Table 2. Classification of materials according to their interactions with magnetic fields.

Type of magnetic effect	Effect on applied magnetic field	Magnetic permeability/susceptibility	Significance	Example
Diamagnetism	Internal magnetization (polarization) opposes the externally applied field;	µ < 1 (or χ < 0);	Least likely to cause an artifact	All biological tissues; silver (dental amalgam alloy)
	Magnetic field lines are ‘thinned’ or ‘dispersed’	Slightly lower permeability than free space;
		Negative susceptibility
Paramagnetism	Internal magnetization (polarization) is in the same direction as the externally applied field;	µ > 1 (or χ > 0);	Far less likely to cause an artifact	Vascular stents [46]; dental amalgam
	Magnetic field lines are ‘concentrated’ in the object	Slightly higher permeability than free space;
		Positive susceptibility
Ferromagnetism	Magnetic field lines are ‘concentrated’ in the object;	µ >> 1 (or χ >> 0);	High potential to cause MRI artifacts	Stainless steel
	Strongly attracted by a magnetic field	High permeability;
		Positive susceptibility

MRI, magnetic resonance imaging; χ, magnetic susceptibility (synonym = magnetizability); µ, magnetic permeability, µ = 1 + χ.