Design of biplanar gradient coils for magnetic resonance imaging of the human torso and limbs

A method is described for design of gradient coils of unconventional geomet ry for MRI that is based on the superpositions of magnetic fields arising f rom individual current elements calculated by the Biot-Savart Law. Use of a n optimization method based on a genetic algorithm enables a wide diversity in the shapes of coil that can be modeled. To exemplify this a two axis, b iplanar gradient set is presented; this geometry offers good access for rec tangular objects whilst holding the coils closer to the region of interest than is possible for cylindrical configurations. The inner dimensions of th e gradient set were 40.0 x 24.4 x 40.0 cm and the gradient efficiencies wer e 0.3 and 0.4 mT m(-1) A(-1) in the z- and y-directions respectively over a 15 cm diameter region. Correction of signals arising from regions for whic h gradient linearity was not optimized was successful for the monotonic reg ion within the set; the largest cuboid from which the MR signal could be pr ocessed to produce an undistorted image is of dimensions 36.3 x 17.2 x 24.4 cm. (C) 1999 Elsevier Science Inc.