Nuclear magnetic resonance methods.

摘要

This invention provides improved methods of investigating a body by nuclear magnetic resonance wherein nuclear magnetic resonance is preferentially excited in a slice of the body and the resulting free induction decay signals are detected in the presence of a magnetic field having first and second gradients (G<Sub>y</Sub>, G<Sub>x</Sub>) in first and second directions respectively in the slice, the sense of the first gradient being periodically reversed.

In one proposed method two experiments are performed in which the phase of the first gradient (Gy) reversal is opposite and the detected signals from the two experiments are edited to obtain a set of signals, for Fourier transformation, occuring when the first gradient has one sense. Two such sets may be obtained, one for each sense of the first gradient, and the data obtained after Fourier transformation re-ordered and added.

In a second proposed method the second gradient (G<Sub>x</Sub>) is applied only when the first gradient (Gy) has a given sense, and the free induction decay signals obtained when both gradients are present, and when only the first gradient is present, are separately processed.

In a third proposed method, the first gradient (Gy) is temporarily removed before each reversal of its sense, and the second gradient (G<Sub>x</Sub>) is reversed while the first gradient is removed, the magnitude of the second gradient being controlled so that the time integral of the second gradient at the beginning of each period when the first gradient has a given sense is the same as at the end of the preceding such period, the free induction decay signals occurring when the first gradient has said given sense only being used for data retrieval.