Abstract: At least one extra NMR measurement cycle is performed without any imposed magnetic gradients during readout and recordation of the NMR RF response. Calibration data derived from this extra measurement cycle or cycles can be used for resetting the RF transmitter frequency and/or for phase shifting other conventionally acquired NMR RF response data to compensate for spurious changes in magnetic fields experienced during the NMR data measuring processes. Some such spurious fields may be due to drifting of the nominally static magnetic field. Another source of spurious fields are due to remnant eddy currents induced in surrounding conductive structures by magnetic gradient pulses employed prior to the occurrence of the NMR RF response signal. Special procedures can be employed to permit the compensation data itself to be substantially unaffected by relatively static inhomogeneities in the magnetic field and/or by differences in NMR spectra of fat and water types of nuclei in imaged volumes containing both.

Abstract: A pattern generator and controller arrangement operats for controlling the component parts of an MRI system. The arrangement comprises a plurality of channels including a main control channel and output channels. The arrangement receiver instructions from the system CPU which then leaves the control and outputting to the arrangement, thereby avoiding the necessity of a large expensive CPU to operate the system with versatility and speed.

Abstract: A device and method are provided for adjusting a radiofrequency antenna of a nuclear magnetic resonance apparatus. In the invention, using capacities preset in the factory, the antenna detuning of an NMR apparatus is limited to a range such that the standing wave rate of a high frequency line which conveys the radiofrequency signal is limited. This line is cut and, at a short distance, a tuning adjustment circuit is inserted. This circuit may be automated: the electric adjustment motors, thus spaced away, do not disturb the magnetic fields of the apparatus. By measuring the real part of the admittance at the input of the adjustment circuit and the phase shift between voltage and current this circuit can be adjusted.

Abstract: An MR scanner performs a prescan before each MR scan sequence in which the optimal RF excitation frequency is automatically determined and applied to the scanner's transceiver. The prescan sequence includes a pair of MR measurements which provide data that allows the precise RF excitation frequency to be determined.

Abstract: In a method of setting the intensity of a high-frequency magnetic field, in order to adjust and set a field intensity of the high-frequency magnetic field in a magnetic resonance imaging system, an amplitude of an excitation high-frequency magnetic field pulse is sequentially changed; magnetic resonance excitation and reading of a magnetic resonance signal are repeatedly performed; and the amplitude of the high-frequency magnetic field pulse, which corresponds to a maximum or minimum value of the magnetic resonance signal of the signals obtained by a plurality of excitation cycles, is used as a reference to set the intensity of the high-frequency magnetic field. An opposite phase high-frequency magnetic field pulse, having the same amplitude as that of the excitation high-frequency magnetic field pulse, and having a carrier wave which is 180.degree.

Abstract: A magnetic resonance imaging system is made up of a static field generator, a gradient field generator, an excitation pulse generator, a receiver, a controller for controlling the static field generator, gradient field generator, excitation pulse generator, and receiver, and an image processor. The controller includes a multi-slice control section and an adjustment/control section. The multi-slice controller sequentially controls use excitation of a plurality of slices by a plurality of excitation pulses of different carrier frequencies in a common static field and a gradient field. Through these excitations, the magnetic resonance data for the plurality of slices is obtained with one excitation repetition period, and the multi-slice imaging can be performed by a predetermined number of repetitive excitations.

Abstract: In magnetic resonance imaging where a subject is placed in a static field and the subject is selectively excited by applying an RF magnetic field in the presence of a gradient magnetic field, the peak RF power of the RF magnetic field is reduced by decreasing the peak amplitude of the RF magnetic field while concurrently reducing the magnitude of the gradient magnetic field. The incremental time duration for the RF magnetic field portion which is reduced in amplitude is proportionately increased. In using an RF pulse having front and back sidelobes with a positive lobe therebetween, the duration of the RF pulse can be reduced by increasing the magnitudes of the sidelobes and concurrently reducing the time periods of the sidelobes. A minimum SAR embodiment can be realized.

