Abstract: The magnetic resonance imaging system applies a uniform static magnetic field and a gradient magnetic field to an object and further applies an excitation rotating magnetic field to cause magnetic resonance phenomena in the object to detect the induced magnetic resonance signals and then to obtain image data by processing the magnetic resonance signals. The system has a power controller for controlling the transmission power in a transmitter for transmitting the excitation rotating field. The system further has a transmission controller for controlling the power controller in response to the magnetic resonance signal which is received by the receiver from the object.

Abstract: The invention relates to a method of mapping the local distribution of B.sub.1 -dispersion of relaxation tim T.sub.1.rho. of the nucleus of a certain element, such as hydrogen or phosphorus of an object, such as e.g. a human body or a part of it, or the trunk of a tree. In the method of this invention, an object area is first subjected to a first excitation pulse, which tilts the magnetization of the nuclei of said object area preferably 90.degree. and thereafter to a locking pulse, whose phase and frequency are selected in a manner that relaxation with respect to the magnetic vector of this locking pulse takes place, followed by performing the required procedures by applying per se known nuclear spin imaging methods, and the above sequence of operations is repeated as many times as desired by changing the amplitude of said locking pulse.

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: Size variation of samples subjected to NMR examinations entails the need for calibration of the radiofrequency excitation which gives rise to the resonance phenomenon measured during experiments. Determination of the most suitable value of the radio-frequency excitation amplitude is carried out by scanning the range of potential amplitudes, starting from one end of the range. During the scanning operation, the variation in excitation amplitude varies in a geometrical progression with the order number of the experimentation. It is shown that, by adopting this procedure, determination of the calibrated amplitude is achieved more rapidly while maintaining constant accuracy of determination.

Abstract: The invention relates to a method and an apparatus for determining the cut (percentage) of one component of a multiphase fluid flowing in a pipeline, for example, oil or other hydrocarbon in a fluid flow that comprises oil, water, gas, and soil components, by use of NMR analysis. The fluid is flowed through an apparatus specifically designed to perform the analysis on the flowing fluid. Carefully sequenced 90.degree. pulse series are used to take advantage of the different spin relaxation times of the selected atomic species when they are constituent parts of molecules having inherently different levels of random molecular motion. The timing between pulses in a series and between series of pulses is chosen so that NMR emissions from unwanted matter do not occur, and FID peaks from the desired matter are registered.

Abstract: A set of n NMR measurements are carried out in an inhomogeneous RF field. The set is parameterized by RF pulse amplitude or duration and for half the measurements the variation of RF pulse/duration is reversed and the RF phase inverted.

Abstract: An automatic tuning circuit for a quadrature coil antenna system of a magnetic resonance imaging system is provided which includes a test coil for applying a test signal to each of a first and a second channel of the antenna to produce a first channel signal on the first channel and a second channel signal on the second channel. A phase meter assembly is coupled to the first and second antenna channels for measuring the phase of the second channel signal relative to the phase of the first channel signal to obtain an error signal. An auto-tune assembly is coupled to the phase meter assembly and to the second antenna channel for adjusting the phase of the second channel signal in response to the error signal to obtain a desired phase relationship between the first and second channel signals.

Abstract: In a multi-slice magnetic resonance imaging system which employs a train of plural RF NMR nutation pulses, the frequency spectrum and/or magnetic gradient employed for succesive pulses is controlled so as to effect more nearly equal full-width-half-magnitude (FWHM) or other spatial dimensions of actual nuclei nutation variation versus distance curves for all of the slice selective nutation pulses. The result is a reduction of any "gap" of non-imaged volume disposed between the succession of selected MRI slice volumes.

