These five principles are basically similar, mainly through some high-frequency electromagnetic waves penetrating the human body surface. Among them, CT tomographic ultrasound (in fact, this is a general term) and B-ultrasound are basically the same, both of which directly image through penetrating electromagnetic wave signals, giving people an intuitive display of internal structure. X-rays were first discovered. It does not use electromagnetic waves, but uses the high-energy particle flow emitted by radioactive substances to penetrate the human body and image on the sensing film. The vibration of nuclear magnetic resonance (NMR) is to give the human body a certain frequency of electromagnetic signal, so that it is consistent with the frequency of some organs and cells of the human body, so that the human cells can obtain new electromagnetic signals with its vibration, and enter the oscilloscope or computer imaging. Generally speaking, it is relatively simple.
If it is harmful, to be honest, human understanding is still limited. At present, we know that improper use of X-rays will definitely cause great harm, and long-term intermittent exposure will definitely be harmful to health. The other four kinds (actually, one kind, all electromagnetic waves) are unknown, and there are no serious medical records at present.
Moreover, there is basically no theoretical pathogenic basis in science, but the human body is still the most mysterious structure known at present.