Shim Coil Set for an Open Biplanar MRI System Using an Inverse Boundary Element Method

Abstract

This paper proposes a numerical method with an inverse boundary element method (IBEM) to design a set of shim coils for an open bipanar superconducting magnetic resonance imaging (MRI) system. For the traditional cylindrical MRI system, claustrophobics will suffer the palpitations and anxiety attacks when they are enclosed in a small area during the scanning process. However, such bipanar structure provides an open room temperature bore, thus improving patients’ comfort. Based on the IBEM, the shim coil skeleton needs to be divided into some small flat triangular elements. By formulating the magnetization distribution by discrete current density, an objective function is constructed to evaluate the minimum error between axial magnetic field and desired magnetic field. In particular, the selfinduction is added into the objective function which is used to adjust the deviation from the ideal target field. Finally, the well-known stream function method is commonly used to map the current density into wires. The algorithm details have been exemplified through biplanar shim coil design examples in this paper. This method can be used for coils on arbitrary surface shapes.