Magnetic Resonance Field Effect Spins in Living Tissue: a Delusive Points Analysis


  • Rodolfo Grosso Núcleo de Ing. Biomédica
  • Franco Simini Universidad de la Republica UDELAR


Magnetic Resonance Imaging uses the physical phenomenon of Nuclear Magnetic Resonance applied to
hydrogen atoms nuclei in living tissue for imaging. The physical phenomena involved are on a nuclear scale and correspond to a convenient manipulation of the spin of the nuclei, as a result of which a net magnetization is obtained on a macroscopic scale. This manipulation begins with the application of a constant magnetic field that has several effects on the spins. In much of the literature, Classical Mechanics is apparently convincingly used to explain these effects. After applying the field, the spins have a quasi-isotropic distribution of directions, there is no simplification of Classical Mechanics which consists of representing all the spins as vectors ups and downs (error 1). In a Classical Mechanical environment, the spins do not precess on the same cone (error 2), there is a spiral for each one until reaching thermal equilibrium. This movement is affected by random disturbances. Both errors come from wrong interpretations of quantum results: 1) Quantum Ups and Downs are eigen states to which intermediate states collapse and should not be confused with upward or downward vectors. 2) comes from confusing the projection on an axis with an eigenvalue. Furthermore, a third error consists in not considering the variation of the angle of the spin with the direction of the magnetic field. A fourth point is that a detailed explanation of thermal equilibrium and the occurrence of net magnetization is not provided in the literature. A demonstration that uses Statistical Thermodynamics is presented here, where equilibrium is shown as the final part of the evolution of macrostates towards the most probable, while the potential energy of the spins decays, which is converted into kinetic energy of the lattice.






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