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6SCIENTIFIC PROGRESS
VOLUME 2 I ISSUE 3 I 2021 ISSN: 2181-1601
RESPIRATORY COMPUTED TOMOGRAPHY
Ulmas Djumabayevich Alaberdiev Kamoliddin Otamurodovich Pardaev
Clinical Interns at the Department of MedicalRadiation Diagnostics Samarkand State Medical Institute
ABSTRACT
Over the past 20 years, X-ray computed tomography (CT) has become one of the most important methods for diagnosing respiratory diseases. This is due to the high accuracy of the method in identifying pathological changes in organs and tissues of the chest cavity. The use of CT has made it possible to replace traditional radiopaque techniques such as bronchography, pneumomediastinography, diagnostic pneumothorax, etc. In those medical institutions where CT is an available research method, linear tomography is practically not used.
Keywords: respiratory, pneumothorax, bronchopneumonia, bronchitis.
In most clinical situations, radiological diagnosis of respiratory pathology can be limited to plain radiography and CT. If necessary, these techniques are supplemented by isotope and ultrasound examinations or magnetic resonance imaging (MRI). Transthoracic puncture or transbronchial biopsy under fluoroscopy is used to verify changes in the chest cavity. Punctures can also be performed under ultrasound or CT guidance. Along with modern bronchological and functional methods, the complex of radiation studies allows you to obtain comprehensive information about the state of the respiratory system.
The meaning of the CT method is to perform three sequential actions: scanning an object with a thin fan-shaped X-ray beam; registration of attenuated X-ray radiation by detectors that allow converting the energy of radiation quanta into electrical pulses; constructing a two-dimensional halftone image of a transverse (axial) cut of the investigated area. The technical details are detailed in the respective manuals.
Like any X-ray method, CT examination is associated with exposure to the body of ionizing radiation. The radiation dose for a standard CT scan is comparable to the dose for linear tomography of the lungs and amounts to 5-8 mSv. In modern devices equipped with automatic exposure correction programs, the dose can be reduced by 1.52 times. When using high-resolution CT (HRCT), when thin (1-2 mm) tomographic sections are performed at a distance of 10-20 mm from each other, the dose is 2-3 mSv. In special protocols of the so-called low-dose CT scan, intended for screening lung pathology, primarily bronchogenic cancer, the radiation dose is comparable to the usual plain radiograph and is equal to 0.2-0.4 mSv. These same protocols are often used today for the initial scanning of patients with already known pathology.It is customary
SCIENTIFIC PROGRESS
VOLUME 2 I ISSUE 3 I 2021 ISSN: 2181-1601
to single out some general indications for CT of the chest cavity organs, most of which involve differential diagnosis of changes detected by conventional radiography or fluorography.
Such indications, in particular, include:
• pathological formation (obvious or suspected) in the chest cavity, including the lungs, mediastinum, pleura and chest wall;
• enlargement of the lymph nodes of the mediastinum and the roots of the lungs (obvious or suspected);
• lobar and segmental infiltrates in the lung, the nature of which is unclear according to plain radiography;
• widespread bilateral changes in the lungs (obvious or suspected), including in interstitial lung diseases;
• pleural effusion of unknown origin;
• trauma and injury to the chest.
In a number of foreign countries, CT is beginning to be used as a screening method for bronchogenic cancer instead of radiography and fluorography. It is well known that CT can reliably detect pathological formations in the lungs of 5 mm or more, while X-ray and fluorography - from 10 mm. At the same time, the detectability of small formations in the lungs at CT does not depend on a number of negative "X-ray" factors (physical and technical conditions of the image, the interposition of bone structures, the correct position of the patient, etc.). In one of the largest studies in this area [9], the use of CT in the examination of the risk group made it possible to identify foci in the lungs in 23.3% of patients, while radiography revealed foci in only 7%. Lung cancer was detected by CT in 27 cases (2.7%), of which 26 tumors were resectable, and 23 (85%) had stage I, and 19 of 23 lesions (75%) in stage I were not visible on radiographs. Other researchers also obtained comparable data. The use of modern low-dose spiral CT protocols made it possible to reduce patient exposure to a level comparable to plain radiography. However, the question of the fundamental feasibility of screening lung cancer using radiation research methods remains a subject of discussion to this day. It is unclear whether these programs can actually reduce mortality in lung cancer patients, or whether such costly programs will be economically viable.
CT examination techniques
Any diagnostic CT examination of the chest cavity organs is a series of tomograms of the area under study. It focuses on the study of lung tissue, respiratory tract, mediastinum, pleura and chest wall. In the initial study, tomograms are performed from the tops to the diaphragmatic sinuses, while the thickness of the tomographic layer and the distance between the layers is 8-10 mm. This technique allows you to study the entire volume of the chest cavity using slices adjacent to each other (adjacent slices),
without missing a significant pathology. If pathology is detected on a series of primary (native) tomograms, to clarify the nature of the changes, special techniques can be used related to the introduction of contrast agents, a decrease in the thickness of the tomographic layer, an exhalation study, etc.
Currently, it is customary to distinguish two main technologies of CT examination: step-by-step (sequential) and spiral [6, 8]. The step-by-step technology involves stopping the X-ray tube after each rotation, during which the table with the patient moves to the next position, and the patient has the opportunity to inhale and hold his breath for the next rotation. This technology is the main and the only one on devices manufactured before the mid-1990s. In later modifications, step-by-step CT continues to be used to study the brain, especially in the area of the base of the skull, bones of the facial skeleton, large joints, as well as for high-resolution CT of the lungs.
High resolution CT
HRCT is a step-by-step scanning option and consists in performing three technological their actions: reducing the thickness of the tomographic layer to 1-2 mm, targeted reconstruction of the studied part of the chest cavity and the use of a special high-resolution imaging algorithm. All three actions are aimed at increasing the spatial resolution as much as possible. The technique is intended to study the most subtle changes in the lung tissue at the level of the anatomical elements of the secondary pulmonary lobule and acini.
Currently, HRCT is used to diagnose interstitial lung diseases, emphysema, and bronchiectasis. Assessment of interstitial lung diseases with HRCT allows to significantly narrow the differential diagnostic range, to objectively speak about the activity of the inflammatory process, to choose the optimal place and type of biopsy, if necessary. In some cases, HRCT makes it possible to get as close as possible to the histo-specific diagnosis, in particular in sarcoidosis, lymphangioleiomyomatosis, histiocytosis, and lymphogenous carcinomatosis (Fig. 5, 6).
Important indications for HRCT are spontaneous pneumothorax and hemoptysis in the absence of changes on plain radiographs. The main cause of spontaneous pneumothorax is emphysema, in the detection of which HRCT has undeniable advantages over any other diagnostic methods. In patients with hemoptysis and a normal chest x-ray, HRCT should precede bronchological examination. This tactic allows you to confidently identify both endobronchial tumors and bronchiectasis, which are invisible during bronchoscopy. An important finding during HRCT in such patients is areas of pulmonary tissue imbibition with blood, which indicates the localization of the source of bleeding even before bronchoscopy.
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