Specific features of design and application of digital X-ray apparatuses for examining lungs

Abstract

In recent years there has been a trend toward an increase in the number of X-ray examinations. This is due to introduction into medical practice of some special X-ray procedures and computer tomography of some organs. Also, digital systems of conversion and processing of images find progressively increasing application in medicine.However, there is a trend toward a continuous increase in the number of patients with tuberculosis all over the world. In most developed countries in the last quarter of the XXth century, the number of patients with tuberculosis increased approximately twofold; in Russia and countries of the CIS, threefold and more. This is the reason why interest is aroused in special-purpose X-ray equipment for examination of lungs, namely, scanning photoroentgenographs for mass-scale prophylactic examination of lungs [2].Ultrasonic or infrared examinations are inefficient for studying lung tissue. Endoscopy of bronchi is also a very difficult procedure. Thus, X-ray examination remains almost the only way of obtaining diagnostic information about lungs, except for laboratory biochemical analyses and tests.It should be noted that medical X-ray examinations and treatment are the second most probable cause of undesirable aftereffects after traffic accidents. However, it is still impossible to abandon X-ray examinations, in particular, of lungs. Therefore, development of low-dose X-ray equipment for mass-scale prophylactic examInations is an urgent problem. Also, an efficient system of control and documentation of individual radiation doses received by people is necessary. According to the Russian Federation Law on the Radiation Safety of People adopted in 1996, the radiation load on patients during X-ray examinations should be recorded in terms of effective dose [5].In 1996, all leading manufacturers of X-ray equipment put on the market of medical equipment various low-dose digital X-ray systems for examination of lungs. These systems differ from each other in the principles of conversion of images.There are image converters based on selenium drum (Philips), stimulated luminophore (Fuji), and large-diameter electronic image intensifiers (Siemens). The IMIX image converter (Medira) is based on the principle of optical transmission of images from the screen to a TV charge coupled device matrix. The main advantage of all these converters is that they allow acquisition of significantly more information during examination, whereas the dose received by patient is somewhat decreased as compared to film photoroentgenography. However, these devices are rather expensive, which makes it virtually impossible for these devices to replace the photoroentgenographs currently used in domestic medical institutions.The main task of the designers of conventional film photoroentgenographs is to increase sensitivity without deteriorating image quality. For example, a modification of the KF-400 photoroentgenographic camera (Russia) with improved optics and a gadolinium hydroxysulfide screen instead of the ZnS (Ag) screen has s...