A Simple Relationship for High Efficiency–Gradient Uniformity Tradeoff in Multilayer Asymmetric Gradient Coils for Magnetic Resonance Imaging

Abstract

High-quality gradient coils are pivotal to advances in magnetic resonance imaging (MRI). We have studied the influence of coil dimensions and target requirements in multilayer, asymmetric, transverse gradient coils. We developed a simple linear function that defines the optimal coil length to produce a maximum figure of merit given an imaging region size and location, coil radius, and gradient nonuniformity. Our method, based on the linear function, yields high-quality solutions. The method introduces two torque/force minimization strategies in order to obtain asymmetric transverse gradient coils that balance minimum torque with a maximum figure of merit. High-performance head, asymmetric gradient coils with simple current patterns and minimum torque can be tailored to a specific magnet design, as we illustrate.Index Terms-Gradient coil design, magnetic resonance imaging (MRI), peripheral nervous stimulation, target field approach.

Toward designing asymmetric head gradient coils for high‐resolution imaging

“…The relaxed target field approach (RTFA) has been used in designing multilayer asymmetric and symmetric gradient coils (10). In this method it is assumed that N layers of current density defined as in Sanchez (10) are flowing in concentric cylindrical surfaces of radii n .…”

“…In this method it is assumed that N layers of current density defined as in Sanchez (10) are flowing in concentric cylindrical surfaces of radii n . The current density distribution is restricted in the axial domain (0 Յ z Յ 2L n ), where 2L n is the coil length for the n th layer.…”

“…The current density distribution is restricted in the axial domain (0 Յ z Յ 2L n ), where 2L n is the coil length for the n th layer. The azimuthal component of the current density is expressed as a sum of orthonormal functions multiplied by the unknown amplitudes nq , where n corresponds to the layer number and q is the number representing the mode of oscillation for the current density function (10).…”

3D Gradient coil design – Toroidal surfaces

“…In addition to the standard primary design aim of arriving at an optimal trade-off between gradient homogeneity, coil efficiency and inductance (see also, [13]), many secondary concerns dictate design considerations for gradient coils. These include: the suppression of eddy currents via shielding (see for example, [14][15][16]); avoiding peripheral nerve stimulation (see for example, [17][18][19]); alleviating patient claustrophobia (see for example, [20]); and minimising acoustic noise caused by Lorentz forces (see for example, [21][22][23][24]).…”

Advanced modelling and optimization of gradient coils and their physical behaviour in traditional and paired MRI systems

“…Some asymmetric coils are designed to be part of a complete asymmetric imaging system while others are designed to be inserted into the bore of regular MRI systems. There is some conjecture as to how well eddy currents within asymmetric coils can be modelled and compensated [42,43,44,45].…”