CT examination is very common in clinical diagnosis. The use of chest CT imaging data can provide reliable diagnostic basis for clinical diagnosis. So, learning to read chest CT images is very important for the diagnosis of clinical diseases.
The content of chest CT images mainly includes the following points: (1) continuous images of chest cross-sections; (2) Various scanning parameters, such as layer spacing, window level, scanning time, layer thickness, voltage, etc; (3) Patient information, including age, gender, and name annotated in Chinese Pinyin. Having the above points is the only complete chest CT imaging data with clinical value. So, how should I read such a complete chest CT image?
Before reading chest CT imaging data, it is necessary to first develop good reading habits, that is, to stack the images in order of layer height, from top to bottom, and then conduct detailed observation. During the observation process, gradually form three-dimensional images in the mind. This habit is not only the focus of reading CT imaging materials, but also a reading technique. If one only focuses on the images of the lesion, it is easy to limit their thinking, resulting in overly limited readings. The results of the reading will also have a certain degree of one sidedness and lack integrity, which can easily affect the accuracy of the conclusion.
So, what are the key reading points to pay attention to when reading a chest CT image correctly?
Key point one: Technical parameters of chest CT. During the chest CT scan, most patients are in a supine position, holding their breath to obtain CT scan images. Generally, the scan is from the apex of the lung to the costophrenic angle. The chest is mainly composed of bones, soft tissue, and lung tissue containing gas, with different densities. In the process of observing the tissue composition of the chest, different window positions and widths should be used to ensure the accuracy of the imaging results. Continuous cross-sectional scanning can reconstruct three-dimensional reconstruction images such as coronal and sagittal views, providing observation basis for more complex anatomical structures. There is a key point to note here, which is that the scanning thickness will directly affect the reconstruction quality of the final image. In other words, the thinner the scanning layer thickness and the smaller the interval, the higher the quality of the reconstructed image.
Key point 2: Observe lung lesions. Adopting a layered stacking method to clarify the nature of non masses and masses, while carefully observing the condition of the lesion site, such as surrounding structure, calcification, density, and appearance. There is a key point here, which is to check whether there are calcified spots that cannot be distinguished by body X-rays or general chest X-rays in the lesion. The purpose of checking this content is to determine the benign or malignant nature of the lesion site. Furthermore, do not fully trust the absolute CT value of a single pulmonary nodule lesion, as the absolute CT value may be affected by the effective partial volume effect. Each CT image has a certain thickness, which is within the thickness of a unit volume and encompasses a large amount of tissue. The CT value at this time is actually an average of the CT values of these tissues, which represents the average CT value and tissue density, and does not exist. This is the partial volume effect.
Key point three: Proper use of contrast agent enhanced scanning. There is more gas in the chest, and the incidence of soft tissue lesions is generally higher. Compared with lung tissue containing gas, the difference lies in density. Although most of the fat in it has a low density, the structure within the mediastinum can be clearly observed and therefore does not require contrast-enhanced scanning. However, in some cases, in order to obtain accurate chest CT images and read them, enhanced scanning is still necessary. So, the following situations require enhanced scanning: (1) Due to the gravity accumulation effect, the location of pleural effusion will change with the change of body position. The use of enhanced scanning can help differentiate pleural and chest wall lesions. (2) Cases of accompanying vascular malformations and lesions. (3) The fat content in the mediastinum is low, and the patient's body is relatively thin. (4) It is necessary to distinguish between enlarged lymph nodes in the mediastinum and malignant tumors.
Key point four: Analyze the representative level. (1) At the level of the main pulmonary artery window: with the left pulmonary artery as the lower boundary and the lower edge of the aortic arch as the upper boundary, the trachea is located behind and the ascending aorta is located in front. At the same level, the ascending aorta is larger than the descending aorta. (2) Aortic arch level: The direction of the aortic arch is generally inclined from right anterior to left posterior, but due to the influence of arteriosclerosis, its direction may not be horizontal in some older patients. At the level of the aortic arch, a triangular thymus can be observed, with its tip pointing forward. (3) Upper level of the aortic arch: The left subclavian artery, left common carotid artery, brachiocephalic trunk, left and right brachiocephalic veins, and five vascular shadows can be observed on the upper level of the aortic arch.