## 1 Introduction
Let us divide these explanations into three main groups: mathematical models for evaluating metal artifacts in X-ray CT; ways to reduce metal artifacts in CT; the main physical and technical factors affecting the level of metal artifacts in the X-ray CT; the technical possibility of solving the problems of designing CT systems for testing TO with fragments with low radiation transparency. Note that these groups are related to each other. Let us dwell on them in more detail. 1. In the scientific literature, many mathematical models of X-ray CT of varying degrees of complexity are described with a sufficient degree of detail, for example, [14; 16; 17; 18; 19; 20]. In [15], a number of general requirements for mathematical models of X-ray CT were formulated. Such requirements include simplicity, high performance, clarity, and variability in the description of the structures of control objects. It is necessary to add the ability to adapt to physical and technical influences (disturbances) to expand the capabilities of mathematical models. These requirements are fully met by the mathematical model from [14]. The advantage of this model is the simplicity of its implementation in the system of mathematical calculations MathCad. This is due to the fact that the MathCad language is exceptionally close to the natural mathematical language [21]. The MathCad system is widely used in the development of methods and tools for nondestructive testing [14; 15; 22; 23; 24]. Based on the foregoing, mathematical models from [14; 15] can serve as the basis for a model for assessing metal artifacts and the degree of their correction when changing the parameters of X-ray CT systems. 2. It was noted above that metal artifacts significantly limit the use of X-ray CT systems in various fields, medicine, science, and technology. There are several approaches to reducing the effect of metal artifacts. Among these approaches are: the use of a priori information about the structure of TO and its fragments [25]; the use of neural networks with the preliminary creation of databases and subsequent training [26]; preliminary segmentation of images of metal fragments with separation of metal zones, subsequent interpolation and corrective insertion [27]; increase in the maximum energy of X-ray radiation [7; 28]; increasing the intensity of the X-ray source [28; 29]; increasing the capacity of the ADC [29; 30]. The first three approaches to reducing metal artifacts are algorithmic, and the last three are physical (technical) since they are associated with a change in the parameters of the X-ray CT system. 3. The technical possibility of solving the problems of designing CT systems for testing objects with fragments with low radiation transparency is determined by the presence on the market of scientific equipment of the main elements of CT systems, which allows reducing metal artifacts to levels that suit the end user. The main elements of CT systems include a radiation source and a detector with an ADC. Currently, high-intensity X-ray machines with a maximum energy of tens to hundreds of keV [31; 32], as well as linear electron accelerators and betatrons with energies from 1 MeV to 9 MeV [29; 33], are used as an X-ray source in CT systems. Over the past decades, the bit capacity of X-ray detectors has increased significantly [34; 35; 36]. The specificity of the simulation model for the formation and processing of information for the problem under consideration lies in the features of the considered TOs and the block to generate a set of projections (sinograms), taking into account the low transparency of the TO for X-rays.