Last revised by Joshua Yap on 13 Oct 2022

Diamagnetism is the property of materials that have no intrinsic atomic magnetic moment, but when placed in a magnetic field weakly repel the field, resulting in a small negative magnetic susceptibility. Materials like water, copper, nitrogen, barium sulfate, and most tissues are diamagnetic.

It should be noted that calcium atoms, in isolation, as they have paired outer-shell electrons, are paramagnetic. However, when calcium is mixed with many other atoms as is the case in physiological calcifications, the result is a diamagnetic substance, which is useful in allowing calcifications to be distinguished from blood products that are paramagnetic on susceptibility weighted imaging.

The figure illustrates the effect of a diamagnetic material (grey circle) on the magnetic field flux lines (blue). The weak negative magnetic susceptibility contributes to the loss of signal seen in bowel on MRI after administration of barium sulfate suspensions.

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