A Novel Target Field Method for Designing Uniplanar Self-shield Gradient Coils of Fully Open MRI Device

Abstract

A new approach to the design of uniplanar self-shield gradient coils for fully open magnetic resonance imaging system is proposed to build a specified gradient magnetic field in a target region. In this new design methodology, the surface current density of the coils is represented by a two-dimensional Fourier series expansion. A cost function is constructed in terms of the summation of squared error and penalty functions. Minimizing the cost function, we obtain the continuous current density distribution for the uniplanar gradient coils. Applying the stream function technique to the resulting continuous current distribution, discrete current patterns can be obtained. Employing the Biot-Savart integral equation to the discrete current loops, the gradient magnetic field has been re-evaluated in order to validate the method proposed. Using this approach, uniplanar self-shield x-gradient coils which are capable of creating a gradient field of 40 mT/m have been designed. The results indicate that with this method a magnetic field with high level of linearity and a satisfied screening effect are obtained.