Abstract: In a method for NMR excitation of a sample, an Rf pulse is applied to an irradiation coil (6) proximate the sample, in the presence of an external DC magnetic field and an adiabatic passage is performed wherein the Rf pulse is controlled such that:B.sub.1 =V A sin 2.pi..nu.t and .DELTA.H=A(cos 2.pi..nu.t+s),orB.sub.1 =v A cos 2.pi..nu.t and .DELTA.H=A(sin 2.pi..nu.t+s),where s=S/A, where S is the frequency offset of a nucleus from the center of the spectrum, and where v allows for variation of B.sub.1 throughout the sample, .DELTA.H is the resonance offset of the nuclear spins, and B.sub.1 is the rf field of a spin-lock pulse.

Abstract: A pair of coupled surface coils are arranged to provide active detuning whereby the shape of the RF field due to the RF current in one coil is modified in a calibrated fashion by the RF current in the second coil whereby a selected fraction of the RF field of one coil may be selectively added or substracted from the RF field of the one other coil thereby shaping the RF field.

Abstract: In a pulsed nuclear magnetic resonance method of analysis, a series of phase cycled radiofrequency pulses of the form 2.theta.; .theta.[.+-.x]; (2.theta.[.+-.,.+-.y]).sub.4, called a depth pulse scheme, may be applied using an irradiation coil which provides an inhomogeneous radiofrequency field across the sample volume, so that signals may only be detected from sample regions where the pulse angle .theta. is close to m.pi./2, where m is an odd integer. However, signals from regions where .theta.=3.pi./2 or 5.pi./2, if such regions exist, can be eliminated by varying some of the pulses from their ideal .theta. of 2.theta. values. The sample discrimination afforded by means of these pulse schemes may be improved by using static or pulsed magnetic field gradients or by using more than one radiofrequency coil.

Abstract: Use of a switch at the end of a .lambda./4 cable inserted between the Rf coil and ground allows the coil to be tuned and detuned at will. This detune switch essentially eliminates coupling between adjacent coils permitting operation of multiple transmit coils at the same frequency. These switches have been employed to prove a previously proposed method of complete sensitive-volume localization using multiple Rf coils and depth pulse schemes. The example illustrated is the case of two coaxial coplanar surface coils. There are important uses in in-vivo spectroscopy.

Abstract: A method of obtaining a localized nuclear magnetic reasonance signal from a sample using a radiofrequency irradiation coil which provides an inhomogeneous radiofrequency field, comprisesapplying to the sample a plurality of radiofrequency pulse sequences, each pulse sequence including an excitation pulse, and at least two other pulses, the pulse sequences differing only in the phase of one or more of the said other pulses, and the phases of at least two of the said other pulses being shifted by 180.degree. in selected sequences of the said plurality, the number of sequences in the said plurality being such that a sequence exists for each possible combination of the said phase shifts for each of the said other pulses, and there being no sequences in the said plurality in which the phases of the said at least two of the said other pulses is shifted by 90.degree.,acquiring an N.M.R. signal after each pulse sequence,and combining the N.M.R. signals obtained to produce a localized N.M.R.

Abstract: In a method of operating a nuclear magnetic resonance (NMR) spectrometer in relation to a sample comprising two types of nuclei, a sequence of radiofrequency pulses and delay periods is applied using two different radiofrequency coils, one for each type of nucleus, each coil providing an inhomogeneous radiofrequency field, so that the two coils generate separate but overlapping sensitive volumes for each of the two types of nuclear species, whereby signal intensity is substantially limited to the overlap volume.

Abstract: A liquid sample comprising a system made up of two types of heteronuclei is pulsed in a particular manner in a nuclear magnetic resonance (NMR) experiment so that the resulting NMR signal from the one type of heteronucleus depends on the scalar-coupled interaction with the other type of heteronucleus. The sequence of radiofrequency pulses is such that the two types of heteronuclei interact via the phenomenon of polarization transfer and by the phenomenon of the correlated motion of the two types of heteronuclei in the transverse plane of the doubly rotating reference frame. The combination of these two phenomena in the one pulse sequence provides NMR signals which are easily made less dependent on the exact magnitude of the heteronuclear scalar coupling constant. The coupled NMR signals for polarization transfer from a system of multiple spin-half nuclei have multiplet components in the normal ratio. Consequently the pulse sequence provides an improved method for obtaining chemical structural information.

Abstract: In a pulsed nuclear magnetic resonance method of analysis, in which a single radiofrequency pulse is applied using an irradiation coil which provides an inhomogeneous radiofrequency field across the sample volume, the inhomogeneity of this field ensures that some sample regions experience a radiofrequency pulse which is closer to a .pi./2 pulse angle than for other regions, resulting in a larger signal intensity from the former regions as compared to the latter. If a second pulse is applied after the first, prior to acquisition of the signal, and if the phase of this pulse is alternated through the four phases: 0.degree., 90.degree., 180.degree. and 270.degree., during a series of transients, then, provided the receiver phase is changed by 180.degree. when the second pulse phase is changed by 90.degree., the signal intensity will accumulate from regions where the second pulse angle is .pi. radians and there will be discrimination against regions where the second pulse angle differs markedly from .pi. radians.