Abstract: A high frequency antenna is provided for an apparatus measuring nuclear magnetic resonance, of the type whose radiating means comprise conductors forming high frequency resonators with a metal casing. They are frequency tuned by adjustment capacitors situated at their ends. For simplifying the frequency tuning of two paired resonators through which flow currents in phase opposition, it is proposed to join together galvanically two ends of these two resonators by a high frequency line section whose length is substantially equal to half the wave length of the energization wave to be emitted. The frequency matching of the antenna may be made by adjusting simultaneously all the adjustment capacitors by means of a common control knob. Coupling of the energization energy is provided magnetically in the middle of this high frequency line section.

Abstract: An MRI system includes an MR signal acquisition section, an imaging processing section, a control signal generating section, and a control section. The MR signal acquisition section excites an MR phenomenon in a portion including a selected slice of an object to be examined, and detects MR signals generated by the MR phenomenon. The imaging processing section processes the MR signals to form an image based on MR data in the selected slice of the object. The control signal generating section generates a control signal for acquiring the MR signals in response to movement of the object. The control section controls the MR excitation operation and the MR signal acquisition operation of the MR signal acquisition section in accordance with the control signal.

Abstract: A method for studying the chemical and structural characteristics of materials is disclosed. The method includes placement of a sample material in a high strength polarizing magnetic field to order the sample nucleii. The condition used to order the sample is then removed abruptly and the ordering of the sample allowed to evolve for a time interval. At the end of the time interval, the ordering of the sample is measured by conventional nuclear magnetic resonance techniques.

Abstract: NMR images formed by means of Fourier zeugmatography contain disturbing artefacts which are caused by coherent interference signals (for example, off-set signals, non-ideal 180.degree. reversing pulses). In accordance with the invention, an additional phase difference (.DELTA..phi.=.pi. in the case of even rows, and .DELTA..phi.=.pi.. (m-1)/m rad/sec in the case of m odd rows) is generated and the signal samples taken from the resonance signals are stored in adjacently situated rows of an image frequency matrix. The values in every second row of the matrix are changed to cancel said additional phase-difference, so that the contributions of the coherent interference signals to the matrix are influenced by the additional phase shift; if the additional phase shift is .pi. rad/sec, the values of every second row of interference signals in the direction of the columns are simply inverted.

Abstract: An electronic module for generating gradient energization signals in magnetic resonance imaging to correct for eddy current effects. An energization profile is modified by an amount related to the magnitude of eddy current fields generated in the vicinity of a gradient coil. This modification produces an energization profile resulting in a gradient magnetic field corresponding to the magnetic field the unmodified energization profile would have produced but for the presence of induced eddy currents.

Abstract: A magnetic resonance diagnostic device has a coil for generating a fundamental magnetic field of constant magnitude in which an examination subject is placed, a coil for generating a number of gradient magnetic fields in which the patient is also disposed, a device for detecting changes in the nuclear magnetic resonance of the patient from an equilibrium position, with the direction of the fundamental magnetic field being continuously changed during examination for inducing the changes in nuclear magnetic resonance which are measured.

Abstract: In measuring a number of echo signal, which normally attenuate chronologically, in a single pulse sequence, such as in multi-echo method or a multi-slice method, each echo signal is received and suitably amplified by a reception amplifier having predetermined levels of gain for different time periods during which the successive echo signals are processed such that the echo signals received at a data collection unit are all of substantially the same amplitude regardless of where they appear in the time sequence. The predetermined levels of gains are obtained by false scanning prior to actual image scanning and calculation and storing in a memory. As a result, the echo signals can be received within a dynamic range which is smaller than using the conventional system.

Abstract: The invention relates to a drive mechanism for adjusting an element by means of which the resonance frequency in an NMR-apparatus can be varied. The mechanism comprises a coil which is exposed to the main magnetic field off the NMR-apparatus. The coil is connected to a current-pulse supply and is deflected out of its rest position by the current pulses. The reciprocating movement of the coil is converted by a stepping mechanism into a stepwise rotary or translational movement of the adjusting element which tunes or matches the RF coil to the RF generator.

