The first X-ray CT scanning equipment was introduced in the United Kingdom in 1972 and is used in clinical medicine. The basic principle is to utilize the difference in density of substances inside an object to reveal the distribution of the constituent substances inside the object. Its greatest advantage lies in its non-destructive nature, but the limiting factors make the discriminatory ability limited, with a spatial resolution of 0.35×0.35mm2, a recognizable minimum volume of 0.12mm3, and a density contrast resolution of 0.3%? National Laboratory of Permafrost Engineering, Institute of Cold and Arid Regions Environment and Engineering, Chinese Academy of Sciences.
CT is a comprehensive use of level X-ray scanning principle, the use of highly sensitive photon detection technology, advanced data processing methods and display technology. Initially, according to the body's different tissues and lesions of different coefficients of absorption of X-rays, the detection of the results of a series of accurate and detailed tissue level images to represent. When these layers are combined, a three-dimensional image of the relevant tissue structure and lesions can be obtained for diagnostic purposes.The main structure of CT consists of two main parts: the X-ray body scanning device and the computer system. The former mainly consists of the generator and bulb tube which produce X-ray beams, and the detector which receives and detects X-rays; the latter mainly consists of the data acquisition system, the central processing system, the tape machine, the operation desk, etc. In addition, the CT machine should include the three-dimensional image of the tissue structure and the lesion for the diagnosis. In addition, the CT machine should also include auxiliary equipment such as image monitors and multi-frame cameras. Spiral CT machine is one of the most advanced CT equipments in the world, with fast scanning speed, high resolution, and excellent image quality (Figure 7-3).
X-ray CT scanning devices have gone through four stages of development since their introduction. The fourth generation of devices currently in use, applying a rotational scanning method, can reveal a three-dimensional image of the object being scanned. The use of computer technology in recent years has made it possible to directly process the large amount of image information received using computers.
Application of X-ray CT scanning device, the internal structure of the geological samples, especially the shape of the characteristics of the research work. At present, some foreign scholars, especially Japanese scholars have carried out attempts to apply this. The main aspects of the research include:
The morphological characteristics of the pores within the rock and their permeability, which serves to carry out the research on the distribution and enrichment rules of the geologic fluids (including petroleum, natural gas, and thermohydrological solutions, etc.), and to explore the permeability of the pores in terms of the morphological parameters of the fluid-containing pores.
Structural study of unconsolidated accumulations and soft rocks. For this kind of research object, due to its loose and weak characteristics, it is difficult to carry out the research on its internal structure, especially to carry out high-precision structural analysis, X-ray CT scanning device can be used to carry out rapid, high-resolution analysis in a short period of time. In recent years, concerns about the recent evolution of the Earth and the human environment have led to a growing interest in the study of modern sediments in lacustrine, marine or fluvial phases.
The study of the morphology and structure of paleontological fossils includes the study of the surface and internal microstructure of paleontological fossils, such as the micro-morphology of the surface of trilobites, and the analysis of coral annual rings.
The use of X-ray CT scanning device in tectonic geology is mainly used to carry out research on the formation mechanism and development process of folds and fractures. In particular, it has been widely used in experimental deformation studies, which can dynamically observe the development and progression of rupture in experimentally deformed rocks. kawakata et al. (1997) conducted X-ray CT scanning of samples from experimental deformation of the westerly granite in recent years and found that the nucleation of the rupture of the main fault started at the instant after the peak stress, and the initial position of the rupture nucleation was located on the surface of the deformed sample rather than on the surface of the sample, and the initial position of the rupture nucleation was located on the surface of the sample. The initial location of the rupture nucleation is at the surface of the deformed sample, not at the center of the sample; after the rupture nucleation, the rupture nucleation gradually expands to the interior of the sample as the axial stress decreases.
Sample preparation for X-ray structural analysis: Generally, the samples should be made into circular slices with a diameter of 3cm±1mm and a thickness of 2-3mm, and the measured surfaces should be oriented and polished (Institute of Geomechanics, Chinese Academy of Geological Sciences). Improved equipment can be used for larger and irregular samples (e.g. University of G?ttingen, Germany).