The Physical Basis of Magnetic Resonance Imaging

  • Gustav Konrad von Schulthess


With the term “spin” we characterize a property of elementary particles such as protons and electrons which can be understood only within the theoretical framework of quantum mechanics. Thus, the NMR phenomenon is quantum mechanical in nature. Nevertheless, NMR can be understood using simple physical models from classical physics. We like to think of a spin as something like a compass needle, which will orient itself along an external magnetic field if it is placed in it. Being governed by the laws of quantum mechanics, spins can align not only parallel, but also antiparallel to an external field. Thus, a system of spins pointing in all spatial directions outside a magnetic field, will end up with some spins aligned parallel and some antiparallel to an external magnetic field, once such a field is applied (Fig. 1.1).
Fig. 1.1

The protons in a sample outside a magnetic field are oriented randomly. When an external magnetic field HO is applied, there are two possible orientations for the component along the external field: either parallel or antiparallel. There are slightly more spins pointing along the energetically more favorable direction


Torque Ferrite Coherence Magnetite Macromolecule 


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Copyright information

© Springer-Verlag Berlin Heidelberg 1989

Authors and Affiliations

  • Gustav Konrad von Schulthess
    • 1
  1. 1.Departement Medizinische RadiologieUniversitätsspital ZürichZürichSwitzerland

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