2. Industrial magnets

2.1 Magnetic Resonance Imaging MRI

This powerful soft-tissue imaging technique (brain, muscles, ...) uses nuclear magnetic resonance (NMR) of water, in particular of the very many hydrogen nuclei that possess a magnetic moment. A continuous magnetic induction B ₀ induces a rotational motion (Larmor precession) of these moments around their axis at frequency f ₀ . This is proportional to the amplitude of the induction B ₀ , the coefficient being the gyromagnetic ratio, specific to each core. These frequencies are high: 42.6 MHz at 1 T for the hydrogen proton. Subjected to a radio-frequency magnetic induction (frequency f _1...