Eddy currents

Eddy currents (also known as Foucault currents) are the result of rapidly changing gradient magnetic fields that in turn induce stray currents in the surrounding conducting materials. They form in accordance to Faraday's Law of Induction.

Eddy currents are unwanted as they generate their own magnetic fields, which oppose the original magnetic field via Lenz's Law, and therefore distort the spatial and temporal performance of the overall desired magnetic field.

There are two main ways of compensating or correcting for eddy currents:

• pre-distort the gradient pulse so that the magnetic field generated by eddy currents improves the original magnetic field
• apply a secondary coil around the main gradient coil to reduce or cancel generated eddy currents, this results in an actively shielded gradient coil

When analyzing diffusion tensor imaging (DTI), it is important to correct for eddy currents, amongst other corrections, before data processing.