Plused Nuclear Magnetic Spin Resonance

THEORY: The physics behind NMR/MRI signal production lies in the physics of spin. This section will cover enough aspects of spin to understand the generation of NMR signals. Although this initial spin discussion is inherently quantum mechanical in nature, we will later need to employ some simple principles from thermodynamics and classical dynamics to further describe the art of NMR. These topics will be thrown into this discussion in an ad hoc manner when necessary. Spin is a specific (internal) manifestation of angular momentum inherent in physical entities. All of the basic constituents of matter (and the constituents of known forces apart from gravity) possess a definite value of spin. Because spin is a notoriously quantum mechanical property, it is naturally “quantized” in discrete, not continuous, values. These values, the possible spin quantum numbers, exist as integer (for bosons) and half-integer (for fermions) values. The symbol most often used to represent the nuclear spin quantum number is the symbol I. Spin itself can be represented in a complex vector space, with the magnitude of a given spin state expressed in terms of a spin quantum number. This relation is given as