Diasonics, Inc.

K Christine Hawryszko

James S Tropp

Kevin A Derby

In a phase encoded chemical shift imaging (CSI) system, phase shifting in k space is used to shift voxels so as to translate them in one or more dimensions so that one or more voxels maximally encloses an object of interest. The position of a structure of interest is located via a 1H 'scout' image, and the Shift Theorem for finite Fourier transforms is applied to shift voxel boundaries in one, two or three dimensions so as to maximally enclose the structure in a minimal number of voxels. Voxel shifts thus may be accomplished computationally by minimal manipulation of the raw data--after the patient has left the imaging facility. The resulting spectral data corresponding to the structure of interest is not as subject to dilution by spectrum of the surrounding tissue.

Fourier shifting of voxel boundaries in MR chemical shift imaging

An automated magnetic field shimming process for magnetic resonance spectroscopic imaging (MRSI) uses doubly phase encoded NMR spin echo responses in conjunction with multiple fourier transformation to derive a spectroscopic plot for each voxel in a three-dimensional array of voxels in an image volume (including portions of a living subject) which is to be subsequently subjected to MRSI using NMR FID or spin echo responses. The thus derived hydrogen peak frequency is taken as a measurement of existing static magnetic field intensity within that voxel and adjusted shim coil currents are calculated so as to reduce or minimize nonuniformity of the static magnetic field. A nonexistent pseudo shim coil having an assumed uniform shim contribution may enhance the resulting field homogeneity. The auto shimming procedure may be applied iteratively as required to achieve the predetermined degree of field uniformity.

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Millbrae, CA, United States of America

K Christine Hawryszko