Method and apparatus for spatial localization of magnetic resonance

Abstract

Spatial localization of NMR signals is obtained by applying a selective 90.degree. RF pulse concurrently with a second order non-linear magnetic field gradient of the form x.sup.2 +y.sup.2 -2z.sup.2, and then applying a selective 180.degree. RF pulse concurrently with a linear magnetic field gradient in the z direction. The resulting spin-echo signal may be analyzed to perform volume-selected magnetic resonance spectroscopy. Spatially localized two-dimensional or three-dimensional magnetic resonance imaging may be accomplished using this spatial localization sequence together with an appropriate Fourier imaging sequence. Likewise, spatially localized one-dimensional, two-dimensional or three-dimensional chemical shift imaging may be obtained by applying one or more stepped phase encoding linear magnetic field gradients along the x, y and/or z directions. Further improvements are obtained in volume-selected magnetic resonance spectroscopy, and in spatially localized magnetic resonance imaging and chemical shift imaging by radial phase encoding using a stepped second order non-linear magnetic field gradient of the form x.sup.2 +y.sup.2 -2z.sup.2 applied after any form of selective excitation of a localized region and before the sampling of the NMR data. Three-dimensional spatial localization may be achieved with the application of a single selective RF pulse by applying such an RF pulse concurrently with appropriate oscillatory or non-uniformly stepped second order non-linear and linear magnetic field gradients.