Simulation Environment to Predict the Effect of Eddy Currents on Image Quality in MRI

Gradient coils generate a magnetic field with a linear spatial variation that superimposes over the main magnetic field of a magnetic resonance imaging (MRI) system; such superimposition of the magnetic fields enables the encoding of the spatial position in MRI. A rapid change in the gradient field induces eddy currents in the conducting structures of an MRI system, resulting in the production of image artifacts. An objective of the gradient coil design phase is to predict both the coil´s performance with respect to eddy currents and the image quality (IQ) before the coil is manufactured. In this paper, an integrated simulation environment is presented that combines the gradient coil design with an image formation simulation to predict the IQ. Here, an unshielded, uni-planar gradient set was simulated. Further, a study was conducted to determine the effect of frequency on the eddy currents induced in the conducting structures of the main magnet coil while exciting the uni-planar gradient set. The knowledge acquired from this study was applied to the IQ simulation, and a time-dependent simulation of a gradient echo pulse sequence was performed. The IQ of the uni-planar gradient set was predicted, and the input and reference images as well the images distorted by the eddy currents are shown.