Local planar gradients with order‐of‐magnitude strength and speed advantage

A three‐axis uniplanar gradient coil was designed and built to provide order‐of‐magnitude increases in gradient strength of up to 500 mT/m on the x ‐ and y ‐axes, and 1000 mT/m for the z ‐axis at 640 A input over a limited FOV (∼16 cm) for superficial regions, compared to conventional gradient coils, with significant gradient strengths extending deeper into the body. The gradient set is practically accommodated in the bore of a conventional whole‐body, cylindrical‐geometry MRI scanner, and operated using standard gradient supplies. The design was optimized for gradient linearity over a restricted volume while accounting for the practical problems of torque and heating. Tests at 320 A demonstrated up to 420‐mT/m gradients near the surface at efficiencies of up to 1.4 mT/m/A. A new true 2D gradient‐nonlinearity correction algorithm was developed to rectify gradient nonlinearities and considerably expand the imageable volumes. The gradient system and correction algorithm were implemented in a standard 1.5T scanner and demonstrated by high‐resolution imaging of phantoms and humans. Magn Reson Med 58:134–143, 2007. © 2007 Wiley‐Liss, Inc.