OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 4 2022 generation, the principle of parallel scanning was used. The measurement time required to obtain one image was ~18 seconds. Devices of the third generation began to use the principle of spiral movement of the x-ray tube and detectors of radiation that passed through the patient. One step corresponded to the linear displacement of the table by a certain amount. In this case the tube and detectors simultaneously rotated one full turn around the patient lying on the table. This technical solution allowed reducing the research time significantly. The number of detectors also increased (up to ~700 pieces). Using third-generation devices made it possible to examine the patient’s abdominal cavity and lungs. In the design of tomographs corresponding to the fourth generation, a set of fixed detectors (1,088 luminescent sensors) was located in the form of a ring (around the patient). Scanning time (when obtaining 1 image) decreased to 0.7 seconds [7]. The main feature of the fifth generation devices (early 1980s) is the use of a fixed electron beam gun. In the process of shooting the electron beam is focused and directed to a tungsten target located under the patient’s table. High-speed solid-state detectors are located in front of targets in the form of an arc with an angle of 216°. There are no significant differences in image quality compared to the previous generation of equipment. At the same time, the scanning time decreased to 33 ms. Such tomographs can be used to study the heart. Zhou et al. [6] presented a new approach to apply laminography to materials. In accordance with this approach the analyzed object moves linearly relative to the fan beam created by the microfocus X-ray tube (Fig. 4). This solution makes it possible to obtain data corresponding to rotation through the angle α for an object located in a parallel beam. The method proposed by Zhou et al. has a number of advantages over classical tomography. In one scan it allows to get an image of the entire volume of the sample. Its practical implementation provides improved image quality of sections (without blur effect). Fig. 4. Implementation of the laminography process according to the scheme proposed by J. Zhou [6] Fig. 3. Schematics of several generations of tomographs [7] a b c d
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