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: A radio-frequency (RF) spectrometer subsystem, for a nuclear magnetic resonance spectroscopy and imaging system, provides high-power RF pulse signals each having an envelope of minimum distortion; a portion of the actual RF magnetic field, in the sample-examination volume, is returned to the spectrometer for subsequent correction of the RF signal characteristics responsive to a comparison of the RF magnetic field sample waveform to the requested pulse envelope waveform.

Abstract: The phase encoding of NMR information is performed using rf pulse sequences. The rf pulse sequences produce a substantially continuous phase variation cross the resonant frequency range of the atoms of an object in order to perform phase encoding. Some of the pulses may be tailored pulses, with each tailored rf pulse including frequencies which cover a bounded continuous frequency range. Either the phase or the amplitude of each tailored rf pulse varies with frequency across this continuous range. If the amplitude is linearly variant across the range, the phase is constant, but if the phase is linearly variant across the range, the amplitude is constant. The tailored rf pulses may be applied in the presence of pulsed magnetic gradient fields of the conventional type to produce the phase variation.

Abstract: A digital interface subsystem, for a magnetic resonance imaging and spectroscopy system, has an internal data bus interconnecting: a master sequencer, receiving instructions from a main system computer; a plurality of controlled generators for providing gradient-field, RF modulation and other required signal waveforms for proper excitation of a sample; and circuitry for analyzing the magnetic resonance response signals from the sample, responsive to the excitation signals for providing image information.

Abstract: The phase of nuclear magnetization in a target placed in a homogeneous magnetic field and excited by a high-frequency magnetic field is encoded by applying a specifying magnetic field with a non-linear gradient thereto, and the specifying magnetic field is scanned across the target, and the encoded NMR signals are received and processed so as to produce an image of the distribution of nuclear magnetic substance in the target.

Abstract: An improved body probe for use in high field Mr data acquisition systems having a two feed balanced inductor circuit using series capacitors to control the effect of stray capacitance and coupling resistors connected across the coil approximately mid-way between the two feed points. This arrangement is superior to prior art body probes operating in whole body high field MR imagers.

Abstract: A modified spin echo sequence is employed to identify fluid movement in a material. The volume of interest is subjected to a static field along one axis (Z) and an RF magnetic excitation pulse transverse to the static field is applied which tilts the nuclear spins in the volume. The tilted nuclear spins are then allowed to precess about the uniform static field in the presence of a gradient field whereby the nuclear spins become dephased. Thereafter, a spin echo of the static spins is created by either a 180.degree. RF pulse or reversal of the gradient field. Upon refocusing of the static nuclear spins a restoration RF pulse is applied to realign the stationary nuclear spins with the static field. Nuclear spins undergoing bulk motion as in fluid flow will be refocused to a different phase than the stationary spins so that the final RF pulse will in general leave these spins with a non-zero transverse magnetic moment. This residual transverse magnetic moment is then detected to identify the fluid movement.

Abstract: The volume of interest is excited. An array of pickup coils with water cores provide an array of signals whose frequencies indicate the magnetic field distribution. These frequencies are estimated and used to produce controlled magnetic field inhomogeneities which substantially cancel the undesired inhomogeneities in the field. The control signals can be stored and updated with each subsequent excitation.

Abstract: A method for reducing baseline errors in NMR signals utilizes NMR signals produced by RF excitation pulses selected to be 180.degree. out of phase relative to one another to derive a baseline error signal. The baseline error signal is then used to compensate for baseline error component in other NMR signals. In the preferred embodiment, the method is useful in NMR imaging pulse sequences to not only achieve compensation of the baseline error, but also to shorten scan time.

Abstract: In an NMR diagnostic apparatus, it is generally necessary to tune a receiver tuning unit with respect to a patient. The NMR diagnostic apparatus is comprised of a standard signal generator for generating a CW signal, a receiver tuning unit which is mainly constructed by a receiver probe head and a series circuit of a capacitor and a variable capacitance diode and receives the NMR signals induced from the CW signal, quadrature detectors which detect the NMR signals, and a signal processor which processes the detected NMR signals so as to produce the control voltages "Vc". The automatic tuning operation is carried out in such a manner that varying the control voltage "Vc" which is applied to the variable capacitance diode enables the receiver tuning unit to be tuned with respect to the object that is positioned in the receiver probe head.

