Abstract: A general method for the design of structures composed of permanent magnetic material for producing and modifying magnetic fields. The method employs a finite set of permissible spatial harmonic modes upon a surface. In particular, it has applications where the structures are finite and open, for which an exact solution is not possible. The method determines an optimum distribution based upon a least squares minimization of the difference between the achievable and desired field within a Region Of Interest (ROI). The method also has application in passively improving the homogeneity of existing magnetic fields (shimming) by distributing magnetic materials in the vicinity of the ROI.

Abstract: A general method for the design of structures composed of permanent magnetic material for producing and modifying magnetic fields. The method employs a finite set of permissible spatial harmonic modes upon a surface. In particular, it has applications where the structures are finite and open, for which an exact solution is not possible. The method determines an optimum distribution based upon a least squares minimization of the difference between the achievable and desired field within a Region Of Interest (ROI). The method also has application in passively improving the homogeneity of existing magnetic fields (shimming) by distributing magnetic materials in the vicinity of the ROI.

Abstract: A method of and apparatus for reducing ghost artifact in image data are disclosed, for use with a Magnetic Resonance Imaging apparatus in which one or more coherent ghost artifacts occur in the image. The apparatus comprises means for converting the sampled data into the image data, and means for analysing the sampled data to determined a correction to reduce the ghost artifact. The method of the invention comprises analysing the sampled data to determine a correction to reduce the ghost artifact.

Abstract: The invention describes apparatus for, and a method of, active acoustic screening and combined active acoustic and magnetic screening, of magnetic field coils, which pass a time varying current and which reside in relatively high static magnetic fields, typically greater than about 0.1 T. The invention is particularly well suited for acoustic screening of magnetic field gradient coils used in Magnetic Resonance Imaging (MRI). In a preferred embodiment a closed loop carrying current is arranged such that two different parts of the loop are mechanically coupled, dimensioned and arranged with respect to one another such that Lorentz forces experienced by the magnetic equipment are substantially reduced and preferably cancelled.In a different embodiment the invention is modified so as to permit simultaneous magnetic and acoustic screening.