OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 4 2022 Methods for studying flat samples. Tomography and synchrotron laminography One of the possible approaches to the problem of studying non-compact (non-isometric) samples is based on the idea of synchronous movement of the X-ray source together with the detector around a stationary object. This approach was proposed in 1932 by Ziedses des Plantes and the method based on it was called planigraphy [4]. In accordance with this method a set of X-ray patterns obtained in one scanning cycle is used to obtain an image of one section of an object located in the focal plane. This concept underlies the method of classical tomography (also called the laminography method); while implementing this method it is necessary to change the position of the object of research along the vertical in order to obtain images of different sections. Despite its simplicity, the method is fast and the images are of good quality (resolution). In the 1970s this approach [5] began to be used in medicine to examine human patients. The adapted principle of classical tomography (laminography) was used in the first generation of medical tomographs (Fig. 1). Brain was studied by the first devices (Fig. 2). It should be noted that the pixel size was 3 mm (in modern devices – 30–200 µm). Compared to modern tomographs, the image shown in the figure is characterized by a rather low quality. Its analysis does not allow us to obtain complete information about the patient’s condition. a b Fig. 1. Scheme of classical tomography (a) [6] and scheme of the first generation tomograph (b) [7] Fig. 2. The first image of the brain obtained by tomography [8] Various classifications of tomographs have been proposed in literature. According to one of these classifications there are five generations of tomographs (Fig. 1, b and Fig. 3) [7] which differ in design solutions and the number of projections recorded by the detectors. When using first-generation scanners, images were obtained by moving one highly directed X-ray tube and one detector along the frame layer by layer. After 160 measurements the frame was rotated through an angle of 1o in the axial direction and the state of the next layer was analyzed. Measurement of the radiation intensity during the analysis of each layer lasted ~4.5 minutes and the imaging took ~2.5 hours. The second generation scanner (mid-1970s) (Fig. 3, a) used a tube that formed a fan-shaped X-ray beam in combination with several detectors, which were opposite each other while rotating around the patient. Because of using a fan beam and several radiation detectors the angle of rotation in devices of this type increased to 30o. In this case, as well as in the devices of the first
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