The working theory of magnet comes from electromagnetic induction. Without magnets, today's technological development will not be improved at all. In the previous industrial era, the existence of magnets did alleviate the sources of many problems, and could speed up the relevant production efficiency. Without magnetic materials, electrification would be impossible, because generators are used for power generation, transformers are used for power transmission, electric machines are used for motors, telephones, radios and televisions, and loudspeakers are used. Magnetic steel coil structure is used in many instruments.
In medicine, MRI can be used to diagnose abnormal tissues of human body and judge diseases. This is the familiar MRI technology. Its basic principle is as follows: the nucleus is positively charged and spins. In general, the arrangement of nuclear spin axis is irregular, but when it is placed in an external magnetic field, the spatial orientation of nuclear spin changes from disorder to order. The magnetization vector of the spin system increases gradually from zero. When the system reaches equilibrium, the magnetization reaches a stable value. If the nuclear spin system is affected by the external forces, such as a certain frequency of radio-frequency excitation of the atomic nucleus can cause resonance effect. After the RF pulse stops, the excited nucleus of the spin system can't maintain this state. It will return to the original arrangement state in the magnetic field, and release weak energy at the same time, which will become radio signals. When these signals are detected and spatial resolution is made, the distribution image of the nucleus in motion can be obtained.
The characteristic of NMR is that flowing liquid does not produce signal, which is called flowing effect or flowing blank effect. Therefore, the blood vessels are gray white tubular structure, while the blood is black without signal. This makes it easy for blood vessels to separate soft tissues. The normal spinal cord is surrounded by cerebrospinal fluid, which is black, and the white dura is set off by fat, which makes the spinal cord show a strong white signal structure. MRI has been applied to the imaging diagnosis of various systems in the whole body. The best effect is the brain, spinal cord, heart big blood vessel, joint skeleton, soft tissue and pelvis. For cardiovascular diseases, we can not only observe the anatomic changes of various chambers, large blood vessels and valves, but also make ventricular analysis, make qualitative and semi quantitative diagnosis, and make multiple sections, with high spatial resolution, showing the whole picture of heart and disease, and its relationship with surrounding structures, which is superior to other X-ray imaging, two-dimensional ultrasound, nuclide and CT examination. Magnetism can not only diagnose, but also help treat diseases.