels, it is necessary to compare adjacent sections. More or less rounded volumetric formations may be metastases to the lungs.

Printing images in the overlapping windows mode (lung and soft tissue) is not justified because pathological formations of the density level between these windows will not be visible.

Recommendations for reading a chest CT scan

Soft tissue window:

• soft tissues, pay special attention to:
  • axillary lymph nodes,
  • mammary glands (malignant neoplasms?)
• four sections of the mediastinum:
  • above the aortic arch (lymph nodes, thymoma/goiter?)
  • roots of the lungs (size and configuration of vessels, expansion and deformations?)
  • heart and coronary arteries (sclerosis?)
  • Four typical locations of lymph nodes:
    • in front of the aortic arch (normally up to 6 mm or not determined)
    • aortopulmonary window (normally up to 4 lymph nodes, up to 15 mm in diameter)
    • bifurcation (normally up to 10 mm, not to be confused with the esophagus)
    • paraaortic (normally up to 10 mm, not to be confused with the azygos vein)

Pulmonary window

• Lung tissue:
  • branching and size of vessels (normal, dilated, deformed?)
  • depletion of vascular pattern (only along interlobar fissures? In bullae?)
  • focal lesions, inflammatory infiltration?
• Pleura:
  • pleural effusions, adhesions, calcifications, hydrothorax, hemothorax, pneumothorax?
• Bones (spine, ribs, shoulder blades, sternum)
  • bone marrow structure?
  • signs of degenerative lesions (osteophytes)?
  • foci of osteolysis or osteosclerosis?
  • spinal canal stenosis?

If there is a significant concentration of KB in the subclavian vein during scanning, artifacts appear at the level of the upper thoracic aperture. The thyroid parenchyma should have a homogeneous structure and be clearly delineated from the surrounding tissue. Asymmetry of the diameter of the jugular veins is quite common and is not pathological. Cross-sections of the branches of the axillary and external thoracic vessels should be distinguished from the axillary lymph nodes. If the patient's arms are raised above the head during the examination, the supraspinatus muscle will be located next to the inner part of the spine of the scapula and the infraspinatus muscle. The major and minor pectoralis muscles are usually separated by a thin layer of fatty tissue.

Normal anatomy

CT sections of the chest are also viewed from below. Therefore, the left lung is visualized on the right side of the image and vice versa. It is necessary to be familiar with the main vessels originating from the aortic arch. The left common carotid artery and the brachiocephalic trunk are adjacent to the subclavian artery in front. Further to the right and in front, the brachiocephalic veins are visible, which after merging on sections form the superior vena cava. In the axillary tissue, normal lymph nodes can often be recognized by their characteristic shape with a hilum of fatty density. Depending on the angle of section, the lymph nodes on the section, the hilum of low density are visualized in the center or along the edge. Normal lymph nodes of the axillary region are clearly delimited from the surrounding tissues and do not exceed 1 cm in diameter.

Chest CT scan normal

Principles of high-resolution CT (BPKT)

Thin slices and a high spatial resolution slice reconstruction algorithm are used to construct the VRCT image. Traditional CT scanners are also capable of performing thinner slices than the standard 5-8 mm. If necessary, the image formation parameters are changed by setting the slice thickness to 1-2 mm on the working console.

High resolution CT scan of the chest

The normal structure of the female mammary gland parenchyma is characterized by a very uneven contour and thin finger-like protrusions into the surrounding fatty tissue. Its bizarre outlines can often be seen. In breast cancer, a solid formation of irregular shape is determined. The neoplasm grows through the fascial sheets and infiltrates the chest wall on the affected side. CT examination performed immediately after mastectomy should help in clearly identifying the recurrence of the tumor.

Chest pathology on computed tomography

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