X-ray examination (X-ray radiography) is an X-ray examination method in which an image of an object is obtained on a luminous (fluorescent) screen.
The screen is a cardboard covered with a special chemical composition, which, under the influence of X-rays, begins to glow. The intensity of the luminescence at each point of the screen is proportional to the number of x-rays incident to it. From the side facing the doctor, the screen is covered with lead glass, protecting the doctor from direct exposure to X-rays.
The fluorescent screen glows poorly, so the fluoroscopy is performed in a darkened room. The doctor should get used (adapt) to darkness within 10-15 minutes to distinguish a low-intensity image. And yet, despite an arbitrarily long adaptation, the image on the luminous screen is discernibly poor, the small details of it are not visible, the radiation load at such an investigation is quite large.
As an improved method of fluoroscopy, X-ray television inspection is used. It is performed using an X-ray image intensifier (URI), which includes an X-ray electron-optical converter (REOP) and a closed-circuit television system.
REOP is a vacuum tube inside which an x-ray fluorescent screen is located on one side, and a cathode-luminescent screen is located on the one side, and an electric accelerating field is located between them with a potential difference of about 25 kV. The luminous image that appears when it is illuminated on a fluorescent screen on the photocathode is converted into a stream of electrons. Under the influence of the accelerating field and as a result of focusing (increasing the flux density), the electron energy increases significantly - several thousand times. Getting to the cathode-luminescent screen, the electron beam creates on it a visible image, similar to the original, but very bright image, which is transmitted through a system of mirrors and lenses to a television tube - vidicon. The electrical signals generated in it enter the TV channel block, and then - on the display screen. If necessary, the image can be captured using a VCR.
Thus, in the URI, a chain of transformations is made for the image of the object under study: X-ray - light - electronic (at this stage, the signal amplifies) - again light - the electronic (here it is possible to correct some characteristics of the image) - again light.
X-ray television inspection does not require a dark adaptation of the doctor. The radiation load on the personnel and the patient is much less when conducted than in routine fluoroscopy. On the television channel, the image can be transferred to other monitors (to the control room, to the study rooms). Television technology provides the ability to record all stages of research, including organ movements.
With the help of mirrors and lenses, an x-ray image from an X-ray electron-optical converter can be entered into a movie camera. This research is called X-ray film. This image can also be directed to the camera, which allows you to perform a series of small-format (10x10 cm) x-rays. Finally, the X-ray television network allows the introduction of an additional module that digitizes the image (analog-digital converter) and performs a serial digital radiography that has already been considered, as well as digital fluoroscopy, which further reduces the radiation load, improves image quality and, in addition , it is possible to enter the image into the computer for further processing.
One important point should be noted. Currently, X-ray machines without URI are no longer produced, and the use of so-called conventional fluoroscopy, i.e. The study of the patient with the help of only a screen that glows in the dark is permissible only under exceptional conditions.
Any fluoroscopic study, with or without URI, has a number of shortcomings, because of which the scope of its application is narrowed. First, in this study, despite a number of previously reviewed improvements, the radiation load remains sufficiently high, much higher than for radiography. Secondly, the spatial resolution of the method, i.e. The ability to detect small details in the radiographic picture is rather low. As a consequence, a number of pathological conditions of the lungs can go unnoticed, for example, miliary tuberculosis or lung carcinomatosis, lymphangitis, some dust lesions, etc. In connection with the above, the use of fluoroscopy as a prophylactic (prophylactic) study is prohibited.
At present, the range of problems to be solved in the diagnosis of fluoroscopy can be reduced to the following:
- control over the filling of the patient's organs with a contrast agent, for example, when examining the digestive canal;
- control over the implementation of instruments (catheters, needles, etc.) when performing invasive radiological procedures, such as cardiac catheterization and blood vessels;
- a study of the functional activity of organs or the identification of functional symptoms of the disease (for example, limitation of diaphragm mobility) in patients who for some reason can not perform ultrasound.