CT Clinical Applications 200 Questions

Author: Chief Editor: Cai Jianfang
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Publish Date: 1999-01-01
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1. What is CT? Who invented it? The CT we usually refer to today is actually X-ray CT, which stands for X-ray Computed Tomography. Its full Chinese name is "X-ray Electronic Computer Tomography." The inventor of CT was Godfrey N. Hounsfield, an engineer at the British EMI company, who invented it based on the research of others, including Dr. Allan MacLeod Cormack, a physics professor at Tufts University in the United States, in 1967. In October 1971, the first head CT machine was first applied clinically at the Atkinson Morley Hospital in the UK and was successful. In November 1972, the British Radiological Society and the North American Radiological Society announced the birth of the CT machine separately. In 1974, Ledley, an engineer at Georgetown Medical Center in the United States, designed a whole-body CT machine, marking a new era in imaging diagnostics. On October 11, 1979, Cormack from the United States and Hounsfield from the UK jointly won the 1979 Nobel Prize in Physiology or Medicine for their contributions to the development of computer-aided X-ray technology. In 1990, China produced the D31 model of domestically made whole-body CT machines, which began to be widely used in hospitals in China.
2. What is the imaging principle and basic structure of a CT machine? In short, the imaging principle of a CT machine is to use pencil-shaped or fan-shaped X-rays to scan the examination area along the longitudinal axis of the human body at a uniform speed for 360°. After passing through a certain layer of tissue in the human body, the X-rays are received by the detector. Different densities of tissues absorb different amounts of X-rays. The higher the tissue density, the more X-rays are absorbed, and the weaker the signal received by the detector; the lower the tissue density, the less X-rays are absorbed, and the stronger the signal received by the detector. This attenuated X-ray amount is converted into an electrical signal and input into an electronic computer. After the computer processes the data, the entire process of displaying the image data on the television screen is completed. A CT machine consists of four parts: (1) X-ray generation system (high-voltage generator and X-ray tube); (2) X-ray detection system (detector, detection loop, and analog-to-digital converter); (3) electronic computer system (computer, disk, and tape, display device, camera); (4) control system.
3. How is the generation and development evolution of CT machines classified? The term "generation" of a CT machine refers to a marker in the research and development process of CT machines. The classification of CT machine generations is mainly based on the relationship between the X-ray tube and the detector, the number and arrangement of the detectors, as well as the movement mode between them. In reality, the classification of CT machine generations does not fully reflect the superiority or inferiority of the CT machine itself, while the performance of the X-ray tube system, the detector, and the speed of the electronic computer are the main components that determine the performance of the CT machine.
First-generation CT machine: The X-ray beam is linear and pencil-shaped, with one or several detectors, using a combination of linear and rotational scanning, resulting in slow scanning times of up to 3 to 6 minutes, limited to head scans.
Second-generation CT machine: There is no fundamental difference from the first-generation CT machine, except that the X-rays are multiple beams, and the number of detectors is increased to dozens, with scanning times reduced to 10 to 90 seconds, beginning to be used for whole-body scans.
Third-generation CT machine: The X-ray beam is fan-shaped, with hundreds of detectors arranged in a fan shape, performing only rotational scanning, with scanning times of 1 to 5 seconds. However, it has more reconstruction programs, local magnification scanning, dynamic scanning, scanning imaging, and gas imaging functions, making it a relatively practical and high-performance machine.
Fourth-generation CT machine: It is basically the same as the third-generation machine, with detectors arranged in a circular shape and fixed around the scanning frame, while only the X-ray tube rotates. This machine can perform fast scanning, increase the amount of information, and produce clearer images.