A TECHNIQUE FOR ACCURATE MAGNETIC-RESONANCE-IMAGING IN THE PRESENCE OF FIELD INHOMOGENEITIES

Static field inhomogeneity in magnetic resonance (MR) imaging produces geometrical distortions and distortions in intensity. The inhomogeneity may be caused either by imperfection in the magnet system or by magnetization of the object being imaged. In this paper we present a technique for producing geometrically accurate MR images with undistorted intensity in the face of high levels of static field inhomogeneity arising from either source. The technique requires the acquisition of two images of the same object with altered gradients. Based on a knowledge of these gradients it employs an automatic postprocessing step that exploits some invariant characteristics of the distortions to produce a rectified image from the two acquired images. No phantom imaging is involved and no operator interaction is required. We present a theoretical justification of the technique and compare it to other techniques, and we present experimental results that show that the technique works. The improved accuracy in geometry and intensity may improve the reliability of sterotactic surgery, may enhance the feasibility of both clinical and industrial imaging via external fields, and may increase the resolution of microscopic imaging.