Tailoring magnetic field gradient design to magnet cryostat geometry

Abstract

Eddy currents induced within a MagneticResonance Imaging (MRI) cryostat bore during pulsing of gradient coils can be applied constructively together with the gradient currents that generate them, to obtain good quality gradient uniformities within a specified imaging volume over time. This can be achieved by simultaneously optimizing the spatial distribution and temporal pre-emphasis of the gradient coil current, to account for the spatial and temporal variation of the secondary magnetic fields due to the induced eddy currents. This method allows the tailored design of gradient coil/magnet configurations and consequent engineering trade-offs. To compute the transient eddy currents within a realistic cryostat vessel, a low-frequency Finite-Difference Time-Domain (FDTD) method using Total-Field Scattered-Field (TFSF) scheme has been performed and validated.