Abstract: A method for correcting image distortion arising from magnetic field gradient nonuniformity in accordance with which the gradient nonuniformity is modeled, the expected distortion in the image calculated, and a geometric correction applied to the distorted image. In the preferred embodiment, polynomial interpolation is used to implement the geometric correction.

Abstract: Two-dimensional projection measurements are formed of the NMR activity within a volume. Measurements are made using different intensities of the main magnetic field, using the different dependencies of relaxation times on magnetic field. The projection measurements are combined to obtain projection images of specific materials within the volume. Projection images are obtained of specific regions within the volume by insuring that the unwanted regions remain insensitized. For improved SNR, projection measurements are repeated to obtain spin-echo signals. The measurements of relaxation times are interleaved so that the data acquisition can occur rapidly.

Abstract: The disclosed method comprises steps of alternately applying a strong static magnetic field and a weak homogeneous static magnetic field to a body being measured (target), selectively exciting nuclear magnetic resonance (NMR) at a specific portion of the target by applying a high-frequency magnetic field and a specifying magnetic field thereto, detecting NMR signals from the thus excited portion, and scanning the target by repeating the selective excitation and the detection.

Abstract: In an imaging apparatus using nuclear magnetic resonance which includes apparatus for generating a static magnetic field, a linear gradient magnetic field and a radio frequency magnetic field, respectively, signal detection device for detecting the nuclear magnetic resonant signal from an object to be inspected, a computer for calculating from the detection signal an image and output device for displaying the result of calculation by the computer, the improvement wherein the size of the object to be inspected is detected by use of ultrasonic wave or light beams and a signal indicative of the detected size of the object is applied to the linear gradient magnetic field generation apparatus so as to control the intensity of the linear gradient magnetic field.

Abstract: A method of tuning an NMR spectrometer is disclosed that includes the step of locating a specimen in a stationary magnetic field, generating a 90.degree. alternating magnetic field excitation pulse at the Larmor frequency of the selected nuclei of the specimen followed by one or more 180.degree. alternating magnetic field refocusing pulses of preselected duration at fixed time intervals having the same phase relationships using a free-running oscillator that is turned off between pulses, measuring the primary echo train of a selected nuclear magnetic resonance signal, changing the strength of the stationary magnetic field to change the Larmor frequency of the selected nuclei, repeating the pulsing step and the measuring step until the maximum primary echo is obtained, and while holding the stationary field at that strength, measuring the desired nuclear magnetic resonance characteristic using the spin-echo method and the free-running oscillator to supply the pulses.

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: 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: In accordance with the present invention, fluid-flow properties of a rock sample based on NMR response of the hydrogen nuclei of interstitial fluids within the pore space of such sample, can be swiftly and accurately achieved using a portable NMR instrument. Inherent instrument inadequacies (DC field inhomogeneity and large phase background jitter) are themselves relied upon to increase the data-throughput efficiency, i.e., the number of NMR responses performed per unit time. Result: Even though the instrument is placed at field sites away from the usual processing center, quick analysis of rock samples as during the drilling of a well, still results. Also, effects of possible echoes during subsequent measurements are prevented by using both the inhomogeneities of the DC field and the essentially random phase spectrum that is inherent in the instrument to average out echoes of prior generated NMR responses.

Abstract: A method of examining a slice of a body by nuclear magnetic resonance in which a steady magnetic field, and a gradient field G.sub.z along the same axis define the slice to be examined. A periodic magnetic field H.sub.1 at the Larmor frequency for the slice is applied in two distinct pulses 1, 2 each in conjunction with the gradient field. The total field integral of the two pulses is chosen to be sufficient to rotate spin vectors of nuclei in the field through an angle of .pi./2 radians. Between the two pulses 1, 2, a further pulse 3 is applied in the absence of the gradient field G.sub.z, which has a field integral sufficient to rotate the spin vectors through an angle of .pi. radians.

