Magnetic permeability is the degree of magnetization of a material that responds linearly to an applied magnetic field. The SI units of permeability are henry per meter (H/m) or newton per square ampere (N/A²).

The intact blood brain barrier prevents that contrast agents penetrate in the normal brain tissue. If the blood brain barrier is damaged by a malignant tumor, the contrast medium can accumulate within the interstitial tumor tissue due to the alterations in the blood brain barrier permeability. Adjacent normal brain tissue does not contain the contrast agent.

Magnetic flux density is the amount of magnetic flux per unit area of a section, perpendicular to the direction of flux. The magnetic flux density is the product of the magnetic field strength and permeability. The SI unit for flux density is weber per square meter. One weber per square meter equals one tesla (T).