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IntroductionFilmless computer X ray apparatuses and even digi tal computer X ray apparatuses are being widely intro duced into domestic medical practice. Moreover, there are many approaches to digital X ray imaging described in the literature at length [8,12].The goal of this work was to describe a widely used approach to digital X ray imaging: luminescent screenoptical system-charge coupled device (CCD) matrixamplifier-analog to digital converter. CCD cooling should increase the signal/noise ratio of resulting image, thereby increasing the diagnostic capacity of the system without increasing radiation load. The goal of this work was to substantiate the necessity of CCD cooling, which improves characteristics of X ray image. Formation of Useful Signal and CCD NoiseThe incident X ray γ quanta received during expo sure time at input screen element constitute the useful signal S in :(1)The variance ∆ 2 S in of input signal or variance of the number of γ quanta ∆ 2 N γ in Poisson statistics is:Transformation of X ray signal gives resulting digital signals for each pixel (image element) I m . The statistical characteristics of the signal are: mean value I 0 and vari ance ∆ 2 I. Because each stage of image transformation introduces additional noise, the relationship between mean value and variance is:where ∆ 2 CCD contains both intrinsic CCD noise and noise of amplifier and analog to digital converter. The number α > 1 is associated with the quantum efficiency of the device [7]. The numerical value of α is determined by the number of preliminary amplification stages and signal transformation system.It follows from Eq. (3) that intrinsic CCD noise sig nificantly deteriorates image quality at low signal ampli tude. Therefore, suppression of intrinsic CCD noise is very important. The resulting useful signal from a CCD matrix is additionally corrupted by the following factors: dark charge (spontaneous generation of electron-hole pairs in accumulation and transfer modes), the tempera ture dependence of the process being described by the fol lowing equation:where Т 0 is initial temperature; ∆T is temperature change corresponding to dark charge doubling; q Т tr (Т 0 ) is dark charge generated during transfer; i Т acc (Т 0 ) is dark current during signal accumulation. In addition, transformation chain noise also contributes substantially to final discrete signal noises as a function of the number of forming elec trons. This noise or output reading noise (∆ 2 N re ) 1/2 is determined by the device design.It follows from Eq. (4) that contribution of the CCD to useful signal variance is:The statistical characteristics of the system are deter mined by mean value I signal and variance of output sig nal ∆ 2 I calculated from Eq. (3).

X-ray (bremsstrahlung) produced by high-power electron accelerators are intensively used in different radiation technologies. An electron accelerator, a scanner, an X-ray converter with cooling system, a conveyor line or a turntable chamber, an irradiated product and a package are the major components of the radiation technological lines (RTL) for X-ray irradiator. The detailed physical and geometrical models of the X-ray irradiator were realized in the form of new mathematical software of the "XR-Soft". The program XR-Soft was designed specially for simulation of industrial radiation processes and calculation of the absorbed dose and temperature distribution within products irradiated by scanning X-ray beams on industrial RTL that is based on the pulsed or continuous type of electron accelerators in the energy range from 0.1 to 50 MeV. The motivation for the development of the program XR-Soft is the creation of accurate and easily accessible tool for prediction of the absorbed dose distribution within irradiated materials, for optimization of the irradiation regimes of radiation facility, and for reducing of experimental routine dosimetric measurements in X-ray processing.

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