Lineshape of Magnetic Resonance and its Effects on Free Induction Decay and Steady-State Free Precession Signal Formation
Larmor-frequencies for different local magnetic field inhomogeneities. For dephasing in an imaging gradient or diffusion weighted gradient (a) the local resonance frequency is proportional to the spatial coordinate (b) according to Equation (6). In case of cylindrical objects, as for example blood filled capillaries in the myocardium (c) the local Larmor frequency exhibits the form of a two-dimensional dipole field (d) according to Equation (7) where and are polar coordinates in a plane perpendicular to the axis of the vessel. Dephasing around spherical objects as exemplified by magnetically labeled cells (e) is described by the three-dimensional dipole field with low volume fraction or its extended version (f) according to Equation (8) or Equation (10). On the alveolar surface () (g) [image adapted from ], the resonance frequency depends on the polar angle only (h).
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