Abstract: A method of suppressing at least one undesired resonance response signal while facilitating reception of at least one other desired NMR response signal from a coupled spin resonance in NMR spectroscopy, utilizes a pair of alternating sequences of RF signal pulses, with each sequence having an initial .pi./2 RF pulse, followed by a .pi. RF signal pulse having a temporal midpoint at a time interval T after the temporal midpoint of the initial pulse (where T=n/4J, with n being an odd integer and J being the spin coupling constant of the hydrogen nuclei) and a final .pi. RF signal pulse with a temporal midpoint at twice the time interval T after the temporal midpoint of the first .pi. RF signal pulse in that sequence. Only one of the pair of sequences is provided with a polarization transfer narrowband .pi. RF signal pulse symmetrically disposed about a temporal midpoint located at substantially a time interval T after the first .pi.

Abstract: A method for the complete inversion of magnetization by adiabatic fast passage during an NMR experiment on a sample having a selected nuclear specie with a Larmor frequency .omega..sub.0. A radio-frequency magnetic field is generated with an amplitude B.sub.1 and an instantaneous frequency .omega.(t) which is non-linearly swept, as a function of time, from a minimum frequency .omega..sub.1 substantially at a maximum offset frequency .DELTA..omega. below the Larmor frequency .omega..sub.0, through the Larmor frequency, to a maximum frequency .omega..sub.h substantially at the maximum offset frequency .DELTA..sub..omega. above the Larmor frequency. The non-linearly swept, monotonic RF signal is applied to the sample-being-investigated for a sweep time interval sufficient to invert the magnetization of the selected nuclear specie. The preferred sweep is a tangential function:.omega.(t)=.omega..sub.0 .+-..gamma.B.sub.1 tan (arcsin (.omega..sub.s t)), (A)or.omega.(t)=.omega..sub.0 .+-..gamma.B.sub.1 tan (.omega..

Abstract: The invention proposes a method and a device in which resonance signals (generated for NMR imaging) are sampled in the presence of a static or semi-static and time modulated gradient magnetic field with the gradient direction of the fields applied being mutually perpendicular. The resonance signals are conditioned prior to the start of sampling. The sampled signals are associated with spatial frequencies (i.e. points in a spatial frequency space (k.sub.x, k.sub.y) which is the (2-D) Fourier transform of the actual (s, y) space), which are determined by the applied gradient fields. The static or semi-static gradient field always produces an increase (for example, in k.sub.x), while the time modulated gradient field always produces an image frequency which lies between two limits (k.sub.y and k.sub.y +k.sub.y). Consequently, the invention enables determination of NMR spectroscopy data in an entire band in the (k.sub.x, k.sub.y) space.

Abstract: Process for the generation and processing of signals for obtaining a nuclear magnetic resonance image, which is free from distortions, from an inhomogeneous polarization field B=Bo+E(x,y,z) using known 2D,FT and 3D,FT image coding methods involving the application of a 90.degree. radiofrequency pulse in plane xOy, then a phase coding during time .tau. followed by frequency coding by applying, along Ox, a reading gradient during the acquisition of the free precession signal, which is then made to undergo Fourier transformations with respect to time and with respect to the gradient or gradients applied.During a second series of sequences involving the successive application of the same gradients, the free precession system is subject to a second 180.degree. radiofrequency pulse at the start of establishing each reading gradient.

Abstract: The present invention decreases the time needed between collection cycles of an NML tool located in a wellbore penetrating an earth formation by zeroing the effect of prior-in-time residual polarization via a surprising change in the operations, viz., using a series of sham polarizing cycles wherein the coil circuit is permitted to ring at the series Q' values higher than the normal Q value. Result: previously non-precessing components of the residual polarization undergo precession and can be subsequently scattered by the next-in-time field. Since all of the sham fields as well as the next-in-time polarizing field are provided with slow-rising amplitude v. time turn-on segments, the precessing components of the polarization existing at the start of the build-up of the fields are easily scattered. Ultimately, all aspects of the residual polarization is destroyed whereby cyclic NML logging speed can be greatly improved.

Abstract: The present invention decreases the time needed between collection cycles of a NML tool located in a wellbore penetrating an earth formation by zeroing the effect of prior-in-time residual polarization via a surprising change in the operating parameters, viz., generating the next-in-time polarizing field with a slow-rising turn-on segment for scattering precessing components of residual polarization thereabout. Result: cyclic NML logging speed can be greatly improved.