Abstract: The effects of a spurious free induction decay (FID) NMR signal due to imperfect 180.degree. RF pulses are eliminated by phase alternating the selective 90.degree. RF pulses and subtracting alternate ones of the NMR signals. The desired signals due to the 90.degree. RF pulses reinforce, while the signals produced by the imperfect 180.degree. pulses cancel. This method also has the beneficial effect of eliminating DC offset in the desired signal which, when present, causes artifacts in NMR images. Another method to eliminate the effects of spurious FID signals due to imperfect 180.degree. pulses is to phase alternate these 180.degree. pulses on successive NMR imaging pulse sequences and add successive NMR signals. In this case, the phase shifted spurious FID signals cancel, while the desired NMR signals reinforce. The latter method does not eliminate the effects of DC offset, however.

Abstract: Apparatus for generating and detecting magnetic field components oscillating at a radio frequency in a direction transverse to a static magnetic field in a nuclear-magnetic-resonance (NMR) system. The apparatus has a plurality of conductive elements spaced from one another and from the axis along which the static magnetic field is directed. The relative amplitudes of alternating currents in the conductive elements are controlled to generate a spatially uniform field. A preferred embodiment uses a standing wave in a coil assembly to control relative current amplitudes, which takes advantage of the current-phase characteristics of such waves. Detection of RF magnetic fields results from an EMF generated in the coil assembly in response to the time-varying magnetic field; the high Q of the coil assembly enhances detection properties.

Abstract: A nuclear magnetic resonance apparatus including magnet apparatus for generating a homogeneous static magnetic field between its magnetic poles, shims of a magnetic substance mounted on the magnetic poles to apply a first gradient magnetic field intensity distribution in a direction orthogonal as to the direction of line of magnetic force of the static magnetic field, gradient magnetic field generating electromagnetic apparatus for generating a second gradient magnetic field having a gradient magnetic field intensity distribution in superimposition with the static magnetic field and for changing the magnetic field gradient of the first gradient magnetic field, an oscillator for generating an oscillating output having a frequency corresponding to the nuclear magnetic resonance condition of an atomic nucleus to be measured, a coil wound around a body to be examined for applying the output of said oscillator as electromagnetic waves upon the body, a receiver for detecting the nuclear magnetic resonance signals r

Abstract: In accordance with the present invention, fluid-flow properties of a rock sample based on NMR response 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. The inherent instrument inadequacy of phase background jitter is controllably augmented by generating (via a computer-initiated DC source current) a DC magnetic field gradient across the sample. Result: A DC field inhomogeneity of D gauss is discontinuously introduced to the steady DC field to maintain high data-throughput efficiency, i.e., the number of NMR responses performed per unit time. And, even though the instrument is placed at field sites away from the usual processing center, quick analysis of rock samples as during the drilling of a well, still occurs.

Abstract: In accordance with the present invention, fluid-flow properties of a rock sample based on NMR response 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. The inherent instrument inadequacy of a DC field inhomogeneity is controllably augmented by an adaptively generated gating code (provided via a computer-controller in feedback relationship with an oscillator-master clock controlling a transmitter-pulser) to ensure that the nuclear magnetization precessional frequency is not a multiple of the RF interrogation frequency. Result: Even though the instrument is placed at field sites away from the usual processing center, quick analysis of rock samples as during the drilling of a well, still results.

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: In a nuclear magnetic resonance spectrometer, this invention relates to an improvement of a lock system for stabilizing a magnetic field intensity. It is an object of the present invention to dissolve a low stability by using a conventional voltage control oscillator and a complex operation in the case of varying a reference material for locking. In the present invention, a radio frequency of a high stable reference frequency source is demultiplied by a variable frequency divider so that a frequency modulation or a modulation of the magnetic field is effected by the output thus demultiplied. When the reference material is changed, the operation can easily be made by varying the demultiplication ratio of the variable frequency divider.

Abstract: Imaging of 1-, 2-, or 3-dimensional specimens is effected based on nuclear magnetic resonance of a chemical species. A specimen is placed in an essentially constant magnetic field H.sub.o, exposed to an electromagnetic pulse, and exposed to an an additional magnetic field H.sub.1 whose strength is linearly increasing across the specimen. A free induction decay signal is sampled after field H.sub.1 is turned off, and sample values are stored for later processing. These steps are carried out repeatedly for different fields H.sub.1, and stored sample values are Fourier transformed into desired frequency spectra at points in the specimen.

