Just because the word "nuclear" is there, it doesn’t mean that it is anything to do with radioactivity!!! It is not about bombs!
BUT..because the average person is worried by the word "nuclear", this type of imaging in hospitals has been renamed as MRI Magnetic Resonance Imaging – and it's absolutely brilliant!
Nuclear physics just means studying the physics of the nucleus of the atom: the central part. After all, we are al made up of atoms and we all have countless billions of nuclei in us, so nuclei are nothing to be afraid of.
NMR (MRI) is extremely complex but here’s a nutshell explanation.
The nucleus of hydrogen is a proton. If protons are in a very strong magnetic field and you fire a very short burst of radio waves at them they wobble about (called a "precession") and send radio waves back. The strength of the magnetic field determines the frequency of the radio waves. Now, protons are hydrogen nuclei, and there is lots of hydrogen in us in the form of water…so if we are put in a magnetic field then this effect can happen in us so the detector gives an idea of the concentration of water by the strength of the return radio signal. If we are put in a magnetic field whose strength varies along our length, then different frequency waves come from different parts of us, so the computer can sort out where all the protons (water) are in our body.
Clever stuff!

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