A contrast agent, which due to their ferromagnetism produce local field inhomogeneities and hence visible image alterations in the tissues where they are present. Therefore, they can act as contrast media. Usually, particles exhibiting superparamagnetism rather than ferromagnetism are used.

See also the related poll result: 'The development of contrast agents in MRI is'

Gadolinium oxide (Gd2O3) is a prototype paramagnetic agent for contrast enhanced MRI. Gd2O3 particles have very high relaxivity. With its high magnetic moment, gadolinium reduces the relaxation time and enhance MR signal intensity. All gadolinium compounds are highly toxic. Very stable complexes are developed to eliminate the toxicity. See also Paramagnetic Substance, Paramagnetism, Paramagnetic Contrast Agents and Contrast Agents, the info sheet gives an overview and more in-dept information about different types of MRI Contrast media.

(c) Magnetic susceptibility is the degree of magnetization of a material in response to a magnetic field. Paramagnetic materials strengthen the magnetic field, diamagnetic materials weaken it. The magnetic susceptibility of ferromagnetic substances is not linear; this is called differential susceptibility.
Differences in magnetic susceptibilities are a frequent cause of MRI artifacts.

See also Susceptibility Artifact, Magnetism, Diamagnetism, Paramagnetism, Ferromagnetism.

The activation of the brain is mirrored in the local changes in metabolism and hemodynamics (brit. haemodynamics). By using heavily T2 weighted scans activated brain areas show an increase in signal intensity as oxyhaemoglobin (brit. oxyhaemoglobin) is diamagnetic and deoxyhemoglobin (brit. deoxyhaemoglobin) is paramagnetic. Oxygen mapping will benefit from high field strength.

See also Blood Oxygenation Level Dependent Contrast, Haemoglobin, Perfusion Imaging, Diamagnetism, Paramagnetism.

Substances exhibiting paramagnetic properties are used as contrast agents in MR imaging. They have a small but positive magnetic susceptibility (magnetizability - tends to align along the magnetic field). Typical paramagnetic substances usually possess an unpaired electron and include atoms or ions of transition elements, rare earth elements, some metals, and some molecules including molecular oxygen and free radicals.

See also Paramagnetism.