Transient eddy current simulation of a uni-planar gradient set

Introduction: Local gradients enable increased gradient strength and faster slew rates, which are both highly desirable to enable high-resolution and fast, real-time imaging(1). The planar gradient set presented in (2) illustrates one such gradient system, where all three gradient axes are incorporated into a uni-planar gradient set that is positioned within the magnet bore. Planar gradients present additional challenges in comparison with conventional gradient coils; additional eddy current sources such as the cooling tubes within the planar gradient set and the conductors of the built in cylindrical gradients can cause a strong distortion effect during their operation. Recently, a computer assisted magnetic resonance imaging (MRI) simulation technique has been introduced to support gradient coil design, which gives consideration to real hardware components in addition to the coils of the gradient (3). An important aspect of the simulation chain are the assessment techniques used to analyze and visualize the strength and timing behavior of the eddy currents. Transient finite element (FEM) simulations were used to characterize eddy currents by considering different materials and conducting structures, such as the cryostat, warm bore and cooling tubes.