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: A pulse control system for a magnetic resonance imaging transmitter has circuitry for detecting the peak value of the RF current in the transmitter coil for a given RF pulse; circuitry for comparing the detected peak value of the RF current with a desired reference peak value for the RF pulse, for determining the difference between the detected and the desired peak values for the RF pulse, and for determining a gain adjustment factor for the transmitter amplifier for the transmitter necessary to produce the desired peak value of the RF current in the transmitter coil; and circuitry for adjusting the gain of the transmitter amplifier in response to the gain adjustment factor to produce the desired peak value of the RF current for the RF pulse.

Abstract: Calibration of radiofrequency excitation involves application of two successive pulses of identical waveform and amplitude. The excitations are applied in series of excitations of variable amplitude from one excitation to the next in order to determine the calibrated value of the excitation pulses to be employed by transition of the amplitude of the received signal through a minimum value. It is demonstrated that this procedure prevents the calibration from being impaired by inhomogeneities of the orienting field of the apparatus. Spatial and spectral inhomogeneities of the excitation are also eliminated by applying throughout the calibration a selection gradient to the body under examination. Defects are eliminated by frequency filtering of the detected signal.

Abstract: Apparatus for shifting the phase of a phase-quadrature signal pair, in at least one of the transmitter and receiver of an NMR system, uses a circuit for shifting the phase of each of the pair of signals by a substantially similar amount responsive to a control signal, and a microcontroller for programmably establishing the control signal data to provide a desired phase shift. Typically, the control signal is of digital data nature and the phase shifter operates to shift signal phase through an angle equal to a selected multiple N of a basic angle. The basic angle is selected such that a plurality of equal angle increments are established by the resolving properties of the data signal. A plurality of phase shifters can be controlled by a single microcontroller.

Abstract: A technique has been developed which reduces blood-flow artifacts in multi-echo, multi-slice magnetic resonance (MR) imaging by rephasing spins which have arbitrary velocity as well as static spins. The technique requires tailoring of the gradient structure along at least one of the three axes so as to null out in the preferred embodiment the zeroth and first moments of the gradient distributions.

Abstract: A portion of a subject (22) which is undergoing respiratory or other motion is disposed in an image region (20) to be examined. A respiratory or other motion monitor (50) monitors the cyclic respiratory motion and provides output signals indicative of chest expansion. A phase encoding gradient selector (60) selects the phase encoding gradient that is to be applied by a gradient magnetic field controller (40) and coil (42). A central phase encoding gradient is selected corresponding to a chest relaxation extreme and minimum and maximum phase encoding gradients are selected corresponding to a chest expansion extreme (FIG. 2). Intermediate degrees of monitored physical movement cause the selection of corresponding intermediate phase encoding gradients. Resonance signals collected during each phase encoding gradient are Fourier or otherwise transformed (80) into a corresponding view.

Abstract: In a system for reducing artifacts in a desired image due to substantially periodic variations in the imaging signal detected from a portion of an object under examination, a method and apparatus for generating from a signal y(t) related to the variations and whose values are not equally likely, a signal .phi.(t) whose values are substantially equally likely for use in distributing events substantially evenly over the variations. In order to provide the signal .phi.(t), an apparatus is disclosed for executing the following steps: (a) establishing a historical data base derived from values of the signal y(t) for a period of time preceding the present time, (b) measuring parameters related to the present value of the signal y(t); and (c) producing a value for .phi.(t) using the present measured parameters and the historical data base; wherein the values of .phi.(t) are more evenly distributed than the values of y(t).

Abstract: Increased spatial sensitivity (FIGS. 4) or spatial tolerance (FIGS. 1) in selectively manipulated NMR sample analysis is excited from a spatially inhomogeneous FR field using pulse sequences which operate to exclude all spins deviating from a selected initial orientation (FIGS. 4 and 5) or to inclusively extend the applicable flip angles over a range of initial spin orientation (FIGS. 1).