Abstract: The present invention decreases the time needed between collection cycles of a NML tool located in a wellbore penetrating an earth formation by zeroing the effect of prior-in-time residual polarization via a surprising change in the operations, viz., using a sham polarizing cycle wherein the coil circuits permitted to ring at a Q' value higher than normal. Result: previously non-precessing components of the residual polarization undergo precession and can be subsequently scattered by the next-in-time field. Since the sham field as well as the next-in-time polarizing field are both provided with slow-rising amplitude vs. time turn-on segments, the resulting polarization existing at the start of the buildup of the fields can be easily scattered. Ultimately, all aspects of the residual polarization are destroyed whereby cyclic NML logging speed can be greatly improved.

Abstract: The present invention decreases the time needed between collection cycles of a NML tool located in a wellbore penetrating an earth formation by zeroing the effect of prior-in-time residual polarization via a surprising change in the operating parameters of the polarizing coil, viz., using a higher Q value than normal or its equivalent for the polarizing coil circuit during cutoff of the polarizing field and ringing of the coil at the proton precession frequency. Result: cyclic NML logging speed can be greatly improved.

Abstract: The present invention decreases the time needed between collection cycles of a NML tool located in a wellbore penetrating an earth formation by zeroing the effect of prior-in-time residual polarization via a surprising change in the operations while guarding against the effects of tuning errors, viz., using a sham polarizing cycle wherein the coil circuit is permitted to ring at a Q' value higher than normal during the initial stages of the sham cycle followed by the establishment of a low Q thereafter. Result: the effect is as if sham ringing is at the higher Q' value, but without the consequences of slow cutoff of the decaying magnetic field introduced during ringing. Hence, the effects of error fields are minimized and previously non-precessing components of the residual polarization undergo precession and can be subsequently scattered by the next-in-time polarizing field. Since the sham field as well as the next-in-time polarizing field are both provided with slow-rising amplitude vs.

Abstract: The present invention decreases the time needed between collection cycles of a NML tool located in a wellbore penetrating an earth formation by zeroing the effect of prior-in-time residual polarization via a surprising change in the operating parameters of the coil circuit while guarding against the effects of tuning errors in the latter, viz., using a higher Q value than normal or its equivalent for the coil circuit during the initial stages of ringing of the coil at the proton precession frequency followed by establishing a lower Q value for the latter stages. Result: the effect is as if ringing is at the higher Q' value with attendent zeroing of the residual polarization, but without the consequences of slow cutoff of the decaying magnetic field introduced during ringing. Hence, the effect of error fields associated with the latter is minimized.

Abstract: The present invention decreases the time needed between collection cycles of an NML tool located in a wellbore penetrating an earth formation by zeroing the effect of prior-in-time residual polarization via a surprising change in the operations, while guarding against the effects of tuning errors, viz., using a series of sham polarizing cycles wherein the coil circuit is permitted to ring at a Q' value higher than normal during the initial stages of each sham cycle followed by the establishment of a low Q thereafter. Result: the effect is as if sham ringing is at the higher Q' value, but without the consequences of slow cutoff of the decaying magnetic field introduced during ringing. Hence, the effects of error fields are minimized and previously non-precessing components of the residual polarization undergo precession and can be subsequently scattered by the next-in-time field. Since the sham fields as well as the next-in-time polarizing field are all provided with slow-rising amplitude v.

Abstract: A nuclear magnetic resonance spectrometry is disclosed in which a 90.degree. pulse and a 180.degree. pulse are applied to nuclei under observation at a time interval of t. Then, the resulting echo signal is observed after a period of t. Either a strong 90.degree. pulse of strong RF waves are applied to nuclei that are not observed. The strong RF waves decouple the nuclei not observed over a broad range. The application of the strong 90.degree. pulse or RF waves is initiated in synchronism with the 180.degree. pulse. The application of the RF waves are terminated before the beginning of the observation of the echo signal. The observation made in this way makes it possible to obtain spectra of quaternary carbons, the spectra including the information about long-range coupling.

Abstract: A matching device uses mutual inductance to couple an NMR radio frequency (RF) coil to an RF power amplifier and RF receiver preamplifier. The device includes a matching coil connected to the RF power amplifier and preamplifier and which is positioned between the NMR RF coil and a decoupling shield in a region where RF flux density, produced by the NMR RF coil, is maximum. This ensures effective coupling to the NMR RF coil and provides a way for adjusting the degree of coupling (hence, input impedance) by varying the area of the matching coil available for intercepting the RF flux.

