CT, an English abbreviation that almost everyone knows, is called CT in Chinese. At present, there are two types of CT technology used in the medical field. The first is the CT technology using X-rays, which is called X-CT for short. The second is to obtain a variety of information images by injecting a small amount of harmless radioactive substances (called nuclides) into the human body, such as organ function and blood flow changes, as well as the absorption, distribution, excretion and transfer of metabolites in the body, which is called E-CT for short. At present, the first type of X-CT is widely used, and the equipment used includes X-ray source, detector, computer and image display. The diagnosis process is that the X-ray source and detector synchronously rotate around the human body in a circle, and each rotation requires parallel displacement, and then rotates again, so many times, forming a tomographic scan.
Principle of human CT scanning imaging
CT instrument is very complicated, but the principle is simple, which consists of three parts: detection, operation and display.
CT scanning imaging of rocks and minerals
The results of underground CT can reflect the "mass" formed by density change on the map.
A large amount of data continuously obtained by the detector is transmitted to the computer and processed according to a certain program. Finally, the three-dimensional image or two-dimensional multi-faceted cross-sectional view of the detected part of the human body is presented on the display, which can be used for doctors to compare and analyze the abnormal distribution of lesions and provide scientific basis for medical records.
The application of CT technology in geophysical exploration is the same as the basic principle of CT technology in human medical diagnosis. Its methods are classified in detail, such as seismic tomography, which is divided into transmission wave chromatography, reflection wave chromatography and refraction wave chromatography. Compared with conventional seismic exploration technology, seismic tomography technology has higher resolution, which is more conducive to the comprehensive and detailed delineation of geological bodies (rock mass or ore body, etc.). ) and draw their spatial positions and shapes. It can be used for the exploration and development of oil and gas, coal fields, metal and nonmetal minerals; It can also be used in engineering exploration, such as the investigation of the infrastructure and stability of high-rise buildings and dams.
Geophysical CT is different from medical CT in that seismic wave tomography and radio wave tomography are now used. The terrain they face is unknown (the human body structure is known), the structural components are diverse and difficult to compare, and the geological structure is complex, accompanied by interference waves such as diffracted waves, refracted waves and multiples, which brings more difficulties to the analysis and interpretation of geophysical CT.
For example, in a large gold mining area in Shandong, its gold production accounts for more than 20% of the total national output. By using seismic CT method and two observation profile detection techniques, the neglected and abandoned gold belt was found, which can continue to be developed and utilized, and the goaf was delineated, which provided a basis for solving the safety problem. In Jinchuan copper-nickel mine area, Gansu province, the location and shape of a concealed ore body were found by seismic CT method, which provided important clues for development. In a newly discovered gold mining area in Liaoning Province, the application of seismic CT method to trace hidden gold veins has achieved good results.
In the Three Gorges Project of the Yangtze River, the slope rock mass of the temporary ship lock and the concrete pier next to the elevator was detected by ct, and the quality of this building with a height and scale that attracted worldwide attention was found out. In a word, the achievements of electromagnetic imaging technology can provide scientific basis for engineering construction and design units in time and accurately.