Abstract: A high frequency energy pulsing system suitable for use in a pulsed microwave spectrometer (10), including means (11, 19) for generating a high frequency carrier signal, and means (12) for generating a low frequency modulating signal. The carrier signal is continuously fed to a modulator (20) and the modulating signal is fed through a pulse switch (23) to the modulator. When the pulse switch (23) is on, the modulator (20) will produce sideband signals above and below the carrier signal frequency. A frequency-responsive device (31) is tuned to one of the sideband signals and away from the carrier frequency so that the high frequency energization of the frequency-responsive device (31) is controlled by the pulse switch (23).

Abstract: The disclosure relates to an NMR tomographic apparatus wherein an improved local resolution is obtained in a selected segment of the examination region. To this end, in a spin-echo-sequence in conjunction with a 90.degree.-Hf-pulse, a first field gradient is generated in one direction for a spatial selection of a first dimension of the segment which is energized to precession and hence signal emission. In an excitation interval with a 180.degree.-Hf-pulse, a second field gradient is generated in a second direction perpendicular to the first cited direction, for achieving a spatial selection of a second dimension of the segment contributing to the echo signal. The echo signal is read out in the presence of a third field gradient which, in turn, is perpendicular to the first and second field gradients. A three dimensional Fourier-Zeugmatography data set for the representation of a series of layers can be picked-up. In addition, it is possible to represent a non-central region.

Abstract: In order to increase the efficiency with which NMR information is received, the peak amplitude of the received NMR signal is reduced. This reduction is obtained by varying the phase of the nuclear spin systems which produce the NMR signal. The phase variation may be obtained by applying a spatially inhomogeneous rf pulse. It may alternatively be obtained by applying a tailored rf pulse having either an amplitude spectrum or a phase spectrum which varies with frequency. It may alternatively be obtained by applying gradient pulses. The phase variation may be produced at one or more of several times during the data acquisition. In addition to reducing the peak amplitude of the NMR signal, the phase variation results in reduced noise from an FFT performed during processing.

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: 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: NMR imaging is achieved in the presence of temporal variations in the magnetic field. The volume is excited using broadband excitation. A signal is picked up in the plane of interest, using a small coil, and used to determine the frequency of the subsequent plane-selecting excitation. A similar coil can be used to pick up the signal used to image the plane using projections all in the same direction. This latter signal is used to provide the demodulation signals to decompose the selected plane into its constituent elements. In both cases, involving the excitation and decoding signals, drifts in the magnetic field are compensated for.

Abstract: An antenna system for nuclear magnetic resonance (NMR) imaging or spectroscopy devices which produce a uniform magnetic field in an object under examination includes transmit and receive antenna arrays each comprising a group of loop antennas. A signal generating circuit produces a set of input antenna signals which are applied to the loop antennas of the transmit array which transmits RF signals of a frequency that perturbs the magnetic moment of nuclei in a volume of the object. The receiving antenna array is responsive to NMR signals produced by the relaxation of perturbed nuclei in said volume for producing a set of output antenna that are applied to a signal processing circuit. A control circuit selectively controls the relative phases and amplitudes of at least one set of antenna signals to control the size and location of the region of the volume in which excitation of nuclei occurs, or from which NMR signals are processed.

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.

Abstract: Conversion apparatus facilitating acquisition of NMR spectroscopy and/or imaging information from a desired one of a plurality of nuclear species, in a system originally capable of acquiring spectroscopy/imaging information for only a single nuclear species, uses: a first frequency converter to provide an excitation signal by heterodyning the transmitter signal of the single species system to the Larmor frequency of the desired one of the plurality of nuclear species, if that desired species is not the original single species; and a second frequency converter to heterodyne the response signal from the Larmor frequency of the desired nuclear species, if that desired species is not the original single species, to the frequency of the single species. The first and second converters are bypassed if the single original species is the desired species.

Abstract: The magnetic resonance imaging system applies a uniform static magnetic field and a gradient magnetic field to an object and further applies an excitation rotating magnetic field to cause magnetic resonance phenomena in the object, and detects the induced magnetic resonance signals and then obtains image data by these magnetic resonance signals. The system has a power controller for controlling the transmission power in a transmitter for transmitting the excitation rotating field. The system further has a transmission controller for controlling the power controller in response to the magnetic resonance signal which is received by the receiver from the object.