Abstract: During measurement cycles for generating and sampling FID signals in NMR imaging devices, a 180.degree. pulse and subsequently a 90.degree. excitation pulse are added to the pulse sequence. The 180.degree. pulse produces an additional echo signal. During (the maximum of) the echo signal, the 90.degree. pulse is generated. The waiting period occurring before the beginning of a next measurement cycle can thus be substantially reduced without giving rise to a significant signal loss in the echo signals to be generated during said cycle. In addition to a reduction of the measurement time, NMR images with different contrasts (other intensity distribution) can be provided.

Abstract: Apparatus is provided in an NMR diagnostic apparatus for reducing or eliminating low frequency cyclic noise. The NMR signals are phase demodulated using reference signals having the same frequency as the excitation signals. A provision is made to change the phases of the output reference signals by 180.degree.. These signals are selectively used to demodulate the received NMR signals which are first divided into two signals of the same phase. The demodulated signals, which are 180.degree. apart, are added thereby eliminating the cyclic noise component.

Abstract: To produce image information from an object it is subjected to a continuous static magnetic field along a Z axis to sets of sequences of orthogonal gradients G.sub.x, G.sub.y and G.sub.z to the magnetic field. Spins in a selected plane (the X-Z plane) are excited by selective rf pulses and an associated G.sub.y gradient and the selected spins are subjected to all three gradients of which the G.sub.z gradient provides twist or warp to each column of spins extending along the Z axis to phase-encode the columns. The spin-echo signals are read out in the presence of a G.sub.x gradient. In each set of sequences a different value of Z gradient is employed. The Fourier transformed spin-echo signals obtained from each sequence, when arranged in order of increasing G.sub.z gradient and subjected to a second Fourier transform represent the distribution of spin density in the Z direction, thus giving a two-dimensional image of the selected X-Z plane.

Abstract: An improved nuclear magnetic resonance (NMR) apparatus for use in topical magnetic resonance (TMR) spectroscopy and other remote sensing NMR applications includes a semitoroidal radio-frequency (rf) coil. The semitoroidal rf coil produces an effective alternating magnetic field at a distance from the poles of the coil, so as to enable NMR measurements to be taken from selected regions inside an object, particularly including human and other living subjects. The semitoroidal rf coil is relatively insensitive to magnetic interference from metallic objects located behind the coil, thereby rendering the coil particularly suited for use in both conventional and superconducting NMR magnets. The semitoroidal NMR coil can be constructed so that it emits little or no excess rf electric field associated with the rf magnetic field, thus avoiding adverse effects due to dielectric heating of the sample or to any other interaction of the electric field with the sample.

Abstract: A method of investigating a body by nuclear magnetic resonance comprising preferentially exciting resonance in a slice of the body, applying a magnetic field to the body having first and second gradients (Gx, Gy) in different directions in the slice with both the gradients being periodically reversed at regular intervals, detecting the free induction decay signals occurring when the gradients are applied and processing the detected signals to retrieve data. The method is an adaptation of the echo-planar technique suitable for obtaining chemical shift information.

Abstract: A method of nuclear magnetic resonance imaging of a body in which the spins of a chosen nucleus in a selected slice of the body are rotated through an angle appreciably greater than 90.degree.. Two r.f. pulses, each accompanied by a magnetic field having a gradient in a direction parallel to the equilibrium axis of magnetic alignment of the spins are applied in sequence. Each r.f. pulse is at the Larmor frequency for the nuclei in the slice in the presence of the associated field gradient and each r.f. pulse is effective to rotate the spins by not greater than 90.degree.. The r.f. pulses together are sufficient to rotate the spins through the desired angle, the gradients of the magnetic fields being in opposite directions.

Abstract: A multi-slice method of NMR imaging wherein a number of discrete slices S.sub.1, S.sub.2, S.sub.3, S.sub.4 are excited simultaneously by using the usual field gradient Gz but an r.f. pulse B.sub.1 which is a mix of a number of pulses of different discrete frequencies, f.sub.1, f.sub.2, f.sub.3, f.sub.4, and recovering data in the presence of an alternating gradient G.sub.2 z in the same direction as used to establish the slices such that discrete spin echo signals of different frequency occur for each slice. Apparatus for use in the method is also disclosed.

