X-Ray Film Photoroentgenography in Modern Medical Practice

Abstract

The goal of this work was to discuss possible ways to reduce the dose load on patients during mass-scale X-ray examinations using film photoroentgenographs. There is a trend in medical roentgenography all over the world toward abandonment of photoroentgenographic methods in favor of conventional X-raying or modern digital methods of X-ray examination. However, because digital apparatuses are rather expensive and implement a radically new approach to photoroentgenographic examination, their introduction into practice will require several years. During this time, conventional film photoroentgenographs will still be used. Approximately 5600 film photoroentgenographs are currently used in domestic health service. New domestic 12F9 photoroentgenographs with high-sensitivity photoroentgenographic cameras KF-400 constitute about 50% of them; already out-dated domestic 12F7 photoroentgenographs with low-sensitivity photoroentgenographic KF-70 cameras constitute 40%; foreign photoroentgenographs with out-dated RK-70 and RK-110 cameras made in the German Democratic Republic, 10%. The main problem of mass-scale photoroentgenography is to reduce the dose load without decreasing the information value of photoroentgenographic images. To solve this problem, domestic 12F9 photoroentgenographs were equipped with modern domestic KF-400 cameras with high-quality input screens and improved optics compatible with both 70 and 100-mm films [1]. The use of a new type of output luminescent screen is the main advantage of the KF-400 photoroentgenographic camera. Until recently, the ERS-Ts-1A luminescent screen based on ZnCdS:Ag has been used in photoroentgenographic cameras. Presently, a new luminescent screen ERS-G-2V based on the rare-earth luminophore Gd2O2S:Tb is used in the KF-400 camera. The main parameters of the luminescent screens are given in Table 1. Table 1 shows that the gadolinium-based ERS-G2V screen provides better image quality than the other model, especially if the effective energy of X-ray radiation is higher than that used in conventional apparatuses. Such screens provide higher resolution and contrast sensitivity, which increases information content of images. Also, it was shown that in screens based on gadolinium luminophores the coefficient of correspondence between the spectral sensitivity of photoroentgenographic film and spectral characteristics of the luminescent screen radiation is approximately 25% higher than in other models. Thus, replacement of the ERS-Ts-1A screen with the ERS-G-2V screen increases the sensitivity of photoroentgenographic cameras more than twofold and the resolution from 2.0 to 2.5 lines/mm. The contrast sensitivity is also improved (2% instead of 3%). The KF-400 camera contains an objective lens with improved characteristics as compared with the previous model KF-70. The lens used in the KF-400 camera provides better light transmission. Its main advantage is that it provides significantly lower vignetting (decrease in brightness from the center of an image to its edges) than the KF-70 model. In the KF-70 camera, vignetting at a distance of 0.7 working diameter is 70%; at a distance of 0.9 working diameter, 90%; whereas in the KF-400 camera vignetting at a distance of 0.9 working diameter does not exceed 50%. Losses in resolution at the edges of an image are also decreased (not more than 20%). The effective frame size of the KF-400 camera is larger than in the previous model. As a consequence, it provides higher sensitivity and significantly higher information content of images.