Abstract: Power line interference artifacts in a magnetic resonance image are minimized by the process of: providing a sequential plurality of imaging signal sequences, the totality of which sequences is required for determining the value of each image pixel in an image array thereof; requesting the start of each sequence of the plurality of imaging signal sequences prior to the actual time at which each such signal sequence should commence; preparing a recognition element prior to the desired actual commencement time; recognizing a predetermined occurrence of a repetitive power line signal parameter to provide a first signal; setting the recognition element responsive to the first signal to only then cause the signal sequence start request to actually cause commencement of the associated signal sequence; and causing each signal sequence to occur in essentially an integral number of sequential repetitive cycles of the power line signal waveform to minimize the magnitude of power line frequency signal interference artif

Abstract: Arrangements for selectively exciting sections of bodies being imaged in NMR systems wherein the rotating magnetic fields are shaped with envelopes defined by the sum of a sinc function and a cosine function.

Abstract: A magnetic resonance imaging signal generating system for controlling the frequency and phase of a high frequency signal capable of use in connection with rotating specific atomic nuclei and/or demodulating resultant magnetic resonance signals. The system includes a memory for storing digital signals which collectively represent the waveform of an analog signal and a mechanism for reading those digital signals from the memory by accessing addresses of the memory at a rate responsive to a frequency control signal to produce a series of digital signals which represent the analog signal having an angular frequency which is a function of the frequency control signal. An offset circuit is provided for offsetting the addresses of the memory means accessed by the reading mechanism in response to the phase control signal. The output of the memory means is used to efficiently and effectively alter the phase and angular frequency of that high frequency signal.

Abstract: The use of longer 180.degree. pulse sequences for the generation of spin echos is made possible according to the invention during NMR tomography using the 2d-Fourier transformation process in that the phase position and, thus, the sense of rotation of the 180.degree. pulses is reversed after every two pulses. The mirror images which appear otherwise when using the known 180.degree. pulse sequences, e.g. the Carr-Purcell-Gill-Meiboom pulse sequence, are avoided by this measure.

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 a Fourier transform nuclear magnetic resonance spectrometer, a signal which is produced repeatedly from a time origin is sampled at regular intervals of time to convert the signal into digital form, the time origin being given repeatedly. Then, the digitized data is accumulated. According to the present invention, delay periods beginning with each time origin and ending with the beginning of each sampling are made different from one another to obtain a pseudofiltering effect simply by using a relatively simple structure of apparatus and performing arithmetic operations on data.

Abstract: A preferred embodiment of a method of removing the effects of nuclear magnetic resonance (NMR) signal baseline error artifacts in imaging applications is disclosed with reference to Fourier transform imaging techniques, of the type frequently referred to as spin warp. In accordance with the method, the phase of the radio frequency (RF) excitation pulse is alternated in adjacent phase-encoding views by 180.degree.. Since the baseline error component is independent of this phase change, the effect of phase reversal of the RF excitation is to modulate the desired image up to the Nyquist frequency in the phase-encoding direction. The artifact due to the baseline error component, however, is unchanged. Views measured with -90.degree. RF excitation are negated prior to reconstruction so that the image is returned to its correct position, while the baseline error artifact is modulated to the edge of the field of view. Since the baseline artifact has limited bandwidth, it does not interfere with the desired image.

Abstract: Reception signal processing apparatus in nuclear magnetic resonance diagnostic apparatus to display as an image the distribution of the spin density or relaxation time of specified atomic nuclei existing in an object utilizing nuclear magnetic resonance phenomena including a phase demodulator for phase demodulating a nuclear magnetic resonance signal evoked by nuclear magnetic resonance phenomena in accordance with two reference waves whose phases are different from one another by 90.degree., an analog-to-digital converter for digitalizing the separated two signals obtained by the phase demodulator, and a phase correction processor for automatically correcting the phase difference between the reference waves and nuclear magnetic resonance signal to produce a frequency spectrum by processing the digitalized signals.

