Apparatus and method for determining the presence of substances in a

Abstract

An apparatus and method of unambiguously determining the presence of specific substances in a sample by NMR and then obtaining a high resolution NMR image of these substances. The sample is placed in a static magnetic field and repetitively subjected to first and second frequency selective RF pulse sequences to excite nuclear spins in the sample and to produce spin echo signals. The first and second pulse sequences are so constructed that signals from the substances are received while signals from the water component of the sample are suppressed. A third frequency selective pulse sequence is applied to the sample during every second repetition of the first and second pulse sequences to edit the acquired NMR spectra. By differencing the NMR signals received in the presence and the absence of the third pulse sequence, the signals of the substance of interest are unambiguously determined. In order to produce an NMR image of the substances, pulsed magnetic field gradients are applied to the sample during a period when no RF pulse sequences are being applied. This phase or frequency encodes spatial distribution information about the substance in the sample. The resultant NMR signal is then Fourier transformed to produce the desired image.