Estimation of static magnetic field and gradient fields from NMR image

Abstract

In the formation of images using nuclear magnetic resonance (NMR) techniques, the undesired components of magnetic fields, namely the spatial fluctuation of the static field and the nonlinear components of the gradient fields, cause image distortions. In order to adjust the magnetic coils finely to minimise this distortion, one needs precise and rapid measurement of the two- or three-dimensional distribution of the magnetic fields. The authors have derived a relationship between these undesired components and the image distortion using a so-called Fourier transform image formation method, and also proposed a way of estimating the undesired components of fields from the image conventionally reconstructed from an appropriately designed reference object. The proposed method can be utilised not only for the measurement of static and gradient fields but also for the correction of image distortion. The feasibility of the method was confirmed by experiment.