95 Artifacts: Magnetic Susceptibility

The relation between the magnetization of a material and the applied external magnetic field is given by the physical property known as magnetic susceptibility. The difference in magnetic susceptibility between adjacent tissues or structures is termed a susceptibility gradient and may cause local magnetic field inhomogeneities, resulting in a nonlinear distribution of resonance frequencies. Because magnetic field gradients are used for spatial encoding, any nonlinear distribution causes image distortion and artificial signal variations. Figure 95.1 presents the consequences of a substantial change in magnetic susceptibility. Figure 95.1A shows the normal image appearance with minor variations in magnetic susceptibility within the tissue and a linear relationship between location and local magnetic field gradient. Figure 95.1B

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