A novel, cylindrical, transverse gradient coil design for magnetic resonance imaging of large samples

摘要

Magnetic resonance imaging (MRI) requires the use of three sets of coils to produce magnetic field gradients, one for each axis, to encode three-dimensional information. The magnetic field generated by gradient coils has to change as linearly as possible with distance so as to avoid heavy distortion of the resulting image of the sample. The reduction of the dimensions of the magnets for MRI applications has made it necessary to construct gradient coils that can be placed in reduced spaces and, at the same time, provide the uniformity necessary for MRI. A novel cylindrical gradient coil design is described to perform high-resolution imaging of large samples, having a large cylindrical zone of gradient uniformity, co-axial with the coil. This design, referred to as the butterfly coil, produces a magnetic field along the axis of the cylinder and a field gradient in the perpendicular direction (transverse gradient). The butterfly coil design has been simulated and compared, both in homogeneity and efficiency, with a preceding gradient coil geometry. The coil has been constructed and experimental measurements performed. The aspect ratio, defined as the ratio between the length h and diameter d of the cylinder of the coil, is very low. In fact, mathematical simulations and experimental measurements have been carried out on a gradient coil system having h/d =1.5. Despite its low-dimensional ratio, this gradient coil system has been proved to be very accurate, both in uniformity and efficiency, in a relatively great volume.