In accordance with Faraday's Law of Induction, rapidly changing gradient magnetic fields can induce stray currents, known as eddy currents, in the surrounding conducting materials.
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.
- 1. Dale B, Brown M, Semelka R. MRI: Basic Principles and Applications, 5th edition. John Wiley & Sons, 2015.