A new approach to shimming: The dynamically controlled adaptive current network

Abstract

Magnetic field homogeneity is important in all aspects of magnetic resonance imaging. A new approach to increase field homogeneity is presented that allows dynamic and adaptive control over the flow of current over a single surface using a network of actively controlled solid-state switches. Computer simulations were completed demonstrating the potential of this approach. Wire patterns were produced using the boundary element method to remove magnetic field inhomogeneities over multiple regions of interest. Field maps and regions of interest histograms were compared with and without the shim present. A prototype was constructed confirming the feasibility of this approach within the magnetic resonance environment. Metal-oxide-semiconductor field-effect transistors were used. Two field maps were acquired with the prototype producing gradient and offset field profiles, respectively. The experimental field profiles were compared with simulation. The wire patterns significantly increased field homogeneity over all regions of interest investigated. The field profiles produced by the prototype matched simulation. No imaging artifacts were produced. An approach to control the shape of a current distribution over a single surface has been described. This method has the potential to improve field homogeneity over any desired region of interest and is particularly well suited for dynamic applications. The method is feasible with current technology and construction techniques.