Abstract: The electromagnet providing the main field of the nuclear magnetic resonance (nmr) imaging system is turned up during the data acquisition region and turned down between data acquisition periods. The data acquisition consists of the excitation of the spins and the reception of the associated signals.

Abstract: In recording two-dimensional nuclear magnetic resonance spectra, J cross peaks which hinder the interpretation of the spectragram and mask cross peaks of incoherent exchange processes or transfers are eliminated by one of two methods. In the first method, for each repetition of a measurement with an evolution period t.sub.1 between the first and second of two successive 90 degree pulses, the interval between the second and third 90 degree pulse (mixing time t.sub.m) is varied systematically in proportion to the evolution period. The two-dimensional spectra obtained is subjected to triangular multiplication or symmetrization so that all peaks which do not possess counterparts at the mirror symmetry positions of the main diagonal are eliminated. In the second method, the mixing time is kept constant and a 180 degree pulse is inserted between the second and third 90 degree pulse with a varying interval t.sub.p between the 180 degree pulse and the second 90 degree pulse for each repetition of a measurement.

Abstract: To produce image information from an object it is subjected to a continuous static magnetic field along a Z axis and to sets of sequences of orthogonal gradients G.sub.x, G.sub.y and G.sub.z to the magnetic field. Spins in a selected plane (the X-Z plane) are excited by selective rf pulses and an associated G.sub.y gradient and the selected spins are subjected to all three gradients of which the G.sub.z gradient provides twist or warp to each column of spins extending along the Z axis to phase-encode the columns. The spin-echo signals are read out in the presence of a G.sub.x gradient. In each set of sequences a different value of Z gradient is employed. The Fourier transformed spin-echo signals obtained from each sequence, when arranged in order of increasing G.sub.z gradient and subjected to a second Fourier transform represent the distribution of spin density in the Z direction, thus giving a two-dimensional image of the selected X-Z plane.

Abstract: A method and apparatus for nuclear magnetic resonance spectroscopy is disclosed which expands the decoupling bandwidth. In the method, a pulse train containing a series of radiofrequency pulses joined without interval is applied repeatedly to a sample, each radiofrequency pulse being phased at 0.degree., 90.degree., 180.degree., or 270.degree., and the radiofrequency carrier of the pulse train is reversed in phase at the interval longer than the repetitive cycle of the pulse train asynchronously with the repetition of application of the pulse train.

Abstract: The T.sub.2 * effects due to inherent inhomogeneities in the static magnetic field are overcome by the use of a 180.degree. RF pulse to produce a nuclear spin echo suitable for obtaining spatial information and by the adjustment of the pulsed gradients such that the occurrence of the spin echo due to the applied gradients coincides with the occurrence of the nuclear spin echo derived from the rephasing of spins in the presence of the inhomogeneities inherent in the main static magnetic field. The 180.degree. RF pulse is applied with the imaging gradients turned off so that long RF pulse lengths can be used, thus reducing RF power requirements. Exemplary applications of the pulse method to multiple angle projection reconstruction and two-dimensional Fourier transform (spin warp imaging) imaging techniques are also described.

Abstract: In a method of heteronuclear decoupling in high resolution pulsed NMR spectroscopy, during acquisition of signals emanating from a nuclear species to be observed (e.g. carbon-13), irradiation of an interfering nuclear species (e.g. protons) is effected by means of a train of composite pulses, each of which approximately inverts the longitudinal magnetization. The pulses are of two types respectively having opposite r.f. phases, and the train constitutes a repeated sequence which consists of 2.sup.N+1 pulses of each type (where N is a positive integer) and which has a form chosen in accordance with specific rules to ensure effective decoupling.

Abstract: A nuclear magnetic resonance analytic apparatus for obtaining tissue metabolism information from a living body member. The apparatus consists of a large high-intensity electromagnet with an inner space having a uniform magnetic field, for receiving the body member. The space has a probe coil mounted therein with which the body member is engageable. For phosphorus-31 metabolite, there is provided a 24.33 MHz RF generator connected through a control logic section and a driver unit to the probe coil via a transmitter/receiver switching unit arranged to in effect switch the probe coil from a normal connection with a demodulation circuit to the driver unit responsive to a burst of RF pulse energy applied to the switching unit by the driver unit via the control logic section by command of a computer. The control logic section controls the system so as to first apply short pulses of the RF signal to the probe coil for a predetermined excitation time period, gating-off the demodulation unit.

