Several magnetic resonance imaging applications require the use of strong magnetic field gradients with high slew rates.  For example, diffusion-weighted imaging benefits from stronger gradients, while breath-hold applications, such as cardiac imaging, can benefit from higher slew rates.  An alternative to the conventional whole-body gradient coil is a planar gradient coil.  Planar gradients provide localized increases in gradient strength and slew rates, while accommodating larger sample sizes than cylindrical geometries allow.  This attribute of planar gradients will be applied towards extending the functionality of the neurology-dedicated 7T MRI scanner.  By replacing the whole-body gradient set with a planar gradient set, it will be possible to image localized regions within the torso.

As a prototype for the larger 7T system, a three-axis planar gradient set is being designed and constructed to fit inside the 9.4T Varian MRI scanner.  The gradient coil was designed to have a slight curve about the longitudinal axis to increase gradient performance and facilitate positioning of the sample.  The gradient wire patterns were designed using a modified target field method.  Torque compensation was incorporated into the design algorithm to decrease acoustic noise during operation.  The wire patterns of each axis were milled out of copper sheet and curved in a roller.  Gradient axes were then mounted on Kevlar trays and nested on top of each other.  Active water-cooling and temperature monitoring was incorporated between each layer.  The gradient coil was potted in a high-thermal conductivity epoxy and secured to the ends of the scanner with glass-filled ultem rods.

CFMM is currently working towards developing a self-shielded planar gradient set for the 7T scanner.  A separate, high-efficiency shim-coil set will be constructed for use with the planar gradient coil.