Abstract: This disclosure is directed to improved equipment in detection of desired nuclei or electron response. In a magnetic field thought to be inhomogeneous, an improvement which incorporates means for summing repetitive samples is disclosed. Excitation is applied to the sample of interest, and the received signal is broken into samples over the life of the received signal and temporarily stored. The flux is varied by varying the magnet current, and several nuclear magnetic resonance signals are received. They are similarly sampled periodically and added to earlier responses. They are preferably stored in a buffer after conversion by an analog-to-digital convertor. After stepping through several magnetic levels, the testing is completed. The summation of the various signals is a signal enhancement technique which overcomes the lack of a uniform optimum field impressed on the sample of interest.

Abstract: A method for line narrowing in nuclear magnetic resonance (NMR) studies in solids is described. The method employs quasi-continuous amplitude modulation of an rf field wherein the field is eliminated at intervals for short periods of time at or about the time when the amplitude for both the maximum and minimum approach zero, these intervals creating windows where the NMR signal can be observed.

Abstract: In a medical NMR apparatus it is desirable that the axial magnetic field, Ho, is uniform. The result can in theory be obtained by accuracy of construction but in practice this cannot readily be achieved. It is now proposed to use a field sensing probe system which indicates the value of that field at a plurality of positions in the examined region and provides error signals indicating deviations from uniformity. The field is automatically corrected in response to the error signals by applying currents to field correcting coils. The errors may be considered as distinct gradient and dishing errors which are corrected individually.

Abstract: In an imaging apparatus using nuclear magnetic resonance, first and second gradient field pulses are applied, the second being of opposite sense to the first. It is preferable to match these so that they entirely cancel. However it is shown to be sufficient if they are as close as possible to the same magnitude and a further `glitch` pulse is used to reduce the total gradient field over the pulse sequence substantially to zero.

Abstract: A method and means of generating an electron spin echo signal having a relatively higher output frequency than the input frequency of the applied 90.degree. and 180.degree. RF pulses applied to an electron spin echo sample located in a static magnetic field by increasing the magnitude of the Zeeman magnetic field by a predetermined amount after the application of the 90.degree. and 180.degree. pulses. Also the spin echo sample is situated in a microwave cavity which has two resonant frequency modes, the first of which has a relatively high Q while the second has a relatively low Q. The 90.degree. and 180.degree. RF pulses are applied to the system at the first resonant frequency having the high Q while the spin echo signal is coupled out of the system at the second resonant frequency having the low Q.

Abstract: A method and apparatus for analyzing a sample comprising gyromagnetic species in which the sample, is placed in a uniform DC polarizing magnetic field and irradiated by an AC magnetic field, at an angle to the DC field, while the DC field is modulated by square wave signal whereby the resultant resonance signal comprises a frequency modulated spectrum centered around the resonance frequency and having sideband components separated by the frequency of the square wave signal and the amplitudes of which are proportional to the difference of two resonance intensities switched by the two extreme intensity values of the DC field. Upon detection of the sidebands by an RF receiver, DC levels, proportional to the intensity of the detected sidebands, are provided, permitting display of the resonance line shape on an oscilloscope.

Abstract: A pulsed N.M.R. spectrometer employing a highly stable magnet (e.g. a superconducting magnet) has a field-frequency lock which is operative to correct the intensity of the magnetic field only at discrete intervals. The lock operates on the principles of a phase locked loop, and utilizes the free induction decay of the magnetic resonance of an appropriate nuclear species incorporated in a reference sample which is subjected to the magnetic field.

Abstract: Nuclear magnetic resonance is excited in a sample subjected a magnetic field having a varying component which defines a localized volume approximating to a line or surface, the field within the localized volume being invariant with time but exhibiting a spatial gradient. The r.f. irradiation is in the form of a pulse train such that the signal received from the sample contains continuous wave components respectively dependent on the density of relevant nuclei in different regions of the localized volume. The amplitudes of these components are determined by coherently detecting the received signal, sampling the detected signal(s) and subjecting the resultant data to Fourier transformation.