Fluoroscopy

Fluoroscopy (X-ray scanning) is a method of X-ray examination in which an image of an object is obtained on a luminous (fluorescent) screen.

The screen is cardboard covered with a special chemical composition, which begins to glow under the influence of X-ray radiation. The intensity of the glow at each point of the screen is proportional to the number of X-ray quanta that hit it. On the side facing the doctor, the screen is covered with lead glass, protecting the doctor from direct exposure to X-ray radiation.

The fluorescent screen glows weakly, so fluoroscopy is performed in a darkened room. The doctor must get used to (adapt) to the darkness for 10-15 minutes to discern the low-intensity image. And yet, despite any lengthy adaptation, the image on the luminous screen is poorly discernible, its small details are not visible, the radiation load during such an examination is quite high.

An improved method of fluoroscopy is X-ray television scanning. It is performed using an X-ray image intensifier (XIIM), which includes an X-ray electron-optical converter (REOC) and a closed television system.

The REOP is a vacuum tube with an X-ray fluorescent screen on one side and a cathode-luminescent screen on the opposite side, and an electric accelerating field with a potential difference of about 25 kV between them. The light image that appears when shining on the fluorescent screen is converted into an electron flow on the photocathode. Under the influence of the accelerating field and as a result of focusing (increasing the flow density), the electron energy increases significantly - several thousand times. Getting on the cathode-luminescent screen, the electron flow creates a visible image on it, similar to the original, but very bright, which is transmitted to a television tube - a vidicon - through a system of mirrors and lenses. The electric signals that arise in it are sent to the television channel block, and then to the display screen. If necessary, the image can be recorded using a video recorder.

Thus, in the URI the following chain of transformation of the image of the object under study is carried out: X-ray - light - electronic (at this stage the signal is amplified) - again light - electronic (here it is possible to correct some characteristics of the image) - again light.

X-ray television scanning does not require dark adaptation of the doctor. The radiation load on the staff and the patient during its implementation is significantly less than during conventional fluoroscopy. The image can be transmitted via a television channel to other monitors (in the control room, in training rooms). Television equipment provides the ability to record all stages of the study, including organ movements.

With the help of mirrors and lenses, the X-ray image from the X-ray electron-optical converter can be fed into a movie camera. Such a study is called X-ray cinematography. This image can also be sent to a photo camera, which allows for a series of small-format (10x10 cm) X-ray images to be taken. Finally, the X-ray television tract makes it possible to introduce an additional module that digitizes the image (analog-to-digital converter) and to perform serial digital X-ray, which has already been discussed earlier, as well as digital fluoroscopy, which further reduces the radiation load, improves the image quality, and, in addition, it is possible to feed the image into a computer for subsequent processing.

One fundamentally 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. examining a patient using only a screen that glows in the dark, is permissible only in exceptional circumstances.

Any X-ray examination, both with and without URI, has a number of disadvantages, which narrow the scope of its application. Firstly, in this examination, despite a number of previously discussed improvements, the radiation load remains quite high, much higher than in X-ray photography. Secondly, the spatial resolution of the method, i.e. the ability to detect small details in the X-ray picture, is quite low. As a result, a number of pathological conditions of the lungs may remain unnoticed, for example, miliary tuberculosis or pulmonary carcinomatosis, lymphangitis, some dust lesions, etc. In connection with the above, the use of X-ray as a screening (preventive) examination is prohibited.

At present, the range of diagnostic problems faced by fluoroscopy can be reduced to the following:

1. control over the filling of the patient's organs with contrast agent, for example when examining the digestive tract;
2. control over the use of instruments (catheters, needles, etc.) during invasive radiological procedures, such as cardiac and vascular catheterization;
3. study of the functional activity of organs or identification of functional symptoms of a disease (for example, limited mobility of the diaphragm) in patients who, for some reason, cannot undergo an ultrasound examination.