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: Nuclear magnetic resonance diagnostic apparatus including means for applying a gradient magnetic field to form an equivalent plane in the magnetic field corresponding to the slice in the predetermined region to be measured for the acquisition of projection data, means for selectively saturating magnetization vectors in the entire region other than the region corresponding to the slice by applying radio frequency signal composed of continuous waves the frequency of which is successively varied in the range of the resonance frequency of the specified atomic nuclei and means for obtaining the projection data in the predetermined directions in the slice by measuring the resonance signals obtained by applying the 90.degree. pulses of resonance frequency of the specified atomic nuclei to the region to be measured while the saturation state of magnetization vectors is maintained.

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: 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 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.

Abstract: An imaging NMR scanner obtains plural spin echo signals during each of successive measurement cycles permitting determination of the T2 parameter for each display pixel after but a single measurement sequence. The amplitude of the NMR spin echo responses is dependent on an "a" machine parameter (the elapsed time between initiation of a given measurement cycle and the occurrence of the NMR response) and upon a "b" machine parameter (the elapsed time between initiation of successive measurement cycles). These a and b machine time parameters are selectively controlled to enhance resultant image contrast between different types of tissue or other internal structures of an object under examination. Special phase control circuits ensure the repeatability of relative phasing between successive NMR responses from the same measured volume and/or of reference RF signals utilized to frequency translate and synchronously demodulate the NMR responses in the successive measurement cycles of a complete measurement sequence.

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: 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: A method and device of NMR spectroscopic analysis of liquids whereby magnzation of the spins of one nuclear species in spin-locked along a certain direction and the spin polarization of this species is transferred to a second species through the modulation of the amplitude and/or phase of rf fields applied to one or both species. The NMR signal can be detected directly from the second species.

Abstract: An impulse resonance spectrometer is provided, wherein high frequency energy in the shape of pulses is applied to a sample material located in a polarizing magnetic field, to detect a nuclear magnetic resonance signal from the sample material. The spectrometer includes a first oscillator which oscillates at a first high frequency for generating a first frequency signal corresponding to a main signal of the nuclear magnetic resonance signal. A nuclear magnetic resonance signal measuring device measures the difference between frequencies of the main signal and a subsidiary signal of the nuclear magnetic resonance signal detected from the sample material by applying the output of the first oscillator to the sample material.

Abstract: In an apparatus for examining human bodies by nuclear magnetic resonance to produce images of cross-sectional slices of such bodies, it is desirable to reduce the recovery time between scans at different angles. A suitable pulse sequence for examination with minimum dispersion is disclosed. Repetition of the sequence with inverted pulses to drive the spins back to equilibrium and reduce recovery time is also disclosed.

Abstract: In a heteronuclear system, the indirect detection of nuclei S, of weak gyromagnetic ratio, coupled to nuclei I, of strong gyromagnetic ratio, is accomplished by generation of zero and double quantum coherence between the I and S spin systems, during a preparatory period, t.sub.p. The zero and double quantum transitions are then interchanged at the midpoint of the evolution period, t.sub.1, producing an echo modulated only by S and I-I interactions at the end of the period t.sub.1, at which time the zero and double quantum coherence is then converted to I spin single quantum coherence yielding a free induction decay wave form S(t.sub.2) for given t.sub.1. The period, t.sub.1, is then varied to obtain a two-dimensional function S(t.sub.1, t.sub.2) which is then fully transformed to the frequency domain obtaining S(.omega..sub.1, .omega..sub.2) whereby the chemical shift of the coupled S spin is obtained along the .omega..sub.1 axis and the chemical shift of the I spin is obtained along the .omega..sub.2 axis.

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.