Nuclear magnetic resonance systems

A method of investigating the distribution of chemicals in a body, the method including the steps of:

• applying magnetic fields to cause nuclear magnetic resonance preferentially in a region of said body at a frequency appropriate to a chosen element;
• applying a periodically reversed magnetic field having a field gradient along said region to produce dispersion in said resonance, the timing of the periodically reversed magnetic field being such that the region is effectively divided into a plurality of smaller regions, the nuclei of the chosen element in each smaller region resonating within a unique frequency band, and dispersion in that band representing a chemical shift to be determined;
• sensing free induction decay and rephasing signals emitted by the nuclei as the field gradient is periodically reversed;
• sampling the free induction decay and rephasing signals and Fourier Transforming the samples so that the frequencies in the samples are dispersed, the dispersion being indicative of both spatial and chemical shift, the gradient being of sufficient amplitude that the spatial shift is larger than the chemical shift by an amount sufficient to avoid ambiguity.

A method of determining the distribution in a body of chemicals including a chosen element, the method including the steps of:

• applying a steady and substantially uniform magnetic field at least in a region of interest of said body;
• applying a first magnetic field having a first gradient in said region together with a pulse of RF energy tailored to saturate the spins of nuclei in the region with the exception of a substantially planar slice thereof perpendicular to the direction of the gradient;
• applying a second magnetic field having a second gradient in a direction in the slice together with an RF pulse sufficient to excite the nuclei in a strip therein;
• applying a third magnetic field having a third gradient in a direction orthogonal to the first and second gradients, said third gradient being periodically reversed to provide a line spectrum free induction decay signal representing free induction decays for a plurality of different locations along said line, such that the spacing of the lines of said spectrum is sufficient to accommodate the chemical shift spectrum of each location in the strip.

A method of determining the distribution in a body of chemicals including a chosen element, the method including the steps of:

• applying a steady and uniform magnetic field at least in a region of interest of said body;
• applying a magnetic field having a gradient in said region together with a pulse of RF energy to excite to resonance nuclei in a substantially planar slice of said region of interest;
• applying a further magnetic field having a gradient in a chosen direction in said slice, the further magnetic field being periodically reversed to provide a line spectrum free induction decay signal representing a plurality of substantially parallel strips in said slice perpendicular to the chosen direction;
• Fourier Transforming the free induction decay signal to obtain line integrals of chemical shifts for each of said strips;
• repeating the preceding steps for a plurality of different directions, in the slice, of the gradient of the further magnetic field, and processing the line integrals for all of said directions to provide said distribution.