An actively shielded gradient coil design for use in planar MRI systems with limited space.

In planar magnetic resonance imaging (MRI) systems, gradient coils are usually placed within a very limited space owing to the physical constraints of the small gap size (pole-pole) distance of the permanent magnet. Typically, the unshielded or partially shielded design scheme is adopted to generate required magnetic fields with reduced system costs. However, non-fully shielded coils can induce large eddy currents on the surrounding metal structures, including magnet poles, that significantly impact the imaging performance. This paper elaborates a new design strategy to resolve the limited space problem. Using the peripheral sections of the MRI system, a set of actively shielded gradient coils are purposefully designed. Between the two magnet poles, the actively shielded gradient coils occupy merely four coil layers (six coil layers are usually required), which offers an excellent shielding effect, thus reducing the image distortions. The saved space can be used to integrate a high-efficient cooling system. Moreover, the design scheme does not significantly increase the fabricating complexity.