Abstract: In a method of heteronuclear decoupling in high resolution pulsed NMR spectroscopy, during acquisition of signals emanating from a nuclear species to be observed (e.g. carbon-13), irradiation of an interfering nuclear species (e.g. protons) is effected by means of a train of composite pulses, each of which approximately inverts the longitudinal magnetization, in the form of a repeated sequence comprising pairs of composite pulses of two types respectively having opposite r.f. phases.

Abstract: Selective excitation is used to define a thick planar slab of excited nuclear spins in a nuclear magnetic resonance (NMR) imaging sample. The thick slab is selected such that the excited spins are contained well within the optimum sensitive region defined by the radio frequency (RF) transmitter and receiver coils. Three-dimensional spatial information of an NMR imaging parameter, such as nuclear spin density or nuclear spin relaxation time, is collected simultaneously from the excited slab and can be used to construct a series of several tomographic section images of the slab. The spatial information is encoded in the NMR signal by application of pulsed gradient magnetic fields subsequent to excitation. Image picture information is obtained from the NMR signals via three-dimensional Fourier transformation.

Abstract: In accordance with the present invention, permeability estimates of a carbonate sample based on spin echo diffusion characteristics of the hydrogen nuclei of interstitial fluids within the pore space of such sample, can be swiftly and accurately achieved using a computer-controlled, portable NMR instrument. Result: Even though the instrument is placed at field sites away from the usual processing center, quick analysis of such samples as during the drilling of a well, still results.

Abstract: In an NMR probe containing an observe coil and a decoupling coil, the signal-to-noise ratio of the observe channel is improved by inserting a back-to-back parallel combination of diodes in series with the decoupling coil to present an infinite impedance in the decoupling channel in its passive state for induced RF signals from the observe coil.

Abstract: A method for obtaining a spatial mapping using nuclear magnetic resonance. A sample is subjected to time dependent magnetic gradient fields having linear components in the X and Y directions, normalized so that the time dependency is eliminated in the vicinity of a line X.sub.0,X.sub.0,Z. A time independent gradient field is applied along this line. An initial RF pulse is applied to rotate the magnetization 180 degrees. This is followed by a 90 degree pulse and then a series of 180 degree pulses. It has been determined experimentally that the relaxation times T.sub.1 and T.sub.2 for ischemic muscle tissue are longer than T.sub.1 and T.sub.2 for normal tissue. The above-described pulse pattern enhances the differentiation between the ischemic and normal tissue, and can provide useful data in applications wherein data can only be acquired during a short period of time.

Abstract: The invention is suitable for a small nuclear magnetic resonance pulse head applicable to a part of the body in the manner of ultrasonic systems. The arrangement generates a field which varies in amplitude with distance from the head, being uniform at surfaces which intrude into the body. Resonance is excited in one such surface and a gradient restricts resonance to one line therein. The phase is then dispersed along the line and the signal sensed as a function of position therealong.

Abstract: A method for adjusting the orientation of the rotation axis for a sample in a nuclear magnetic resonance (NMR) experiment includes using a field gradient in a specific direction with respect to the external magnetic field of the NMR experiment to establish a calibrated reference direction with which the rotation axis may be aligned. Preferably, the magnetic field gradient is at an angle of 54.7.degree.. A preferred embodiment of this invention includes automatic control steps in the method.

Abstract: In a NMR pulse sequence dispersion caused by inhomogeneity in the steady axial magnetic field may be reduced by applying a 180.degree. `spin-echo` RF pulse. However, whereas it is possible in known pulse sequences to apply a 90.degree. RF pulse in the presence of a selected gradient and to phase correct it adequately, this is not true for the 180.degree. pulse needed in a simple echo system (or the multiple pulses of more complex systems). It has been thought that a 180.degree. pulse could not then be use. It is proposed to apply the 90.degree. H.sub.1 pulse in the absence of an axial field gradient. For this purpose it is desirable to apply the RF field and sense the resonance with different coils. The RF coils should be of substantially greater extent in the axial direction than the resonance sensing coils.

Abstract: A method of deriving image formation from an object using nuclear magnetic resonance signals comprises the steps of subjecting an object to a static magnetic field along one axis, applying a first gradient to said magnetic field which varies in a direction orthogonal to said axis together with a 90.degree. high frequency pulse, reversing the direction of said magnetic field gradient and simultaneously applying a gradient to said magnetic field which varies in a direction parallel to said one axis and then reversing the direction of said last-mentioned gradient and reading out the free induction signal from said object.